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  1. - Top - End - #121
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    Default Re: Venus or Mars for terraforming and colonisation?

    Quote Originally Posted by Tyndmyr View Post
    The potato's just not going to stay together.
    I'm not sure that actually matters when every molecule in the potato is travelling fast enough to cause instant fusion with anything it hits, TBH. Plus, you said it yourself, the kinetic energy of the potato has to go *somewhere*, and since you can keep adding kinetic energy to the potato without upper limit (it just gets closer and closer to lightspeed as you do), something's gotta happen if, for example, you lob a potato with kinetic energy equivalent to the gravitational binding energy of the Earth into the planet.

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    Default Re: Venus or Mars for terraforming and colonisation?

    Quote Originally Posted by Tyndmyr View Post
    Yeah, gravity in different directions effectively cancels out.*

    For instance, if you are directly between the moon and the earth, there's a point where the gravity of the two cancels(much closer to the moon), and you'll experience zero g. This is one type of Langrage point.

    There may be some slight variations, because gravity in practice is never exactly even, so there may be local areas where you can get marginally higher gravity than what Mars normally has, but this would be a very small effect, it's not going to be noticeable on a human level.

    *in most cases. If the gradient is extremely high, such as while falling into a black hole, there are...severe effects. Mostly this won't matter on a planetary scale, though, and can be ignored.



    Assuming such terraforming is possible, that would be cool, but it is probably not an easier problem than building a reliable space station. We've actually built space stations, scaling those up to bigger and better ones is a far smaller jump than going to planet scale terraforming.

    Honestly, we haven't even gotten down management of earth's greenhouse effect. If we can't handle that, Venus's seems like hard mode.
    Weird and fascinating. Pretty cool little factoid there.


    Quote Originally Posted by Tyndmyr View Post
    Indeed.

    And still, problems of such a magnitude are tiny in comparison to fixing an entire world such as Venus.

    The effort required to nudge climate even a degree or two lower on a planetary scale is truly immense. Difficult to contemplate doing successfully even on the planet we're currently on. Even stopping the warming is a pretty big challenge, let alone reversing it.
    Terraforming is weird because in a very real way, it's actually easier than doing minute adjustments to an already existing planet. Like, we can't cool Earth by bombarding it with asteroids, because that would be much much worse than the problem in the first place. And you don't need to worry about introducing something that'll take over the ecosystem because getting anything to live on the other planet is a pretty big success.

    Though the other big thing is terraforming very much is still a dream. We are lacking in key technologies to even make it possible, and by the time we figure those out, terraforming may be pointless. While global warming is a very real and relevant threat that we can do something about today.
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  3. - Top - End - #123
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    Default Re: Venus or Mars for terraforming and colonisation?

    Quote Originally Posted by Forum Explorer View Post
    Wait really? I thought being surrounded by all that mass would effectively put the pressure of the entire planet on you.
    Pressure is different from gravity. Pressure is from all the stuff above and around you being pulled down by gravity. At Earth's center of mass there is no gravity, but there is extreme pressure.
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    Default Re: Venus or Mars for terraforming and colonisation?

    Quote Originally Posted by Lord Torath View Post
    Pressure is different from gravity. Pressure is from all the stuff above and around you being pulled down by gravity. At Earth's center of mass there is no gravity, but there is extreme pressure.
    Which is one of those things that makes perfect sense but still takes a few moments to wrap my head around.


    And to bring it back to what got us on this subject: If you dig down, you experience more pressure, not gravity. A force acting against you can effectively act as an artificial gravity, kinda like how spinning a space station doesn't actually create gravity but the centrifugal force of the motion acts on your body like gravity would.

    So how far down would you need to dig on Mars to have the pressure act to bolster the gravity you are experiencing?
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    Default Re: Venus or Mars for terraforming and colonisation?

    Quote Originally Posted by Forum Explorer View Post
    So how far down would you need to dig on Mars to have the pressure act to bolster the gravity you are experiencing?
    Fluid pressure doesn't work like that; unless you're dealing with a very high pressure gradient, the net effect is essentially neutral - the fluid pushing "down" on you is also pushing "down" on the fluid around you, which causes the fluid around you to push "up" (and "in") on you and essentially cancel out the pressure pushing "down." The pressure is trying to squeeze you into a smaller you-shaped box, not alter your position in the fluid column.

    If you are dealing with a very high pressure gradient, then the effect you would expect to see is that the parts of your body lower in the fluid column will be compressed, forcing your blood into the parts of your body higher in the fluid column, i.e. the pressure would be working against gravity; this is essentially how a g-suit works. Most likely, this would not be particularly beneficial to your long-term well-being; it certainly would not work to boost the apparent gravity of the planet to something closer to a standard gravity. If the pressure gradient is sufficiently extreme, you might even be able to "float" at a given level in the fluid column... but if you're in an environment with a pressure gradient that extreme, you're probably dead.
    Last edited by Aeson; 2021-02-28 at 12:20 AM.

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    Default Re: Venus or Mars for terraforming and colonisation?

    Quote Originally Posted by Aeson View Post
    If you are dealing with a very high pressure gradient, then the effect you would expect to see is that the parts of your body lower in the fluid column will be compressed, forcing your blood into the parts of your body higher in the fluid column, i.e. the pressure would be working against gravity; this is essentially how a g-suit works. Most likely, this would not be particularly beneficial to your long-term well-being; it certainly would not work to boost the apparent gravity of the planet to something closer to a standard gravity. If the pressure gradient is sufficiently extreme, you might even be able to "float" at a given level in the fluid column... but if you're in an environment with a pressure gradient that extreme, you're probably dead.
    A few examples: the pressure of 100 km of air1 = 10 m water = 760 mm liquid mercury (very roughly). The denser the liquid, the steeper the pressure differential. If you could stand in a vat or pool of mercury, your feet would experience roughly 2 atmospheres of pressure more than your head would. You can't though, as mercury is about 13 times denser than your body is2.

    1. I should clarify that this is 100 km of air on Earth, where the air gets more diffuse as you go up it. Half that air pressure comes form the first 5.5 km of air.
    2. I suppose someone could put you in a tube with just enough room for your body, put a lid on it, and then fill it full of mercury. The buoyant force would jam you pretty hard against the lid, though.
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    Default Re: Venus or Mars for terraforming and colonisation?

    Anecdotally, the Apollo astronauts who went to the surface of the moon had less bone and muscle deterioration than the ones that stayed in the command module- enough less to suggest there was actually some recovery from the trip out while they were down there. This suggests that even very low planetary gravities are better for human physiology than NO effective gravity.

    A low orbit spin gravity station like the proposed Voyager Station (Formerly Von Braun Station) is easy to reach, but there is nothing THERE- everything has to be imported and/or recycled.

    Mars surface is easier to reach than the lunar surface, thanks to aerobraking in even the thin martian atmosphere. It's easier to survive on mars with the right equipment and local resources, if things dont go horribly wrong. It's easier to ESCAPE the moon if things DO go horribly wrong.

    As for Venus surface terraforming, the biggest problem is planetary rotation. Even the MOON has a faster day/night cycle (1 full day every month) than the surface of venus. (about 2 months of day and 2 months of night) You can imagine what that would mean for anything that would be living outdoors if you managed to solve all the other insolvable problems of terraforming venus.

    Venus cloud cities are much more promising- due to atmospheric superrotation, the habitable band of the venus atmosphere has about 24 hours of day and 24 hours of night. And a breathable air mix is a lifting gas on venus. resources would have to be filtered from the air, which makes solids difficult to get, but energy would be plentiful. But it's not an approach we have much experience with.
    Last edited by Rakaydos; 2021-02-28 at 09:47 AM.

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    Default Re: Venus or Mars for terraforming and colonisation?

    Quote Originally Posted by Rakaydos View Post
    Anecdotally, the Apollo astronauts who went to the surface of the moon had less bone and muscle deterioration than the ones that stayed in the command module- enough less to suggest there was actually some recovery from the trip out while they were down there. This suggests that even very low planetary gravities are better for human physiology than NO effective gravity.
    They were in space for only 8 days. I didn't think the effect would be detectable that quickly.
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    Default Re: Venus or Mars for terraforming and colonisation?

    Quote Originally Posted by Rakaydos View Post
    Anecdotally, the Apollo astronauts who went to the surface of the moon had less bone and muscle deterioration than the ones that stayed in the command module- enough less to suggest there was actually some recovery from the trip out while they were down there. This suggests that even very low planetary gravities are better for human physiology than NO effective gravity.
    Or that being depressed about not actually walking on the moon makes your muscle deterioration worse.

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    Default Re: Venus or Mars for terraforming and colonisation?

    As for the potato thing, I suppose I am picking nits a bit. We certainly agree that it would be a very bad thing for the planet regardless, and it is a touch off topic. Back to settlement!

    Quote Originally Posted by Rakaydos View Post
    Anecdotally, the Apollo astronauts who went to the surface of the moon had less bone and muscle deterioration than the ones that stayed in the command module- enough less to suggest there was actually some recovery from the trip out while they were down there. This suggests that even very low planetary gravities are better for human physiology than NO effective gravity.

    A low orbit spin gravity station like the proposed Voyager Station (Formerly Von Braun Station) is easy to reach, but there is nothing THERE- everything has to be imported and/or recycled.
    The big issue is, well, the gravity well. The rocket equation is brutally hard on lift, and getting mass to space stations is already expensive enough. Getting material to say, Mars or Venus is ludicrously expensive. Even Musk is optimistically projecting $4bil for a minimally manned exploration trip to Mars. That's far short of what's needed for actual settlement.

    By contrast, launch prices for a Falcon 9 into LEO are now sub-$3k/lb. That isn't cheap, certainly, but if you want stuff, being able to ship a lot more is amazingly helpful.

    And then, once it's built, you can go from the station to elsewhere far more cheaply than you can from the surface of a planet. Going back down into a gravity well makes it really hard to move onward from there.

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    Default Re: Venus or Mars for terraforming and colonisation?

    I'm always amazed at the difference in size between the vehicle that took astronauts to the moon, and the vehicle that got them back from the moon.
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    Default Re: Venus or Mars for terraforming and colonisation?

    Quote Originally Posted by Tyndmyr View Post
    The big issue is, well, the gravity well. The rocket equation is brutally hard on lift, and getting mass to space stations is already expensive enough. Getting material to say, Mars or Venus is ludicrously expensive. Even Musk is optimistically projecting $4bil for a minimally manned exploration trip to Mars. That's far short of what's needed for actual settlement.

    By contrast, launch prices for a Falcon 9 into LEO are now sub-$3k/lb. That isn't cheap, certainly, but if you want stuff, being able to ship a lot more is amazingly helpful.

    And then, once it's built, you can go from the station to elsewhere far more cheaply than you can from the surface of a planet. Going back down into a gravity well makes it really hard to move onward from there.
    The thing about a trip to Mars is that a visit isn't much easier than a settlement. You can go to the moon with just a fortnight of supplies, but even just getting to Mars will mean you need systems which don't rely on consumables. That $4 bil already includes robotic ISRU of water in the plan (for propellant, but easily diverted to other uses), and to get the CO2 for methane you need to be processing the atmosphere, so you will already be producing nitrogen as a by-product. Compact processes exist that can turn methane into ethylene, and from there you can begin polythene part production using 3d printing as well as more specialised processes (material for polytunnels). The extra equipment required to become entirely self sufficient is a small percentage of the equipment already required just to survive and get home.

    A metal industry is slightly harder, but one of the advantages of using stainless steel is that it can easily be recycled. Lets say you land 3 vehicles. You only need 1 of those to get home, so cutting up the other two for parts makes sense. Even without additional industry that is 200 tons of high quality raw materials. That should be enough to bootstrap a foundry.

    If you can visit for $4 bil I would estimate you could probably establish a basic settlement for $6 bil. For $8 bil* you could do it relatively safely, taking enough supplies with you to ensure the crew don't starve before the next window to come home. Water and air recycling are a required risk even for a visit, and the robotic ISRU should have your return propellant ready before you even set off, meaning you can be confident of your ability to create methane (especially if you have a man** with a spanner on site).

    The other thing you are neglecting is the increased cost of a rotating station. If it is rotating it needs to be structural, and that means heavy. All that material has to be brought from somewhere, probably a gravity well. You are then building your structures out of extra material that you have brought out of a gravity well rather than just building in the gravity well. Sure, it will suck to get people on and off it, but how many times do you reckon you can fly a person up and down before it becomes less efficient that flying up their entire house? If it is actually meant as a colony most people will not be moving particularly frequently, so ease of construction dominates over ease of movement.

    * All these numbers are highly optimistic, but I think the ratios are about right.
    **Or woman. Person with a spanner doesn't have the same ring to it though.

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    Default Re: Venus or Mars for terraforming and colonisation?

    Well, there's a few things that pose problems for settlement. First off, lifespan. Pretty much everything has a finite lifespan, and while redundancy is always attempted in spaceflight, the longer the trip, the more you need.

    Second, a genuine settlement isn't just a few people waiting for death. You need enough people to have kids that aren't wholly inbred, and keep the population goin'. We're not sure exactly what the minimal population is for humans, but perhaps 100-200 would be a decent bet, and more gives you more genetic diversity in case of accident. Certainly the number is a good deal higher than the couple people going to visit it(I believe the current tenative plan is six).

    Rotating doesn't have to actually be heavy. You can separate pods with a cable and spin 'em, at the simplest. You've only got to worry about tensile strength, and cables are pretty good at that.

    And of course, fairly few of the goods needed by a settlement are available locally. A few raw materials, perhaps. Even there, the selection is fairly limited, and things like fumes matter inside an enclosed environment.

    Consider that even food isn't the sort of thing that the ISS is self sufficient on. You're gonna have to feed these folks, probably for a long time.

    Comms to orbit are also a lot faster and more stable than comms to mars/venus.

    You could put a station nearly double the size of the ISS into orbit given current launch costs for the price of that one time visit to mars.

    Compared to colonizing mars? You could have a space station that looks like something from wild science fiction.

    For reference, the ISS can hold a permanent crew of 6, plus a few visitors, and is approximately the equivalent of a 6,000 square foot house.
    Last edited by Tyndmyr; 2021-03-01 at 02:18 PM.

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    Default Re: Venus or Mars for terraforming and colonisation?

    Quote Originally Posted by Tyndmyr View Post
    As for the potato thing, I suppose I am picking nits a bit. We certainly agree that it would be a very bad thing for the planet regardless, and it is a touch off topic. Back to settlement!
    You're not really picking nits.

    The assertion was: "one potato at sufficient velocity could vaporize the Earth", and trying to find flaws in how it got that velocity isn't attacking the thing which I actually said -- I had never given you any implementation details on how it got to that velocity, after all.


    Quote Originally Posted by Tyndmyr View Post
    The big issue is, well, the gravity well. The rocket equation is brutally hard on lift
    The key thing here is to launch from higher in the well.

    I'm honestly not sure why we keep building launchpads at sea level* instead of on the top of a mountain. We have access to a significant number of mountains, and we could find quite a few more with international cooperation.

    But for Mars, I think the gravity well sweet-spot is the Moon.

    We'd want to establish a moon base or several, process regolith and moon-rocks into a railgun-type launch system, forge hefty station parts and then launch them to an orbit where they could be easily assembled, and build the chonky radiation-resistant system-ship hulls out there instead of on the Earth.

    Some of this could probably be done by robots which are launched from Earth, but hopefully we'll get a breeding population of humans up there too.



    *) Well, other than the politics of throwing money at specific states, but I don't like that reason.

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    Default Re: Venus or Mars for terraforming and colonisation?

    Quote Originally Posted by Nifft View Post
    You're not really picking nits.

    The assertion was: "one potato at sufficient velocity could vaporize the Earth", and trying to find flaws in how it got that velocity isn't attacking the thing which I actually said -- I had never given you any implementation details on how it got to that velocity, after all.
    The implementation is definitely the challenging part for sure. But hey, fun concept at any rate.

    The key thing here is to launch from higher in the well.

    I'm honestly not sure why we keep building launchpads at sea level* instead of on the top of a mountain. We have access to a significant number of mountains, and we could find quite a few more with international cooperation.
    That would help quite significantly. Unfortunately, the Earth's geography is unsuited for it.

    Essentially, to get into orbit, you gotta fly up out of the atmosphere, then pile on a ton of sideways speed to hit orbital velocity. Rotate a sphere, and the edge will be moving at a higher speed than any other part.

    That's why everyone attempts to launch as close to their equator as other factors reasonably allow, and the US launches from Florida. More of that rotational speed to start. Height helps in that it decreases the atmospheric climb, but we have a tragic shortage of mountains along the equator, and that factor is huge.

    But for Mars, I think the gravity well sweet-spot is the Moon.

    We'd want to establish a moon base or several, process regolith and moon-rocks into a railgun-type launch system, forge hefty station parts and then launch them to an orbit where they could be easily assembled, and build the chonky radiation-resistant system-ship hulls out there instead of on the Earth.
    Escaping from the Moon isn't *that* bad. The gravity is quite light, and there's really no atmosphere. It's still non-trivial, but it's 20-odd percent of the escape velocity from earth.

    Unfortunately, the regolith is very poor in most materials. There's quite a lack of water, which gets used in an immense amount of processes, for instance. There's no atmosphere, so any of the lighter gasses are pretty inaccessible as well. Even stuff like Carbon, readily accessible on earth, pretty scarce there. This makes fabrication of rockets from local materials extremely challenging.

    On top of that, the dust is highly abrasive, which might create a lot of problems for a launch site. Every rocket taking off would tend to sandblast the launch site.

    Doesn't mean that a lunar base isn't worthwhile at all...for what we can use from there, harvesting locally may be cheaper to truck out to orbit than lugging it up from earth, particularly if things like a railgun launcher can be made to work in the environment. But probably more likely to be a mining station than a launch facility.
    Last edited by Tyndmyr; 2021-03-01 at 03:55 PM.

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    Default Re: Venus or Mars for terraforming and colonisation?

    I believe most proposals for moon manufacturing assume a supply of material from asteroids.

    I'm really not an expert on these things, but I think it should be possible to have rockets and launch pads that channel all the exhaust and debris away from the rocket.

    The whole idea behind building spacecraft on the moon, or at least transfer heavy vehicle parts from the surface into orbit around the moon, is that the energy requirement is much lower per kg of payload, which means the rockets that go from the moon into space and then beyond can be much smaller and less powerful.

    1: Send parts for the processing of asteroid ore and the construction of lunar launch rocket to the moon.
    2: Assemble a rocket factory on the moon.
    3: Push metal-rich asteroids to land on the moon.
    4: Build rockets for travel throughout the solar system on the moon.
    5: Send the rocket into orbit around Earth,
    6: Lift only crew, supplies, and advanced electronics from Earth to the waiting rocket.
    (7: Profit)

    In theory, with sufficiently advanced and efficient rocket factories and fuel refineries on the moon, the costs for getting space ships into space becomes much smaller.
    A Saturn V had a fueled up weight of 3000 tons, of which only 50 tons were actually going to the moon. We can build better rockets now, but the energy requirements remain largely the same and we still don't have anything massively better than RP1,
    I don't feel confident with plugging in numbers into the rocket equation, but it would be interesting to see how much of the most efficient fuel on the hypothetically most efficient rockets would be needed to get say 10 tons from both the Earth and the Moon into orbit. Looking at a Saturn V and a Lunar Module, I suspect the difference is mind-boggling.
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    Default Re: Venus or Mars for terraforming and colonisation?

    Quote Originally Posted by Yora View Post
    Looking at a Saturn V and a Lunar Module, I suspect the difference is mind-boggling.
    Saturn 5 was huge, but the mass a Saturn 5 put into orbit was pretty excessive too. The whole third stage of a Saturn 5 went to orbit, full of propellant, to get the astronauts to the Moon relatively quickly.
    The end of what Son? The story? There is no end. There's just the point where the storytellers stop talking.

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    Default Re: Venus or Mars for terraforming and colonisation?

    Quote Originally Posted by Yora View Post
    I believe most proposals for moon manufacturing assume a supply of material from asteroids.
    Astroid mining would be inordinately useful, but sending it back down into any gravity well represents an efficiency loss if you're using it for spaceflight.

    Earth is a deeper well than the moon, certainly, but both require quite a lot of propellant just to get back up to orbit, a cost that an orbital station doesn't incur.

    I'm really not an expert on these things, but I think it should be possible to have rockets and launch pads that channel all the exhaust and debris away from the rocket.
    Mostly, certainly, but it tends to sandblast the station itself. Whatever systems you have, to include exaust management systems, are going to take some brutal wear and tear.

    I don't feel confident with plugging in numbers into the rocket equation, but it would be interesting to see how much of the most efficient fuel on the hypothetically most efficient rockets would be needed to get say 10 tons from both the Earth and the Moon into orbit. Looking at a Saturn V and a Lunar Module, I suspect the difference is mind-boggling.
    A given rocket can lift approximately 6 times as much payload from the moon as from earth into orbit. Earth LEO is usually used as a rough standard.

    For comparison, the Saturn V can lift 260,000 lbs to Earth LEO, whereas the Falcon Heavy can lift only 141,000. The latter is *far* cheaper, though, so it represents a massive cost savings.

    The current ISS is only about 925,00 lbs, though. So, from a payload perspective, we most certainly could build a larger one at present, and at a higher orbit than the ISS is at(it's quite low).

    Rough ballpark, every Falcon launch could lift roughly enough station mass to support one additional permanent crew member. There have been over a hundred launches so far. We could certainly aim higher.

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    Default Re: Venus or Mars for terraforming and colonisation?

    I think if you were planning on building a permanent inhabited station in orbit (e.g. one on which you expect people to actually live their lives on) then you'd want to have it quite a bit higher than the ISS, which has to have its orbit boosted every couple of months due to atmospheric drag--a problem that just gets worse the larger the mass of the station, because you need more fuel to make the boost burns.

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    Default Re: Venus or Mars for terraforming and colonisation?

    Quote Originally Posted by factotum View Post
    I think if you were planning on building a permanent inhabited station in orbit (e.g. one on which you expect people to actually live their lives on) then you'd want to have it quite a bit higher than the ISS, which has to have its orbit boosted every couple of months due to atmospheric drag--a problem that just gets worse the larger the mass of the station, because you need more fuel to make the boost burns.
    Once you've gotten big enough to solve the shielding problem, definitely. I suspect shielding is the main reason for the current altitude.

    Just having lots and lots of mass for the periphery would help with that a great deal. Big ol' water tanks and such. They sort of double as armor for micrometeorite strikes too. If you go big, you have to store a lot of stuff somewhere, you might as well stash it where it provides useful shielding.

    That said, building at roughly the ISS altitude and boosting it later isn't a showstopper. Drag should scale roughly on the cross section of the station, not on density. Assuming you're building in 3 dimensions, the square cube law works in your favor, and drag scales much more slowly than mass.

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    Default Re: Venus or Mars for terraforming and colonisation?

    Quote Originally Posted by Tyndmyr View Post
    Once you've gotten big enough to solve the shielding problem, definitely. I suspect shielding is the main reason for the current altitude.

    Just having lots and lots of mass for the periphery would help with that a great deal. Big ol' water tanks and such. They sort of double as armor for micrometeorite strikes too. If you go big, you have to store a lot of stuff somewhere, you might as well stash it where it provides useful shielding.

    That said, building at roughly the ISS altitude and boosting it later isn't a showstopper. Drag should scale roughly on the cross section of the station, not on density. Assuming you're building in 3 dimensions, the square cube law works in your favor, and drag scales much more slowly than mass.
    The mass though is exactly the thing that resists acceleration to a higher orbit.
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    Default Re: Venus or Mars for terraforming and colonisation?

    ISS should have big wings, set far below it in the atmosphere, like an orbital hydrofoil.

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    Quote Originally Posted by Nifft View Post
    ISS should have big wings, set far below it in the atmosphere, like an orbital hydrofoil.
    I agree, 100%.
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    Default Re: Venus or Mars for terraforming and colonisation?

    I have no idea if that's practical or not, but it sounds seriously awesome. Reason enough right there, I think.

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    It's really not. Practical, I mean.

    Wings trade thrust for lift and drag. The lift would keep the station steady at a given velocity, but the drag would rapidly diminish that velocity, thus reducing the lift. The wing would start descending farther into the atmosphere, further increasing the drag, and eventually the entire station would be pulled down into the atmosphere. To avoid that, you'd need a constant source of thrust to overcome the drag force.

    Plus, the air is really thin up there, so at orbital speed, the wings would be supersonic. Dragging a shock wave along with you is a great way of converting velocity into waste heat, which just requires even more energy poured into your thrusters. It's much more economical to occasionally burn some fuel to boost the ISS into a slightly higher orbit than to constantly burn it to maintain the same average orbit.
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    Default Re: Venus or Mars for terraforming and colonisation?

    Quote Originally Posted by Lord Torath View Post
    Plus, the air is really thin up there, so at orbital speed, the wings would be supersonic.
    From what I remember, part of the definition for what makes "space" (usually outside America the Kármán line at 100km altitude) is that a typical aircraft would have to be travelling so fast there for its wings to generate enough lift to keep it aloft that it would be at orbital velocity anyway.

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    Default Re: Venus or Mars for terraforming and colonisation?

    Quote Originally Posted by Tyndmyr View Post
    Astroid mining would be inordinately useful, but sending it back down into any gravity well represents an efficiency loss if you're using it for spaceflight.

    Earth is a deeper well than the moon, certainly, but both require quite a lot of propellant just to get back up to orbit, a cost that an orbital station doesn't incur.



    Mostly, certainly, but it tends to sandblast the station itself. Whatever systems you have, to include exaust management systems, are going to take some brutal wear and tear.



    A given rocket can lift approximately 6 times as much payload from the moon as from earth into orbit. Earth LEO is usually used as a rough standard.

    For comparison, the Saturn V can lift 260,000 lbs to Earth LEO, whereas the Falcon Heavy can lift only 141,000. The latter is *far* cheaper, though, so it represents a massive cost savings.

    The current ISS is only about 925,00 lbs, though. So, from a payload perspective, we most certainly could build a larger one at present, and at a higher orbit than the ISS is at(it's quite low).

    Rough ballpark, every Falcon launch could lift roughly enough station mass to support one additional permanent crew member. There have been over a hundred launches so far. We could certainly aim higher.
    I think the major argument is you can actually make a space elevator on the moon without it tearing apart, or getting shot by rogue missiles.
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    Default Re: Venus or Mars for terraforming and colonisation?

    Quote Originally Posted by Tvtyrant View Post
    I think the major argument is you can actually make a space elevator on the moon without it tearing apart, or getting shot by rogue missiles.
    I sort of like the idea of a space elevator on the Moon, but. The thing about space elevators is they have to be near the equator. All of the water that we know of at the Moon is at the poles, it's a long way from the poles to the equator, even on the Moon, it's further on Mars (where I think the known water is also near the poles).
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    Default Re: Venus or Mars for terraforming and colonisation?

    For anyone who's interested, Blue Origin is going to try spinning up some centrifugal gravity in orbit: NASA and Blue Origin upgrading New Shepard spacecraft for artificial gravity.

    All sorts of opportunities for testing the effects of spun-up low gravity (1/6 G).
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    Default Re: Venus or Mars for terraforming and colonisation?

    I think it sounds like it's more about getting a capsule to really high suborbital altitude and then having it spin while it's dropping back to Earth, before it has to start breaking.
    Using a sub-orbital rocket instead of a ridiculously tall crane.
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