Living on Mars?

[ArcticMoue]

Hey!
I read an article recently about how scientist have discovered how to potentially grow plant life on mars by replicating the soil as best they can and they've successful so far, this got me thinking about what it'd be like if we moved there - as in would it be anything like Earth? Considering nothing went wrong, that is. My theory is that it'd be no different, especially as the population there grows, because humans don't change; the only thing changing is the location and we can still *******s half way across the world so we'd be the same on mars.
I still suspect there'd be corruption, crime, pollution and all that other stuff that gives us a bad name on earth. But I have no idea how it'd be set up on mars, would there be measures put in place to stop us from ruining society and mars like we are the earth? I think it'd be really cool to live on another planet and it'd be cool to be alive to see it happen but I think we should only planet-jump if we/the governments actually decide to take proper care of this place and make it a safe and decent place to live.

[LordEntrails]

Define "it".

And just because you can grow plants on earth using soil that simulates Martian soil does NOT mean you can grow that same plant on Mars. Its a step inthe right direction, yes. But it is not equivalent.

Would their be corruption and everything else? You're going to have to define that. And, perhaps more importantly, it depends who colonizes Mars and what their drivers are. Are you talking colonization by a for profit company? By a national agency? By a non-profit organization driven by philosophical goals? Are you curious about the first generation of colonists or the thousandth?

Go read some good sci-fi if you want well-thought out contemplation of such possibilities. Asimov and his contemporaries were/are very good at that.

[ArcticMoue]

I'm starting to assume I wasn't clear enough, this is my first thread haha

I just meant in general, any type of corruption and human marring we're doing on earth. The main focal point would be that would mars end up like earth with corrupt governments, animals going extinct before their time, pollution from cars/factories/etc, crime/murder/theft/etc, poverty and exploitation of poverty, rich stealing from the poor and so on.

Would life on mars be just as bad there as it is on earth (which is under the consideration that life is sustainable up there) or, considering the probable decline on earth, would whoever owns/controls/funds the colonisation of mars put measures in place to ensure we don't ruin mars as a planet, the ecosystem or the economy.

My theory is it'll be the same as it is here, but I wanted to hear someone else's thoughts on that haha

[factotum]

The thing is, the initial group of people that actually *go* to Mars would presumably be carefully chosen for things like psychological stability--they'd have to be, since the journey to Mars takes six months and you don't want people who are likely to fly off the handle cooped up in a small environment for that length of time. At the very least that would mean the Mars society would have to be somewhat different to how it is here on Earth. There's also the point that the population on Mars would be very small for a long time, given the costs of getting people there, so you'd need to be comparing this with small communities here on Earth, not inner cities and the like. When everyone knows everyone else there are fewer opportunities for theft, murder and the like, if only because of the extreme likelihood of being caught.

[Lazymancer]

I read an article recently about how scientist have discovered how to potentially grow plant life on mars by replicating the soil as best they can and they've successful so far,
Link? Wasn't Martian soil covered in hydrogen peroxide (which is not good for anything organic)?

[Balyano]

Link? Wasn't Martian soil covered in hydrogen peroxide (which is not good for anything organic)?

It was Perchlorates. Bad for your thyroid. Far as I know we don't know if the perchlorates are wide spread, or if the location where they were detected were an anomaly. Even if they are all over the place I would assume that any soil you want to grow things in will be chemically altered first anyway. Shouldn't be to hard to rig up a bit of machinery to cheaply eliminate the unwanted chemicals.

Edit: Looks like they are found all over mars. But they are also a few orders of magnitude more common there than in the atacama desert on earth. This means it would be very profitable for the martian settlers to try and extract THIS COMPONENT OF ROCKET FUEL!!! and use the ''waste'' (soil) for agriculture.

[Lazymancer]

It was Perchlorates.
No. H2O2. Hydrogen Peroxide. The one we use it to bleach hair and remove any traces of organic substances. But - yes. Perchlorates are there too.

[Anonymouswizard]

The thing is, the initial group of people that actually *go* to Mars would presumably be carefully chosen for things like psychological stability--they'd have to be, since the journey to Mars takes six months and you don't want people who are likely to fly off the handle cooped up in a small environment for that length of time. At the very least that would mean the Mars society would have to be somewhat different to how it is here on Earth. There's also the point that the population on Mars would be very small for a long time, given the costs of getting people there, so you'd need to be comparing this with small communities here on Earth, not inner cities and the like. When everyone knows everyone else there are fewer opportunities for theft, murder and the like, if only because of the extreme likelihood of being caught.

Reminds me of Red Mars, where the people sent in the first colonisation mission consist of at least two camps as to what kind of society they're going to build, and later clash with both Earth and each other over who gets to govern Mars and whether or not it should be Terraformed. The initial society consists of about fifty people and might as well just be a large, very long interplanetary scientific expedition.

Note: any long term Martian living or colonisation would require us to know how plants develop in low-g environments, and it's theorised that long term exposure to Martian gravity would even stop Earth born humans from being able to tolerate 1g of gravity, let alone those who grow up on Mars. For all we know a martian society might be impossible.

[Lvl 2 Expert]

Gravity is still about one third of what it is here, the length of a day is less than an hour longer, we'd have to bring our own atmosphere and pack it inside buildings we can't really leave while still having to build tough enough to withstand Martian sand storms. I figure the main problem of colonizing Mars is not that one specific thing is bad, it's that everything is bad. The soil, the temperatures, you name it, it's worse than on 90 percent of places on Earth, if not 100. And the combination of all those circumstances is definitely worse than anywhere on Earth.

This means that before it really starts making sense to put people on Mars for the sake of moving people off Earth, we will need to have Earth packed to the limits. It's easier to grow food inside a large Earth building than on Mars, so as farm ground runs out, expect farm buildings, not farms on Mars. It's easier, waaaaay easier, to build up a good livable home in the Gobi desert than on Mars, so as living space runs out, expect living in the desert, not on Mars. In fact, a self sustaining floating city sounds downright easy to make compared to a Mars habitat for the same number of people. Give me an old ferry, a hundred people, a bunch of solar panels, fishnets and a water filtration system and I'm halfway there. (Okay, I'll be about ten percent there, maybe. But any similarly sized shopping list for a Mars expedition of a hundred people gets me maybe half a percent there.) Not to mention that most predictions don't actually indicate that much population growth for the foreseeable future. There will still be growth during the next 50 years or so, mostly in/out of Africa and certain parts of Asia, but after that the worlds population should stabilize or even decline. These models are far from perfect and definitely do not account for say possible future extreme life extension technologies, but you get my overall drift: The situation needs to get a lot worse before moving to Mars is the sensible option.

What I could see happening is limited amounts of people moving to Mars, the Moon, Ceres or certain asteroids, not because we don't want them here, but because we need them there. At some moment in the future there might be a point where it's easier and cheaper to mine for certain resources off-world than it is to find or manufacture them down here. Tritium could become an important component to the energy chain, in which case it could make sense to gather it on the Moon, in which case it could make sense to have a small human crew up there in addition to a small warehouse full of computers, one or more AI's or whatever we have that's close enough and the physical machines that do the actual work.

What living there would be like? It'd be a lot like life in the ISS. It's cramped, everything stinks and your health is steadily deteriorating, but you're surrounded by some of the most brilliant and motivated minds Earth has produced, and you get to have an experience few people will ever have.

I don't believe in the gameshow approach, in just shooting random people up there and believe they'll somehow end up paying for themselves. In fact, there's a good chance being selected as part of the elite that will run the whateveritis mine on Mars means giving up large parts of the human experience. For instance: what sounds cheaper to you: sending a new astronaut when needed, selected from the best minds available and trained by the best Earth schools for the job at hand, or letting people up there have kids and try to raise them into what the colony might need eighteen years from now, all the while having them consume precious resources?

And there could be a time where we actually are properly colonizing other planets, but at that point human technology and society will have changes so much that it's hard to predict what will happen. Yeah sure, there will probably be crime and love and corruption and money and drugs and pollution and charities and politics and sports and war and sex and prostitution and games and gambling and music and all those things that have been part of the human experience for so long, but in what form? No idea. I only know one thing: when that time comes there will be plenty of people living in the Gobi desert.

[Bohandas]

Hey!
I read an article recently about how scientist have discovered how to potentially grow plant life on mars by replicating the soil as best they can and they've successful so far, this got me thinking about what it'd be like if we moved there - as in would it be anything like Earth? Considering nothing went wrong, that is. My theory is that it'd be no different, especially as the population there grows, because humans don't change; the only thing changing is the location and we can still *******s half way across the world so we'd be the same on mars.
I still suspect there'd be corruption, crime, pollution and all that other stuff that gives us a bad name on earth.

Pollution loses much of it's relevance on Mars though because 1.) There's no natural ecosystems to destroy and 2.) The planet is colder than Earth and could stand to warm up a bit

[Lvl 2 Expert]

Pollution loses much of it's relevance on Mars though because 1.) There's no natural ecosystems to destroy and 2.) The planet is colder than Earth and could stand to warm up a bit

Pollution does not always take the shape of the warming of the whole planet. For instance: In a glass dome filled with air shone upon by sunlight pollution can take the shape of ozon, which is poisonous in high concentrations with nowhere to go.

On second thought, I'm not even sure if that would count as pollution or just ****ty design, but the point is more general: there's not such a thing as one single universal effect of pollution.

[Avigor]

I am firmly convinced that we'd have to practically rebuild Mars before we could live on it long-term; mining iron from it might be worthwhile, but honestly we'd be better off just going to the asteroid belt for mining (or just building our own planet outright).
What would we have to do to properly live on Mars as if it were Earth?

Somehow inject enough additional mass below the crust to increase the gravity to Earth levels.
Install a spinning, liquid iron core.
Wait for the planet to stop acting like a giant volcano and cool down a bit.
Add enough atmosphere to actually be able to breathe; this would require the choice of either keep the gasses in proper proportion to avoid toxicity, or follow this by installing plants capable of converting CO2 to O2 (and possibly more conversions depending on what gasses you start with) to Earth levels.
Add enough water so that it isn't an outright desert.

The first two steps might occur simultaneously, and 4+5 could probably be covered by throwing a comet at the planet, but yeah you get the picture, the idea of living on Mars should be abandoned IMO. Going there to prove we can reach it, sure. But don't plan on living there!

On a related side note, does anyone know how accurate the heart problems of "The Space Between Us" were? Because we already know that astronauts have trouble with muscle and bone loss in orbit, and I can't help but expect that trying to live on Mars would include similar problems IRL if anyone was born there...

[Taro]

I don't get people who want to live there, it looks so dull and boring.

[factotum]

we can't really leave while still having to build tough enough to withstand Martian sand storms.

This means that before it really starts making sense to put people on Mars for the sake of moving people off Earth, we will need to have Earth packed to the limits.

Martian sand storms aren't actually all that bad because the atmosphere is so thin--it can't carry sufficient sand to cause real damage, although you'll need to pop outside and wipe the sand build-up off your solar panels every now and again.

As for "moving people off Earth"--I don't think that's ever going to be a practical reason for putting colonies on Mars. The sheer amount of energy required to move any people up the gravity gradient to Mars makes it impractical to send large numbers of people there (assuming sensible levels of technology)--I think it's far more likely any colony we create on the Moon, Mars, or anywhere else in the solar system will be primarily for scientific research. To even match the rate at which the Earth's population is increasing you'd need to send something like 75 million people per year over to Mars, and that's just not going to happen.

[Bohandas]

Pollution does not always take the shape of the warming of the whole planet. For instance: In a glass dome filled with air shone upon by sunlight pollution can take the shape of ozon, which is poisonous in high concentrations with nowhere to go.

On second thought, I'm not even sure if that would count as pollution or just ****ty design, but the point is more general: there's not such a thing as one single universal effect of pollution.

All you need is to suss out a way to build a smakestack that sticks out beyond the dome but doesn't let your oxygen out along with the waste gases. Not precisely simple per se but a probably cakewalk compared to the other technical challenges of a mars colony.

[Lazymancer]

As for "moving people off Earth"--I don't think that's ever going to be a practical reason for putting colonies on Mars. The sheer amount of energy required to move any people up the gravity gradient to Mars makes it impractical to send large numbers of people there (assuming sensible levels of technology)
Which is why real colonies will be massive space stations. With 1g and all the jazz.


To even match the rate at which the Earth's population is increasing you'd need to send something like 75 million people per year over to Mars, and that's just not going to happen.
IIRC, the number was around 100 million people (each with cargo of up to ~1 ton) per year. Doable only if we'll build and master space elevators.

[Lvl 2 Expert]

IIRC, the number was around 100 million people (each with cargo of up to ~1 ton) per year. Doable only if we'll build and master space elevators.

And still not in any way more practical than "colonizing" the Mars sized surface that is Earths deserts, polar regions and seas.

Seriously, if you can make Mars livable, you can turn even the ocean floor into a palace. At least the temperature is a nice steady just above freezing, you're only a few kilometers from a year round reachable emergency pickup location and there's plenty of water. Even if transport's completely free somehow, Mars is not a pleasant place. And terraforming is a big project, way bigger than even making every place on Earth perfectly pleasant to live. At least we have a nice moderate (by human standards) weather- and ecosystem to start with. So that's what I would take as my minimum technological baseline for when any decent amount of humans start living on Mars: Project Earth complete.

[Anonymouswizard]

Gravity is still about one third of what it is here, the length of a day is less than an hour longer, we'd have to bring our own atmosphere and pack it inside buildings we can't really leave while still having to build tough enough to withstand Martian sand storms. I figure the main problem of colonizing Mars is not that one specific thing is bad, it's that everything is bad. The soil, the temperatures, you name it, it's worse than on 90 percent of places on Earth, if not 100. And the combination of all those circumstances is definitely worse than anywhere on Earth.

This means that before it really starts making sense to put people on Mars for the sake of moving people off Earth, we will need to have Earth packed to the limits. It's easier to grow food inside a large Earth building than on Mars, so as farm ground runs out, expect farm buildings, not farms on Mars. It's easier, waaaaay easier, to build up a good livable home in the Gobi desert than on Mars, so as living space runs out, expect living in the desert, not on Mars. In fact, a self sustaining floating city sounds downright easy to make compared to a Mars habitat for the same number of people. Give me an old ferry, a hundred people, a bunch of solar panels, fishnets and a water filtration system and I'm halfway there. (Okay, I'll be about ten percent there, maybe. But any similarly sized shopping list for a Mars expedition of a hundred people gets me maybe half a percent there.)

Lots of good points, although I will note the other situation that'll potentially make us relocate to another body: the sun's expansion makes Earth uninhabitable. But even then I think we're more likely to pick a gas giant moon than Mars.

If we can get space elevators and give it half a millennia I can see permanent states being formed on other bodies in the solar system, but I honestly don't think it's likely we'll reach that. It's like interstellar empires probably won't be a thing, even if it turns out that FTL travel is possible, unless we can get instant travel and very, very good computers it just likely won't be worthwhile.


Not to mention that most predictions don't actually indicate that much population growth for the foreseeable future. There will still be growth during the next 50 years or so, mostly in/out of Africa and certain parts of Asia, but after that the worlds population should stabilize or even decline. These models are far from perfect and definitely do not account for say possible future extreme life extension technologies, but you get my overall drift: The situation needs to get a lot worse before moving to Mars is the sensible option.

Yeah, I recently started reading The Expanse, and the 'Earth has a population of thirty billion without major increases in life expectancy' was one of the harder things to suspend my disbelief for. I mean, I could have excepted the high teens, but that's over double what the current estimate for the stabilised human population without longevity treatments is.


What I could see happening is limited amounts of people moving to Mars, the Moon, Ceres or certain asteroids, not because we don't want them here, but because we need them there. At some moment in the future there might be a point where it's easier and cheaper to mine for certain resources off-world than it is to find or manufacture them down here. Tritium could become an important component to the energy chain, in which case it could make sense to gather it on the Moon, in which case it could make sense to have a small human crew up there in addition to a small warehouse full of computers, one or more AI's or whatever we have that's close enough and the physical machines that do the actual work.

What living there would be like? It'd be a lot like life in the ISS. It's cramped, everything stinks and your health is steadily deteriorating, but you're surrounded by some of the most brilliant and motivated minds Earth has produced, and you get to have an experience few people will ever have.

Because almost anything else requires shifting too much mass into orbit (and then back down again), right? I'm fairly certain we can theoretically engineer a habitat that'll solve all the problems, or at least reduce them, but that it requires more mass than we can realistically put into orbit.


I don't believe in the gameshow approach, in just shooting random people up there and believe they'll somehow end up paying for themselves. In fact, there's a good chance being selected as part of the elite that will run the whateveritis mine on Mars means giving up large parts of the human experience. For instance: what sounds cheaper to you: sending a new astronaut when needed, selected from the best minds available and trained by the best Earth schools for the job at hand, or letting people up there have kids and try to raise them into what the colony might need eighteen years from now, all the while having them consume precious resources?

Hmmmm.... so the choices are single gender colonies (I recommend male only because it's a lot harder to work around no eggs than no sperm), shipping contraception over, or steralising the astronauts (maybe we could skimp a bit on the rocket's shielding and get it cheaply). Assuming pregnancies even work in low gravity of course, I'm not certain we have any real data on that.


And there could be a time where we actually are properly colonizing other planets, but at that point human technology and society will have changes so much that it's hard to predict what will happen. Yeah sure, there will probably be crime and love and corruption and money and drugs and pollution and charities and politics and sports and war and sex and prostitution and games and gambling and music and all those things that have been part of the human experience for so long, but in what form? No idea. I only know one thing: when that time comes there will be plenty of people living in the Gobi desert.

Either that, or the idea of 'living somewhere' will have been rendered redundant by advances in technology, or it becomes practical to offload lots of manufacturing to the Gobi desert while people live in nicer areas.


Which is why real colonies will be massive space stations. With 1g and all the jazz.

IIRC there are massive engineering problems with massive space stations. The first one is getting the materials into orbit, especially if we want a comfortable 1g (which means we also want a low rpm), and that's first off a lot of material to build our structure. Then we have to be certain we're building it out of materials that'll withstand the stresses of something that size rotating. But assuming we can build it out of iron we can probably capture an asteroid or twelve that'll give us enough raw materials. We still need to ship up soil and maybe atmosphere, but it's a start. I assume we're going for a full O'Neil cylinder by the way, and aren't cutting corners on a Torus design (which will give us less livable space per gram of material).

[Lazymancer]

And still not in any way more practical than "colonizing" the Mars sized surface that is Earths deserts, polar regions and seas.
The point is to get people closer to the extraterrestrial resources, no?

Also, I argued for building space station, not terraforming Mars.


IIRC there are massive engineering problems with massive space stations. The first one is getting the materials into orbit, especially if we want a comfortable 1g (which means we also want a low rpm), and that's first off a lot of material to build our structure.
Which is why "Doable only if we'll build and master space elevators."

Also, I'm guessing only the early stations will be made from Earth materials - it makes more sense to move production of stations to the Belt or near Mars (wherever resources are).


Then we have to be certain we're building it out of materials that'll withstand the stresses of something that size rotating.
This problem is related to the space elevator. But we are already making nanotubes, so it's a question of time until we get sufficient production going.


We still need to ship up soil and maybe atmosphere, but it's a start
Actually, both soil (well, not proper soil, but the non-biological materials that could be used by microflora to make proper soil) and air could also be easily made off-Earth.

[factotum]

The point is to get people closer to the extraterrestrial resources, no?

There aren't any resources on Mars that we can't find here on Earth, though, and if you're just going out there to get resources it would be far easier to capture and mine Earth-crossing asteroids than to colonise and mine Mars.

[Eldan]

Can we make earthlike atmosphere on Mars? I mean, oxygen shouldn't be a problem, but is there any good source of nitrogen?

[Anonymouswizard]

Which is why "Doable only if we'll build and master space elevators."

Also, I'm guessing only the early stations will be made from Earth materials - it makes more sense to move production of stations to the Belt or near Mars (wherever resources are).

The first bit you'd never actually said.

Also, I did admit that it would be easier to construct them from asteroids. I was just assuming that we were going to be sticking these stations in the L4 and L5 points to start off with, nice stable orbits and they're not so far away it'll take years to get any resources they mine back. Maybe we'll also have a station in the belt to kick asteroids closer so we can plonk them in Earth orbit for mining, but I think we should assume that most space habitation for the near future will be exploiting near-Earth resources.


This problem is related to the space elevator. But we are already making nanotubes, so it's a question of time until we get sufficient production going.

Well sure, we can do it if we can build a space elevator, but that's not actually a given. There are at least theoretical ways to set up a space hab without having an elevator to ferry stuff up to it, and so I ignored any technology that wouldn't be required. It also makes more sense if we're discussing a self sustaining colony, as instead of being able to send somebody up in the space elevator we'd have to launch a vehicle.


Actually, both soil (well, not proper soil, but the non-biological materials that could be used by microflora to make proper soil) and air could also be easily made off-Earth.

Didn't know about soil, did know about atmosphere. Okay, so we just need to get a bunch of asteroids into orbit and use those to manufacture our nanotubes.

[Lazymancer]

There aren't any resources on Mars that we can't find here on Earth, though, and if you're just going out there to get resources it would be far easier to capture and mine Earth-crossing asteroids than to colonise and mine Mars.
And again it is implied that I want to colonize Mars. However, I've already stated my opinion - which was the opposite (i.e. space stations), and then repeated it, after it was suggested that I support terraforming of Mars.



The first bit you'd never actually said.

Doable only if we'll build and master space elevators.


I think we should assume that most space habitation for the near future will be exploiting near-Earth resources.
Why? The big problem is to get out of gravity well. Getting to Moon/Mars/Belt afterwards is just a question of drifting through space.


Well sure, we can do it if we can build a space elevator, but that's not actually a given.
No, it's a given. We have technology since the late 00s and can start building crude versions already. The only problem is politics. Which we are not supposed to discuss, apparently.


Didn't know about soil, did know about atmosphere. Okay, so we just need to get a bunch of asteroids into orbit and use those to manufacture our nanotubes.
Why do we need to push asteroids? They are heavy. It makes more sense to process them on spot - and then push the processed minerals back to Earth.

[Eldan]

Asteroids might have a few other nice uses, though. As anchors for space elevators, or hollowed out as stations. So towing a few into a high orbit might not be a bad idea.

[Grey_Wolf_c]

No, it's a given. We have technology since the late 00s and can start building crude versions already. The only problem is politics.

No, the problem is constructing the ribbon. No-one has achieved making carbon nanotubes longer than a few millimeters. We need them to be at least 35000 km long. That is not a politics issue.

In fact, it may be that it is physically impossible to build nanotubes that long (i.e. because there is just a limit to how long they can be, and braiding is just not strong enough for it). In which case, it might be a reason to colonize Mars: a space elevator might be more doable there, and since it seems the soil on Mars is practically rocket Fuel,it could turn out to be the fueling station for all our spaceship needs.

Speaking of, I understand we could build a space Elevator on the Moon out of steel ETA: actual existing materials (but not steel). Unfortunately, it doesn't sound like there is anything we'd want to mine in the moon that'd need a Space Elevator.

Grey Wolf

[Leewei]

Hey!
I read an article recently about how scientist have discovered how to potentially grow plant life on mars by replicating the soil as best they can and they've successful so far, this got me thinking about what it'd be like if we moved there - as in would it be anything like Earth? Considering nothing went wrong, that is. My theory is that it'd be no different, especially as the population there grows, because humans don't change; the only thing changing is the location and we can still *******s half way across the world so we'd be the same on mars.
I still suspect there'd be corruption, crime, pollution and all that other stuff that gives us a bad name on earth. But I have no idea how it'd be set up on mars, would there be measures put in place to stop us from ruining society and mars like we are the earth? I think it'd be really cool to live on another planet and it'd be cool to be alive to see it happen but I think we should only planet-jump if we/the governments actually decide to take proper care of this place and make it a safe and decent place to live.
Mars has an atmosphere that's 0.6% of Earth's. Humans can't exist at that pressure; we'd need to get it to at least 35% of Earth's to make it livable.

To some extent, this is possible by living in boreholes. Dig in a several kilometers and air pressure will increase. It's likely we'd still need pressurized environments.

Mars pretty much lacks a magnetosphere, so some form of shielding is necessary against radiation. Lots of rock would do the trick - those boreholes are looking like an even better idea.

The downsides of digging in are pretty substantial, though.
- Enormous initial energy and material investment.
- Energy cost to enter or leave the hole.
- Waste removal and expansion considerations.

Extremely hostile environments would change the way humans living there would view pollutants. Some materials would be hard enough to obtain that recycling would become far more viable. Given the costs involved, fission reactors to power the colony would be necessary. This leads to radioactive waste, which would need to be isolated from the habitat.

A different approach would be to postpone a Mars presence, and instead set up mass drivers in the asteroid belt beyond that planet. We could then hurl asteroids into Mars to add mass - especially water - to the planet.

[Anonymouswizard]

Oh yeah. I'll admit you did now, but it was to a completely differen point.


Why? The big problem is to get out of gravity well. Getting to Moon/Mars/Belt afterwards is just a question of drifting through space.

Because time is not free. The closer resources are the less time it takes to bring them back to Earth. While it is just a question of drifting through space, a Mars journey with technology that currently looks feasible requires you to leave and return at specific points in time that are years apart.

It may be that a resource that will take a year to collect is more economical than a greater one that'll take four years to see the first benefits from.


No, it's a given. We have technology since the late 00s and can start building crude versions already. The only problem is politics. Which we are not supposed to discuss, apparently.

We can start building tiny ones which do not work as proof of concept. Beanstalks are nice, but they have two major problems (the cable and car propulsion) which mean they might not be viable for centuries, if ever. Of those, the cable is the tricky one.


Why do we need to push asteroids? They are heavy. It makes more sense to process them on spot - and then push the processed minerals back to Earth.

Because again, time is money, and if we can make the trip once (for in theory less fuel than it takes to fly the asteroid over here in pieces, because we have less need to put it in stuff) then we only spend the time once. Plus asteroids do have other potential uses, as has been noted by Eldan.

[Grey_Wolf_c]

they have two major problems (the cable and car propulsion) which mean they might not be viable for centuries, if ever. Of those, the cable is the tricky one.

A few years back, there was a "space elevator climbers" yearly competition (it also had a ribbon competition, but that never went anywhere). By the end, the teams where bringing in climbers that were powered by lasers. I honestly don't think that car propulsion would be a problem, if we did have the ribbon. Which, as I and you both agree, we don't.

Grey Wolf

[Lazymancer]

No, the problem is constructing the ribbon. No-one has achieved making carbon nanotubes longer than a few millimeters.

Nanotechnology: Spinning continuous carbon nanotube yarns (www.nature.com/articles/419801a), 2002
Here we show that carbon nanotubes can be self-assembled into yarns of up to 30 cm in length simply by being drawn out from superaligned arrays of carbon nanotubes, and that the strength and conductivity of these yarns can be enhanced by heating them at high temperatures. Our findings should help to translate the remarkable mechanical, electrical and thermal properties of carbon nanotubes to a macroscopic scale.

By 2013 Rice University (Pasquali team) started producing nano-fiber (tensile strength: 2.4 GPa) by the meters. Currently they are collaborating with Cambridge (Windle) to combine their processes and improve it further.

[Grey_Wolf_c]

Nanotechnology: Spinning continuous carbon nanotube yarns (www.nature.com/articles/419801a), 2002
Here we show that carbon nanotubes can be self-assembled into yarns of up to 30 cm in length simply by being drawn out from superaligned arrays of carbon nanotubes, and that the strength and conductivity of these yarns can be enhanced by heating them at high temperatures. Our findings should help to translate the remarkable mechanical, electrical and thermal properties of carbon nanotubes to a macroscopic scale.

By 2013 Rice University (Pasquali team) started producing nano-fiber (tensile strength: 2.4 GPa) by the meters. Currently they are collaborating with Cambridge (Windle) to combine their processes and improve it further.

2.4 GPa is insufficient (the ribbon needs, IIRC, about 50 GPa). Heck, Kevlar has a better GPa than that (3.6), and suffice it to say Kevlar is NOT a cadidate for the ribbon. Without clicking through your link, I'm going to guess those are multi-walled nanotubes, rather than the single-walled nanotubes that are the ones who theoretically could be up to 160 GPa. The latter are the ones which we haven't made more than "a few decimeters", from a quick google just now. Oh, and something that I had not seen before: new studies finding that the rosy theoretical strength might not hold up (http://www.nature.com/news/2006/060522/full/news060522-1.html) (warning, have not read the full article, nor clicked through to the actual study), which highlights what I've always seen as a danger: that when dealing with atom-perfect structures, you simply can't produce large amounts without one or two atoms off, and it just takes a couple of atoms out of place for the thing to snap.

Grey Wolf

[Anonymouswizard]

A few years back, there was a "space elevator climbers" yearly competition (it also had a ribbon competition, but that never went anywhere). By the end, the teams where bringing in climbers that were powered by lasers. I honestly don't think that car propulsion would be a problem, if we did have the ribbon. Which, as I and you both agree, we don't.

Grey Wolf

Yeah, as far as I'm concerned the big problem with the climbers is that we don't know if they'll hold up when we get to full scale, we can already make proof of concept climbers or scaled down versions if we need to. We don't know if the ribbon is even possible, we have theoretical materials that might be able to maintain the strength needed at the required length, but it's definitely a 'might' not a 'will'.

[Bohandas]

There aren't any resources on Mars that we can't find here on Earth
Yes but mars has tgem in raw form, where as pretty soon the ones on earth are all going to be tied up in things that have already been manufactured and purchased. We're going to need more if we're going to continue to make more.

[Bohandas]

IIRC there are massive engineering problems with massive space stations.

Plus, I don't think many people would want to live in such a place permanently, not even trekkies like me.

[Grey_Wolf_c]

I don't think many people would want to live in such a place permanently, not even trekkies like me.

Most people would also not want to live permanently in a place with no sanitation, clean water or access to reliable sources of food, and yet over a billion people do so anyway. If being on the space station means having a job and a future for your kids, there'd be queues, no matter how bad the living conditions were, so long as they were better than the ones on Earth.

GW

[MikelaC1]

animals going extinct before their time

Since there are no animals native to Mars, there is no chance of them going extinct....

[Lord Torath]

Speaking of, I understand we could build a space Elevator on the Moon out of steel. Unfortunately, it doesn't sound like there is anything we'd want to mine in the moon that'd need a Space Elevator.

Grey WolfHow high would that elevator reach? Generally a space elevator terminates at the "Geo"synchronous orbit, as I understand it. But for the tidally-locked Moon, that's a point roughly 385,000 km away (Earth is in a "Geo"stationary orbit around the moon). For the lunar elevator, are they looking at a tower rather than a ribbon?

[Bohandas]

Since there are no animals native to Mars, there is no chance of them going extinct....

Precisely

http://s2.quickmeme.com/img/1d/1d85353e6b3891ee996be77eb4a4f8b2b9338e40f3daa413c8 0361c08d8bec3d.jpg

[Grey_Wolf_c]

How high would that elevator reach? Generally a space elevator terminates at the "Geo"synchronous orbit, as I understand it. But for the tidally-locked Moon, that's a point roughly 385,000 km away (Earth is in a "Geo"stationary orbit around the moon). For the lunar elevator, are they looking at a tower rather than a ribbon?

Oh, yes, ludicrously long (https://en.wikipedia.org/wiki/Lunar_space_elevator). That said, it seems I mispoke - wikipedia does not susgest steel as a construction material, so wherever I read that was probably wrong. Interestingly, I see in the wikipedia that the design calls for a double elevator, anchored (as it must) at the equator, but with a secondary ribbon going to the pole, where the lunar base is more realistically to be placed. I had not seen that design before, but it makes sense, if it is achievable.

As to ribbon vs tower, (assuming "ribbon" hangs from the planet and "tower" rests on the planet), it would still be a ribbon, held taut by the moon's 28-day long spin on its own axis. Although I suspect that to a certain degree, the elevator might also be assisted by Earth's gravity pull on its end.

Grey Wolf

[Lazymancer]

2.4 GPa is insufficient
So? You were arguing that we can't get more than "a few millimetres". But we never expected to make one huge molecule, it's the fibre we were always after - and it is the technology that already exists. Now we simply need to perfect it.

"2.4 GPa" demonstrates that Pasquali fibre is not some mush. We've got to 5.6 GPa by 2015 (Kumar), and will keep on improving it for years to come - despite not even spending any significant amount of money on this research. If we'll get serious, we may even have space elevator in a decade. But we can't have that, can we? Which is why "space elevator is a pipe dream" is being repeated endlessly.


Oh, and something that I had not seen before: new studies finding that the rosy theoretical strength might not hold up (http://www.nature.com/news/2006/060522/full/news060522-1.html)
Hardly anything new. Moreover, it is the _existing_ (circa 2006) technologies that are investigated.

[Grey_Wolf_c]

So? You were arguing that we can't get more than "a few millimetres". But we never expected to make one huge molecule, it's the fibre we were always after - and it is the technology that already exists. Now we simply need to perfect it.

Single walled nanotubes is not equivalent to multiwalled nanotubes. Being able to produce the latter doesn't do squat for the prospects of the space elevator, that cannot use them. Only the former count. And I stand by my statement that we have not figured that out yet. Your claim that we are now making it by the meter and that only "politics" stands in the way is particularly misdirecting if not outright wrong.

So yes, we have not produced more than a few millimeters (a few dozen, as it turns out) of a material capable of building the space elevator. You telling me that a similar, but much weaker, material also exists is irrelevant.


"2.4 GPa" demonstrates that Pasquali fibre is not some mush. We've got to 5.6 GPa by 2015 (Kumar), and will keep on improving it for years to come - despite not even spending any significant amount of money on this research.

No, we won't. The upper theoretical limit for multi-walled carbon nanutubes is significantly below the minimum necessary for the space elevator. Just because single and multiwall nanotubes are both carbon nanotubes, the research into one does not mean we have figured both out.


If we'll get serious, we may even have space elevator in a decade. But we can't have that, can we?

And this just reads like the ravings of a conspiracy theorist, so I'm done with you.

Grey Wolf

[Anonymouswizard]

"2.4 GPa" demonstrates that Pasquali fibre is not some mush. We've got to 5.6 GPa by 2015 (Kumar), and will keep on improving it for years to come - despite not even spending any significant amount of money on this research.

The bolded part is an assumption, this is somewhere where we're not sure where the practical upper limits are. Maybe we can create magical 200GPa carbon nanotubes, maybe doing so takes more energy than launching 1030 rockets and high sophisticated nanofabrication, we don't actually know.

[Yora]

Note: any long term Martian living or colonisation would require us to know how plants develop in low-g environments, and it's theorised that long term exposure to Martian gravity would even stop Earth born humans from being able to tolerate 1g of gravity, let alone those who grow up on Mars. For all we know a martian society might be impossible.

Research stations (basically like the ISS) seem perfectly reasonable, but I don't think Mars could be regarded as habitable for any permanent settlers. Microgravity does really strange and uncomfortable things to a body and even though Mars has some gravity, I don't think the human body will work properly in such an environment. But that's just for healthy adults. When you think of permanent settlement you also have to include developing children and I actually don't even want to imagine what it would do to them. Bone, muscle, and nerve development would all probably turn our very funky, likely leading to severe disabilities.

[Lazymancer]

The bolded part is an assumption, this is somewhere where we're not sure where the practical upper limits are. Maybe we can create magical 200GPa carbon nanotubes, maybe doing so takes more energy than launching 10[sup]30[sup] rockets and high sophisticated nanofabrication, we don't actually know.
Sun rising tomorrow in the east is also an assumption. It simply happens every morning. Day after day. We aren't sure whether it will do so tomorrow. Maybe it will magically rise again, maybe not. We don't actually know, do we?

To put it another way: instead of putting the label of "assumption" on anything and pretending the each and every possible event has the same chance to happen, we need to evaluate how probable the "assumption" is - since every potential event can be called an assumption.

In this specific case, we have new technology that not only did not exhaust basic approaches (we literally get new methods every year), but didn't even perfect any of the existing. Thus, it is practically certain we will get much better at making carbon nanotubes, and we will be getting better soon. Leaps of qualitative improvement (more than doubling within 2 years) suggest that improvement will be significant.

[MikelaC1]

, I don't think the human body will work properly in such an environment. But that's just for healthy adults. When you think of permanent settlement you also have to include developing children and I actually don't even want to imagine what it would do to them. Bone, muscle, and nerve development would all probably turn our very funky, likely leading to severe disabilities.

Or they could turn out like John Carters child (Edgar Rice Burroughs version please) and turn out to be Superman :smallsmile:

[Anonymouswizard]

Sun rising tomorrow in the east is also an assumption. It simply happens every morning. Day after day. We aren't sure whether it will do so tomorrow. Maybe it will magically rise again, maybe not. We don't actually know, do we?

No, it is an expectation. There are reasons it might not rise in the East (international consensus to exchange the directions of east and west, suddenly being put out by a highly advanced alien race), but it is expected it will.


To put it another way: instead of putting the label of "assumption" on anything and pretending the each and every possible event has the same chance to happen, we need to evaluate how probable the "assumption" is - since every potential event can be called an assumption.

In this specific case, we have new technology that not only did not exhaust basic approaches (we literally get new methods every year), but didn't even perfect any of the existing. Thus, it is practically certain we will get much better at making carbon nanotubes, and we will be getting better soon. Leaps of qualitative improvement (more than doubling within 2 years) suggest that improvement will be significant.

Ah, here we're getting into the fact that one of our things, the sun rising in the East, is based on lots of previous data, while the other, that we'll keep getting better at making carbon nanotubes, is based on the fact that we haven't stopped yet.

Let me put it this way, we might be able to make carbon nanotubes that strong. However, there is literally no guarantee that a) we will do it within the lifetime of any poster on this forum, and b) that we won't hit a roadblock in say 17 months that caps the tensile strength of the carbon nanotubes due to the manufacturing methods not being precise enough or some other problem. Instead of looking at things that are decades to centuries away, like space elevators and fusion plants, why don't we look at stuff that is years away, like better fission reactors?

[HandofShadows]

One problem with living on Mars that I have not seen mentioned yet: Dust. It will be everyplace. And it will be a much bigger problem on Mars than it is here on Earth.

[Lazymancer]

No, it is an expectation. There are reasons it might not rise in the East (international consensus to exchange the directions of east and west, suddenly being put out by a highly advanced alien race), but it is expected it will.
And how is it different from expectation of technological progress?


Ah, here we're getting into the fact that one of our things, the sun rising in the East, is based on lots of previous data, while the other, that we'll keep getting better at making carbon nanotubes, is based on the fact that we haven't stopped yet.
It's like saying that we should account for sun rising only during November of 2017. And that happened only a few times so far.

Why isn't expectation of improvement based on the fact that we've been getting better things we were doing for centuries?


Let me put it this way, we might be able to make carbon nanotubes that strong. However, there is literally no guarantee
Before making statements such as this, you need to remember the sun: is it possible to say "there is literally no guarantee that sun will rise tomorrow in the east"? If it is - then your statement is meaningless.


that we won't hit a roadblock in say 17 months that caps the tensile strength of the carbon nanotubes due to the manufacturing methods not being precise enough or some other problem.
As I've pointed out, we have multiple approaches and none had been developed exhaustively. I.e. the technology is not mature. Consequently, chances of some critical roadblock are negligible.


Instead of looking at things that are decades to centuries away, like space elevators and fusion plants, why don't we look at stuff that is years away, like better fission reactors?
What does this have to do with the topic?

[Knaight]

There's also the point that the population on Mars would be very small for a long time, given the costs of getting people there, so you'd need to be comparing this with small communities here on Earth, not inner cities and the like. When everyone knows everyone else there are fewer opportunities for theft, murder and the like, if only because of the extreme likelihood of being caught.
Crime rates in small communities are vastly higher than they're often depicted, and corruption in general is yet more common.


As I've pointed out, we have multiple approaches and none had been developed exhaustively. I.e. the technology is not mature. Consequently, chances of some critical roadblock are negligible.

The maximum material strength being lower than the necessary minimum is a critical roadblock, and their presence is hardly a negligible chance.

[Lazymancer]

The maximum material strength being lower than the necessary minimum is a critical roadblock, and their presence is hardly a negligible chance.
There is no "maximum material strength" as such. There is maximum theoretically possible (which is in low hundreds of GPa and cannot be a "critical roadblock"), and the maximum which we can do/will be able to actually achieve. The latter heavily depends on the production method used.

I.e. there is no one single maximum. For each approach the maximum will be different.

[Lvl 2 Expert]

Do you know if the tensile strength of carbon nanotube fiber twisted into helices, much like rope or metal wire, has been tested? If so, how much stronger is that arrangement when compared to straight fibers?

I think the point of twisted rope is more about getting the strands interconnected. If you have a long rope of a hundred strands, and each strand is broken, but each one in a different spot, the rope still has 99% of its original strength, while just a bundle of straight fibers would have been completely severed by that point. Something as tiny as carbon nanotubes, which we probably can't make long enough to individually go all the way up to geosynchronous orbit anyway, would most likely benefit quite a lot from some sort of twisting/braiding/webbing.

[Grey_Wolf_c]

Wouldn't exposing Martian permafrost to sunlight in a low pressure chamber cause it to rapidly boil, and therefore provide easier access to clean water? I also think that cultured meat becoming a mature technology would make it much easier to feed Mars colonies, though they'd probably want to bring some live animals to ensure a steady supply of tissues.
...
You quoted me to talk about this, but not sure why. I was talking about conditions on Earth, not on Mars, and how some people would find life in a space station an upgrade to their conditions here.

I can't comment on the generating water from permafrost - would need to know how much of it is present in likely landing sites (I'm aware one of the poles has plenty of frozen brine, but poles make for very poor base locations). We are also quite proficient at this point at water recycling, so it's not usually a concern (and it might be that any ship that takes humans outside the magnetosphere for any amount of time will use water as radiation shielding anyway, so you'd end up with plenty of water when you got to Mars).


Do you know if the tensile strength of carbon nanotube fiber twisted into helices, much like rope or metal wire, has been tested? If so, how much stronger is that arrangement when compared to straight fibers?

As I understand it, it's not any "stronger" by MPa measures. Braiding means you need a longer thread to cover the same distance, which means that it is overall heavier, which if anything reduces its ability to be a space elevator tether.

However, as Lvl 2 Expert points out, you braid because real life is a bitch, and braiding allows a form of redundancy and safety that means any stress due to breaking is kinda shared by all the threads at once, which leads to an overall stronger cord by the measure that matters (likelihood of snapping). It also may be the only way to create the tether. I doubt we will ever create strands of anything 100,000 km long, so braiding is the only way we will get tethers that long.

So, returning to your question: yes, braiding carbon nanotubes is being done, whenever the practical applications of them are discussed, vs. the single-strand properties.

Grey Wolf

[Lazymancer]

Do you know if the tensile strength of carbon nanotube fiber twisted into helices, much like rope or metal wire, has been tested? If so, how much stronger is that arrangement when compared to straight fibers?
I might be unaware of some exceptions, but AFAIK all macro-scale fibers are spun.

[factotum]

...
I can't comment on the generating water from permafrost - would need to know how much of it is present in likely landing sites (I'm aware one of the poles has plenty of frozen brine, but poles make for very poor base locations).

I always thought the Martian polar caps were dry ice--e.g. frozen carbon dioxide? Or is this frozen brine underneath the CO2?

[hamishspence]

Visible at the north pole, present but under CO2 ice at the south pole:

https://en.wikipedia.org/wiki/Water_on_Mars

[Grey_Wolf_c]

I'm not really a fan of space elevators on planetoids, due to the massive risks they can pose if they collapse

... they don't? The tether is absurdly light. That's the point, and the problem of why we can't build it. It's like being hit with a feather in freefall... except it is much, much, much lighter than a feather.

Yes, the whole thing will weight tons, but stretched out over 100,000 km. The scenarios I have seen for collapse suggest that it will mostly burn up in the atmosphere, or get blown all over the place by the winds. But it's not going to hurt much, because it doesn't have the density. Admitedly, I haven't seen similar scenarios modeled for, say, Mar's thin atmosphere or the Moon's no atmosphere, but I can't imagine that even in vacuum freefall a feather would hurt that much.

Grey Wolf

[factotum]

but I can't imagine that even in vacuum freefall a feather would hurt that much.


Depends how long it has to accelerate in vacuum freefall. Given sufficient distance, a featherweight object left to fall on the Moon would reach a speed of 2.38km/sec (Lunar escape velocity) or nearly so. A typical feather might mass 0.01g, and travelling at 2380m/s would have a kinetic energy of about 56J. Doesn't sound like much, but it's in the same ballpark as an arrow fired from a short bow, and since we're not talking about an actual feather but a broken fragment of the space elevator, it'll probably be quite sharp as well, and may also be heavier than that 0.01g figure I mentioned above--we only have to increase that to 0.1g to have an object with the same kinetic energy as a .45 ACP round fired from a pistol.

[Tvtyrant]

Hey!
I read an article recently about how scientist have discovered how to potentially grow plant life on mars by replicating the soil as best they can and they've successful so far, this got me thinking about what it'd be like if we moved there - as in would it be anything like Earth? Considering nothing went wrong, that is. My theory is that it'd be no different, especially as the population there grows, because humans don't change; the only thing changing is the location and we can still *******s half way across the world so we'd be the same on mars.
I still suspect there'd be corruption, crime, pollution and all that other stuff that gives us a bad name on earth. But I have no idea how it'd be set up on mars, would there be measures put in place to stop us from ruining society and mars like we are the earth? I think it'd be really cool to live on another planet and it'd be cool to be alive to see it happen but I think we should only planet-jump if we/the governments actually decide to take proper care of this place and make it a safe and decent place to live.

To put it bluntly, human civilization is based on massive agricultural investment in narrow bands of prime land and then sent to large population centers. Almost the entire population is located within subtropical and temperate zones with arable land, all major nations require major ports to be economically viable, and the ecological fertility of Earth is at the boiling point in many places despite those places being little more then camps for people to live in while receiving grain out of more fertile zones.

Civilization, in other words, cannot be exported to other planets because grain shipments from Kansas can't reach there. If we want to make Mars habitable we might at least try settling the Sahara desert first.

[Grey_Wolf_c]

Depends how long it has to accelerate in vacuum freefall. Given sufficient distance, a featherweight object left to fall on the Moon would reach a speed of 2.38km/sec (Lunar escape velocity) or nearly so. A typical feather might mass 0.01g, and travelling at 2380m/s would have a kinetic energy of about 56J. Doesn't sound like much, but it's in the same ballpark as an arrow fired from a short bow, and since we're not talking about an actual feather but a broken fragment of the space elevator, it'll probably be quite sharp as well, and may also be heavier than that 0.01g figure I mentioned above--we only have to increase that to 0.1g to have an object with the same kinetic energy as a .45 ACP round fired from a pistol.

Fair enough. I haven't double checked your math, but it sounds reasonable. Now, on the moon that wouldn't concern me much (since th tether would be unlikely to hit anything), but I do wonder how much the thin atmosphere of Mars would manage to slow down a Mars tether.


To put it bluntly, human civilization is based on massive agricultural investment in narrow bands of prime land and then sent to large population centers. Almost the entire population is located within subtropical and temperate zones with arable land, all major nations require major ports to be economically viable, and the ecological fertility of Earth is at the boiling point in many places despite those places being little more then camps for people to live in while receiving grain out of more fertile zones.

Civilization, in other words, cannot be exported to other planets because grain shipments from Kansas can't reach there. If we want to make Mars habitable we might at least try settling the Sahara desert first.

I don't disagree with any of this, except in a general "we really should stop taking over ecosystems and turning them into our private farms"... but I make an explicit exception to the Sahara, because It'd be nice to turn its expansion around.

That said, do you have an opinion on the development of urban vertical farms? A recent article (https://www.vox.com/energy-and-environment/2017/11/8/16611710/vertical-farms) went through the history of the approach, saying that it looks like tech is almost there to make them economically viable*. We may soon have the ability to grow food at the population centers, which would be an interesting development in the nature of human civilization, although I'm ambivalent of how big the consequences would be.

Grey Wolf

*It also admits to having said so 5 years ago, but the cost curve is definitely trending in the right direction, so they should be viable in our lifetimes, even if this particular one also fails

[LordEntrails]

I will add one observation;

If humans don't colonize space; we will die.

We (the human species) have a choice, die on Earth when Sol dies, or, travel into space to colonize elsewhere and live on as a species when Sol dies.

[Grey_Wolf_c]

I will add one observation;

If humans don't colonize space; we will die.

We (the human species) have a choice, die on Earth when Sol dies, or, travel into space to colonize elsewhere and live on as a species when Sol dies.

Humans will die whether or not we colonize space.

If all we are worried is about the death of the Sun, I think we can push of the issue for several orders of magnitude longer than humans have existed, and let technological innovation continue to make the problem easier.

Now, I am sympathetic to the reality that civilization-killing asteroids and other single-planet dangers do exist, but if one of those happens, and the Mars colony depends on Earth for survival, we haven't actually put our eggs in more than one basket. And the bottom line right now is that Mars does not sound independently viable.

Grey Wolf

[Lvl 2 Expert]

I only know one thing: when that time comes there will be plenty of people living in the Gobi desert.


If we want to make Mars habitable we might at least try settling the Sahara desert first.

Team desert! (Or ocean surface, or sea floor, or...)

[Lord Joeltion]

I don't disagree with any of this, except in a general "we really should stop taking over ecosystems and turning them into our private farms"... but I make an explicit exception to the Sahara, because It'd be nice to turn its expansion around.
Just want to point out that the Sahara probably has a role on other ecosystems of the planet. I'd rather not mess around with the single biosphere equilibrium we have ATM, and suggest to perfect crop growth and try to make synthetic proteins economically viable. Until we can successfully terraform a single massive body, at least.


Now, I am sympathetic to the reality that civilization-killing asteroids and other single-planet dangers do exist, but if one of those happens, and the Mars colony depends on Earth for survival, we haven't actually put our eggs in more than one basket. And the bottom line right now is that Mars does not sound independently viable.
Most planetary level cosmic threats are probably a lot easier to solve than the economical sink-hole colonizing a deserted planet would ever be. And the death of the sun is so far from us as species that we may as well be concerned about the heat-death of the universe itself (http://multivax.com/last_question.html)

[hamishspence]

... they don't? The tether is absurdly light. That's the point, and the problem of why we can't build it. It's like being hit with a feather in freefall... except it is much, much, much lighter than a feather.

Ben Bova's Solar System series (Mercury novel) depicted "falling space elevator" as extremely devastating - because, while it's low density, it's huge. The term "skytower" is used for it.

Some elevators might burn up:

https://en.wikipedia.org/wiki/Space_elevator_safety

but this one was on the order of 100 or more metres in diameter. And that might have been at its thinnest point.

The end coming down from nearly 25000 km up, would also have more time to accelerate to dangerous speeds, with air resistance not being able to mitigate those speeds enough. (The end above the geostationary platform, when the whole thing is severed, would go spinning off into space.)

Relevant bits from the novel:

Although buckyball fibers are lighter in weight than any material that is even half their tensile strength, a structure of more than thirty-five thousand kilometers' length weighs millions of metric tons.
The skytower wavered as it tore loose from the geostationary platform, disconnected from the centrifugal force that had pulled it taut. One end suddenly free of its mooring, its other end still tethered to the ground, the lower half of the tower staggered like a prizefighter suddenly struck by a knockout blow, then began its long, slow-motion catastrophic collapse.
...
The lower half of the skytower slowly, slowly tumbled like a majestic tree suddenly turned to putty. Its base, attached to the rotating Earth, was moving more than a thousand kilometers per hour from west to east. Its enormous length, unsupported now, collapsed westward in a long, long, long plunge to Earth.
...
Slowly at first, but then with ever-increasing speed, the skytower's lower half collapsed to the Earth. Its immense bulk smashed into Ciudad de Cielo, the tethers at its base snapping like strings, the shock wave from its impact blowing down those buildings it did not hit directly. The thunder of its fall shattered the air like the blast of every volcano on Earth exploding at once. Seconds later the falling tower smashed down on the northern suburbs of Quito like a gigantic tree crushing an ant hill. The city's modern high-rise glass and steel towers, built to withstand earthquakes, wavered and shuddered. Their safety-glass facades blew out in showers of pellets. Ordinary windows shattered into razor-sharp shards that slashed to bloody ribbons the people who crowded the streets, screaming in terror. Older buildings were torn from their foundations as if a nuclear explosion had ripped through the city. The old cathedral's thick masonry walls cracked and its stained glass windows shattered, each and every one of them. Water pipes ruptured and gas mains broke. Fire and flood took up their deadly work where the sheer explosive impact of the collapse left off.
And still the tower fell.
Down the slope that led to the sea, villages and roads and farms and open fields and trees were smashed flat, pulverized, while the shock wave from the impact blew down woodlands and buildings for a hundred kilometers and more in either direction, as if a giant meteor had struck out of the sky. A fishing village fell under the shadow of sudden doom, its inhabitants looking up to see this immense arm of God swinging down on them like the mighty bludgeon of the angel of death.
And still the tower fell.
Its length splashed into the Pacific Ocean with a roar that broke eardrums and ruptured the innards of men, beasts, birds, and fish. Across the coastal shelf it plunged and out beyond into the abyssal depths. Whales migrating hundreds of kilometers out to sea were pulped to jelly by the shock wave that raced through the water. The tsunami it raised washed away shoreline settlements up and down the coast and rushed across the Pacific, flooding the Galapagos Islands, already half-drowned by the greenhouse warming. The Pacific coast of Central America was devastated. Hawaii and Japan were struck before their warning systems could get people to move inland. Samoa and Tahiti were hit by a wall of water nearly fifteen meters high that tore away villages and whole cities. People in Los Angeles and Sydney heard the mighty thunderclap and wondered if it was a sonic boom.
And still the tower fell, splashing all the way across the Pacific, groaning as part of its globe-girdling length sank slowly into the dark abyssal depths. When it hit the spiny tree-covered mountain backbone of Borneo it snapped in two, one part sliding down the rugged slopes, tearing away forests and villages and plantations as it slithered snake-like across the island.
The other part plunged across Sumatra and into the Indian Ocean, narrowly missing the long green finger of Malaysia but sending a tsunami washing across the drowned ruins of Singapore. Along the breadth of equatorial Africa it fell, smashing across Kenya, ploughed into the northern reaches of Lake Victoria, drowning the city of Kampala with a tidal wave, and continued westward, crushing cities and forests alike, igniting mammoth forest fires, driving vast herds of animals into panicked, screaming stampedes. Its upper end, still smoking from the titanic electrical discharge that had severed it, plunged hissing into the Atlantic, sinking deep down into the jagged rift where hot magma from the Earth's core embraced the man-made structure that had, mere minutes earlier, stood among the stars.
Across the world the once-proud skytower lay amidst a swath of death and desolation and smoking ruin, crushing the life from people, animals, plants, crushing human ambition, human dreams, crushing hope itself.

[Grey_Wolf_c]

Ben Bova's Solar System series (Mercury novel) depicted "falling space elevator" as extremely devastating - because, while it's low density, it's huge. The term "skytower" is used for it.

I'm sorry, I am sure he is a great writer, but Ben Bova is not an actual engineer that we could consider an authority on the subject. He's describing an object that I do not recognise as a realistic space elevator, which is a very thin, relatively wide tether that would burn up in the atmosphere. Anyone can write florid descriptions of destruction (I remember reading a similar one in one of the Mars novels - probably Red? - about the collapse of the Martian Space Elevator). That doesn't make them realistic.


As the elevator cable's thickness decreases, maintenance requirements and failure risks increase. Conversely, as thickness increases, maintenance requirements and failure risks decrease, but the catastrophic damage caused in the event of failure increases. It just doesn't seem worth it to build these on planetoids, especially if their Hill spheres become populated with exponentially more debris over time.

None of that in any way answer my question "why do you think that a falling space elevator "pose[s] a massive risk". Unless you meant financial, I suppose, but then so does all other space technology.

Yes, there is debris in space. But having a space elevator would make it a lot easier to clean, and a lot cheaper too, so I'd imagine that, if anything, the risk posed by it would be reduced if we did get a space elevator built. But even if it didn't, it doesn't actually address the concern of the dangers of a collapsing space elevator.

Grey Wolf

[hamishspence]

I'm sorry, I am sure he is a great writer, but Ben Bova is not an actual engineer that we could consider an authority on the subject.

He does have something of a long career in "realistic sci-fi" though. His space elevator (millions of tonnes) is probably at the high end of the bulk scale, but he's not the only one to depict them that way.

[Lazymancer]

but this one was on the order of 100 or more metres in diameter. And that might have been at its thinnest point.
That's quite big for the thinnest point. It would make sense to build dozens (if not hundreds) of lesser space elevators instead. Moreover, space elevator should be primarily described as (a system of) cables going near each other, rather than a building.

Either way, the assumption is that there could be no potential response. But remember: megastructures don't work like regular buildings. Especially, if one is over 36 thousand km long. Middle sections could take hours to fall (I'm too lazy to calculate exact time, but g at 10.000 km is about 1.5 m/s^2), and that suggests a possibility of response.

For example, emergency cabins with rockets can ride up - or be already riding up, as every third cabin - and direct falling trajectory of cable, blow it up into pieces for better management, or even haul it upwards to be reconnected with the upper part (which will be lowered accordingly). There are many possible response scenarios.

As a "conspiracy theorist" (because acknowledging that science is heavily influenced by non-scientific factors is a definite sign of insanity) I'd like to say that Ben Bova's description presents a very biased point of view on space elevator.

[Grey_Wolf_c]

He does have something of a long career in "realistic sci-fi" though. His space elevator (millions of tonnes) is probably at the high end of the bulk scale, but he's not the only one to depict them that way.

Sure, but it is also not equivalent to the one being discussed. The only theoretically valid material for the elevator will not behave in the way described. Saying that a space elevator shouldn't be built because a novel once described one as being dangerous is not what I'd call conductive to the argument, especially if the one in the novel looks nothing like the one we theoretically could build.

From what I can see in wikipedia, the expected weight of the initial ribbon would be 750 tons, according to NASA's advanced concepts theoretical design. So Ben Nova's version is simply not comparable.

Grey Wolf

[Lord Torath]

Ben Bova's Solar System series (Mercury novel) depicted "falling space elevator" as extremely devastating - because, while it's low density, it's huge. The term "skytower" is used for it.

Some elevators might burn up:

https://en.wikipedia.org/wiki/Space_elevator_safety

but this one was on the order of 100 or more metres in diameter. And that might have been at its thinnest point.

The end coming down from nearly 25000 km up, would also have more time to accelerate to dangerous speeds, with air resistance not being able to mitigate those speeds enough. (The end above the geostationary platform, when the whole thing is severed, would go spinning off into space.)

Relevant bits from the novel:
The lower half of the skytower slowly, slowly tumbled like a majestic tree suddenly turned to putty. Its base, attached to the rotating Earth, was moving more than a thousand kilometers per hour from west to east. Its enormous length, unsupported now, collapsed westward in a long, long, long plunge to Earth.The TOP end of the tower is moving even more quickly from west to east. If the break was right at the geostationary point, then bit just below the break would be doing about 10,800 kmph in the same direction as the base, and would have the very same angular speed as the base. Yes, you'll have gravity pulling the thing down, but it's going to be a very slow pull. It took over an hour for the bits of Challenger to fall back to Earth, and it was only a few dozen miles up. And the only thing pulling the cable to the side is atmospheric wind, which only extends up 100 km. The other 21,940 km will be pulled straight down to earth. The tower will collapse in a pile, not wrapping around the earth.

(Plus, a tower 100 m across? None of the semi-viable designs I've heard of are anywhere near that size).

[hamishspence]

I'd like to say that Ben Bova's description presents a very biased point of view on space elevator.

His one was only destroyed because it had been sabotaged.

And the only thing pulling the cable to the side is atmospheric wind, which only extends up 100 km.

I think the idea was that, once broken, the angular tension created by difference between the bottom (effectively moving at 1000 kph) and the top (effectively moving at geostationary orbit speed) was what was dragging it out in a "wrap-round".

Mercury was written back in 2005, but set 100+ years from now. Nanotech, in Bova's books, has progressed enormously.

[Lord Torath]

I think the idea was that, once broken, the angular tension created by difference between the bottom (effectively moving at 1000 kph) and the top (effectively moving at geostationary orbit speed) was what was dragging it out in a "wrap-round".Except that the top and the bottom have the same rotational velocity, which is also the same as the Earth itself. That's why it's called "Geostationary Orbit". There's no angular tension between the top and the bottom, just in-line tension, which will tend to pull the tower straight down.

[hamishspence]

Except that the top and the bottom have the same rotational velocity, which is also the same as the Earth itself. That's why it's called "Geostationary Orbit".

The angular tangential velocity is going to vary though, all along its length.


Angular tangential velocity of a Geostationary Satellite: approx 11068 kph or 6877.8 mph.

Angular tangential velocity of object sitting on Earth's surface: 1674.4 kph or 1040.4 mph

Hence, tension.

Here, there's several simulations of a breaking space elevator. There's some whipping back and forth, but the end, is a wrap-round:

http://gassend.net/spaceelevator/breaks/

[Lord Torath]

The angular velocity is going to vary though, all along its length.


AngularRadial velocity of a Geostationary Satellite: approx 11068 kph or 6877.8 mph.

AngularRadial velocity of object sitting on Earth's surface: 1674.4 kph or 1040.4 mphFixed that for you. Angular velocity is rotational speed. The platform, the tower, and the earth are all rotating at 1 revolution per 24 hours. They have the same rotational or angular velocity.

[hamishspence]

I'm sorry, I am sure he is a great writer, but Ben Bova is not an actual engineer that we could consider an authority on the subject. He's describing an object that I do not recognise as a realistic space elevator, which is a very thin, relatively wide tether that would burn up in the atmosphere.


Regarding the bulk of the elevator - a point is made in the original Arthur C. Clarke article:

http://spaceref.com/space-elevator/the-space-elevator-thought-experiment-or-key-to-the-universe-by-sir-arthur-c-clarke.html

that the weaker the material, the more massive the tether needs to be - and that it will taper outwards - being much wider at the top, than at the ground. It also talks about "megatons (millions of tons) of material"


The very minimum requirement for a space elevator is, obviously, a cable strong enough to support its own weight when hanging from geostationary orbit down to earth, 36000 km below. That is a very formidable challenge; luckily, things are not quite as bad as they look because only the lowest portion of the cable has to withstand one full gee.

As we go upwards, gravity falls off according to Newton's inverse square law. But the effective weight ofthe cable diminishes even more rapidly, owing to the centrifugal force* on the rotating system. At geostationary altitude the two balance and the net weight is zero; beyond that, weight appears to increase again -- but away from the Earth.

* My brief apologies to purists for invoking this fictitious entity.

So our cable has no need to be strong enough to hang 36000 km under sea-level gravity; allowing for the effects just mentioned, the figure turns out to be only one-seventh of this. In other words, if we could manufacture a cable with sufficient strength to support 5000 km (actually, 4960) of its own length at one gee, it would be strong enough to span the gap from geostationary orbit to Equator. Mathematically -- though not physically -- Jacob's ladder need be only 5OOO km long to reach Heaven.... This figure of 5000km I would like to call 'escape length', for reasons which will soon be obvious.
With a stepped, or tapered, cable it would be theoretically possible to construct the space elevator from any material, however weak. You could build it of chewing gum, though the total mass required would probably be larger than that of the entire universe. For the scheme to be practical we need materials with a breaking length a very substantial fraction of escape length. Even Kevlar 29's 200 km is a mere 25th of the 5000 km goal; to use that would be like fuelling the Apollo mission with damp gunpowder, and would require the same sort of astronomical ratio.

So, just as we were once always seeking exotic propellents, we must now search for super-strength materials. And, oddly enough, we will find them in the same place on the periodic table.

Carbon crystals have now been produced in the laboratory with breaking lengths of up to 3000 km -- that is, more than half of escape length. How happy the rocket engineers would be, if they had a propellant whose exhaust products emerged with 60% of escape velocity!

Whether this material can ever be produced in the megaton quantities needed is a question that only future technologies can answer; Pearson [8] has made the interesting suggestion that thezero gravity and vacuum conditions of an orbiting factory may assist their manufacture, while Sheffield [15] and I [10] havepointed out that essentially unlimited quantities of carbon are available on many of the asteroids.





Angular velocity is rotational speed. The platform, the tower, and the earth are all rotating at 1 revolution per 24 hours. They have the same rotational or angular velocity.

Angular speed was the term used in the Wikipedia article (since velocity is always on the same vector)

https://en.wikipedia.org/wiki/Geostationary_orbit

Every part of the tether has the same speed in radians per second - but the top is moving (in miles per hour) at a different tangential speed

https://en.wikipedia.org/wiki/Speed#Tangential_speed

from the bottom. Presumably that's why the "broken elevator" simulations depict the cable not collapsing vertically downward.





There's no angular tension between the top and the bottom, just in-line tension, which will tend to pull the tower straight down.

The point I'm trying to make, is that an elevator that breaks anywhere significantly above the ground, is not going to end up in a neat vertical heap, but trail out.

Think of a sling being spun around, with a heavy weight on the end. Then have it break just below the weight- the weight goes flying off - but the strap is still being spun. What is the strap going to do in the moments after the weight flies off?

The A. C. Clarke article above, also takes the "draped along the equator" interpretation:

But what if the elevator is severed?

Well, if the elevator is cut through at the Earth's surface, it would de exactly the opposite of a terrestrial building. It wouldn't fall down -- but would rise up into the sky! In theory, the loose end might be secured and fastened down again; but that would be, to say the least, a tricky operation. It might even be easier to build a new system....

If the break occurred at any altitude up to about 25000 km, the lower portion of the elevator would descend to Earth and drape itself along the equator while the now unbalanced upper portion would rise to a higher orbit.

[Lazymancer]

His one was only destroyed because it had been sabotaged.
That's not "only". Sabotage is considered to be one of - is not the - top reasons of potential space elevator collapse.

[hamishspence]

Sabotage is considered to be one of - is not the - top reasons of potential space elevator collapse.

True.


It would make sense to build dozens (if not hundreds) of lesser space elevators instead. Moreover, space elevator should be primarily described as (a system of) cables going near each other, rather than a building.


In Ian Stewart & Jack Cohen & Terry Pratchett's The Science of Discworld, humanity is shown as using a bunch of space elevators, all strung out along the equator, to get out into the Solar System, before eventually leaving it in inhabited asteroid ships, after the next Snowball Earth (caused by asteroid impact in this case?).

Possibly large-scale construction is easier than preventing massive climate change on this scale.

The base of the elevator the protagonists visit, is shown as coming out of a pyramid several km high - possibly because starting from a high building, an "artificial Everest", allows you to overcome many of the problems the atmosphere presents.

Going by the Arthur C. Clarke article - the less good your material, the bigger your collection of elevator cables needs to be if it is not to break.

[Rakaydos]

Humans will die whether or not we colonize space.

If all we are worried is about the death of the Sun, I think we can push of the issue for several orders of magnitude longer than humans have existed, and let technological innovation continue to make the problem easier.

Now, I am sympathetic to the reality that civilization-killing asteroids and other single-planet dangers do exist, but if one of those happens, and the Mars colony depends on Earth for survival, we haven't actually put our eggs in more than one basket. And the bottom line right now is that Mars does not sound independently viable.

Grey Wolf
The problem with "we have plenty of time" is "If not now, when?"
Looking at climate change as a comparison, will we decide to avoid a far off astronomical danger in time to develop all the technology needed to survive that danger?

[danzibr]

Interesting thread!

What living there would be like? It'd be a lot like life in the ISS. It's cramped, everything stinks and your health is steadily deteriorating, but you're surrounded by some of the most brilliant and motivated minds Earth has produced, and you get to have an experience few people will ever have.
This made me lol. Been there?

All I can really think of is John Carter (regarding this thread).

[LordEntrails]

Humans will die whether or not we colonize space.

If all we are worried is about the death of the Sun, I think we can push of the issue for several orders of magnitude longer than humans have existed, and let technological innovation continue to make the problem easier.

Now, I am sympathetic to the reality that civilization-killing asteroids and other single-planet dangers do exist, but if one of those happens, and the Mars colony depends on Earth for survival, we haven't actually put our eggs in more than one basket. And the bottom line right now is that Mars does not sound independently viable.

Grey Wolf


The problem with "we have plenty of time" is "If not now, when?"
Looking at climate change as a comparison, will we decide to avoid a far off astronomical danger in time to develop all the technology needed to survive that danger?

Yes. How do you (Grey Wolf) expect "technological innovation" that would help the human race live on places other than the Earth to be invented if we don't start "small" with things like space stations and Mars colonization?

As Rakaydos says, we have to start somewhere.

My point is not pro or con Mars colonization. My point is to shed a tiny light on the need to develop space fairing technologies. One can argue a thousand points, but in the end it's a biological need if we chose to survive.

[Lvl 2 Expert]

Interesting thread!

This made me lol. Been there?

I wish.

Not even so much for the whole having been in space thing, but because that would mean I had been both a world class student and a pretty extreme badass. I'd brave a few months of astronaut sock smell that saturated the filters a long time ago for that. Instead I'm just a sort of okay at times student and a more regular badass.

I have visited the place on Google Streetview (https://www.google.com/streetview/#international-space-station/cupola-observational-module), which is pretty cool in and of itself, but not the same thing. (Plus it seems that that is/might be(?) a mock-up that only looks like the real thing but sits on Earth.)


As the elevator cable's thickness decreases, maintenance requirements and failure risks increase. Conversely, as thickness increases, maintenance requirements and failure risks decrease, but the catastrophic damage caused in the event of failure increases. It just doesn't seem worth it to build these on planetoids, especially if their Hill spheres become populated with exponentially more debris over time.

On the other hand, there is a potential case to be made for space elevators on planetoids and small planets/moons involving velocity. The top of a space elevator moves faster than the bottom, so a ship docked to the top of an elevator will still have a bunch of velocity compared to one landing on the planet. It doesn't slow down as much when docking, and doesn't need to be sped up again as much afterwards. So the elevator might be worth it in energy conservation. You can increase the effect by spinning the planetoid up, while simultaneously creating artificial gravity for any people on the planet, as long as they have a roof that won't mind becoming a floor. This costs kind of a lot of energy though...

The main problem with this is that I don't think it works at all with anything even sort of resembling the current generation of spacecraft. Flying from Earth out to Mars is not a matter of flying up in a straight line. It's about escaping Earths gravity well to get to an independent orbit around the sun. From there on you speed up to reach a wider orbit, which will make you fall behind on Earth in rotation. Mars is in a wider orbit still, so you're gaining on it, and you aim to reach the same orbit as Mars by the time your place around the sun matches up. If a vessel like this undocks from Ceres at a high speed relative to the planet it probably goes into some weird elliptical orbit it can't really get out of. But it could be a beneficial thing for far future craft or objects aimed at leaving the (inner) solar system...



Here, there's several simulations of a breaking space elevator. There's some whipping back and forth, but the end, is a wrap-round:

http://gassend.net/spaceelevator/breaks/

Those are pretty cool. That's sort of what I'd expect happening too (although I'm glad someone did the calculations because I would not be sure by a long shot): the cable gets pulled down by its own weight, at which point its higher absolute velocity starts translating to a higher angular velocity, which makes it wrap around the earth in the direction it was moving in.

It's kind of counter intuitive, at first glance I'd somehow be expecting the elevator cable to slow down and wrap in the opposite direction, but that makes no sense and is based on experience with small objects in an environment full of air that has not matched velocity with the object.

[factotum]

Every part of the tether has the same speed in radians per second - but the top is moving (in miles per hour) at a different tangential speed

https://en.wikipedia.org/wiki/Speed#Tangential_speed

from the bottom. Presumably that's why the "broken elevator" simulations depict the cable not collapsing vertically downward.


Wouldn't orbital mechanics have something to do with it as well? Let's treat each part of the tether as a separate object. In that case, all the pieces between the ground station and the geostationary satellite are travelling at less than orbital speed for their altitude, so once the tether breaks they will start falling into lower orbits. Now, as an object drops down into a lower orbit its speed increases, so wouldn't that cause a differential speed that would cause the tether to bend?

I really need to get a copy of Universe Sandbox so I could simulate that...

[hamishspence]

Wouldn't orbital mechanics have something to do with it as well? Let's treat each part of the tether as a separate object. In that case, all the pieces between the ground station and the geostationary satellite are travelling at less than orbital speed for their altitude, so once the tether breaks they will start falling into lower orbits. Now, as an object drops down into a lower orbit its speed increases, so wouldn't that cause a differential speed that would cause the tether to bend?

That might work as well. Differential speed, going by the modelling shown, would also rip the thing apart, at least toward the end of the process.

Regarding the size of these cables - I think the point is that they're freight elevators - designed to make it easy to transport thousands of tonnes of material into space (and thousands of tonnes of lunar or asteroid mined material back down to Earth)? They are a tool in the "industrialization of space".

[Mechalich]

Yes. How do you (Grey Wolf) expect "technological innovation" that would help the human race live on places other than the Earth to be invented if we don't start "small" with things like space stations and Mars colonization?

Simple answer: transhumanism.

If at some point in the future the technology is developed to make uploading the human mind into a quantum computer or other substrate viable then suddenly all of the space travel problems that are related to maintaining homeostasis in 50-80 kg of living mammal disappear. Transporting robot bodies or just server boxes around the universe is orders of magnitude less complicated than hauling actual people from place to place. The technical challenges of building a starwisp to go to Alpha Centauri are significantly less daunting than those of getting humans to any point in the solar system beyond Mars, and if you had digital uploading you could actually put humans in the starwisp.

In terms of making human life beyond the earth viable you cannot avoid considering changing the 'human life' part of the equation and it may in fact be the part the most amenable to change.

[Grey_Wolf_c]

The problem with "we have plenty of time" is "If not now, when?"
Looking at climate change as a comparison, will we decide to avoid a far off astronomical danger in time to develop all the technology needed to survive that danger?

I was answering a post who claimed that we had to leave Earth before the death of the Sun. With a seven billion year deadline, I really don't think that leaving "right now" is at all a concern.


Yes. How do you (Grey Wolf) expect "technological innovation" that would help the human race live on places other than the Earth to be invented if we don't start "small" with things like space stations and Mars colonization?

As Rakaydos says, we have to start somewhere.

My point is not pro or con Mars colonization. My point is to shed a tiny light on the need to develop space fairing technologies. One can argue a thousand points, but in the end it's a biological need if we chose to survive.

You are engaging in a fallacy that the only way to develop the technology needed is colonize other planets. Such argument is, in a word, nonsense. Like multiple people have pointed out, we'd be better served colonizing the deserts/poles/sea bottoms of the Earth first. It will teach us far more, far safely, far cheaper, with far more immediate benefits.


Regarding the bulk of the elevator - a point is made in the original Arthur C. Clarke article:

http://spaceref.com/space-elevator/the-space-elevator-thought-experiment-or-key-to-the-universe-by-sir-arthur-c-clarke.html

that the weaker the material, the more massive the tether needs to be - and that it will taper outwards - being much wider at the top, than at the ground. It also talks about "megatons (millions of tons) of material"
Seriously, stop relying on sci fi writers, and maybe start looking at the actual engineering designs by NASA and others. The current design for the space elevator tapers at both end, not just the ground, with the widest point midway.

If he talks about "megatons" of material, then he too, like Nova, is wrong. NASA designs calls for a 750 ton cable. Now, taking actual engineer's word for it, it would have less density than a feather. The terminal velocity of a feather in Earth atmosphere is not sufficient for it to cause any kind of damage, no matter how many feathers you dump at once from high orbit, nor how it wraps around the Earth.


The elevator's utility is partially based on its operational lifetime and maintenance costs, which may encourage designers to use thicker cables. Destruction won't necessarily be limited to the surface, especially for objects in low orbits that're unfortunate enough to get hit. My math may be off, but for a km-long section of a cm-wide Martian elevator with a mass of ~125 kg, terminal velocity is ~36 km/s. Since aerosynchronous orbit is ~20 megameters above the surface, and gravity drops as altitude increases, it seems that no single section will reach that downwards velocity before impact. While I can't speak on the cable's resistance to atmospheric friction, at least multiple megagrams to gigagrams of cable would hit the Martian surface at hypersonic speed if it doesn't burn up.
Your math is wrong, because you don't account for the atmospheric friction, which is crucial when dealing with an object with the density and air resistance of a feather.

As to your pet idea, given that MEXTs are just space elevators but with massive hooks that you need to attach to, I don't see how they are no less subject to sabotage, and therefore would cause the same or more damage (since they'd have to have much higher density materials) if attacked. And given NASA's record of trying to capture fast moving objects with hooks, I find the actual practical problem of MEXT to be significantly higher than that of a Space Elevator. Not that I can really compare, since I'm having trouble even finding realistic assessments of the likely issues of MEXTs.

Grey Wolf

[hamishspence]

Seriously, stop relying on sci fi writers, and maybe start looking at the actual engineering designs by NASA and others. The current design for the space elevator tapers at both end, not just the ground, with the widest point midway.

If he talks about "megatons" of material, then he too, like Nova, is wrong. NASA designs calls for a 750 ton cable.

That would be the prototype space elevator - the "Redstone rocket" to the serious industrial space elevator's "Saturn V". Just because the first space elevator might be that big, doesn't mean that all future space elevators are constrained to that size.

Bova was probably using A.C. Clarke's concept, as the basis for his own version.


Now, taking actual engineer's word for it, it would have less density than a feather. The terminal velocity of a feather in Earth atmosphere is not sufficient for it to cause any kind of damage, no matter how many feathers you dump at once from high orbit, nor how it wraps around the Earth.


A feather-density object that weighs many tons, and is hitting target at many kph, is going to do damage. Low density, does not mean harmless.

[Grey_Wolf_c]

That would be the prototype space elevator - the "Redstone rocket" to the serious industrial space elevator's "Saturn V". Just because the first space elevator might be that big, doesn't mean that all future space elevators are constrained to that size.

Bova was probably using A.C. Clarke's concept, as the basis for his own version.
There is no certainty there exists a material that could create that design. NASA's 750 ton design is the final design. There isn't a bigger one after it, AFAICT, just more of the same.


A feather-density object that weighs many tons, and is hitting target at many kph, is going to do damage. Low density, does not mean harmless.
It also doesn't mean it's harmful. I've put forth my numbers. You have not actually made your case, other than quoting sci fi books as if that would be authoritative. But they are not.

GW

[hamishspence]

You have not actually made your case, other than quoting sci fi books as if that would be authoritative. But they are not.

A. C. Clarke knows more about what would be needed than most sci-fi writers, at least - being virtually "the father of the space elevator".

[Bohandas]

Ben Bova's Solar System series (Mercury novel) depicted "falling space elevator" as extremely devastating - because, while it's low density, it's huge. The term "skytower" is used for it.

Some elevators might burn up:

https://en.wikipedia.org/wiki/Space_elevator_safety

but this one was on the order of 100 or more metres in diameter. And that might have been at its thinnest point.

The end coming down from nearly 25000 km up, would also have more time to accelerate to dangerous speeds, with air resistance not being able to mitigate those speeds enough. (The end above the geostationary platform, when the whole thing is severed, would go spinning off into space.)

Relevant bits from the novel:

Although buckyball fibers are lighter in weight than any material that is even half their tensile strength, a structure of more than thirty-five thousand kilometers' length weighs millions of metric tons.
The skytower wavered as it tore loose from the geostationary platform, disconnected from the centrifugal force that had pulled it taut. One end suddenly free of its mooring, its other end still tethered to the ground, the lower half of the tower staggered like a prizefighter suddenly struck by a knockout blow, then began its long, slow-motion catastrophic collapse.
...
The lower half of the skytower slowly, slowly tumbled like a majestic tree suddenly turned to putty. Its base, attached to the rotating Earth, was moving more than a thousand kilometers per hour from west to east. Its enormous length, unsupported now, collapsed westward in a long, long, long plunge to Earth.
...
Slowly at first, but then with ever-increasing speed, the skytower's lower half collapsed to the Earth. Its immense bulk smashed into Ciudad de Cielo, the tethers at its base snapping like strings, the shock wave from its impact blowing down those buildings it did not hit directly. The thunder of its fall shattered the air like the blast of every volcano on Earth exploding at once. Seconds later the falling tower smashed down on the northern suburbs of Quito like a gigantic tree crushing an ant hill. The city's modern high-rise glass and steel towers, built to withstand earthquakes, wavered and shuddered. Their safety-glass facades blew out in showers of pellets. Ordinary windows shattered into razor-sharp shards that slashed to bloody ribbons the people who crowded the streets, screaming in terror. Older buildings were torn from their foundations as if a nuclear explosion had ripped through the city. The old cathedral's thick masonry walls cracked and its stained glass windows shattered, each and every one of them. Water pipes ruptured and gas mains broke. Fire and flood took up their deadly work where the sheer explosive impact of the collapse left off.
And still the tower fell.
Down the slope that led to the sea, villages and roads and farms and open fields and trees were smashed flat, pulverized, while the shock wave from the impact blew down woodlands and buildings for a hundred kilometers and more in either direction, as if a giant meteor had struck out of the sky. A fishing village fell under the shadow of sudden doom, its inhabitants looking up to see this immense arm of God swinging down on them like the mighty bludgeon of the angel of death.
And still the tower fell.
Its length splashed into the Pacific Ocean with a roar that broke eardrums and ruptured the innards of men, beasts, birds, and fish. Across the coastal shelf it plunged and out beyond into the abyssal depths. Whales migrating hundreds of kilometers out to sea were pulped to jelly by the shock wave that raced through the water. The tsunami it raised washed away shoreline settlements up and down the coast and rushed across the Pacific, flooding the Galapagos Islands, already half-drowned by the greenhouse warming. The Pacific coast of Central America was devastated. Hawaii and Japan were struck before their warning systems could get people to move inland. Samoa and Tahiti were hit by a wall of water nearly fifteen meters high that tore away villages and whole cities. People in Los Angeles and Sydney heard the mighty thunderclap and wondered if it was a sonic boom.
And still the tower fell, splashing all the way across the Pacific, groaning as part of its globe-girdling length sank slowly into the dark abyssal depths. When it hit the spiny tree-covered mountain backbone of Borneo it snapped in two, one part sliding down the rugged slopes, tearing away forests and villages and plantations as it slithered snake-like across the island.
The other part plunged across Sumatra and into the Indian Ocean, narrowly missing the long green finger of Malaysia but sending a tsunami washing across the drowned ruins of Singapore. Along the breadth of equatorial Africa it fell, smashing across Kenya, ploughed into the northern reaches of Lake Victoria, drowning the city of Kampala with a tidal wave, and continued westward, crushing cities and forests alike, igniting mammoth forest fires, driving vast herds of animals into panicked, screaming stampedes. Its upper end, still smoking from the titanic electrical discharge that had severed it, plunged hissing into the Atlantic, sinking deep down into the jagged rift where hot magma from the Earth's core embraced the man-made structure that had, mere minutes earlier, stood among the stars.
Across the world the once-proud skytower lay amidst a swath of death and desolation and smoking ruin, crushing the life from people, animals, plants, crushing human ambition, human dreams, crushing hope itself.

http://lesswrong.com/lw/k9/the_logical_fallacy_of_generalization_from/

[Grey_Wolf_c]

A. C. Clarke knows more about what would be needed than most sci-fi writers, at least - being virtually "the father of the space elevator".

Unless he also somehow knew more about it 50 years ago than NASA engineers today, I'm still not going to take his word over theirs.

GW

[hamishspence]

While it's possible that the fictionalized versions are impossibly big - I was under the impression that, eventually, they would need to be big, to support a thriving space industry.

[Grey_Wolf_c]

While it's possible that the fictionalized versions are impossibly big - I was under the impression that, eventually, they would need to be big, to support a thriving space industry.

This is no different from saying "Isaac Asimov had FTL drives. Therefore, eventually, they would need to exist, to support a thriving space industry."

Clarke, Asimov et al are not constrained by physical realities. Clarke was able to assume a material capable of holding up its own weight even when it weighted megatons. But since we don't know of any such material, saying "if the Space Elevator was made of unobtainium and then fell over it would destroy Earth, therefore all Space Elevators are dangerous" is a non-sequitor.

Grey Wolf

[hamishspence]

This is no different from saying "Isaac Asimov had FTL drives. Therefore, eventually, they would need to exist, to support a thriving space industry."

Clarke, Asimov et al are not constrained by physical realities. Clarke was able to assume a material capable of holding up its own weight even when it weighted megatons.

As he pointed out:


With a stepped, or tapered, cable it would be theoretically possible to construct the space elevator from any material, however weak. You could build it of chewing gum, though the total mass required would probably be larger than that of the entire universe. For the scheme to be practical we need materials with a breaking length a very substantial fraction of escape length.

Presumably, the super-massive cable would have a similar density to the tiny cable, but be the tiny cable, scaled up (many tiny cables, making up one immense one).

The first stage, would be much lighter, than the final cable:


The space elevator may be regarded as a kind of bridge, and many bridges begin with the establishment of a light initial cable -- sometimes, indeed, no more than a string towed across a canyon by a kite. It seems likely that the space elevator will start in the same way with the laying of a cable between geo stationary orbit and the point on the equator immediately below.

This operation is not as simple as it sounds, because of the varying forces and velocities involved, not to mention the matter of air resistance after atmospheric entry. But there are two existing technologies which may provide a few answers, or at least hints at them.

The first is that of submarine cable laying, now considerably more than a century old. Perhaps one day we may see in space something analogous to the triumphs and disasters of the Great Eastern, which laid the first successful transatlantic telegraph cable -- the Apollo Project of its age.

But a much closer parallel, both in time and sophistication, lies in the development of wire-guided missiles. These lethal insects can spin out their metallic gossamer at several hundred kilometres an hour. They may provide the prototype of the vehicle that lays a thread from stationary orbit down to earth.

Imagine a spool, or bobbin, carrying some 40000 km of filament, a few tenths of a millimetre thick at the outer layers, and tapering down to a tenth of this at the core -- the end that finally reaches Earth. Its mass would be a few tons, and the problem would be to play it out evenly at an average velocity of a kilometre a second along the desired trajectory. Moreover, an equivalent mass has to be sent outwards at the same time, to ensure that the system remains in balance at the stationary orbit.


My perspective, is that an industrial-size space elevator might be dangerous if broken - but that this potential danger simply has to be accepted, and planned for - not just assuming "whole thing will burn up harmlessly".

[Grey_Wolf_c]

Presumably, the super-massive cable would have a similar density to the tiny cable, but scaled up.

No, that does not follow. The length is the same and the width and depth are about the same, but one is heavier than the other by multiple orders of magnitude. Therefore, its density is equally larger by multiple orders of magnitude.

Edit: also, I'm done with you until you stop quoting sci-fi writers as if they were authoritative.

GW

[hamishspence]

No, that does not follow. The length is the same and the width and depth are about the same, but one is heavier than the other by multiple orders of magnitude.

Length is the same - but width and depth are vastly higher.

[Grey_Wolf_c]

Length is the same - but width and depth are vastly higher.

So then they are not comparable, and I'm still waiting for you to substantiate your assertion that the collapse of any space elevator (including those that DON'T weight megatons) would be dangerous.

GW

[hamishspence]

So then they are not comparable, and I'm still waiting for you to substantiate your assertion that the collapse of any space elevator (including those that DON'T weight megatons) would be dangerous.


I'm not sure how dangerous the 750 ton one would be if it broke. Probably not very.

I could see the middle of the collapsing cable moving faster than the terminal velocity of a feather, but slow enough not to have burned up before it hits something in its path though.

There's also the question of what scales in between 750 tons and 1 million tons, are worth taking into consideration, when it comes to "possible space elevators that might be constructed in the future".

[Bohandas]

If he talks about "megatons" of material, then he too, like Nova, is wrong. NASA designs calls for a 750 ton cable. Now, taking actual engineer's word for it, it would have less density than a feather. The terminal velocity of a feather in Earth atmosphere is not sufficient for it to cause any kind of damage, no matter how many feathers you dump at once from high orbit, nor how it wraps around the Earth.

What if they were all stuffed into a 30 foot wide, 100 foot tall conical pillow made of flame-retardant material

[hamishspence]

Regarding the possibility of many small elevators, rather than one big one - it should be noted that if there's a break in one, the collapsing elevator may hit the others:

http://gassend.net/spaceelevator/problems/index.html

[Grey_Wolf_c]

What if they were all stuffed into a 30 foot wide, 100 foot tall conical pillow made of flame-retardant material

That'd be an impressive feat of sabotage, I'll grant you that. Imagine if they also added boosters and covered it in frictionless paint.

GW

[Lord Torath]

I was answering a post who claimed that we had to leave Earth before the death of the Sun. With a seven billion year deadline, I really don't think that leaving "right now" is at all a concern.We actually only have 2-3 billion years. In that time, the sun will have heated up enough to fry all life on Earth. So we only have half of forever to figure out how to leave. :smallamused:

A feather-density object, even if very massive, will hit terminal velocity almost immediately. First, there is the issue of air drag. Then there is the issue of bouyancy. These forces will contribute to a very low terminal velocity, and a huge deceleration. How massive an elevator are we realistically considering, 750 tons, + car? ROund it up to a thousand tons.

The Chelybinsk meteor (https://en.wikipedia.org/wiki/Chelyabinsk_meteor) was 65 feet in diameter and had a mass or 12,000 - 13,000 metric tons. It did not reach the surface, but exploded at high altitude. Our elevator fragments are likely to have an initial velocity much lower than that of the meteor. After all, the elevator is at rest at 22,000 km up, while the much more massive meteor was already moving along very quickly. It's estimated to have been moving at 60 -70,000 km/h. our cable would be lucky to accelerate to 6,000 km/h.

The Chelybinsk meteor had a mass an order of magnitude larger than our elevator cable, and a velocity another order higher than the cable. Energy goes by mass and square of velocity, so our cable will have three orders of magnitude less energy than the Chelybinsk Meteor. To my knowledge, there were no fatalities from the meteor (although a couple thousand were injured by flying glass). Reducing the damage by 3 orders of magnitude means under ten people will be injured by our falling tether.

[LordEntrails]

Simple answer: transhumanism.

...

In terms of making human life beyond the earth viable you cannot avoid considering changing the 'human life' part of the equation and it may in fact be the part the most amenable to change.

You're supporting my statement, not contradicting it. We need to develop technologies. I'm not argueing which ones.


I was answering a post who claimed that we had to leave Earth before the death of the Sun. With a seven billion year deadline, I really don't think that leaving "right now" is at all a concern.
I think you are caught up in defending your other ideas without considering what I am trying (poorly?) to communicate. My statement was not about exo-colonization prior to the end of Sol (though agreed that is the final issue to deal with), or when it gets too hot, or when an asteroid hit, or any other single possible event. The point I'm making is that as some time in the future, some event will happen that will end life on Earth. I could care less about debating which event or when. Such doesn't matter to the single point, that at some time, life on Earth will end.


You are engaging in a fallacy that the only way to develop the technology needed is colonize other planets. Such argument is, in a word, nonsense. Like multiple people have pointed out, we'd be better served colonizing the deserts/poles/sea bottoms of the Earth first. It will teach us far more, far safely, far cheaper, with far more immediate benefits.
Thanks for trying to politely insult me. Again, you misunderstand me. I am not argueing. I'm also not stating a preference for any one technology or effort/project except to say that at some point the human race must figure out a way to live outside of our solar system or die. I'm not saying it should be this century or in the next billion years. It just needs to happen before the human race becomes extinct (or else we will be extinct).



Seriously, stop relying on sci fi writers, and maybe start looking at the actual engineering designs by NASA and others. The current design for the space elevator tapers at both end, not just the ground, with the widest point midway.
Agree with this. Though many sci-fi writers have great imaginations and try to be potentially feasible, they are not engineers or scientists. I will second the request to please stop trying to present fiction as scientific or technical theory.


A. C. Clarke knows more about what would be needed than most sci-fi writers, at least - being virtually "the father of the space elevator".
Which is to say, not much.


Unless he also somehow knew more about it 50 years ago than NASA engineers today, I'm still not going to take his word over theirs.

Agreed. 50+ year old fictional or theoretical notions are beyond obsolete.

[halfeye]

Your math is wrong, because you don't account for the atmospheric friction, which is crucial when dealing with an object with the density and air resistance of a feather.

I think Bova was exaggerating, for drama, cities are actually pretty rare in terms of land use, the probability of hitting one at random is slight.

However, I really doubt that a space elevator can be as light as 750 tonnes.

As well as that, this thing would be coming in at orbital speeds, and the atmosphere is only 100 miles thin. Down here, 100 miles is a long way to walk, but in terms of the distance to London from New York, it's a very small fraction, and the length of a space elevator is about seven or eight times that.

[hamishspence]

I think Bova was exaggerating, for drama, cities are actually pretty rare in terms of land use, the probability of hitting one at random is slight.

However, I really doubt that a space elevator can be as light as 750 tonnes.

The 750 ton one is a ribbon rather than a circular-cross-section one. 16mm wide at its widest point:

https://en.wikipedia.org/wiki/Space_elevator


One plan for construction uses conventional rockets to place a "minimum size" initial seed cable of only 19,800 kg.[2] This first very small ribbon would be adequate to support the first 619 kg climber. The first 207 climbers would carry up and attach more cable to the original, increasing its cross section area and widening the initial ribbon to about 160 mm wide at its widest point. The result would be a 750-ton cable with a lift capacity of 20 tons per climber.

IMO this was not intended to be "the biggest space elevator that will ever be built" but a prototype - a testbed - a way of proving that space elevators work. Once done, I think, if successful, NASA will plan bigger ones.

[halfeye]

IMO this was not intended to be "the biggest space elevator that will ever be built" but a prototype - a testbed - a way of proving that space elevators work. Once done, I think, if successful, NASA will plan bigger ones.

They have a rocket that can lift 750 tonnes to orbit? :smallconfused: :smalleek: :smallwink:

[hamishspence]

They have a rocket that can lift 750 tonnes to orbit? :smallconfused: :smalleek: :smallwink:

The 750 ton elevator's built a little at a time, the first component being only 20 tons. It's 750 tons in its final configuration.

The FAQ here:

http://www.pbs.org/wgbh/nova/space/edwards-elevator.html

mentions that while the first one would only be able to lift 13 tons, future ones might be able to lift 1000 tons.


Q: How big can the elevator get? What I mean is, what is the maximum amount of cargo that a theoretical elevator could take up into orbit at once?
Anonymous

Edwards: An upper limit is difficult to state, but we have already considered possible systems that could carry up to 1,000 tons. These are very large and require massive engineering but should be viable.

[Rockphed]

The 750 ton one is a ribbon rather than a circular-cross-section one. 16mm wide at its widest point:

https://en.wikipedia.org/wiki/Space_elevator



IMO this was not intended to be "the biggest space elevator that will ever be built" but a prototype - a testbed - a way of proving that space elevators work. Once done, I think, if successful, NASA will plan bigger ones.

In other words if we want more mass possible per climber, we need bigger space elevators. And I'm pretty sure that mass per climber is directly proportional to cross-section area. Nevertheless, a standard shipping container is 2.3 tons empty, so unless we were trying to move raw materials to earth in bulk we can probably do everything we want with 20 ton climbers. If we want to get crazy, we will make 1500 ton ribbons instead.

[Lazymancer]

A. C. Clarke knows more about what would be needed than most sci-fi writers, at least - being virtually "the father of the space elevator".
He is not. The concept dates back at the very least to 19th century (Tsiolkovsky). Modern design was developed in 1950s - by scientists, not Clarke.


However, I really doubt that a space elevator can be as light as 750 tonnes.
That's the initial one. Fully functional will be heavier - but nowhere near the "100 meters in diameter" nonsense.

EDIT: need more sleep. Read as "750 kg"

[hamishspence]

He is not. The concept dates back at the very least to 19th century (Tsiolkovsky). Modern design was developed in 1950s - by scientists, not Clarke.

Hence "virtually" - he was the guy who did a lot of the work of bringing the concept into the public eye - and he's the one that gets mentioned in the above FAQ.

Q: Several science fiction authors have written on this subject. Was Arthur C. Clarke the first? Who has come closest to current theory?
Mitch Burte, Andover, Massachusetts

Edwards: I believe Clarke was the first in a novel, and his most recent novel with Stephen Baxter uses the newest data. They did a very good and accurate job.


Something similar applied with communications satellites, before Sputnik:

http://lakdiva.org/clarke/1945ww/


I'm pretty sure that mass per climber is directly proportional to cross-section area. Nevertheless, a standard shipping container is 2.3 tons empty, so unless we were trying to move raw materials to earth in bulk we can probably do everything we want with 20 ton climbers.


I see moving materials to space in bulk, as one of the main benefits of space elevators (though these might be less "raw" and more "components for stations or spaceships".

That said, shipping stuff down at the same time as stuff is being shipped up, does provide energy that can be used for lifting things up, if it's set up right.

[Rockphed]

I see moving materials to space in bulk, as one of the main benefits of space elevators (though these might be less "raw" and more "components for stations or spaceships".

That said, shipping stuff down at the same time as stuff is being shipped up, does provide energy that can be used for lifting things up, if it's set up right.

I used the size of a cargo container because a lot of our current transportation infrastructure is built around moving things in cargo containers. Pretty much the only things not moved in cargo containers are bulk raw materials (e.g. coal, ore, grain, oil, etc.). And if we want to get those down from space we can either stuff them into descenders with regenerative braking, or just strap some heat shielding and drop them in a body of water. So long as the container is light enough for a climber to carry up, volume doesn't matter a lot, so they could theoretically float.

[hamishspence]

If a cable was built with 1000 ton load climbers, the climber might end up, most of the time, carrying 50 loaded regular containers weighing 20 tons, rather than any single 1000 ton item.

[Rakaydos]

I'm not sure why this thread has gone into SpaceElevator digressions.

Shouldn't we be talking about "150 tons to LEO, refuel, 150 tons to mars" SpaceX BFR?

[hamishspence]

I'm not sure why this thread has gone into SpaceElevator digressions.


Fairly early on, there was the "shipping people to Mars in large numbers will only be viable if we have space elevators" argument:




IIRC, the number was around 100 million people (each with cargo of up to ~1 ton) per year. Doable only if we'll build and master space elevators.

and later, there were questions on whether a crashing space elevator (on Earth, or on Mars) would be dangerous, or not.

[Bohandas]

This is no different from saying "Isaac Asimov had FTL drives. Therefore, eventually, they would need to exist, to support a thriving space industry."

Clarke, Asimov et al are not constrained by physical realities. Clarke was able to assume a material capable of holding up its own weight even when it weighted megatons. But since we don't know of any such material, saying "if the Space Elevator was made of unobtainium and then fell over it would destroy Earth, therefore all Space Elevators are dangerous" is a non-sequitor.

Agreed. I mean, seriously, Clarke's most famous work is a movie about killer robots, magic aliens, and magic alien robots. Take him with a grain of salt.

[Rakaydos]

Fairly early on, there was the "shipping people to Mars in large numbers will only be viable if we have space elevators" argument:



and later, there were questions on whether a crashing space elevator (on Earth, or on Mars) would be dangerous, or not.
But that argument is specius, if the BFR enters operation, and especially if it is later supplemented with something resembling the 2016 ITS rocket.

[Lvl 2 Expert]

They have a rocket that can lift 750 tonnes to orbit? :smallconfused: :smalleek: :smallwink:
20 tonnes.

https://en.wikipedia.org/wiki/Space_elevator

One plan for construction uses conventional rockets to place a "minimum size" initial seed cable of only 19,800 kg.[2] This first very small ribbon would be adequate to support the first 619 kg climber. The first 207 climbers would carry up and attach more cable to the original, increasing its cross section area and widening the initial ribbon to about 160 mm wide at its widest point. The result would be a 750-ton cable with a lift capacity of 20 tons per climber.

Still a lot, roughly a truckload, but at least weight wise in reach of our rockets (no idea how the actual cable stretching thing would happen).

[Lazymancer]

Hence "virtually" - he was the guy who did a lot of the work of bringing the concept into the public eye
I'm sorry, but a journalist who gives a tl;dr on Theory of Relativity for general public does not become the go-to expert on the topic.

Why should - much less rigorous - science fiction grant such authority?


Something similar applied with communications satellites, before Sputnik:
So, Sputnik was launched because of Clarke? Those damn commies, stealing American inventions...




I'm not sure why this thread has gone into SpaceElevator digressions.
Because any serious expansion into space requires ability to put a lot of stuff into said space. Rockets simply aren't cutting it.


But that argument is specius, if the BFR enters operation, and especially if it is later supplemented with something resembling the 2016 ITS rocket.
What is specious? Let's say we need to put 1 ton of cargo into space per person (I'm being generous).

A very rudimental colonization requires ability to put millions of people into outer space: that means millions of tons.

BFR - if it works - can haul 150 ton at once. I.e. deliver 150 people per launch. To have at least one million of people going into space per year (a very rudimental colonization) we need almost 7,000 BFR launches per year. I don't see this happening.

[hamishspence]

So, Sputnik was launched because of Clarke? Those damn commies, stealing American inventions...


Sputnik wasn't a communications satellite in geostationary orbit - all it did was bleep, in low orbit.

Clarke isn't the only person labelled "the father of satellite communications" but he's one of them.

[Lazymancer]

Sputnik wasn't a communications satellite in geostationary orbit - all it did was bleep, in low orbit.

Clarke isn't the only person labelled "the father of satellite communications" but he's one of them.
Okay. What was the point of the whole "Clarke wrote about satellite communications"?

[hamishspence]

I'm sorry, but a journalist who gives a tl;dr on Theory of Relativity for general public does not become the go-to expert on the topic.

Why should - much less rigorous - science fiction grant such authority?

Clarke understood more about space technology than the average journalist would about relativity, I think. His speciality was hard sci-fi, and he wasn't just a sci-fi writer - he was an inventor, a futurist, and so on:

https://en.wikipedia.org/wiki/Arthur_C._Clarke

As such, he's more of an authority than a soft-sci-fi writer without this kind of background, would be.

Plus, the people actually working on space elevators, emphasise his accuracy, and repeat the same thing he said about how, theoretically, there is no upper limit on the size of a space elevator- or at least, that it is difficult to state.


Q: How big can the elevator get? What I mean is, what is the maximum amount of cargo that a theoretical elevator could take up into orbit at once?
Anonymous

Edwards: An upper limit is difficult to state, but we have already considered possible systems that could carry up to 1,000 tons.

[Bohandas]

BFR - if it works - can haul 150 ton at once. I.e. deliver 150 people per launch. To have at least one million of people going into space per year (a very rudimental colonization) we need almost 7,000 BFR launches per year. I don't see this happening.

I think a million people per year is a bit more than rudimentary. Let's start with Plymouth levels and work up.

[hamishspence]

Can we agree that, if Mars is to be the subject of widespread colonisation, space elevators (on Earth and Mars) will help facilitate it?

[Lazymancer]

Clarke understood more about space technology than the average journalist would about relativity, I think.
Nevertheless, he is not an authority on subject. Not without presenting an actual research.


repeat the same thing he said about how, theoretically, there is no upper limit on the size of a space elevator- or at least, that it is difficult to state.
Limit is practical. 100 meter wide elevator tower would make sense only for an extremely advanced (mature) development of space elevators. The one we are not going to reach until we literally build hundreds - if not thousands - of space elevators all around globe, and the proceed to improve them again and again.

I.e. that is not something that is being discussed or suggested when we talk about actual space elevators.



I think a million people per year is a bit more than rudimentary. Let's start with Plymouth levels and work up.
I'm sorry, but having a hundred people on Mars is called "scientific expedition", not "colonization".

[Lazymancer]

Can we agree that, if Mars is to be the subject of widespread colonisation, space elevators (on Earth and Mars) will help facilitate it?
Then there is a problem (which I mentioned) that there simply is no reason to colonize Mars. Future is space stations, not planet-based colonies.

[hamishspence]

I could see colonising The Moon as a better "stepping stone in the process of advancing space technology" than colonising Mars. Mars might be more of a digression.

[Rakaydos]

I'm sorry, but having a hundred people on Mars is called "scientific expedition", not "colonization".

There's a pretty large gap between 100 person "scientific station" and a million per year "Evacuate the earth minimum shipping amount."

The SpaceX plan is to make it economically viable for 1 million pioneers to spend their own money to live on mars. They estimate that a million person colony has enough redundancy and population base to operate an industry that can make them ACTUALLY independant from earth.

They arnt going to make that viable with elevator cable "launches" every other week (because it takes half that time for the climber to go each way) and needing to repair LEO velocity paintchip damage. They need DAILY launches from hundreds of pads around the world to bring down the costs to airliner-like... so that's what they want to build.

[halfeye]

I've said it before, living on Venus is a better idea than living on Mars (probably in another thread). Sure the temperature needs to come down, but a sunshade made out of thousands of autonomous solar sails around the https://en.wikipedia.org/wiki/Lagrangian_point Venus/Sol L1 point should do that fine, and keep the temperature down afterward if needed.

Space elevators on Earth are a great idea, hopefully we will build one and eventually more in the future, but for now we're stuck with rockets, because they work using the materials and techniques we have now.

On the whole, I agree that space not planets ought to be our species' future main home, but almost all of those now living on Earth will never leave it, most of the future non-Earth population will be born off the Earth, sure there are problems to be overcome, but I have no doubt that they can be overcome.

[hamishspence]

I've said it before, living on Venus is a better idea than living on Mars (probably in another thread). Sure the temperature needs to come down, but a sunshade made out of thousands of autonomous solar sails around the https://en.wikipedia.org/wiki/Lagrangian_point Venus/Sol L1 point should do that fine, and keep the temperature down afterward if needed.

And possibly be used as a solar power generator as well?

[halfeye]

And possibly be used as a solar power generator as well?

I suspect not with current technology, they would be a bit far off. The Earth/Sol L1 is at about 1.5 million kilometres from Earth, so I'd guess the Venus/Sol L1 would be something like 0.75 to 1.0 million kilometres from Venus.

[hamishspence]

It doesn't have to generate power for the residents of the proposed Venus colony - instead it can generate power for space stations under the "sunshade".

[Bohandas]

A million people isn't a colony, it's a mass exodus

[Tvtyrant]

There's a pretty large gap between 100 person "scientific station" and a million per year "Evacuate the earth minimum shipping amount."

The SpaceX plan is to make it economically viable for 1 million pioneers to spend their own money to live on mars. They estimate that a million person colony has enough redundancy and population base to operate an industry that can make them ACTUALLY independant from earth.

They arnt going to make that viable with elevator cable "launches" every other week (because it takes half that time for the climber to go each way) and needing to repair LEO velocity paintchip damage. They need DAILY launches from hundreds of pads around the world to bring down the costs to airliner-like... so that's what they want to build.

And as mentioned before, this is meaningless until we can make artificial selfsufficient food sources on Earth. Putting the donkey before the race car here.

[Grey_Wolf_c]

They arnt going to make that viable with elevator cable "launches" every other week (because it takes half that time for the climber to go each way)

That's not how a space elevator would be used. The design allows for multiple climbers on the tether at any given time. Yes, each one takes days to arrive, but once the first one arrives, the next one is just a couple of hours behind it. Also, the pods will be disposable: either flung into deep space, or put in a shell and dropped back to Earth. But they won't be taking up tether time to go back down.

GW

[Rakaydos]

That's not how a space elevator would be used. The design allows for multiple climbers on the tether at any given time. Yes, each one takes days to arrive, but once the first one arrives, the next one is just a couple of hours behind it. Also, the pods will be disposable: either flung into deep space, or put in a shell and dropped back to Earth. But they won't be taking up tether time to go back down.

GW

Doesnt matter. One climber or many, the cable can only support a certian mass of climbers at a time.

[Rakaydos]

And as mentioned before, this is meaningless until we can make artificial selfsufficient food sources on Earth. Putting the donkey before the race car here.

Google "vertical farm."

[Tvtyrant]

Google "vertical farm."

If they actually worked third world countries wouldn't be destroying their trade balance by purchasing grain shipments from the US, they would be building vertical farms.

You need a system that can actually work without massive and continuous external inputs from a wealthier place, otherwise Mars becomes forever dependent on material shipments from Earth. This is not a good situation to be in when you have no balancing exports.

[Bohandas]

If they actually worked third world countries wouldn't be destroying their trade balance by purchasing grain shipments from the US, they would be building vertical farms.

By that logic regular farms don't work either or else the third world would grow their own food in regular farms.

[Tvtyrant]

By that logic regular farms don't work either or else the third world would grow their own food in regular farms.

They only work in specific regions. Civilization is an export, hence why those regions have seen mass migration to cities as food imports replace tiny self sustaining farms.

Comparing the two, if vertical farms work like third world farms no one in their right mind is going to go to Mars.

[Grey_Wolf_c]

Doesnt matter. One climber or many, the cable can only support a certian mass of climbers at a time.

It does matter, especially when I hear nonsense like "it takes two weeks between launches" as a "problem" for space elevators. By all means tell me what numbers you have in mind, because I'm tired of having the burden of evidence dumped on me every time someone comes boldly announcing that space elevators are useless but can't be bothered to actually do even basic calculations themselves.

GW

[Rockphed]

It does matter, especially when I hear nonsense like "it takes two weeks between launches" as a "problem" for space elevators. By all means tell me what numbers you have in mind, because I'm tired of having the burden of evidence dumped on me every time someone comes boldly announcing that space elevators are useless but can't be bothered to actually do even basic calculations themselves.

GW

My understanding is that when people say things about how big of a climber a space elevator can support, they typically are talking about the case where they have the tether pretty much full and are just putting one on the bottom as fast as they take one off the top. If you have a bunch of climbers spaced evenly over the tether, they mostly add to the tension rather than to the orbital mechanics.

[Bucky]

Also, the pods will be disposable: either flung into deep space, or put in a shell and dropped back to Earth. But they won't be taking up tether time to go back down.

GW

This seems wasteful. Mass in orbit is valuable. The pods should be recycled in place, either used in architecture, broken up for parts, scrapped for raw material or decomposed and used as extra reaction mass.

Near the top of the tether it might be worthwhile to use the previous batch of crawlers as counterweights to assist the climb of a new group of ascending crawlers.

[Rakaydos]

It does matter, especially when I hear nonsense like "it takes two weeks between launches" as a "problem" for space elevators. By all means tell me what numbers you have in mind, because I'm tired of having the burden of evidence dumped on me every time someone comes boldly announcing that space elevators are useless but can't be bothered to actually do even basic calculations themselves.

GW
I'm not saying the elevator is somehow worse than "1 launch every other year" disposable SLS. I understand the elevator is scalable- if you need more capacity, you spend some capacity bringing up more filaments to make the tether stronger.

But there's no fundamental reason a rocket cannot me made with enough margin that it refuels and reflies after a single day. (Elon apparently wanted a 12 hour turnaround- the engineers convinced him that 24 hours was reasonably possible.) For the cost of creating a single edge-of-theoretically-possible elevator filament, how many reusable heavy lift rockets can you assemble and get a thousand flights out of, each?

Space elevators are popular because rocket technoligy has been stuck in the 70s for almost half a century. Looking at the lack of progress national spaceflight programs made, it's easy to believe that the saturn 5 was the best rocket that CAN exist.

But that's wrong. Microchips, CAD programs, new material technologies and new manufacturing techniques mean rockets can be... and with both Blue Origin and SpaceX, along with smaller companies like Electron and Reaction Engines Limited, are becoming... so much better options. The Space elevator isn't even possible yet, and it's already becoming obsolete.

[halfeye]

I'm not saying the elevator is somehow worse than "1 launch every other year" disposable SLS. I understand the elevator is scalable- if you need more capacity, you spend some capacity bringing up more filaments to make the tether stronger.

But there's no fundamental reason a rocket cannot me made with enough margin that it refuels and reflies after a single day. (Elon apparently wanted a 12 hour turnaround- the engineers convinced him that 24 hours was reasonably possible.) For the cost of creating a single edge-of-theoretically-possible elevator filament, how many reusable heavy lift rockets can you assemble and get a thousand flights out of, each?

Including non-reusable fuel? Not many.


Space elevators are popular because rocket technoligy has been stuck in the 70s for almost half a century. Looking at the lack of progress national spaceflight programs made, it's easy to believe that the saturn 5 was the best rocket that CAN exist.

Saturn 5 was the '60s, it doubtless changed a little over time, but it first went to the moon in '69.


But that's wrong. Microchips, CAD programs, new material technologies and new manufacturing techniques mean rockets can be... and with both Blue Origin and SpaceX, along with smaller companies like Electron and Reaction Engines Limited, are becoming... so much better options. The Space elevator isn't even possible yet, and it's already becoming obsolete.

Rockets burn fuel, it's a large part of their cost, the fuel costs in going up a space elevator ought to be a lot less, economics is the main advantage the space elevator has.

[Grey_Wolf_c]

This seems wasteful. Mass in orbit is valuable. The pods should be recycled in place, either used in architecture, broken up for parts, scrapped for raw material or decomposed and used as extra reaction mass.

The NASA design calls for using the first few thousands to build up the counterweight at the far end of the elevator.


Near the top of the tether it might be worthwhile to use the previous batch of crawlers as counterweights to assist the climb of a new group of ascending crawlers.

Unless you can show me how that'd even be done, I don't think that is a thing that could happen with the tether-crawler design.


For the cost of creating a single edge-of-theoretically-possible elevator filament, how many reusable heavy lift rockets can you assemble and get a thousand flights out of, each?

Again, stop shifting the burden of evidence onto me. This is your argument, YOU present the numbers that make your case. Figure out what ballpark numbers Elon is promising, and compare them to the numbers expected for a space elevator. Simply saying "I'm sure that X-Space will be cheaper" is not an actual argument.

GW

[Rakaydos]

Including non-reusable fuel? Not many.

Rockets burn fuel, it's a large part of their cost, the fuel costs in going up a space elevator ought to be a lot less, economics is the main advantage the space elevator has.

"Propellant

Musk has famously stated at the National Press Club that the cost of propellant is only 0.3% the cost of the [falcon 9] rocket, which yields about $200,000 for a $60m launch."
https://space.stackexchange.com/questions/8330/what-is-the-cost-breakdown-for-a-falcon-9-launch

The 2017 BFR is fueled with about 4000 tons of Natural Gas (Methane) and Medical grade oxygen. Best estimate put the fuel costs at $500,000 dollars for 150 tons to orbit. (Methane is cheaper per ton than the Falcon 9's Kerosene) The rocket itself is more expensive, but is intended to be flown 1000 times per airframe, amortising the costs significantly.

@greywolf: https://www.sciencedaily.com/releases/2012/04/120412105109.htm
Not up to space elevator standards, but I'm not including BFR refurbishment or amortization costs either, so I'll call it a wash.
At $15 per gram of carbon nanotubes, and a minimum strand mass of 750 tons (earlier in this thread) is 750 million grams, or over 11 billion dollars for a single strand.

With the same money, you could refuel the BFR over 20,000 times, presumably putting 150 tons into orbit each time.

[Bohandas]

It should be noted that the fuel is non-renewable as well

[Rakaydos]

It should be noted that the fuel is non-renewable as well

Fuel is cheap. Precision engineered spacecraft (or escape-length atom-precise nanotubes) are expensive.

[Knaight]

Fuel is cheap. Precision engineered spacecraft (or escape-length atom-precise nanotubes) are expensive.

Fuel is also a pollutant when burned - and while that's pretty negligible at current rates (e.g. haloform production associated with the space shuttle which is at .25% of the world total (https://www.nasa.gov/centers/kennedy/about/information/shuttle_faq.html)) it can't be reasonably assumed that that stays true given a significant uptick in launches. Hydrogen-oxygen systems are generally better about this, but they aren't completely pure fuels as used and still cause problems.

Meanwhile if a space elevator is successfully produced the energy requirements drop precipitously.

[factotum]

Not up to space elevator standards, but I'm not including BFR refurbishment or amortization costs either, so I'll call it a wash.
At $15 per gram of carbon nanotubes, and a minimum strand mass of 750 tons (earlier in this thread) is 750 million grams, or over 11 billion dollars for a single strand.

With the same money, you could refuel the BFR over 20,000 times, presumably putting 150 tons into orbit each time.

And what do you do then? Just stop supplying your space colonies and space stations, which we're assuming you're going to have by this point (given the purpose of the thread)? Whereas if you built the space elevator, and hopefully did a decent job of it, you can keep using it to send stuff up.

[Rakaydos]

And what do you do then? Just stop supplying your space colonies and space stations, which we're assuming you're going to have by this point (given the purpose of the thread)? Whereas if you built the space elevator, and hopefully did a decent job of it, you can keep using it to send stuff up.

I cant see to find maintinance costs for multi-KM atomic-precice structures that undergo regular mechanical stress. Can you please suggest some values?

[Rakaydos]

Fuel is also a pollutant when burned - and while that's pretty negligible at current rates (e.g. haloform production associated with the space shuttle which is at .25% of the world total (https://www.nasa.gov/centers/kennedy/about/information/shuttle_faq.html)) it can't be reasonably assumed that that stays true given a significant uptick in launches. Hydrogen-oxygen systems are generally better about this, but they aren't completely pure fuels as used and still cause problems.

Meanwhile if a space elevator is successfully produced the energy requirements drop precipitously.

If that becomes a problem, they CAN reuse fuel, though not as cheaply. The Sabatier Reaction turns CO2 and H2O into CH4 and O2, and they are already building this tech for the mars end of the journy. Build it on the earth end as well, and counting the fuel lost in space forever, it's actually a net exporter of CO2.

[Knaight]

If that becomes a problem, they CAN reuse fuel, though not as cheaply. The Sabatier Reaction turns CO2 and H2O into CH4 and O2, and they are already building this tech for the mars end of the journy. Build it on the earth end as well, and counting the fuel lost in space forever, it's actually a net exporter of CO2.

Methane-oxygen rockets are almost certainly not good enough for fuel purposes, and CO2 is far from the only pollutant of concern.

[Bucky]

Unless you can show me how that'd even be done, I don't think that is a thing that could happen with the tether-crawler design.


Sure. The crawler gets partway up the tether and then meets and attaches to a separate cable lowered from the station at the geostationary point. The station hooks the other end to the deadweight crawler, which is suspended off to one side of the main tether.

As the ascending crawler climbs, it lowers the deadweight crawler, which provides most of the energy. Motors onboard the station handle the rest. Sometime between when the ascending crawler reaches the geostationary point and when it arrives at the counterweight, the deadweight crawler detaches and falls, taking precautions to avoid striking the tether on the way down.

The main benefit is that reduced energy requirements near the top of the elevator translate to reduced crawler weight at the bottom.

[Rakaydos]

Methane-oxygen rockets are almost certainly not good enough for fuel purposes, and CO2 is far from the only pollutant of concern.

You're welcome to explain that to Elon Musk. He's going all-in on his new methane-burning Raptor engine.

https://www.youtube.com/watch?v=If29t-bEYWM

[Rockphed]

You're welcome to explain that to Elon Musk. He's going all-in on his new methane-burning Raptor engine.

https://www.youtube.com/watch?v=If29t-bEYWM

As with many things, Musk's pursuit of something has very little to do with how effective that thing ends up being.

[LordEntrails]

...
But there's no fundamental reason a rocket cannot me made with enough margin that it refuels and reflies after a single day. (Elon apparently wanted a 12 hour turnaround- the engineers convinced him that 24 hours was reasonably possible.) For the cost of creating a single edge-of-theoretically-possible elevator filament, how many reusable heavy lift rockets can you assemble and get a thousand flights out of, each?...
To be fair, you should say '..how many theoretically reusable heavy lift rockets..'

Because 1000 flight launch vehicles have never been built and are still only theoretical.

[Knaight]

You're welcome to explain that to Elon Musk. He's going all-in on his new methane-burning Raptor engine.

https://www.youtube.com/watch?v=If29t-bEYWM

If this design actually works, I'll eat those words. As is though, I'm roughly as convinced by it as I am by the hyperloop, which appears to be going nowhere fast.

[Lvl 2 Expert]

You're welcome to explain that to Elon Musk. He's going all-in on his new methane-burning Raptor engine.

https://www.youtube.com/watch?v=If29t-bEYWM

He's dropping the car company and the several dozen other projects is funding/advertising?

[monomer]

If this design actually works, I'll eat those words. As is though, I'm roughly as convinced by it as I am by the hyperloop, which appears to be going nowhere fast.

Blue Origin BE-4 is also a Methalox engine. This is the engine that will be used in New Glenn, and probably ULA's Vulcan. I would like to know why you don't think it can be done, though.

(Just as a note, the USAF requires assured access to space, which means they need two distinct launch systems in case one gets grounded. Right now they have Falcon, Atlas, and Delta. Delta is being retired, and they can't use Russian-made RD-180 engines on the Atlas for national security launches. This means they will be dependent on either Vulcan or New Glenn flying. I would be surprised if they were hinging everything on an engine that can't work.)

[Rakaydos]

If this design actually works, I'll eat those words. As is though, I'm roughly as convinced by it as I am by the hyperloop, which appears to be going nowhere fast.

The rocket engine works.

https://www.youtube.com/watch?v=e7kqFt3nID4

The rocket as a whole needs some development and construction, but that's how the world works... the SLS has been in developmenet much longer tha the BFR is expected to, due to the difference between corporate priorities (profit) and govermental priorities. (jobs)

[Bohandas]

As with many things, Musk's pursuit of something has very little to do with how effective that thing ends up being.

Yeah, I have difficulty taking Musk entirely seriously.

Didn't he also once say that he was legitimately worried about the world being overrun by evil robots like in The Matrix or Terminator?

[Rakaydos]

Yeah, I have difficulty taking Musk entirely seriously.

Didn't he also once say that he was legitimately worried about the world being overrun by evil robots like in The Matrix or Terminator?

You clearly havn't been paying attention to modern politics. 'Bots are already being used as a weapon to shape the way people think at a national level. Just because they arnt carrying a gun, doesnt mean they cant be used to change our way of life- just look at the Net Neutrality controversy.

[Bohandas]

Military drones are more Phantom Menace style evil robots, what Musk is worried about is that the robots will take over and turn us into batteries.

[Rakaydos]

Military drones are more Phantom Menace style evil robots, what Musk is worried about is that the robots will take over and turn us into batteries.

Can you source your claim for what musk is worried about? Because twitterbots and facebook fake news pushers are far more dangerous than military drones.

[Lacuna Caster]

Venus is decent, and certain altitudes have survivable air pressures and temperatures. Unfortunately, the denser atmosphere and scarcity of water might make it harder to leave. On the bright side, exosphere skimming during a gravity slingshot could allow Venus to provide Martians with nitrogen for megahabitat atmospheres, and Martians could probably trade a few things for it.
I can buy that Mars is a potential fixer-upper, but colonising Venus seems like a very very long-term project to me. I suppose that if you erected a giant parasol at the lagrange point to cut off sunlight you could cool the surface enough to allow landings, but otherwise you're committed to living in giant blimps above a seething cauldron of volcanic gasses and acid rain, with no particularly easy access to building materials. What's the advantage over living in space?

I vaguely recall that Lunar soil is missing some key elements compared with Mars, so it's not as favourable for long-term settlement projects unless you're willing to trade in large volumes with the asteroid belt. I wouldn't complain if someone wants to fund a settlement, though.

I'm not sure if vertical farming is mature enough to feed a Mars colony, but cultured meat would definitely cut the volume needed to sustain a stable population that doesn't use in vitro fertilization or gametogenesis to resist genetic homogenization.
Explain?

[Lacuna Caster]

The 2017 BFR is fueled with about 4000 tons of Natural Gas (Methane) and Medical grade oxygen. Best estimate put the fuel costs at $500,000 dollars for 150 tons to orbit. (Methane is cheaper per ton than the Falcon 9's Kerosene) The rocket itself is more expensive, but is intended to be flown 1000 times per airframe, amortising the costs significantly.
I personally think that launch loops or space fountains are more plausible than elevators from an engineering perspective, and some analyses put the amortised cost of those approaches as low as 3 dollars per kilo. Still, if Musk is talking about 500K dollars for 150K kilograms of payload, then... that's pretty damn competitive, actually. Huh.


As with many things, Musk's pursuit of something has very little to do with how effective that thing ends up being.
Explain?

[Grey_Wolf_c]

I can buy that Mars is a potential fixer-upper, but colonising Venus seems like a very very long-term project to me. I suppose that if you erected a giant parasol at the lagrange point to cut off sunlight you could cool the surface enough to allow landings, but otherwise you're committed to living in giant blimps above a seething cauldron of volcanic gasses and acid rain, with no particularly easy access to building materials. What's the advantage over living in space?

Does Venus have a half-decent magnetosphere? Protection from solar radiation would be a definite plus.

I would hope that by the time we set up a colony in Venus we'd have mastered robotics to the point they could go down to do the mining for us, rather than send human beings into the mines.


I vaguely recall that Lunar soil is missing some key elements compared with Mars, so it's not as favourable for long-term settlement projects unless you're willing to trade in large volumes with the asteroid belt. I wouldn't complain if someone wants to fund a settlement, though.

Luna's main selling point is the lack of gravity well, and how that makes ship manufacturing, re-servicing and retooling easier (0-g manufacturing might not be that easy). If that is true, then anything missing from Luna will be easy enough to import, precisely because launching ships from Luna will be cheap.



I'm not sure if vertical farming is mature enough to feed a Mars colony, but cultured meat would definitely cut the volume needed to sustain a stable population that doesn't use in vitro fertilization or gametogenesis to resist genetic homogenization.Explain?
The trivial answer to this would be "because vertical farms are barely mature enough to feed an Earth population". But I suspect you mean the part about IV and genetic homogenization, in which case, I too would like to hear a detailed explanation for that.

GW

[Rakaydos]

I personally think that launch loops or space fountains are more plausible than elevators from an engineering perspective, and some analyses put the amortised cost of those approaches as low as 3 dollars per kilo. Still, if Musk is talking about 500K dollars for 150K kilograms of payload, then... that's pretty damn competitive, actually. Huh.

That's just the fuel costs, but yea. Even allowing for, say, tripling the cost per flight for airframe amortization and maintinance, it's the same order of magnatude as the various launch infrastructure.

Also, check out the Orbital Ring concept- it's basically a space fountain that doesnt touch down anywhere, with relatively short (100-200km) cables to earth keeping it stable.

[Excession]

Does Venus have a half-decent magnetosphere? Protection from solar radiation would be a definite plus.

Venus does not have an internally generated magnetic field, but it's not quite that simple. https://www.astrobio.net/also-in-news/a-magnetic-surprise-from-venus/ has more information. Still sounds like Venus's upper atmosphere is not a great place to be in terms of radiation.

[halfeye]

I can buy that Mars is a potential fixer-upper,

I on the other hand don't think that's so. The gravity is way too low for an Earthlike atmosphere to stay long past it being dropped in.

The lack of gravity is perhaps a problem for child development and human life in general.

It's cold and that can't easily be fixed.


but colonising Venus seems like a very very long-term project to me. I suppose that if you erected a giant parasol at the lagrange point to cut off sunlight you could cool the surface enough to allow landings.

That's what I'm saying, we can make lightsails ten km wide with current tech, and self driving cars look as if they will be here very soon, so that's do-able, and we know that temperate regions drop in temperature 30 degrees centigrade on Earth in half a year, so getting the temperature of Venus down isn't a thousand year problem, though it's not a five week one either.

Once the temperature is somewhere reasonable, plant life would love all the CO2, and bacteria would love the sulphur, then it's a matter of getting some water there, and then it'll be a nice place.


What's the advantage over living in space?

Suitable gravity for Earthlife without messing about with that life. Space is definitely the way to go in the long run, but for a planet other than Earth, Venus looks the best to me.


I vaguely recall that Lunar soil is missing some key elements compared with Mars, so it's not as favourable for long-term settlement projects unless you're willing to trade in large volumes with the asteroid belt. I wouldn't complain if someone wants to fund a settlement, though.

Explain?

The Moon is very near, and the gravity is low enough to get off it again without too much fuss.

It's a couple of weeks away, not a couple of years, so we can get help there, or move someone from there here, if the timescale isn't too tight (appendicitis would have to be dealt with in situ). It's a lot better than Mars in terms of accessibility, and we know the temperature is on average tolerable.

I think a viable Moonbase is one of the first steps we ought to take into space, it's on the way wherever we're going.

[Grey_Wolf_c]

we know the temperature is on average tolerable.

Wait, what?

GW

[Rakaydos]

Wait, what?

GW

Lol... he's not WRONG exactly... but that's the danger of averages. it's too hot during the 14 days of daylight and too cold during the 14 days of night, but if you could average that out somehow, either by being underground or some kind of heat battery, it shouldnt be too bad.

[Grey_Wolf_c]

Lol... he's not WRONG exactly... but that's the danger of averages. it's too hot during the 14 days of daylight and too cold during the 14 days of night, but if you could average that out somehow, either by being underground or some kind of heat battery, it shouldnt be too bad.

Even if I accepted that, wouldn't the likely Lunar base be in the pole, in one of the eternal dark craters where there is a chance to find water?

GW

[Rakaydos]

Even if I accepted that, wouldn't the likely Lunar base be in the pole, in one of the eternal dark craters where there is a chance to find water?

GW
Sure. would be about as "livable" as an antarctic base, if antarctica had no air.

[factotum]

I on the other hand don't think that's so. The gravity is way too low for an Earthlike atmosphere to stay long past it being dropped in.

I'm sure you keep bringing this up, and I keep giving the same answer--define "long". There is evidence that Mars used to have running water on its surface--running water which had time to erode rocks. Therefore, it must have had a decently thick atmosphere for millions of years. I'm pretty sure everybody would be OK with us giving Mars an atmosphere, knowing we'll have to top it up after a few million years.

[Leewei]

@halfeye:

Gravity's impact on child development is potentially a real problem. We need more research on what would happen, but current indications are that microgravity is bad. Mars isn't exactly microgravity (~3/8 G), but could still be problematic. This is your best point against a Martian outpost.

The atmospheric issue is brought on not by gravity, but by solar wind and very weak magnetosphere. Mars' gravity, as low as it is, can sustain an atmosphere with enough pressure to support life. This is supported by the planet's own geological record. We'd still need to somehow produce enough of a magnetic field to deflect the erosive charged particles being kicked out by the sun. Fission plants powering a planet-wide electrical grid would be one possibility. Another one is colliding asteroids in orbit around Mars to produce a substantially larger moon, which would then jump-start convection in the planet's interior by way of tidal forces.

If Mars can sustain an atmosphere, warming is possible using carbon dioxide, methane, or other greenhouse gasses. Between the challenges of heating up or cooling down bodies in a vacuum, heating up is far, far easier to accomplish. (Note that the interior of Mars is toasty. The planet's core is still magma.)

By comparison, Venus has an enormous amount of heat. Even with the sun's radiation blocked, the planet would need ages to cool down. This isn't a thousand year problem, but a million year one. Losing heat into a vacuum is just that slow.

Until we can put structures on Venus that don't immediately melt into slag, we'd be stuck in orbit at microgravity.

I agree with the lunar outpost idea. The moon is certainly the next step in a logical progression from Antarctic stations and ISS. The challenges look similar to those presented by creating an outpost on another planet.

[Tvtyrant]

I imagine the most interesting aspect of colonization is how quickly colonists would become their own species. The gravity on the moon is so low that very large, low muscle humans would quickly become the norm. Less pressure on joints and heart could easily lead to 10+ foot tall humanoids who can't breed with Earthlings at all.

[Grey_Wolf_c]

Another one is colliding asteroids in orbit around Mars to produce a substantially larger moon, which would then jump-start convection in the planet's interior by way of tidal forces.
Oh, there's an interesting idea. It'd take a hellishly large amount of asteroids, though, and I'm not sure how well they'd coalesce into a moon. Wouldn't you need to smack 'em hard enough to melt them together?


Until we can put structures on Venus that don't immediately melt into slag, we'd be stuck in orbit at microgravity.

No, the plan would be to have balloons floating in 1-atm, rather than in orbit. I believe that at that altitude, gravity would still be pretty Earth-like, and the amount of sulfuric acid rain would be manageable. What the people in said balloon cities would do to pass the time, though, that's where "having robots that can go down to the surface to mine" would come in.

ETA:

I imagine the most interesting aspect of colonization is how quickly colonists would become their own species. The gravity on the moon is so low that very large, low muscle humans would quickly become the norm. Less pressure on joints and heart could easily lead to 10+ foot tall humanoids who can't breed with Earthlings at all.
I don't know about that. IVF would allow for a significant period of interbreeding even after the point where it becomes physically unfeasible.

GW

[halfeye]

The atmospheric issue is brought on not by gravity, but by solar wind and very weak magnetosphere. Mars' gravity, as low as it is, can sustain an atmosphere with enough pressure to support life.

Citation needed. The cause of atmosphere loss AIUI is the speed of gas molecules exceeding escape velocity, which is why all that's left is CO2 (which is heavy, and thus has a low enough velocity at current Martian temperatures that it doesn't exceed escape velocity). The kinetic energy of gas molecules depends on temperature, only, that's what temperature is, and thus the speed at a given temperature depends on the mass of the molecule. Hydrogen and helium escape from Earth because their velocity is above escape velocity, luckily hydrogen usually bonds with something else before that happens, but helium is rare and getting rarer.


This is supported by the planet's own geological record.

As guesstimated from Earth. It's possible that at some time a big comet, or a lot of littler ones dumped enough water there to make things flow, but how long that would last is debateable. There can be erosion from sandstorms, and we know there are quite a few of those.


We'd still need to somehow produce enough of a magnetic field to deflect the erosive charged particles being kicked out by the sun. Fission plants powering a planet-wide electrical grid would be one possibility. Another one is colliding asteroids in orbit around Mars to produce a substantially larger moon, which would then jump-start convection in the planet's interior by way of tidal forces.

The gravity is still too low.


If Mars can sustain an atmosphere, warming is possible using carbon dioxide, methane, or other greenhouse gasses. Between the challenges of heating up or cooling down bodies in a vacuum, heating up is far, far easier to accomplish. (Note that the interior of Mars is toasty. The planet's core is still magma.)

That's a very big "if".


By comparison, Venus has an enormous amount of heat. Even with the sun's radiation blocked, the planet would need ages to cool down. This isn't a thousand year problem, but a million year one. Losing heat into a vacuum is just that slow.

As I said, Earth loses 30 degrees celcius in six months, we have less cloud cover, but we aren't half that hot, we need a reasonable simulation of Venus' atmosphere to begin to guess what would happen. If the winds dropped, the back might freeze out too fast.


Until we can put structures on Venus that don't immediately melt into slag, we'd be stuck in orbit at microgravity.

Yeah, we need to get that temperature down, electronics without solder is difficult, iron would hold up, but the electronics would be a problem.


I agree with the lunar outpost idea. The moon is certainly the next step in a logical progression from Antarctic stations and ISS. The challenges look similar to those presented by creating an outpost on another planet.

It's the obvious first place to go after LEO.

[Tvtyrant]

I don't know about that. IVF would allow for a significant period of interbreeding even after the point where it becomes physically unfeasible.

GW

That is fair I suppose. I imagine the communities would seperate pretty quick though, as Mooninites couldn't survive on Earth and Earthlings would be tiny compared to natural Mooninites.

Even 1 generation in would be a big difference, as the cartilidge in a Mooninite would fill with liquid and not compress during the day and would grow more during childhood.

You might get a lot of old folk colonization as it would keep their mobilility more into old age though. The moon as a retirement center is the moat hilarious ending.

[halfeye]

That is fair I suppose. I imagine the communities would seperate pretty quick though, as Mooninites couldn't survive on Earth and Earthlings would be tiny compared to natural Mooninites.

Even 1 generation in would be a big difference, as the cartilidge in a Mooninite would fill with liquid and not compress during the day and would grow more during childhood.

You might get a lot of old folk colonization as it would keep their mobilility more into old age though. The moon as a retirement center is the moat hilarious ending.

I don't think it will happen that quickly, but once people begin to adapt to space, we've achieved it, the colonisation of space is begun, from then on, it's humans in space.

[Grey_Wolf_c]

As I said, Earth loses 30 degrees celcius in six months,

Wait, what? You mean every winter? The heat wasn't lost, it just migrated South.

GW

[Leewei]

@halfeye:

Fair enough to ask for citations:

https://en.wikipedia.org/wiki/Atmospheric_escape#Thermal_escape_mechanisms

You're thinking Jeans Escape.

https://en.wikipedia.org/wiki/Atmosphere_of_Mars

NASA data shows that solar storms (i.e. lack of magnetosphere) are the culprit.

Note that the gravity on Mars is significant (~3/8 G) and could hold a lot more of an atmosphere than Mars currently has. Intuitively, one would think Mars would hold a bit under half of Earth's atmospheric pressure based on gravitational difference. Maybe a bit less than half of that -- half the atmosphere pulled by half the gravity. Instead, it's a hair over half a percent of Earth's.

Mars' geological record is hardly a "guesstimate".

http://geology.com/stories/13/rocks-on-mars/

Note the mudstone in the 2nd image. Mars certainly has had liquid water; the atmosphere must have been above water's triple point for a fair amount of the planet's history to produce this kind of rock.

Earth's annual temperature cycle you reference is atmospheric. Venus's entire planetary mass is enormously hot. This makes it somewhat more efficient at radiating heat, but adds orders of magnitude to what must be radiated off to make the surface livable.

TL/DR Magnetosphere, not gravity for Martian atmosphere. Venus takes far longer to cool than you indicate. Gravity's effect on human population is an important unknown.

[LordEntrails]

...
Didn't he also once say that he was legitimately worried about the world being overrun by evil robots like in The Matrix or Terminator?
Then I don't think you understand what he's talking about. He's not talking about a Roomba or a RPV/Drone. Go do a little reading on Deep Learning machines. Sure, Deep Q only learned to play Pong and it took it a few hundred games to learn. But how quickly could a similar computer play a thousand games of Pong if allowed to run at clock speed? And then if it learned that self-survival might be important? What else might it learn?


You clearly havn't been paying attention to modern politics. 'Bots are already being used as a weapon to shape the way people think at a national level. Just because they arnt carrying a gun, doesnt mean they cant be used to change our way of life- just look at the Net Neutrality controversy.

Our children will have to face the issue of computers that can learn faster than they can. And if those computers are connected to our existing computer controlled production facilities...

[halfeye]

Wait, what? You mean every winter? The heat wasn't lost, it just migrated South.

GW

I know it went. I suppose I don't care that much where it went, on the personal level. How did it migrate south (presumably north in the southern hemisphere)? The tropics don't get hotter in winter that I'm aware of.

@ Leewei

That Jeans escape thing does seem to be what I was talking about, I don't like that graph, Venus is way too cool, it's nearly Earth mass which is right, but it's temperature is 600+ degrees celcius, which ought to be about 900 degrees Kelvin, I'm not so sure Jupiter is that cool either.

[Leewei]

Oh, there's an interesting idea. It'd take a hellishly large amount of asteroids, though, and I'm not sure how well they'd coalesce into a moon. Wouldn't you need to smack 'em hard enough to melt them together?Deimos + Phobos + various bodies from the asteroid belt. Some of them, such as Ceres, could instead be smacked into Mars to increase surface heat and water presence. Velocities involved would be enormous due to the planet's gravitational pull. Care would be needed to decelerate these bodies. Even a relatively small delta V between bodies translates into an enormous amount of energy (i.e. heat and ejected mass). Collisions would vaporize a fair amount of mass, which would then precipitate into a dust cloud. Over time, the dust would either settle onto Mars, or onto the new moon.

Collisions with smaller bodies seem pretty ideal. The mass hitting the nascent moon would have its force dispersed into heat more than blowing bits off. With a regular enough stream of mass, the heat generated would melt the entire mass into a ball of slag.

It's a neat idea which could work out well in the long run, but it's also enormously costly compared to the artificial magnetosphere idea (which also comes with a planetary energy grid).


No, the plan would be to have balloons floating in 1-atm, rather than in orbit. I believe that at that altitude, gravity would still be pretty Earth-like, and the amount of sulfuric acid rain would be manageable. What the people in said balloon cities would do to pass the time, though, that's where "having robots that can go down to the surface to mine" would come in.Russia landed an explorer on Venus's surface. It died quickly after broadcasting a brief amount of image and technical data. The 870 degree Fahrenheit surface temperature simply does not allow for any modern mechanism to work.

Those balloons would need a lot of redundancy. Buoyancy seems a lot less reliable than inertia for holding up an outpost.

https://en.wikipedia.org/wiki/Atmosphere_of_Venus

50kph winds and sulfuric acid clouds don't seem insurmountable. 1atm pressure, Earth-similar temperature, and Earth-similar gravity all look fairly favorable.

I'm not convinced that Venus could be terraformed over the long run, but it absolutely has potential for the site of a manned research station. We'd need a heck of a good reason for humans to be there, though.

[Lacuna Caster]

Oh, there's an interesting idea. It'd take a hellishly large amount of asteroids, though, and I'm not sure how well they'd coalesce into a moon. Wouldn't you need to smack 'em hard enough to melt them together?
If you can get enough asteroids together that their gravitational effects would be significant enough to jump-start Mars' internal magma conveyor, I suspect they'll take care of smushing themselves.

I have some significant reservations about restarting Mars' tectonic processes, though- the place had volcanoes ten times higher than everest, once upon a time, and I don't wanna poke that bear. I think inducing an artificial electromagnetic field would be much easier to control.

However, if you're prepared to engineer megastructures on that scale... then it's probably easier to just erect greenhouse canopies (http://battleangel.wikia.com/wiki/Mars) across the surface as when you need to expand. That way you don't have to worry about losing atmo to space, or little things like dust storms, winter and unscheduled rain.


No, the plan would be to have balloons floating in 1-atm, rather than in orbit. I believe that at that altitude, gravity would still be pretty Earth-like, and the amount of sulfuric acid rain would be manageable. What the people in said balloon cities would do to pass the time, though, that's where "having robots that can go down to the surface to mine" would come in.
IIRC, the conditions on the venusian surface are so hellish that even robots don't even have an easy time operating- the lifetime of our probes so far has been on the order of hours, versus months or years for martian rovers. There are designs for refrigerating (https://www.newscientist.com/article/dn12905-antique-fridge-could-keep-venus-rover-cool/) the electronics and so forth, but it still seems like a non-trivial technical problem to me.


I don't know about that. IVF would allow for a significant period of interbreeding even after the point where it becomes physically unfeasible.
I suspect that DNA tailoring and related technologies are going to render the question rather quaint (http://battleangel.wikia.com/wiki/Venusian) long before you see much in the way of natural genetic drift.

Hmm. I really have Alita on the brain these days.

[Leewei]

I don't like that graph, Venus is way too cool, it's nearly Earth mass which is right, but it's temperature is 600+ degrees celcius, which ought to be about 900 degrees Kelvin, I'm not so sure Jupiter is that cool either.I see what you mean. It appears the graph subtracts 273 degrees from Venus's surface temperature rather than adding to it.

In any case, the second article, especially the NASA link showing the impact of solar storms on Mars, is what's critical. The first article merely provides definitions of the methods of atmospheric loss.

[Grey_Wolf_c]

I know it went. I suppose I don't care that much where it went, on the personal level. How did it migrate south (presumably north in the southern hemisphere)? The tropics don't get hotter in winter that I'm aware of.

I don't care how it got there - just that your claim that Earth lost 30K in 6 months is not true. The total heat reservoir of Earth did not go down by 30K, it just moved around where those 30K are at any given time.


Those balloons would need a lot of redundancy. Buoyancy seems a lot less reliable than inertia for holding up a city.

Not having crunched the numbers, I think they'd come to be about the same level of overall reliability. The biggest issue for any orbiting craft around Venus is that it must spend half of its time Sun side, and that's gonna be a nightmare for reliability, I suspect. But I know little of this other than the "NASA actually proposed a floating city for Venus, and some argue it is simpler than landing on Mars". If you are interested in going deeper than that, I can't really rebut your arguments one way or the other; I simply don't know enough about it, and I am not in a position to learn it - sorry.


If you can get enough asteroids together that their gravitational effects would be significant enough to jump-start Mars' internal magma conveyor, I suspect they'll take care of smushing themselves.

Yeah, but before we get there we'd have a 3-Body-problem from hell.


IIRC, the conditions on the venusian surface are so hellish that even robots don't even have an easy time operating- the lifetime of our probes so far has been on the order of hours, versus months or years for martian rovers. There are designs for refrigerating (https://www.newscientist.com/article/dn12905-antique-fridge-could-keep-venus-rover-cool/) the electronics and so forth, but it still seems like a non-trivial technical problem to me.

Well, yeah, it goes without saying that when discussing the viability of extraterrestrial construction, we always sooner or later hit a non-trivial technical problem. But the nice thing about those is that they might be difficult, but they are not unsurmountable (unlike, say, the tether material, which is so close to the edge of inviability that it might just be on the other side of it). It's not like I am suggesting we could set up a city-sized balloon in Venus next week.

Grey Wolf

[Lacuna Caster]

That's what I'm saying, we can make lightsails ten km wide with current tech, and self driving cars look as if they will be here very soon, so that's do-able, and we know that temperate regions drop in temperature 30 degrees centigrade on Earth in half a year, so getting the temperature of Venus down isn't a thousand year problem, though it's not a five week one either.

Once the temperature is somewhere reasonable, plant life would love all the CO2, and bacteria would love the sulphur, then it's a matter of getting some water there, and then it'll be a nice place.
Yeah, unfortunately, as Leewei touched on, the reason why Venus is so hot in the first place is because it's atmosphere is stuffed with very effective greenhouse gases, and it has a lot of volcanism, which suggests that even without sunlight it would take quite a while for surface temperatures to drop. It's an intriguing scenario, but I think you'd need to chemically modify the atmosphere first. I dimly recall someone proposing that you could seed the Venusian atmosphere with some kind of airborne algae that could sequester the carbon, but I think there's a critical shortage of water thanks to the sulphuric acid acting as a dessicant?

As for Mars- I don't know what effects reduced gravity are likely to have on foetal development, but on that score I'd be more concerned about perchlorates in the soil, which we know have an impact on thyroid function. Parts of Mars can actually reach 25 degrees C in the summer, so I'm not too worried about average temperatures if you stay underground or build greenhouse structures. And Mars appears to have all the elements necessary for life, along with substantial mineral deposits for building projects. Sure, it'd be tough, but once people are there I think they'll figure it out. Necessity and invention, yo.

[factotum]

The biggest issue for any orbiting craft around Venus is that it must spend half of its time Sun side, and that's gonna be a nightmare for reliability, I suspect.

Venus isn't *that* much closer to the Sun than we are--in fact, the temperature at the cloud tops is around -70C, because the albedo of the clouds are so high they reflect away most of the incoming heat. It's the small remnant which gets trapped *under* the clouds that gives rise to the hellish temperatures at the surface. It's also worth noting that the Magellan spacecraft which was sent to map Venus' surface via radar was orbiting the planet for more than four years without any major reliability issues--the main reason they had to terminate the mission was because the solar arrays had degraded to the point they couldn't reliably power the spacecraft, so if our hypothetical Venus orbiter used something other than solar cells to power it, it could presumably last much longer.

[Lacuna Caster]

Well, yeah, it goes without saying that when discussing the viability of extraterrestrial construction, we always sooner or later hit a non-trivial technical problem. But the nice thing about those is that they might be difficult, but they are not unsurmountable (unlike, say, the tether material, which is so close to the edge of inviability that it might just be on the other side of it)
Yeah, I suppose that's true- even a 50-day robot working life might be long enough to be useful if you have a service/repair station in orbit and a lot of initial capital investment, and one imagines that material sciences will advance a bit in the next few centuries.

Aside from the gravity, though, I'm just not seeing a major cost/benefit advantage? I guess if it turns out that < 1g is really seriously bad for long-term human health, you could make an argument for it, but I'd almost incline to genetically modify humans to suit Mars before tackling the challenges of terraforming Venus.

[Grey_Wolf_c]

Venus isn't *that* much closer to the Sun than we are--in fact, the temperature at the cloud tops is around -70C, because the albedo of the clouds are so high they reflect away most of the incoming heat. It's the small remnant which gets trapped *under* the clouds that gives rise to the hellish temperatures at the surface. It's also worth noting that the Magellan spacecraft which was sent to map Venus' surface via radar was orbiting the planet for more than four years without any major reliability issues--the main reason they had to terminate the mission was because the solar arrays had degraded to the point they couldn't reliably power the spacecraft, so if our hypothetical Venus orbiter used something other than solar cells to power it, it could presumably last much longer.

Yeah, that wasn't the issues I had in mind. More radiation exposure for any humans on board the hypothetical Venus orbital base. As someone posted, there is a weird pseudo-magnetic field on the far side of Venus (plus, you know, having a planet in the way is probably good protection too).


Aside from the gravity, though, I'm just not seeing a major cost/benefit advantage?

But that's the issue that started this all: is there really a major cost/benefit to any extraterrestrial base right now? It really always comes down to "putting our eggs in more than one basket", in which case the benefit is infinite and cost is therefore irrelevant to some (including, let me be clear, me), but the benefit is 0 and costs therefore excessive for others.

I don't have an answer to this. I have not seen anything that suggests that having a colony in mars or Venus would be economically beneficial. There might be some economic benefits to a Moon base, but that'd never be really self-sufficient, and it's not much of a second basket when anything that destroys Earth would probably take the moon with it as well. So, yeah, I admit that my idea of a floating Venus colony with quasi-magical mining robots its probably more sci-fi than anything else.

¯\_(ツ)_/¯

Grey Wolf

[Leewei]

And Mars appears to have all the elements necessary for life, along with substantial mineral deposits for building projects. Sure, it'd be tough, but once people are there I think they'll figure it out. Necessity and invention, yo.If you dig around in the right areas, Mars has uranium (https://en.wikipedia.org/wiki/Ore_resources_on_Mars). (Some evidence even suggests a naturally triggered runaway fission reaction on the red planet in the distant past.)

[Lvl 2 Expert]

Oh, there's an interesting idea. It'd take a hellishly large amount of asteroids, though, and I'm not sure how well they'd coalesce into a moon. Wouldn't you need to smack 'em hard enough to melt them together?

Probably about all of them, if it's possible at all. Ceres contains a quarter of the mass of the main belt, and it's quite small compared to our moon (https://upload.wikimedia.org/wikipedia/commons/1/16/Ceres_Earth_Moon_Comparison.png).

And as you said, getting them to stick together is going to be a bit of a trick. The escape velocity on Ceres is about 500m/s. That's quite fast even compared to say the speed of sound (+-350m/s), but I'd still worry that landing nine asteroids gently and screwing the tenth attempt up would turn it into a bowling party. Getting the combined body to orbit Mars (after you've managed to weld them together or wait long enough for that to happen by itself) is also going to take a bit of energy.

But hey, if it saves more energy in the long run... I'm just not sure if giant engineering projects like this will ever be preferable to just building large space ships for people to live in. Maybe if you specifically want something from Mars, you can't automate the process far enough and you want the circumstances to be nice for the employees and closed Mars habitats are not an option for some reason (like you're mining using massive earthquakes or something.)

[halfeye]

I don't care how it got there - just that your claim that Earth lost 30K in 6 months is not true. The total heat reservoir of Earth did not go down by 30K, it just moved around where those 30K are at any given time.

Yes, the overall exposure of the Earth to sunlight is pretty static due to our orbit being nearly circular. The south pole gets warmer when the north pole gets cooler. This is due to the axial tilt, and the relative amount of solar heating arriving being lower in winter than in summer. It gets down to freezing in winter here. It gets up to 30 degrees Centigrade in summer. That's a 30 degree swing, it's local to parts of each hemisphere in each respective winter-summer cycle, but it's a significant effect produced as far as I know solely by varying solar illumination. There is still some sunlight here in winter, days last 8 hours instead of 16, and the angle of the sun is much lower, but it still shines, and it's still too bright to look at. Cut it out completely and you would get a much more significant effect. For Earth, I don't think I would recommend a sunshade, winters are cold enough here anyway, but a limited sunshade is definitely one possible solution to global warming. Thinking further, an eqatorial sunshade that cooled the tropics but allowed the temperate zone to rise in temperature might be nice, but it probably wouldn't work out.

[Leewei]

That 30 degrees Celcius is fair to use -- in fact, it's probably understating the heat our planet radiates into space by a fair amount. Consider the temperature drop each night following sunset.

That said, ground temperature is far more constant, and solid matter holds far more heat than a gas at a similar temperature. According to Google, Venus is 10,000 times the mass of its atmosphere. Venus's atmosphere is about 100 times as massive as Earth's, for that matter. Surface area is similar to Earth, but the total amount of heat stored on this pizza oven of a planet is staggeringly high.

If you only need to radiate off 1% of Venus's total heat (very dubious), you'd need 10,000 years to drop 30° K. (1% cancels out the x100 atmospheric size, leaving 10,000 times the mass.) Assuming you can make the planet somehow livable at 600° K, it would need to radiate for 100,000 years. 200,000 years gets you to a comfortable 300° K.

This is just spitballing, of course. Hotter bodies radiate heat faster, it likely will take more than 1% of the mass cooling to make Venus's surface livable, and the heat radiated annually from Earth is probably more than 30° K. Still, this illustrates an optimistic time frame of many multiple thousands of years for Venus to become habitable.

[Rockphed]

That 30 degrees Celcius is fair to use -- in fact, it's probably understating the heat our planet radiates into space by a fair amount. Consider the temperature drop each night following sunset.

That said, ground temperature is far more constant, and solid matter holds far more heat than a gas at a similar temperature. According to Google, Venus is 10,000 times the mass of its atmosphere. Venus's atmosphere is about 100 times as massive as Earth's, for that matter. Surface area is similar to Earth, but the total amount of heat stored on this pizza oven of a planet is staggeringly high.

If you only need to radiate off 1% of Venus's total heat (very dubious), you'd need 10,000 years to drop 30° K. (1% cancels out the x100 atmospheric size, leaving 10,000 times the mass.) Assuming you can make the planet somehow livable at 600° K, it would need to radiate for 100,000 years. 200,000 years gets you to a comfortable 300° K.

This is just spitballing, of course. Hotter bodies radiate heat faster, it likely will take more than 1% of the mass cooling to make Venus's surface livable, and the heat radiated annually from Earth is probably more than 30° K. Still, this illustrates an optimistic time frame of many multiple thousands of years for Venus to become habitable.

Looking at wikipedia, there is an up to 25 K variation in some parts of the US over the course of a single day. Now, the Venusian atmosphere is currently very well mixed such that there doesn't seem to be any difference between day-side and night-side temperature wise, so completely blocking sunlight from Venus would probably only result in twice as much energy leaving as currently (using a really bad simplifying assumption about how planetary temperatures work).

[halfeye]

That said, ground temperature is far more constant, and solid matter holds far more heat than a gas at a similar temperature. According to Google, Venus is 10,000 times the mass of its atmosphere. Venus's atmosphere is about 100 times as massive as Earth's, for that matter. Surface area is similar to Earth, but the total amount of heat stored on this pizza oven of a planet is staggeringly high.

The Earth is flipping hot too. Lava comes out at about 1k Celcius. The temperature that needs to go at Venus is in the atmosphere, and maybe in the crust.

[Knaight]

That 30 degrees Celcius is fair to use -- in fact, it's probably understating the heat our planet radiates into space by a fair amount. Consider the temperature drop each night following sunset.

Much the same way that the summer winter cycle represents a local change in thermal energy storage from the northern to southern or southern to northern hemispheres the day-night cycle represents a local change of thermal energy that is constantly moving in the opposite direction of the apparent direction of the sun.

There's also the matter of how temperature isn't heat, and if we were concerned about heat we'd be using a power unit. That also makes our lives easier, as earth is very close to an equilibrium between heat out and heat in (it's every so slightly off, hence warming), and you can basically neglect everything but direct sunlight for heat in and call it a day.

[factotum]

You're not going to dump *any* heat from Venus until you strip off its atmosphere. At the moment, as I said above, the actual amount of solar radiation reaching the ground is less than on Earth because of the amount that gets reflected away by the clouds; it's purely the greenhouse effect which keeps temperature so high. Therefore, you've got to remove the clouds before you can start radiating heat into space, and that's not going to be easy!

[Rockphed]

You're not going to dump *any* heat from Venus until you strip off its atmosphere. At the moment, as I said above, the actual amount of solar radiation reaching the ground is less than on Earth because of the amount that gets reflected away by the clouds; it's purely the greenhouse effect which keeps temperature so high. Therefore, you've got to remove the clouds before you can start radiating heat into space, and that's not going to be easy!

The temperatures on Venus are fairly stable, therefore heat in equals heat out. Based on some sketchy numbers I found on the internet, Venus has an albedo of .8, so only 20% of the solar energy hitting it is absorbed. Thus it is absorbing 59,794,200,993,800,000 J per second and emitting 59,794,200,993,800,000 J per second. If we removed solar input, how long would it take the atmosphere to drop 10 K?

[Leewei]

The Earth is flipping hot too. Lava comes out at about 1k Celcius. The temperature that needs to go at Venus is in the atmosphere, and maybe in the crust.The calculations I put up included the assumption that we'd only need to cool 1% of Venus's mass - the atmosphere and the crust.

Good points from Knaight and Rockphed regarding both planets being essentially at thermal equilibrium.

[halfeye]

The calculations I put up included the assumption that we'd only need to cool 1% of Venus's mass - the atmosphere and the crust.

I did like the idea of that calculation, but I'm pretty sure that the crust is a lot less than 1% of Venus's mass. Earth's crust is on average something like 20 miles thick, call that 40km to be generous. Earth is 6,300 km in radius, so (approximating wildly) the crust is something like 0.3% of the volume, we don't need Venus's crust to initially be quite that thick, though it would be nice if it dropped to the right sort of temperature reasonably quickly.

[factotum]

Venus doesn't have plate tectonics, though, so the crust will tend to stay in one place rather than moving around as it does on Earth--that gives the heat more chance to seep down into the depths.

[Leewei]

@halfeye:
You're right that the interior of our planet is enormously hot -- moreso than the surface of Venus, if you go down far enough.

Our lithosphere is about 2% of planetary mass and has an average temperature of around 400° C. This still is in the same order of magnitude as my earlier very rough estimate (1% at 300° C). That is, around a hundred thousand years to cool down.

If you want to bring this value down, I'd suggest going after the heat radiation and heat storage (as opposed to temperature, which we've been covering so far).

I'd be surprised if we end up at 100,000 years on the dot; still, you need to somehow decrease this by four orders of magnitude to make the endeavor worthwhile.

[Leewei]

Venus doesn't have plate tectonics, though, so the crust will tend to stay in one place rather than moving around as it does on Earth--that gives the heat more chance to seep down into the depths.I wonder if this is, in fact, what's happening on Venus?

Our own core is very hot due to a mix of residual heat from our planet's formation and the decay of radioactive elements. If Venus also has the same, which I'd find very believable, I'd expect the planet's interior to be much hotter than the surface. That'd mean heat was traveling from rather than into the depths of our sister planet.

[Rockphed]

I wonder if this is, in fact, what's happening on Venus?

Our own core is very hot due to a mix of residual heat from our planet's formation and the decay of radioactive elements. If Venus also has the same, which I'd find very believable, I'd expect the planet's interior to be much hotter than the surface. That'd mean heat was traveling from rather than into the depths of our sister planet.

Venus does not seem to have plate tectonics, per se. However, the entire surface of Venus is much younger than the age of the solar system. I don't remember if it is 100,000 or 1,000,000 years old, but the entire surface is about the same age. Furthermore, there are what appear to the extinct volcanoes on its surface. I am willing to bet that the interior of the planet is hotter than the surface.

Edit: So I hunted down some numbers on the heat capacity of carbon-dioxide and the mass of the Venusian atmosphere. It looks like the atmosphere is about 4.8*10^20 kg. The specific heat of carbon-dioxide at 750 K is about 1.148. Assuming that the specific heat is piecewise linear (i.e. it is constant from 700 to 750 at the 750 value), it would take 127 hours for the surface temperature of Venus to drop 50 K. That number has all kinds of bad assumptions built in to it, but I think they all cancel out. It does assume that solar irradiation is completely blocked. If we are willing to wait a couple months for that temperature drop (i.e. wait 1270 hours), we would only need to block 10% of solar irradiation. Even that is very much beyond our current tech. I doubt we could block 1% of solar irradiation of Venus with any kind of reliability at the moment.

[Lacuna Caster]

Venus does not seem to have plate tectonics, per se. However, the entire surface of Venus is much younger than the age of the solar system. I don't remember if it is 100,000 or 1,000,000 years old, but the entire surface is about the same age. Furthermore, there are what appear to the extinct volcanoes on its surface. I am willing to bet that the interior of the planet is hotter than the surface.

Edit: So I hunted down some numbers on the heat capacity of carbon-dioxide and the mass of the Venusian atmosphere. It looks like the atmosphere is about 4.8*10^20 kg. The specific heat of carbon-dioxide at 750 K is about 1.148. Assuming that the specific heat is piecewise linear (i.e. it is constant from 700 to 750 at the 750 value), it would take 127 hours for the surface temperature of Venus to drop 50 K. That number has all kinds of bad assumptions built in to it, but I think they all cancel out. It does assume that solar irradiation is completely blocked. If we are willing to wait a couple months for that temperature drop (i.e. wait 1270 hours), we would only need to block 10% of solar irradiation. Even that is very much beyond our current tech. I doubt we could block 1% of solar irradiation of Venus with any kind of reliability at the moment.
Well, solar materials (https://en.wikipedia.org/wiki/Solar_sail#Materials) aren't beyond our capacity, it's just the sheer scale of manufacture that's a problem. If you could shuttle a particularly aluminium-rich asteroid to the lagrange point and introduce some van-neumann factory-machines to handle construction, it doesn't strike me as physically infeasible. Technologically that's on an order of decades-to-centuries, not hundreds of thousands of years.

I think Leewei's original estimate included waiting for the crust to cool down as well? How does that work out?


Oh, since SpaceX and re-usable rockets came up earlier, this might be of some interest:
http://www.sciencealert.com/nasa-first-international-space-station-refurbished-space-x-mission

[Grey_Wolf_c]

Oh, since SpaceX and re-usable rockets came up earlier, this might be of some interest:
http://www.sciencealert.com/nasa-first-international-space-station-refurbished-space-x-mission

Do you know if they recovered the boosters for a third run? I scanned the article, and it doesn't seem to say (may have missed it, I admit it, sorry if I did). I saw there was a video, but I'm in a bit of a hurry, and couldn't sit to watch it.

Thanks,

GW

[Lacuna Caster]

Looks like a smooth touchdown (https://youtu.be/OPHbqY9LHCs?t=1401), so yeah, in principle the boosters should be good for another run.

EDIT: The long-term cost Musk is talking about here (https://www.airspacemag.com/space/is-spacex-changing-the-rocket-equation-132285884/?page=3) is closer to 50$ per kilo, but maybe Rakaydos is more familiar with the price structure there?

[Tvtyrant]

What about tipping asteroids into Venus and using the impacts to jettison gas?

[Rockphed]

Well, solar materials (https://en.wikipedia.org/wiki/Solar_sail#Materials) aren't beyond our capacity, it's just the sheer scale of manufacture that's a problem. If you could shuttle a particularly aluminium-rich asteroid to the lagrange point and introduce some van-neumann factory-machines to handle construction, it doesn't strike me as physically infeasible. Technologically that's on an order of decades-to-centuries, not hundreds of thousands of years.

I think Leewei's original estimate included waiting for the crust to cool down as well? How does that work out?

My "1% on a good day" estimate was in regards to the sheer scale of blocking out the sun. I imagine that within a couple centuries we could figure out how to do it. I'm less certain that we will ever want to.

I used earth's crust mass to approximate the mass of Venus's crust and I am assuming that it is all quartz. Earth's crust is about 2.8 x 10^24 kg. Quartz has a heat capacity of 730 J/(kg K). In that case, the time to reduce the temperature of all of Venus's crust and all of its atmosphere by 50 K is 541 years. I am fairly certain that that is not actually a useful number.

[Rockphed]

Just take a chunk of the atmosphere to Mars and elsewhere with a fleet of self replicating exosphere skimmers equipped with collapsible solar sails, then sprinkle pulverized comets across the molten sucker.

I'm pretty sure I just showed that the atmosphere is not the problem vis-a-vis cooling Venus. The problem is the 700K rocks that need to cool down. I could probably construct a model for a reasonable heat gradient and use that to calculate the total heat that needs to be removed.

Also, unless we slow the comets down first, I am pretty sure that comets have more kinetic energy in their orbits than they would remove by being cold.

[Giggling Ghast]

I was actually thinking the other day about how science fiction has traditionally depicted a Mars colony. It either ends up as a total craphole or succeeds from Earth and we end up in an interplanetary war.

[DavidSh]

With neither atmosphere or sun, a black body with surface temperature 300K emits about 460 Watts per square meter.
Rock conducts heat at a rate of about (1.5 Watts per square meter) per (Kelvin per meter), therefore supporting a temperature gradient of about 300 Kelvin per meter. 700K rocks need only be a few meters down below a comfortable surface temperature, if the only heat source is internal, and there is no atmosphere to shift the radiation to a cooler effective surface.

Please check these numbers. I was surprised.


-G.G. -- Aye, I just finished up two novels by PKD where the Mars colonies were pretty unpleasant places to live.

[Lord Torath]

Transporting most of the atmosphere elsewhere is a multipurpose aspect to Venusian terraforming. Not only do you supply other locations with useful chemicals, you also reduce friction based heating from cometary material sprinkling, minimize the amount of toxic compounds that'll form alongside the hydrosphere, and lower the final surface pressure to a more survivable and useful figure. Ideally, the comets would be placed into orbit around Venus after the L1 solar shade has been built, and their powdered contents would be used to make it snow across the entire planet until the surface supports liquid water. (emphasis mine)

The amount of atmosphere doesn't hugely affect the amount of energy transferred when you crash a comet into a planet1. High atmospheric friction2 with the comet means there is less kinetic energy in the comet when it hits the ground. A thinner atmosphere means that more of the kinetic energy is transferred directly to the ground. In either case, the same amount of energy is added to the planet's heat budget: energy equal to the comet's mass times the square of its speed relative to the planet.

1. The atmosphere can affect how much of the impact energy stays on the planet. A thicker atmosphere will make it harder for debris (and thus energy) from a large impact to escape the planet. No real difference for small impacts, though.

2. Friction between the atmosphere and the comet/meteoroid itself is pretty negligible. Most of the heating is caused by the compression of gas at the normal shock generated by the comet moving faster than the speed of sound in the atmosphere it's moving through.

[Rockphed]

With neither atmosphere or sun, a black body with surface temperature 300K emits about 460 Watts per square meter.
Rock conducts heat at a rate of about (1.5 Watts per square meter) per (Kelvin per meter), therefore supporting a temperature gradient of about 300 Kelvin per meter. 700K rocks need only be a few meters down below a comfortable surface temperature, if the only heat source is internal, and there is no atmosphere to shift the radiation to a cooler effective surface.

Please check these numbers. I was surprised.


-G.G. -- Aye, I just finished up two novels by PKD where the Mars colonies were pretty unpleasant places to live.

That does sound a little low. I am going to assume we need to cool the equivalent of 20 meters of Venusian rock to achieve our aims. On the other hand, people don't need multiple meter thick walls on their ovens to be able to support 400 degrees higher temperatures inside. I'll see what I come up with with that new information. If anybody has a better material for the properties of rock than quartz, I would love to hear it. Maybe I should look up basalt.

Edit: Using Basalt instead of quartz, 20 meters of cooled rock, and assuming that the rate of radiation will be constant over the time frame, getting Venus down to earth temperatures (i.e. 16 C) will take 27.24 years. That seems almost doable if we can build a sun-shade big enough to blanket all of Venus in shadow and stick it at the Venus L1 point. Now to go figure out how big it would need to be.

Edit2: I did some math, and it looks like a total shade would be 1.8 times the diameter of Venus. It would have an area about 80% of Venus's surface area.

[Knaight]

Rock conducts heat at a rate of about (1.5 Watts per square meter) per (Kelvin per meter), therefore supporting a temperature gradient of about 300 Kelvin per meter. 700K rocks need only be a few meters down below a comfortable surface temperature, if the only heat source is internal, and there is no atmosphere to shift the radiation to a cooler effective surface.

Please check these numbers. I was surprised.

I don't have time to check them now, but I will note that one dimensional radial heat transfer looks pretty different than one dimensional linear heat transfer, with cylindrical and spherical systems also being pretty dramatically different. This looks like a linear heat transfer calculation that you've done.

[Rockphed]

Thanks for the correction and elaboration.

Unless I'm mistaken, the most optimal impact trajectory for the cometary snow would be straight down with no acceleration beyond that provided by Venusian gravity, right? Maybe snowmakers could detach from the towed comet, release their ground up payloads as they descend at 90° angles, then reenter stable orbits to rendezvous with the comet via hydrogen oxide rockets. If most of the atmosphere has been siphoned by exospheric skimmers, there'd be less exothermic reactions between imported water and local acids. With enough comets performing recursive Venus flybys, we could even shorten the Venusian day.

The venusian day is currently negative five thousand some odd hours. That is right, it rotates backwards. I'm not sure if the proper adjective for what we want to do is shortening or lengthening at this point. Venus also has a 177.36 degree orbital obliquity (earth has 23 degrees). Maybe what we really want is to try to fix that orbital inclination to something closer to 20 degrees with the day going the right way before we start trying to change the length of the day.

[halfeye]

The venusian day is currently negative five thousand some odd hours. That is right, it rotates backwards. I'm not sure if the proper adjective for what we want to do is shortening or lengthening at this point. Venus also has a 177.36 degree orbital obliquity (earth has 23 degrees). Maybe what we really want is to try to fix that orbital inclination to something closer to 20 degrees with the day going the right way before we start trying to change the length of the day.

While the temperature is way too hot that stuff doesn't matter, IMO, and I'm not sure it would matter when the temperature was survivable either, it's the sort of thing that life can adapt to fairly quickly.

Let me be clear, in my opinion living in space (in habitats in space in the first place) is important, living on other planets or bodies is less so, but of the planets Venus is available to us for long term use with less effort than any other planet would be. It would be possible to live on the Moon or Mars as if you were under the sea or something, and we couldn't do that on Venus, but if you want to be able to walk around without a spacesuit one day, getting to that stage will be easier on Venus.

[Rakaydos]

I'mma rain on all your parades... I may be championing all kinds of cutting edge rockets like SpaceX, but throwing asteroids around? Altering the spin of planets? You people have no idea the magnitude of the forces required.

[Leewei]

Flinging an asteroid directly at its target takes enormous energy. Slightly altering an asteroid so its course eventually brings it to orbit a planet is a different matter. It still takes enormous amounts of energy, but it's far, far less than the direct route.

Changing rotational direction of Venus is pretty mind-boggling.

[Grey_Wolf_c]

Changing rotational direction of Venus is pretty mind-boggling.

Also, unnecessary, AFAICT. Other than the sun rising in the "west", what exactly is the problem that would be solved by flipping Venus' rotation axis?

GW

[halfeye]

Also, unnecessary, AFAICT. Other than the sun rising in the "west", what exactly is the problem that would be solved by flipping Venus' rotation axis?

GW

I agree, except for the notation, for me west is where the sun sets, that overrules the other language issues with Venus's rotation. As I read wikipedia, Venus actually has a fairly normal rotation that's just backward compared to Earth with very little axial tilt, which would mean there would be much less in the way of seasonal change.

[Rockphed]

I agree, except for the notation, for me west is where the sun sets, that overrules the other language issues with Venus's rotation. As I read wikipedia, Venus actually has a fairly normal rotation that's just backward compared to Earth with very little axial tilt, which would mean there would be much less in the way of seasonal change.

Um, the venusian sidereal day is five-thousand some hours. The apparent day is two-thousand some. If you ignore the spinning backwards bit, the axial tilt is 3 degrees (my previous post was under the assumption that the axial tilt was about 90 degrees:smallredface:). My previous post was advocating pushing the tilt somewhere other than "pointed at the sun for a good chunk of the year", not trying to flip the thing over. If anything, simply changing the spin rate is probably cheaper and faster than trying to flip the planet over.

[factotum]

If anything, simply changing the spin rate is probably cheaper and faster than trying to flip the planet over.

I'd argue otherwise? The actual moment of inertia of the planet is going to be roughly the same regardless of which direction you try to spin it in, and spinning it perpendicular to its axis of rotation can be done very slowly--yes, it might take years for the planet to finish turning over, but it's still a lot easier than making a major change to its axial spin rate.

Having said that, both ideas are so far beyond anything we can reasonably expect to be doing in the next thousand years that I don't think they're worth discussing--the energy requirements are colossal.

[Leewei]

Right, we should be using comets, not asteroids. Comets can be contained in stress resistant polymer shells composed of local chemicals, then redirected with a combination of gravity tractors, thrusters fueled by local chemicals, reflective coatings, and gravitational slingshots assisted by asteroids, planetoids, and other comets. By exploiting cyclical Hohmann transfer orbits, we can set up a comet "railroad" that goes between Venus and Mars, which will provide both planets with useful volatiles, shipping access, and rotation modification. Sure, it'll cost a lot of energy to set this up, but it's a multipurpose system that can help accelerate the development of a stable, interplanetary civilization.

As for whether we can reasonably expect to be doing this in the next 1000 years, I think it's quite possible and worth discussing. Ideas that seem unrealistic today can seem obvious tomorrow, and even the most incredible concepts can add flavor to science fiction, at the very least.I'm pretty agnostic to where the mass comes from, but aren't comets inaccessible and rare? If you're using comets to change Venus's rotation, it's going to take a heck of a lot of them.

For that matter, it isn't at all clear to me why Venus's rotational direction needs to change.

[factotum]

I'm not a physicist, so I can't tell you how much time it'd take to apply all of this mass towards changing Venus's rotation. All I know is that we have a lot of comets to work with, and it'd be worth fetching them even if we don't use them for this purpose.

The problem you have is energy, again. Changing the orbits of Kuiper belt material to bring it down into the inner Solar System wouldn't be too hard because they're not travelling very fast when they're out there, but pulling them into a useful orbit when they're actually *in* the inner Solar System and travelling at ridiculous velocities (something like 1.4x Venus' orbital velocity when they're at the same orbital distance, I think) would be an incredibly difficult thing to do.

[Leewei]

The problem you have is energy, again. Changing the orbits of Kuiper belt material to bring it down into the inner Solar System wouldn't be too hard because they're not travelling very fast when they're out there, but pulling them into a useful orbit when they're actually *in* the inner Solar System and travelling at ridiculous velocities (something like 1.4x Venus' orbital velocity when they're at the same orbital distance, I think) would be an incredibly difficult thing to do.The Kuiper belt is also mind-bogglingly huge. Detecting useful matter in this region is a staggering challenge which we'd need to overcome before putting it to use. Distances are between 30AU and 50AU from the sun, compared to a bit more than 3AU for the asteroid belt past Mars (which is at 1.5AU from Sol, or 0.5AU from Earth's orbital path).

A simple, 2D comparison of the Kuiper belt to the rest of the solar system suggests you'd need to survey a region nearly twice as large as the rest of the system. Matter in the Kuiper belt would be far more diffuse and poorly-lit than it is closer to the sun. It may well be that there is a lot of stuff out there worth putting to use, but the challenge of doing so is an order of magnitude harder compared to using other sources.

[Bohandas]

While we're on the topic of superconstruction pipe-dreams, what if we generated power by building a massive coil around a rapidly spinning magnetar (turning it into a gigantic dynamo) and running a long wire of superconducting YBCO from it back to our own solar system. Once the decades required for the electricity to travel the lightyears of distance had passed we would have a nearly unlimited supply of power.

Also what if we launched a bakery into orbit so we could have actual pie in the sky

EDIT:

What kind of engine do you need to put a castle in the air?

[halfeye]

Assuming the Kuiper Belt has a total mass between 0.04 to 30 Earth masses

Where the fritz did you get that lower bound? There are Pluto, Eris, Sedna, Haumea and many others, surely the combination of just those named takes it above that?

[factotum]

Where the fritz did you get that lower bound? There are Pluto, Eris, Sedna, Haumea and many others, surely the combination of just those named takes it above that?

Those bodies are not very massive--they're mostly made of lighter materials like ice and are quite small. Eris is the most massive known Kuiper belt object at 0.0028x Earth mass, Pluto is a touch lighter, Haumea is less than 1/1000th Earth mass and I don't think Sedna's mass has been measured--so even if all four bodies were as massive as Eris (which they're not) the total would only be 0.0112 Earth masses, quite a bit less than WhatThePhysics' lower limit.

[Lacuna Caster]

Also what if we launched a bakery into orbit so we could have actual pie in the sky
Have the crew of the ISS not done this yet? It sounds like a neat photo-op.

'Mannequin Skywalker'. Heh.

[factotum]

Have the crew of the ISS not done this yet? It sounds like a neat photo-op.

I can see a couple of problems trying to cook a pie on the ISS. First is that you'll get bits of pastry, flour and who knows what else floating around in the microgravity and potentially causing issues. Secondly, I don't think conventional ovens work well in microgravity because there's no convection, so hot air tends to cluster around the heating elements--I suppose you could fix that one by using a fan-assisted oven, though.

[Rockphed]

I can see a couple of problems trying to cook a pie on the ISS. First is that you'll get bits of pastry, flour and who knows what else floating around in the microgravity and potentially causing issues. Secondly, I don't think conventional ovens work well in microgravity because there's no convection, so hot air tends to cluster around the heating elements--I suppose you could fix that one by using a fan-assisted oven, though.

I thought conventional ovens cooked things via radiation. Or maybe there is an oven temperature when the primary heating method changes from convection to radiation.

[LordEntrails]

Who said you had to cook the pie on the ISS? Just ship it up there...

[georgie_leech]

I thought conventional ovens cooked things via radiation. Or maybe there is an oven temperature when the primary heating method changes from convection to radiation.

They heat the air in the oven, which transfers heat to the food through conduction. Microwave ovens use resonant frequencies to increase the effectiveness of the energy delivered to specific parts of the food based on position, which is why they tend to do things like be frozen on the outside until you bite a piece of molten cheese. Neither is really radiative heat transfer the way it works outside of the atmosphere.

[factotum]

A grill cooks things through radiation. Ovens do it via transferring heat from the heating elements (or the gas flame, if you have a gas cooker) to the air inside the oven, and thence to the food, as georgie_leech said. That's why fan ovens exist--they're more efficient at transferring the heat.

[Rakaydos]

All this talk of pies, shipping, and fan ovens makes me wonder how much it'd cost to add a spin gravity module to the International Space Station. :smallsigh:

There was a proposal, but apparently there was problmes isolating the vibrations of the bearings from delicate zero-g expiriments elswhere on the station.

[factotum]

I would have thought the bigger problem would be preventing friction in the bearings transferring the rotation of the centrifuge to the main body of the station.

[Lacuna Caster]

I would have thought the bigger problem would be preventing friction in the bearings transferring the rotation of the centrifuge to the main body of the station.
You could probably compensate with microthrusters, but I thought the standard solution was having a counterweight spinning in the other direction?

Dunno how to fix the vibration problem, though. Could you just install some kind of floor-ventilation system to suck out all the flour and debris and create a crude proxy-gravity? There's a Nature paper in the making here, I just know it.

[Leewei]

Mass produce probes, and have some of them be statites with collapsible solar sails. The latter group's sensory capabilities should be maximized due to the sails blocking solar radiation, and the units remaining stationary relative to obscurable stars.
It'd take a heck of a lot of probes to survey a region with an inner diameter of around 200AU (2 x pi x R, where R is 30 AU). Can you somehow quantify what you'll need and speculate on where you'll get the material to build them?

[Ravens_cry]

It'd take a heck of a lot of probes to survey a region with an inner diameter of around 200AU (2 x pi x R, where R is 30 AU). Can you somehow quantify what you'll need and speculate on where you'll get the material to build them?
Asteroids and comets? For something building current tech probes, you need water*, carbon*, metals, and silica.
*For fuel and plastics

[Leewei]

Asteroids and comets? For something building current tech probes, you need water*, carbon*, metals, and silica.
*For fuel and plasticsThere's some context here. The survey is being done to find comets to use for terraforming worlds such as Venus or Mars. I'm wondering how reasonable it is to survey, since it may well be you'd use up more than you got from the Kuiper belt.

[georgie_leech]

There's some context here. The survey is being done to find comets to use for terraforming worlds such as Venus or Mars. I'm wondering how reasonable it is to survey, since it may well be you'd use up more than you got from the Kuiper belt.

Specifically Venus, as supposedly the temperature will help offset the energy input by the comet slamming into the planet, which supposedly is being done to correct the direction of rotation? Because... I can't actually follow why that's supposed to be necessary, so because reasons?

[Bohandas]

They heat the air in the oven, which transfers heat to the food through conduction. Microwave ovens use resonant frequencies to increase the effectiveness of the energy delivered to specific parts of the food based on position, which is why they tend to do things like be frozen on the outside until you bite a piece of molten cheese. Neither is really radiative heat transfer the way it works outside of the atmosphere.

based on composition

[georgie_leech]

based on composition

Partly. But the reason why relatively weak radiation is able to heat food uses both resonant frequencies, and patterns of constructive interference. It's why most microwaves rotate meals; certain areas within the microwave will be warmed faster than others, so rotating the food should ensure a more even cook. In theory at least. In practice, pockets of molten cheese continue to sit beside Frozen bits in our hot pockets :smalltongue:

[factotum]

In practice, pockets of molten cheese continue to sit beside Frozen bits in our hot pockets
:smalltongue:

There's another reason for that behaviour--microwaves basically work by heating the water in the food, but they're not very good at heating ice. Since the heating is also uneven, as you say, and the clumps of ice are of differing sizes, you will tend to get bits that melt first and then heat very quickly while the other bits are still frozen and not absorbing microwaves very well. This is why you're supposed to stir frozen things partway through cooking, or else leave them to stand for a couple of minutes to allow the hot parts to melt the still-frozen bits.

[Rockphed]

There's another reason for that behaviour--microwaves basically work by heating the water in the food...

Microwaves also heat fats and some sugars, but mostly they heat the water.

[Bucky]

While we're on the topic of superconstruction pipe-dreams, what if we generated power by building a massive coil around a rapidly spinning magnetar (turning it into a gigantic dynamo) and running a long wire of superconducting YBCO from it back to our own solar system. Once the decades required for the electricity to travel the lightyears of distance had passed we would have a nearly unlimited supply of power.


The amount of current we can get through the wire without superconductivity breaking down is proportional to the cross-section of the wire.

Multiply that cross-section by the several thousand lightyears to the closest magnetar and you have a LOT of wire.

That means you need a lot of energy to position it. Simply dropping it off from a moving rocket isn't good enough, the wire needs to be stationary.

In fact, it's probably more energy than you could ever hope to transfer even in millions of years of operation.

Once you have the wire in place, you still need to worry about things like galactic drift, objects passing through the space occupied by the wire etc. so it's unlikely you could actually keep the wire in place for millions of years without needing to re-string it.

Oh, and the dynamo might not work as well as you want it to because superconductivity also breaks down in intense magnetic fields.

[Mando Knight]

The amount of current we can get through the wire without superconductivity breaking down is proportional to the cross-section of the wire.

Multiply that cross-section by the several thousand lightyears to the closest magnetar and you have a LOT of wire.

That means you need a lot of energy to position it. Simply dropping it off from a moving rocket isn't good enough, the wire needs to be stationary.

In fact, it's probably more energy than you could ever hope to transfer even in millions of years of operation.

Once you have the wire in place, you still need to worry about things like galactic drift, objects passing through the space occupied by the wire etc. so it's unlikely you could actually keep the wire in place for millions of years without needing to re-string it.

Oh, and the dynamo might not work as well as you want it to because superconductivity also breaks down in intense magnetic fields.

I think that at the point where you're literally building a dynamo out of a hyper-condensed star, maintaining superconductivity in the wire you're using might not actually be the most ridiculous feat you're attempting.