Space combat

[redwizard007]

I ran into a discussion on Reddit about the uselessness of starfighters in space combat. My first reaction was to chuckle and move on. The whole concept of space combat is laughable in the first place, at least based on current technology, so why waste time theorizing... Then my inner nerd came out, and here I am. Wondering what is, and isn't plausible.

Let's assume a few basics.
1. The hulls of ships are not paper thin wafers that are subject to failure when encountering space dust.
2. AI has NOT replaced manual control of most combat systems.
3. Ships of various sizes exist, and my be outfitted for a combat role (with varying degrees of success.)
4. Two or more factions are locked in an ongoing space conflict.

So, what does combat look like?

Are lasers, explosives, projectiles, or something more exotic used?

What sort of sensors would make sense in space to aid in navigation, station keeping, and targeting?

What are some possible countermeasures that would probably develop?

Are shields ever going to be a thing?

[Chen]

Guided weaponry (missiles or otherwise) are likely going to be the most likely way to conduct space combat. Things are just moving far too fast for any type of other weaponry to work very effectively, certainly not weaponry manually controlled by humans.

[halfeye]

I ran into a discussion on Reddit about the uselessness of starfighters in space combat. My first reaction was to chuckle and move on. The whole concept of space combat is laughable in the first place, at least based on current technology, so why waste time theorizing... Then my inner nerd came out, and here I am. Wondering what is, and isn't plausible.

Let's assume a few basics.
1. The hulls of ships are not paper thin wafers that are subject to failure when encountering space dust.
2. AI has NOT replaced manual control of most combat systems.
3. Ships of various sizes exist, and my be outfitted for a combat role (with varying degrees of success.)
4. Two or more factions are locked in an ongoing space conflict.

So, what does combat look like?

Are lasers, explosives, projectiles, or something more exotic used?

What sort of sensors would make sense in space to aid in navigation, station keeping, and targeting?

What are some possible countermeasures that would probably develop?

Are shields ever going to be a thing?

A nuke is devastating. It's unreasonable to assume that any armour much less than half a mile of lead is going to save you from a nuke. You just can't make spaceships with half a mile thick lead armour.

Therefore antimissile defences have to be a thing, and spacing so a hit doesn't take out multiple ships have to be things. Shields are not yet known technology, if they can stop nukes great, but so far they aren't hard sci-fi.

[tiornys]

I think it would play out a lot like sub-to-sub combat. You have an environment where it's hard to detect things, and where trying to detect things is likely to do a better job of revealing where you are than finding where other things are. On top of that, the environment is fundamentally hostile, so all you have to do to kill a ship (or at least its pilots) is disrupt its structural integrity. Stealth and superior detection abilities would be key because the side that strikes first is overwhelmingly favored to win an engagement.

[Sean Mirrsen]

Lots and lots of antimissile systems to prevent getting point-blank-nuked out of existence, ablative shields to prevent getting peppered to death by various debris, thermal and radio decoys to mask your exact position (because masking your presence is futile), powerful laser-based "main guns", expendable drones carrying projectile weapons to attack with precision and deny the target a chance to dodge (lightspeed signal to drone then relatively slow railgun fire is better than the slow railgun fire all the way to moving target), and many more kinds of missiles than we can currently envision.

[Tyndmyr]

I ran into a discussion on Reddit about the uselessness of starfighters in space combat. My first reaction was to chuckle and move on. The whole concept of space combat is laughable in the first place, at least based on current technology, so why waste time theorizing... Then my inner nerd came out, and here I am. Wondering what is, and isn't plausible.

Why is it laughable? Missiles to shoot at satellites, satellites with cannon aboard are real world things.


Let's assume a few basics.
1. The hulls of ships are not paper thin wafers that are subject to failure when encountering space dust.
2. AI has NOT replaced manual control of most combat systems.
3. Ships of various sizes exist, and my be outfitted for a combat role (with varying degrees of success.)
4. Two or more factions are locked in an ongoing space conflict.

So, what does combat look like?

Are lasers, explosives, projectiles, or something more exotic used?

What sort of sensors would make sense in space to aid in navigation, station keeping, and targeting?

What are some possible countermeasures that would probably develop?

Are shields ever going to be a thing?

Probably would look akin to naval ships nowadays. Missiles and guns. Torpedos don't really make sense as a separate weapons class, because this is taking place within a single medium, not two. So Torpedos are just really big missiles in a space context.

I suggest watching The Expanse for some ideas. First two seasons free on Amazon prime, and it's pretty good otherwise.

[Lord Torath]

Have you ever visited Atomic Rockets (http://www.projectrho.com/public_html/rocket/)? Warning: This is a time sink nearly as bad as TV Tropes.

They go into depth about this sort of thing. Here's their page on space fighters (http://www.projectrho.com/public_html/rocket/fighter.php).

[Mando Knight]

The main critical technology isn't in weapon or sensor design, it's propulsion and power supply. Without better propulsion technology, even a 1.5 km/s tank gun would be difficult and expensive to dodge (and the muzzle velocity will be different without supersonic drag effects). Without a better power supply, missiles and conventional cannon are the only vessel-to-vessel weapons you can expect to be used.

[pendell]

I ran into a discussion on Reddit about the uselessness of starfighters in space combat. My first reaction was to chuckle and move on. The whole concept of space combat is laughable in the first place, at least based on current technology, so why waste time theorizing... Then my inner nerd came out, and here I am. Wondering what is, and isn't plausible.


I think I'm going to argue a bit with some of your assumptions, actually.



Let's assume a few basics.
1. The hulls of ships are not paper thin wafers that are subject to failure when encountering space dust.


The issue here is that armor adds mass and , I think, is also a heat sink. Heat is a major concern in spacecraft. So I'd be surprised if spacecraft were built any heavier than they had to be. I would expect "defense" to consist of things like point-defense weapons or perhaps even smaller objects around the spacecraft for protection, as opposed to physical armor.



2. AI has NOT replaced manual control of most combat systems.


Actually, it would not surprise me if the bulk of combat spacecraft were unmanned, as almost all spacecraft are today. AI doesn't require as much oxygen, food, can take far more acceleration than humans can. Perhaps there would be a mother ship occupied by humans which would control drones, but I would expect in the near term combat spacecraft to be autonomous. I simply can't think of a good reason to add a human being with all the life support and engineering requirements that entails to the mix to do a job a computer can do equally well.

The rest seem fair enough.



Are lasers, explosives, projectiles, or something more exotic used?


I would expect a kinetic kill vehicle to be the basic weapon of choice : Get close enough to the other guy that he can't maneuver away, then put a bunch of solid objects right in his path. Space debris and garbage does terrible things to modern spacecraft ; combatants will simply take advantage of this to deliberately put stuff in the other ship's way.

Also, if the ship is unmanned, perhaps we could radio over a computer virus and convert it into one of our ships, or at least so thoroughly wreck its software that it becomes a floating lump of metal.

Lasers show a degree of promise , because there is no atmosphere to spread the beam and weaken it's effect. But they are still dreadfully inefficient mechanisms for delivering energy to a target.

Missiles, carrying propellant, are an expensive proposition. I think I'd rather have a guided projectile; use a rail gun or some such to accelerate a kinetic weapon at the target, give the projectile some maneuvering jets, sensors, and a computer for course correction. But I don't see any reason to waste room on the projectile for propellant when we can leave the major boost unit back on the launching ship, which can then be re-used for more weapons.

Explosives are wasteful in space because there is no air for the shock wave to move through; explosives would only be useful in a direct hit, and if you're going for a direct hit anyway, might as well just use straight out mass.

Nuclear weapons would not have shock effect (again, no air) but could kill with heat and radiation and EMP effects. While definitely useable, I still think that's using a cannon to kill a grasshopper; nuclear weapons are not as efficient in space as they are in atmosphere. I'd still want a kinetic kill vehicle if it could be made to serve.

Wherever there are ships there's the need to stop and search them for contraband; a guard vessel would have to match speeds and deploy a boarding party. I would expect them to be armed with gyrojet pistols (rocket - less recoil) and perhaps clubs or swords adapted for zero G. You wouldn't want something that would rip open the pressure hole, and sharp pointy objects should work well against people wearing pressure suits.

I heard some mention "stealth" . My understanding is that stealth is very hard in space because no clouds, no horizon to cut off visibility. We track every satellite and many space rocks *now* with our current technology. I don't think there is an easy way to obscure it because, again, heat. The less a ship reflects light, the more heat it absorbs, the worse for it.

So I think, in the near term, "stealth" would consist of false flags or spoofing, false transponders or what not , to disguise one class of ship as another. Perhaps several ships weaving in and out or around an asteroid or similar body to disguise the number and type. But I don't see something like the modern stealth fighter in space any time soon.



What sort of sensors would make sense in space to aid in navigation, station keeping, and targeting?


Plain optics are a lot better in space because there are no clouds, there is no horizon, and things which are invisible on radar aren't to optics. There's also radar which would have the same uses it has on space. Lasers and masers both for communications and for tracking.


Are shields ever going to be a thing?


Yes (https://www.extremetech.com/extreme/181773-physics-students-figure-out-how-to-make-star-wars-deflector-shields-in-real-life). Not any time soon, but there's already a proof of concept to create a plasma field around a ship, which would deflect energy and other objects as well. It will probably be quite some time before such a thing is practical enough to be mounted on a ship, however.

At any rate, that's my vision of space combat: Autonomous drones commanded from a manned command ship, which is itself defended by sensor scrambling, a point defense system, and specialized defense drones carrying lasers.

Respectfully,

Brian P.

[Excession]

Nuclear weapons would not have shock effect (again, no air) but could kill with heat and radiation and EMP effects. While definitely useable, I still think that's using a cannon to kill a grasshopper; nuclear weapons are not as efficient in space as they are in atmosphere. I'd still want a kinetic kill vehicle if it could be made to serve.

I would expect nuclear weapons to be used, but as propulsion (https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)) rather than warheads. An "Orion Missile", to give it a name, gets better power to weight than a conventional rocket motor or rail gun. That makes it faster and more able to manoeuvre than a non-Orion target. The final warhead could be either a single penetrator for big targets, like planets, or a nuclear bomb powered shotgun round to increase your chance of hitting an evading target.

Even if it misses, you have hopefully forced your target to use more weight in reaction mass to dodge than your missile weighs, meaning you will win in a war of attrition.

[Darth Ultron]

So, what does combat look like?

The Expanse is a good fictional example.

In general, Space Combat will be very close at first, a lot like ''ships of the line".

Space is huge. You can't really attack from too far away as everything is moving, and you'd need a smart or manned weapon. So, basically, most would have to wait until they got close.



Are lasers, explosives, projectiles, or something more exotic used?

In general, AI missiles with payloads. Lasers could...maybe...be used for close combat. Though modern lasers come up a bit short on this.

As the USA does now have rail gun technology, it does seems like this would be the most likely near future space weapon.




What sort of sensors would make sense in space to aid in navigation, station keeping, and targeting?

Radar, ''light'' dar, mass sensors, heat sensors..much like what the military uses today.

A fun twist will be visual...along the lines of telescopes. A ship will block the light from stars, planets and other such things in space. A good telescope and computer could detect such things.



What are some possible countermeasures that would probably develop?

Well, ''stealth" for sure...ways to mask or hide everything a ship emits. Though the 'blocking light' will be a hard one to over come.



Are shields ever going to be a thing?

Maybe?

We can..sort of..project plasma...that..well...sort of might intercept or block incoming attack fire. But maybe not. And even so, it would be hard to time it right.

Independent drone shields might work.

[tiornys]

I heard some mention "stealth" . My understanding is that stealth is very hard in space because no clouds, no horizon to cut off visibility. We track every satellite and many space rocks *now* with our current technology. I don't think there is an easy way to obscure it because, again, heat. The less a ship reflects light, the more heat it absorbs, the worse for it.

So I think, in the near term, "stealth" would consist of false flags or spoofing, false transponders or what not , to disguise one class of ship as another. Perhaps several ships weaving in and out or around an asteroid or similar body to disguise the number and type. But I don't see something like the modern stealth fighter in space any time soon.
I think I'm envisioning engagements at a much larger distance than most people. If engagements are taking place on the scale of the inner solar system, then I agree that stealth is unfeasible. An engagement on the scale of, say, Neptune's orbit should be large enough to have the type of detection issues I'm thinking of.

[Mando Knight]

I heard some mention "stealth" . My understanding is that stealth is very hard in space because no clouds, no horizon to cut off visibility. We track every satellite and many space rocks *now* with our current technology. I don't think there is an easy way to obscure it because, again, heat. The less a ship reflects light, the more heat it absorbs, the worse for it.

So I think, in the near term, "stealth" would consist of false flags or spoofing, false transponders or what not , to disguise one class of ship as another. Perhaps several ships weaving in and out or around an asteroid or similar body to disguise the number and type. But I don't see something like the modern stealth fighter in space any time soon.

Vehicles "weaving in and out" of asteroids would show up more easily, as they'd be expending energy to do so. Stealth in space would be more like a minefield: can you correctly identify all orbiting satellites at a distance without a map? An attack ship would not be able to support all of the sensors used for ground-based tracking without compromising its effectiveness as a weapon-carrying system, and incomplete sensor data can be deadly if your opponent can place proximity mines in your path, especially since detecting small debris (yet large enough to build a small mine into) is a problem even for ground-based active tracking sensors.

[Mechalich]

The first question you have to answer when considering space combat is: why is it happening at all? It is critically important to imagine a scenario wherein two groups reasonably have something to actually fight over in space. This is harder than it sounds.

First, so far as we can determine right now, space colonization is not economically viable. The best we can currently imagine is moving asteroids around and bringing them back to Earth orbit to harvest their easily accessible ores (rare earths and a few others mostly, also bulk metals like nickel and zinc if you can work out some transport issues. There is no impetus to build space colonies whatsoever. The best you get is the 'in space' equivalent of deep sea oil rigs and Antarctic research stations.

Second, space is huge. There's so much territory available that there's no reason to compete for anything and key resources like water happen to be ridiculously abundant. Once you have the technology to move about around a solar system in a viable low-cost way, you have the technology to mine and produce everything you ever need and the ability to just jet off to some random Kuiper Belt object and to ignore the universe for the next ten thousand years. It becomes difficult to imagine 'war' in a scenario where resource-based conflict is essentially impossible. If you go interstellar this gets even worse - the galaxy is stupidly huge, there are tens of billions of star systems (and tens of billions more brown dwarfs and rogue planets) that no one is bothering with and that are freely available. Why would anyone hunt you down? Unless you posit some sort of awesome - and completely impossible - warp drive - the idea of exerting control over any other star system becomes pretty laughable.

Third, at the levels of technology one is likely to see in a 'space war' scenario, it may not make sense to fight in a physical medium at all. Perhaps all 'combat' takes place in the digital realm as various entities attempt to invade each others host servers and terminate their existence without conducting physical combat at all. This is certainly going to be cheaper and likely just as effective. Causing a critical error in the infrastructure of a space colony is a sure-fire way to kill all the residents (if there are any flesh and blood residents) and almost certainly much easier to arrange than firing missiles.

Now, you could have space war with an invading alien intelligence of some kind - which wishes to destroy you simply because it does. However, this is an 'apes or angels' scenario and the technological variance is probably sufficiently wide that one side simply looses outright. it takes very careful arranging - generally a sort of Mass Effect style 'all these civilizations are using the more advanced technology of a previous cycle and can't measurably advance beyond it' scenario to allow any two species to fight with anything remotely resembling equality. Battlestar Galactica is actually a fairly good example of how this can unfold, since it posits an irreconcilable ideological conflict that causes an actual war to happen in the first place and even that's dependent upon the specific personal grievances of a handful of individuals (the Cylons could just let the humans flee and do nothing, they have to deliberately choose not to).

So, if considering space combat, well before you get into any sort of technical speculations as to how this fighting is going to go down, remember to work on a plausible reason to even have a conflict in the first place, and that economic motives - responsible for basically all known military conflicts in human history - are pretty much right out. You need some kind of ideological conflict that causes people to unleash extreme levels of carnage on each other, since unleashing weapons in space probably means complete target annihilation on even a single hit.

[LordEntrails]

Hmm, agree, and disagree, with lots of what has been said. My thoughts;

Weapons;
- Kinetic kill launch via magnetic rail guns. No guidance. It would be easy to put out a thousand 1kg high density slugs (every second) with a velocity of 3km/second, giving each projectile 4.5 MJ of energy. No drag, so they keep that energy until they hit something. Each one is going to put a hole through most any system/armor/spaceship. Making such weapons would be simple, cheap, reliable, useful, and within today's technology. (plus, if the enemy ship is coming towards the projectile, then the energy goes up, exponentially!)
- Shields and defenses are going to be better at reducing damage from energy weapon systems, hence one more reason for KKVs and not energy weapons.

Without need for guidance, you could have lots and lots of them. So you could lay out a blanket/screen of them. They are small, and therefore the target would need active sensors to detect them. Meaning they would give away their position (see sensors below). And even if detected and avoided, doing so would require significant energy, and as mentioned, until we have multiple generations of power technology breakthrough, energy (and reaction mass) is going to be key to winning in space.

Sensors;
- I'm not convinced about optical. Ranges are going to be millions of kilometers, and the detection arc of things are going to be tiny. Someone can do the math on a 200 meter wide ship at a million km, but it's tiny. And light out in deep space (where you are going to control a system) is fractional so you are only going to "see" a ship when it passes in front of a star or planet, or when it's propulsion drive gives it up.
- Passive detection; picking up active scanners from other ships will always be a must, and once combat start, ships are going to need.
- Active sensors will probably be laser based, though radar or other frequency ranges might prove better, especially if the projectiles like I described above are in use, then millimeter wave or smaller to get resolution on those screens of kinetic kill weapons I mentioned.
So, detection of enemies is going to be due to them either using active sensors or using their propulsion. i.e. when they emit energy of one type or another. Of course, except for dropping into a system from deep space, most ships (except sentry platforms) are going to be maneuvering or communicating, since they will be there to do something useful (and useful work requires energy emissions).

Propulsion & Energy;
- Certainly won't be combustion based. Will have to be something like ion, plasma or nuclear (orion) propulsion as you need something powered by a source with nuclear level (or better) energy densities.
This is where we are really technologically deficient right now.

Combat Range;
- As mentioned with weapons, ranges are going to be extreme. As soon as you can detect the enemy, you are going to put KKVs in their way, from millions of kilometers away.

Tactics & Implications;
- AIs are probably going to be a thing, because there is enough capability to do what's needing that exists today.
- Remote "fighter" will probably only receive data from a command ship or station. Something that already can't hide it's location because it's orbiting a station or is the carrier or battleship. The fighters will want to stay as stealthy as possible and may just be firing platforms for the KKVs.
- Ship design. Again, computers allow for better redundancy than humans. Ships are going to need redundant systems because they are going to get lots of 10 cm diameter holes in them from the 1kg KKVs.
- Now, KKVs, (or guided missiles) require ship mass be sacrificed to use (i.e. ammunition). Energy weapons don't, so maybe, if you can get an energy weapons to deliver higher energy levels (4.5MJ/kg of fuel) then maybe....
- Energy weapons would be better for ships matching your trajectory, or fleeing. Kinetic get a big bonus during closing actions.

[LordEntrails]

The first question you have to answer when considering space combat is: why is it happening at all? It is critically important to imagine a scenario wherein two groups reasonably have something to actually fight over in space. This is harder than it sounds.
Good question. Not hard if you are thinking fiction or far future.


There is no impetus to build space colonies whatsoever.
Wrong.
1) Survival of the species is one. See the thread on climate change or a dozen others.
2) Survival of individuals. At some point the population of Earth with exceed the planet's ability to provide.
3) Because it can be imagined. Human imagination is huge, and the need to know what's out of sight is arguably a racial impetus.


Second, space is huge.
Yep.

There's so much territory available that there's no reason to compete for anything and key resources like water happen to be ridiculously abundant. Once you have the technology to move about around a solar system in a viable low-cost way, you have the technology to mine and produce everything you ever need and the ability to just jet off to some random Kuiper Belt object and to ignore the universe for the next ten thousand years.
Wrong :) You're not thinking big enough.
We used to think that the planet was so big we could never know it all. Then we though their would always be enough open land. Then we though dumping garbage in the ocean would never impact things because it was so big.

You said it yourself "key resources". Key resources are whatever their is a limit or scarcity to. That might be habitable planets, rare ore, strategic transit points (warp gates?). But their will be something that is scarce, and people will fight over it, even often when fighting is more expensive than exploring to find the resource elsewhere.


It becomes difficult to imagine 'war' in a scenario where resource-based conflict is essentially impossible. If you go interstellar this gets even worse - the galaxy is stupidly huge, there are tens of billions of star systems (and tens of billions more brown dwarfs and rogue planets) that no one is bothering with and that are freely available. Why would anyone hunt you down? Unless you posit some sort of awesome - and completely impossible - warp drive - the idea of exerting control over any other star system becomes pretty laughable.
Maybe, but maybe we are not alone. Maybe their is something that is scarce. I think their will be.


Third, at the levels of technology one is likely to see in a 'space war' scenario, it may not make sense to fight in a physical medium at all. Perhaps all 'combat' takes place in the digital realm as various entities attempt to invade each others host servers and terminate their existence without conducting physical combat at all. This is certainly going to be cheaper and likely just as effective. Causing a critical error in the infrastructure of a space colony is a sure-fire way to kill all the residents (if there are any flesh and blood residents) and almost certainly much easier to arrange than firing missiles.
Possible. But that are surmises that you can connect and attack the enemies infrastructure. If they are not connected to your network, or to an open network, then you can't attack them this way. And air gaping critical systems that can only be accessed by locals is easy to do. Probably the default for future systems exactly because of this.


Now, you could have space war with an invading alien intelligence of some kind - which wishes to destroy you simply because it does. However, this is an 'apes or angels' scenario and the technological variance is probably sufficiently wide that one side simply looses outright. it takes very careful arranging - generally a sort of Mass Effect style 'all these civilizations are using the more advanced technology of a previous cycle and can't measurably advance beyond it' scenario to allow any two species to fight with anything remotely resembling equality. Battlestar Galactica is actually a fairly good example of how this can unfold, since it posits an irreconcilable ideological conflict that causes an actual war to happen in the first place and even that's dependent upon the specific personal grievances of a handful of individuals (the Cylons could just let the humans flee and do nothing, they have to deliberately choose not to).
But you just came up with reasons to have conflict, which you said their wasn't! *G*


So, if considering space combat, well before you get into any sort of technical speculations as to how this fighting is going to go down, remember to work on a plausible reason to even have a conflict in the first place, and that economic motives - responsible for basically all known military conflicts in human history - are pretty much right out. You need some kind of ideological conflict that causes people to unleash extreme levels of carnage on each other, since unleashing weapons in space probably means complete target annihilation on even a single hit.
I'd also add that you really have to understand what technologies you are going to "allow". Because how effective a shield is, what energy sources or propulsion or sensor systems are going to completely dictate how combat evolves.

[Excession]

I'm not convinced about optical. Ranges are going to be millions of kilometers, and the detection arc of things are going to be tiny. Someone can do the math on a 200 meter wide ship at a million km, but it's tiny. And light out in deep space (where you are going to control a system) is fractional so you are only going to "see" a ship when it passes in front of a star or planet, or when it's propulsion drive gives it up.

2015 TG387 is about 300 km across, but was spotted at a distance of around 80 AU, or 12 billion km. Perhaps someone could run the numbers to scale that to only millions of km, and a spaceship sized object instead of a planetoid. You also need to take into account that telescopes for space warfare will have a much larger budget, be more numerous, and be in space themselves. Also any engine exhaust will be much more visible than a cold dead rock.

I suspect passive telescopes will still have their place, especially as it covers distance better than radar, which drops off at 1/r⁴ where passive is 1/r². Remote radar transmitters can help with that, but space is big and hard to cover.

[Bohandas]

I believe that would be 300 meters

[Mechalich]

Wrong :) You're not thinking big enough.
We used to think that the planet was so big we could never know it all. Then we though their would always be enough open land. Then we though dumping garbage in the ocean would never impact things because it was so big.

There is still open land on planet Earth, quite a bit of it in fact. More importantly, you only need more space if you have more people, and to have that you need exponential growth. However, exponential human population growth is coming to an end. The human population is going to hit a maximum number (probably around 11 billion) and then start to fall. Subsequent to that, in any 'colonize space' scenario, the population is going to be either falling or at best stable. Barring some bizarre reason that suddenly increases the population, which is basically limited to some sort of massive life extension tech, you're talking about exploring space without any population pressure to do so.


You said it yourself "key resources". Key resources are whatever their is a limit or scarcity to. That might be habitable planets, rare ore, strategic transit points (warp gates?). But their will be something that is scarce, and people will fight over it, even often when fighting is more expensive than exploring to find the resource elsewhere.

There are 90 elements that occur in nature in appreciable amounts. They are actually distributed far more equally in space than they are here on Earth. At a tech level where space colonization becomes viable, that's all there is. None of them are worth fighting a war over when you can just go find - or more realistically send drones to find - another unoccupied source. In order to have resource conflict n space you have to invent some form of MacGuffinite, which is to say you have to handwave something into existence.


But you just came up with reasons to have conflict, which you said their wasn't! *G*

The point is you have to cheat. You cannot develop a system where space war naturally occurs as an emergent property, you have to manually create it by fiat to make it happen within a universe. Good example: No Man's Sky. No Man's Sky has a universe that is almost as vast as the real one (just less interesting) in it, random people attack your spacecraft because the game demands this happen, even though the in game math makes it so that fighting almost always costs more resources than you could gain. It's an inherently counterproductive approach.

If you wish to build a fantastical setting that has a reason for space war and has it so the two sides can actually fight - as opposed to one side simply summarily annihilating the other with the resource equivalent of a handwave - you have to set up your staging very, very carefully. You also have to fit things with a rather tightly limited technological framework, otherwise you get The Dark Forest scenario where all wars are ended by incalculably powerful first strikes (there are real problems with the Dark Forest idea, and Cixin Liu is not nearly as smart as he thinks he is, but star-killing technologies do ruin you space war real quick).

In general, all space wars must be civil wars to some degree. You can only fight another power with roughly the same technological capabilities you yourself possess. If you don't have faster than light that basically means you can only fight people really close by (within a few dozen light years probably) unless you posit some kind of technological plateau at a fairly low level. Civil wars also have the advantage of having a much greater inherent ideological bent rather than being about resource issues.

A good example of the kind of hoops that must be jumped through to have a space war can be found in the Dread Empire's Fall series by Walter John Williams. In it a long term and exceedingly powerful space dwelling empire artificially limits technological development according to their ideology in idiosyncratic ways, allowing for ships with absurdly powerful anti-matter drives but not for highly advanced computers, forcing a requirement for actual crew. The same empire spent centuries limiting possible expansion, preventing the empire from ballooning beyond a controllable size (FTL exists via fixed-location wormholes) and forcing the people living there to all consider themselves members of a singular empire. That same empire also built a military fleet as a monument to vanity even though they didn't actually need one, so that when war breaks out there's actually ships to fight with and a template for building more. Stability is then shattered when the rulers of this empire kill themselves off, leaving power in their hands of their formerly subject species, producing a huge spike in instability. And when war finally happens pretty much everyone accepts certain rules as a given so that no one indulges in options such as pointing their anti-matter warhead missiles at planets and causing global cataclysms because that would be uncivilized. It's a master class in how much forcible world-building is necessary to produce a marginally plausible space war.

[Darth Ultron]

Sensors;
- I'm not convinced about optical. Ranges are going to be millions of kilometers, and the detection arc of things are going to be tiny. Someone can do the math on a 200 meter wide ship at a million km, but it's tiny. And light out in deep space (where you are going to control a system) is fractional so you are only going to "see" a ship when it passes in front of a star or planet, or when it's propulsion drive gives it up.


You forget the big bright planets and the sun. The amount of light is set, so if you suddenly detect a drop in the amount of light, you know something must be blocking the light. Granted this might take some more advanced tech.

Seriously they can detect the drop in light of a planet light years away from across a star...

And even more to the point, more or less, you will know the direction that things will comes from....and that will often be ''from Earth".

At first, with no real ''leap" in tech.....space travel will be long and hard. Just to get anywhere takes a long time and a lot a fuel. So any ship will need to carry all the fuel it needs, plus life support for a crew with it.

In general, space stations and bases and even big ships will be too much of value to waste in war. It is likely that, at first, any and all damage will be avoided. In a space war at such a time, you'd really want to capture things...not just destroy them.

For the most part...you can't just planet hop at will. You have to wait for the right time, for when the planets are in the right spots, and then launch your ship. And even then the trip will take at least weeks, and maybe years. And that is only if you launch at the right time....any other time, and your trip takes much longer.

And the average ship won't be able to carry enough fuel to launch, travel through space, and slow down to enter orbit of another planet...and maneuver.

And in general, a ship can't resupply in space. It is possible to get materials in space to make fuel and air and water...maybe, if you have the right source. But it's not something the common ship would be able to do...you'd need more of a ship dedicated to doing that function. But, there is no food in space....other then what is brought from Earth.

So a good, first step, is to send out robots to build ''rest stops".....but that is a huge under taking....and would come after a couple space stations were built around Earth.

[factotum]

Once you start talking about engagements taking place at millions of kilometre's range I really wonder what sort of weapons you're expecting to use? Even the best lasers don't have a perfectly coherent beam over those distances, plus you have the problem of firing at a target that isn't actually where you see it being due to lightspeed delays. (Even if you manage to hit them with your beam, they can quickly manoeuvre out of the way and it will take you quite a while to regain your target lock). Missiles at such a range are entirely impractical, because they wouldn't have enough fuel to make the trip and still be able to manoeuvre to hit the target at the end--not to mention that the exhaust flare would make them very easy to see.

So, barring some sort of magical future weapon that goes FTL, I agree with those who say that space combat would likely take place at relatively short range.

[Sean Mirrsen]

You forget the big bright planets and the sun. The amount of light is set, so if you suddenly detect a drop in the amount of light, you know something must be blocking the light. Granted this might take some more advanced tech.

Seriously they can detect the drop in light of a planet light years away from across a star...Yes, advanced tech. Like telescope lenses meters across, and constantly scanning the skies for months.

Optical occlusion monitoring is still a very viable thing to detect the presence of a ship, but it does absolutely nothing for identification. It's merely an "early warning" thing, something to detect a nearby object moving against the starfield backdrop. Until you get active scanning on it, or it gives itself away with engine plumes, or gets close enough, a ship on optical sensors will only be suspicious if you're in an area of space that nothing is supposed to be in.


And even more to the point, more or less, you will know the direction that things will comes from....and that will often be ''from Earth".
Orbital trajectories don't work that way. You could more or less anticipate something's approach vector by looking at the optimal transfer orbit from Earth given an estimated departure time and thrust profile, but with "combat" craft, that would operate at far beyond the minimal dV budgets of modern government-funding-driven research craft, there would be tremendous capacity for adjusting the approach vector.


At first, with no real ''leap" in tech.....space travel will be long and hard. Just to get anywhere takes a long time and a lot a fuel. So any ship will need to carry all the fuel it needs, plus life support for a crew with it. Long time, yes. Lot of fuel, eh. Relatively. Something like an appropriately modernized VASIMR array could get you places comparatively quickly, and without massive fuel tanks. Well... heavy fuel tanks at least. They'd still be pretty large.


For the most part...you can't just planet hop at will. You have to wait for the right time, for when the planets are in the right spots, and then launch your ship. And even then the trip will take at least weeks, and maybe years. And that is only if you launch at the right time....any other time, and your trip takes much longer.Point-thrust craft, yes. Continuous burn makes things a lot, lot easier. Recall that thing in The Martian where the Purnell maneuver got the ship, already on the way from Mars to Earth, back to Mars, faster than the original supply probe from Earth could have gotten there? That's basically what the difference between point-thrust and continuous-thrust is. An MPD or VASIMR thruster powered by a decently sized nuclear reactor and a hefty tank of hydrogen (or argon, xenon, anything you have an abundance of), can get you places in the Solar System a lot faster, and with a lot less fuss, than traditional rockets. You could argue that going to planets that are far out of optimal position is inefficient, even with continuous burn, but it's the same thing - military ships will not care as much. If it has to be done, they'll just requisition extra fuel, and pack a tanker for the return trip if they have to.


And the average ship won't be able to carry enough fuel to launch, travel through space, and slow down to enter orbit of another planet...and maneuver.

And in general, a ship can't resupply in space. It is possible to get materials in space to make fuel and air and water...maybe, if you have the right source. But it's not something the common ship would be able to do...you'd need more of a ship dedicated to doing that function. But, there is no food in space....other then what is brought from Earth.

So a good, first step, is to send out robots to build ''rest stops".....but that is a huge under taking....and would come after a couple space stations were built around Earth.Yeah, the average ship won't be able to launch from Earth and go places. Presumably, that's why the average ship will not launch from Earth in these scenarios. Be it docking stations in Earth orbit, or landing bays on Luna, there's plenty of easier ways to get spaceborne. Most ships will have to be built in space in the first place, in order for us to have any kind of serious space presence.

Also, well, yes and no. A plasma-thruster-driven ship can use hydrogen as reaction mass. So long as their nuclear powerplant is operational, or they have enough solar collectors, they can 'resupply' anywhere they can get water, or methane. Not with food, obviously, but that's an entire different issue.

[Excession]

Once you start talking about engagements taking place at millions of kilometre's range I really wonder what sort of weapons you're expecting to use? Even the best lasers don't have a perfectly coherent beam over those distances, plus you have the problem of firing at a target that isn't actually where you see it being due to lightspeed delays. (Even if you manage to hit them with your beam, they can quickly manoeuvre out of the way and it will take you quite a while to regain your target lock). Missiles at such a range are entirely impractical, because they wouldn't have enough fuel to make the trip and still be able to manoeuvre to hit the target at the end--not to mention that the exhaust flare would make them very easy to see.

So, barring some sort of magical future weapon that goes FTL, I agree with those who say that space combat would likely take place at relatively short range.

Missiles don't have to keep firing their engines. They could use engines to change to an orbit that intercepts the target, then turn them off and coast for weeks or months, then restart the engines to perform terminal guidance. They could use their engines multiple times to adjust to the target's movement or evade anti-missile fire. Even if you were using simple solid fuel rocket engines, you'd just use multiple stages. These missiles are less like an air-to-air missile or ICBM, and more like a space probe.

[GloatingSwine]

A nuke is devastating. It's unreasonable to assume that any armour much less than half a mile of lead is going to save you from a nuke. You just can't make spaceships with half a mile thick lead armour.

Nukes are far far less devastating than you think in space.

The main product of a nuclear initiation is gamma rays which are very weak interactors, Without an atmosphere to absorb the energy and create an overpressure wave, and remembering that the inverse square law applies to the amount of energy transferred to the target's cross section the destructive effects will be much more limited than they would be in atmosphere.


Stealth and superior detection abilities would be key because the side that strikes first is overwhelmingly favored to win an engagement.

There is no stealth in space.

You are emitting heat all the time, you cannot refrain from emitting heat without cooking your crew and systems. You are against a background of about two Kelvin.

Everything in space is visible all the time to passive infra-red observation. That also makes spoofing very difficult. Anyone can see your drives operate and deduce your capabilities from the amount of energy you are emitting. You can't have a small disposable IR "noisemaker" because if it emitted as much energy as your main drive it would accelerate too fast.


- Kinetic kill launch via magnetic rail guns. No guidance. It would be easy to put out a thousand 1kg high density slugs (every second) with a velocity of 3km/second, giving each projectile 4.5 MJ of energy. No drag, so they keep that energy until they hit something. Each one is going to put a hole through most any system/armor/spaceship. Making such weapons would be simple, cheap, reliable, useful, and within today's technology. (plus, if the enemy ship is coming towards the projectile, then the energy goes up, exponentially!)

If you want to try and capture something, anything, your weapon is useless.

Space is big and it is mostly full of nothing. There is nothing to bring any two fleets to battle other than a fixed object they wish to fight over.

This gives the defender a massive advantage because they will have their backs to the thing they are defending, requiring much greater precision from the attacker if they want it even slightly intact.

Without either guidance or an abort feature, you are more likely to hit the thing you are fighting for than the people you are fighting.

[The Glyphstone]

A nuke needs to make hull contact to create a pressure wave, so in essence it would just be a far more expensive kinetic kill weapon.

[Tyndmyr]

Vehicles "weaving in and out" of asteroids would show up more easily, as they'd be expending energy to do so. Stealth in space would be more like a minefield: can you correctly identify all orbiting satellites at a distance without a map? An attack ship would not be able to support all of the sensors used for ground-based tracking without compromising its effectiveness as a weapon-carrying system, and incomplete sensor data can be deadly if your opponent can place proximity mines in your path, especially since detecting small debris (yet large enough to build a small mine into) is a problem even for ground-based active tracking sensors.

Astroids fields are very, very sparse. Unlike in movies, it's almost entirely empty space, with an asteroid out there somewhere. Weaving through them won't really be a thing in terms of cover/concealment.

Mines, like in aquatic combat, will only be used at tactical locations. Mining the open sea doesn't make sense. Given 3d space, mining open space makes far, far less sense. Space is big. Tossing a mine in a dock? Sure. But beyond such obvious tactical uses, mines mostly don't matter in space.

[Resileaf]

Yes (https://www.extremetech.com/extreme/181773-physics-students-figure-out-how-to-make-star-wars-deflector-shields-in-real-life). Not any time soon, but there's already a proof of concept to create a plasma field around a ship, which would deflect energy and other objects as well. It will probably be quite some time before such a thing is practical enough to be mounted on a ship, however.

Ignoring the current subject for a moment, this is the kind of news that make me the most excited for the future. Every step closer we get to sci-fi technology in real life, the closer we get to a real world of space exploration.

[hamishspence]

Astroids fields are very, very sparse. Unlike in movies, it's almost entirely empty space, with an asteroid out there somewhere. Weaving through them won't really be a thing in terms of cover/concealment.

Ours is. That doesn't mean all asteroid belts are. Young planetary systems may have much denser belts.

Ringed planets might have what looks like an asteroid belt around them, too (though their belts are more likely to be chunks of ice than chunks of rock).

[factotum]

Missiles don't have to keep firing their engines. They could use engines to change to an orbit that intercepts the target, then turn them off and coast for weeks or months, then restart the engines to perform terminal guidance.

Which works fine, so long as your target doesn't realise they're being fired at and doesn't make any attempt to take evasive action during that very long time period--which really isn't very likely, is it?


Ours is. That doesn't mean all asteroid belts are. Young planetary systems may have much denser belts.


There's a limit to how dense the belt can be before it gets pounded into gravel due to inter-asteroid collisions. That may well be denser than our asteroid belt, but dense enough to provide the sort of cover we're talking about here? I doubt it.

[hamishspence]

There's a limit to how dense the belt can be before it gets pounded into gravel due to inter-asteroid collisions.

A belt that is part-way through the process of forming a planet, was what I was thinking of.

[tyckspoon]

Hmm, agree, and disagree, with lots of what has been said. My thoughts;

Weapons;
- Kinetic kill launch via magnetic rail guns. No guidance. It would be easy to put out a thousand 1kg high density slugs (every second) with a velocity of 3km/second, giving each projectile 4.5 MJ of energy. No drag, so they keep that energy until they hit something. Each one is going to put a hole through most any system/armor/spaceship. Making such weapons would be simple, cheap, reliable, useful, and within today's technology. (plus, if the enemy ship is coming towards the projectile, then the energy goes up, exponentially!)
- Shields and defenses are going to be better at reducing damage from energy weapon systems, hence one more reason for KKVs and not energy weapons.

Sensors;
- I'm not convinced about optical. Ranges are going to be millions of kilometers, and the detection arc of things are going to be tiny. Someone can do the math on a 200 meter wide ship at a million km, but it's tiny. And light out in deep space (where you are going to control a system) is fractional so you are only going to "see" a ship when it passes in front of a star or planet, or when it's propulsion drive gives it up.


So your proposal is basically bullet-hell spraying huge regions of space with projectiles in the hopes that your target - which is itself a mobile-self propelled ship - will still be somewhere approximately in the covered area in the 1 to 3 weeks (1 mil km at 3km/sec is about 4 standard Earth days of travel time) worth of time it will take for your weapons to cover the space between yourself and where your sensors (themselves operating on a small but notable delay due to lightspeed limitations) saw something that might be an enemy. A determination that you yourself say will be difficult to confirm at the range you want these engagements to be, so you might not even be shooting at an enemy force. To do this you propose to carry around megagrams worth of mass in otherwise dead weight, fired out of a weapon system that itself will require an immense energy source, and that will probably either have insane maintenance requirements or have several hundred 'barrels' mounted on the ship to support the rate of fire you suggest.

.. I don't think that's anywhere near as obvious or efficient a solution as your post suggests, and I sincerely hope there's nothing in the target area you actually care to have survive, because this is much more likely to thoroughly destroy everything else in the zone than it is any actual military target. (It would be excellent for destroying a fixed emplacement, but that's just another one of the things that stops making sense to try to use in a space war.)

That 4-day delay to time on target is also why everybody else says space battles, if they happen, would happen at relatively short ranges. "Let's throw a bunch of lethal ordnance in the general direction of probably an enemy and hope for the best" is not the kind of plan people go with if they have any other choices.

[Darth Ultron]

Once you start talking about engagements taking place at millions of kilometre's range I really wonder what sort of weapons you're expecting to use?

For the first generation of space combat, the only real option is only a couple kilometers at the most. Basically like 17th century combat.



Optical occlusion monitoring is still a very viable thing to detect the presence of a ship, but it does absolutely nothing for identification.

Alone it won't tell you everything, but it does let you know something is there.



and more like a space probe.

Technically more like a Drone.

[LordEntrails]

We're all making a awful lot of assumptions. And depending upon what assumptions you make as to location, technology, range, objective, etc things change drastically. It would be interesting to live long enough to see what actually happens.

[monomer]

We're all making a awful lot of assumptions. And depending upon what assumptions you make as to location, technology, range, objective, etc things change drastically. It would be interesting to live long enough to see what actually happens.

One of the more realistic nearish-future space combat scenarios is in Larry Niven's World of Ptavvs, where a number of groups are trying to get to Neptune in chemical reaction drive ships, groups of which left either the Earth or the Belt hours to days apart. They don't have unlimited fuel, so a lot of the strategy is deciding how hard and how long they need to accelerate and decelerate to intercept. In this case, the limited combat is similar to submarine combat mentioned earlier, as the pursuers fire missiles at a target they can only really calculate the distance to, and need to wait hours to determine if they made a hit. This was written in the 60s, though, and the amount of raw computing power we have available was basically unthinkable back then, so smarter missiles would probably be used. The take-away is that acceleration budget will remain to be a huge factor in determining the outcome of a battle as long as we have to fight inertia, and that course changes have to be thought about well in advance, as you can't just simply make a turn like ships do in movies.

A slightly more extreme example is in Niven's The Protector, where extremely long-lived aliens in buzzard-ramjet spaceships (which basically have unlimited fuel, though ) are fighting in interstellar space while travelling to another system. The Protector fires off some weapons, and a few months or years later a number of the other ships explode.

Fighting while in a planet's orbit is even weirder as you can't just fly to where you want to. If you speed up, your orbit increases so you'll be well above your target if you're trying to catch up, and making a plane change (basically turning) is a complex, fuel-consuming task. You would definitely need an AI-assisted pilot to get where you need to be.

[Lvl 2 Expert]

One of the most counter intuitive parts of space battles would probably be the motion involved. Tanks or ships approach the same general area and face off from basically a standstill, relative to the speed of their projectiles. And even planes can go head to head, pull up alongside eachother or chase eachothers tails. If a spaceship even needs to close on another ship to fire the best solution is probably to plot a course that will allow for a munitions launch window while denying the opponent one for as little energy as possible. The ships are traveling in completely different directions, never get close to each other and hurl away from their fight just as fast as they came in. If your munitions are good enough and your travel distances large enough the whole maneuver can take weeks or longer to complete as well, with crew two getting plenty of time to decide whether they use their critical fuel to dodge or just let the darned missile finish them off. It looks very unlike Star Trek, basically.

[LordEntrails]

One of the more realistic ... and need to wait hours to determine if they made a hit.

... The Protector fires off some weapons, and a few months or years later a number of the other ships explode.



... If your munitions are good enough and your travel distances large enough the whole maneuver can take weeks or longer to complete as well, with crew two getting plenty of time to decide whether they use their critical fuel to dodge or just let the darned missile finish them off. It looks very unlike Star Trek, basically.

Agree with both of you. But several others have already complained that my thoughts on combat engagement ranges were wrong and that combat would have to be at much closer ranges and timeframes.

But, of course, it depends upon the technologies and objectives you assume are available.

[Excession]

Which works fine, so long as your target doesn't realise they're being fired at and doesn't make any attempt to take evasive action during that very long time period--which really isn't very likely, is it?

Planets, moons, and asteroid bases can't dodge. Everything else needs to spend reaction mass to dodge, and if crewed they're limited in what sort of g-forces and hard radiation they can use to do it. The goal is for the target to run out of reaction mass before you run out of missiles.

[jayem]

If the ship is doing anything interesting (I.E accelerating) it's infra-red signature is going to be visible for light minutes.


A ship that uses 1 watt of power is going to have a temperature of 64k. (-210 deg C), radiating light with a peak wavelength of 45 micrometers (7THz). There will be about 10^20 photons emitted per second.

Even the eye can respond to individual photons. So it seems to me a reasonable first estimate for our slow-detection distance is about one light second (I.E 300,000km or earth to the moon) per watt of power the target ship/item uses. How long it takes to build up that into something it can identify from background is another matter. [Something like this with the reflected light from a 1962 laser is how in fact how the distance to the moon is measured accurately]

Solar radiation is about 10^18 photons per square meter so our thing ought to be easily detectable at about 1 m/Watt (or to take a short cut. We'd damm well know if a 60Watt bulb is turned on in the room even if we were not looking at it).

Punting a guess I'm going to guess a half decent near future system ought to be somewhere in the middle, and at least 10 km / watt.
The VLA (radio telescopes) is looking at resolving things 0.2 Arc seconds apart or about a meter at a million miles.


So it seems to me that a small fleet (to get the wide baseline) could arrive at the moon and (subject to laser power and focusing *) almost immediately target all the satellites around earth. At which point they'd need countering at those distances.

The (exceedingly hot) counter ships would show up at even greater distances. Correcting for speed (and even acceleration) is easy and they can't change their acceleration that quickly.

*The pulses from the laser mentioned above are spread over 6km at these distances so clearly work is needed on the focusing/aiming. I'm guessing firing from outside the atmosphere would help a lot and there is probably other low hanging fruit.

[Darth Ultron]

But, of course, it depends upon the technologies and objectives you assume are available.

Well, all we have is reality. And for the most part, even the most advanced weapons don't really work all that well for space combat.

In general, most space war would not have much ''space combat''. To destroy or damage a base, station or ship just does not make a lot of common sense. The ''Scorched Space" way of war is a very bad way to do Space War.

Again, much like the Age of Sail, it would be of far greater value to capture things. You don't want to blow up and enemy Battlestar, you want to capture it and add it to your fleet. And this will be even more important when a ''fleet" is like five ships.

So you sure want to avoid catastrophic damage...and maybe even precision damage too. It might be best to just do 'hand to hand' fighting. Again, this goes back to more the Age of Sail.

It's also likely most civilized space powers would agree to a Space Geneva Convention. Something like ''do not target life support systems" would be at the top of the list.

[LordEntrails]

The goal is for the target to run out of reaction mass before you run out of missiles.


If the ship is doing anything interesting (I.E accelerating) it's infra-red signature is going to be visible for light minutes.

Those two are reasons I like the small KKV's. The would probably not be detectable until in the terminal phase. They would quickly be cold and of such a size that until very close until they could be detected. The closer the weapon is before being detection, the more reaction mass / energy you have to use to get out of the way in time. Meaning for a relatively light mass of the KKV and the energy to launch it, the enemy probably has to spend many factors more to get out of the way. Hence you are winning the war of attrition.


In general, most space war would not have much ''space combat''. To destroy or damage a base, station or ship just does not make a lot of common sense. The ''Scorched Space" way of war is a very bad way to do Space War.
Sure, so is "scorched earth" But humans have and continue to use that means of war.


Again, much like the Age of Sail, it would be of far greater value to capture things. You don't want to blow up and enemy Battlestar, you want to capture it and add it to your fleet. And this will be even more important when a ''fleet" is like five ships.

So you sure want to avoid catastrophic damage...and maybe even precision damage too. It might be best to just do 'hand to hand' fighting. Again, this goes back to more the Age of Sail.
Not if it takes less resources to destroy the entity than the amount of resources you expand offsett byt the value of what you capture.


It's also likely most civilized space powers would agree to a Space Geneva Convention. Something like ''do not target life support systems" would be at the top of the list.
No, no it's not likely. Human history and current events say otherwise.

We have the Geneva Convention today, yet Syria still does not follow it. Al Quaeda does not abide. When humans go to war, all sides only follow the rules when convenient and break them when they determine doing so outweighs following them, just look at Dresden or Hiroshima for how the winning side broke the rules in WWII (and got away with it).

"Age of Sail" and "civilized" make me think you have a very romantic notion of war. It's not. It's mean, ugly and vile. Many humans (not all) will do anything to prevail when the option is death or extinction.

[factotum]

One of the more realistic nearish-future space combat scenarios is in Larry Niven's World of Ptavvs, where a number of groups are trying to get to Neptune in chemical reaction drive ships, groups of which left either the Earth or the Belt hours to days apart.

:smallconfused: The ships in World of Ptavvs (along with pretty much every other Larry Niven Known Space work) use fusion drives, not chemical rockets? Oh, and their ultimate target is Pluto, which, in the backstory of the novel, was a moon of Neptune that got knocked out of orbit when an alien spacecraft rammed it at near-lightspeed.

[Darth Ultron]

"Age of Sail" and "civilized" make me think you have a very romantic notion of war. It's not. It's mean, ugly and vile. Many humans (not all) will do anything to prevail when the option is death or extinction.

Not at all. But a lot of human war has been the more civilized combat then the more five year old ''I willz killz you 4evers!" A great many nations do go by the Rules of War with things like don't use poison gas and don't attack medical people and things.

And remember, for the first century or more of Life in Space, the only ones that will be around are the civilized nations and ones that otherwise agree with the civilized out look. The ''others'' won't really have any sort of ready space access.

The first space station and bases will likely be ''International" ones....where all civilized nations can join and go....but of course, they will have a strict ''no weapons ever" type rule.

Really only the Big Nations, like America, Russia and China, would be able to build their own things...though likely with allies. It's a bit of a given that Star Base One Alpha will be a joint American, British, Australian, Canadian, Polish,and Ukrainian military base. And it's a bit of a given that the first Battlestar, America, will be from the USA(followed by the Battlestar Victory(UK), Battlestar Błyskawica(Polish) and Battlestar Perun (Ukarine).)

And no doubt Russia and China would not be too far behind....with the Star Cruiser Ocktober and Star Cruser Liaoning.

But all the ''others" are not likely to get any sort of military craft operation in space for a long, long, long, long time.

So for a long while, Space will only be open to nations that did sign the Geneva Convention, and would sign a similar one for Space. So, again, a much more civilized space war.

[Rockphed]

The VLA (radio telescopes) is looking at resolving things 0.2 Arc seconds apart or about a meter at a million miles.

The VLA might be able to resolve things 0.2 Arc seconds apart if it is operating at 10 GHz in the widest configuration. At about 2.4 GHz it can resolve things about 1 arc second apart, and resolution should scale inversely with frequency (so higher frequencies have tighter resolutions). It is also composed of 27 dishes each 25 meters in diameter. Also, to do that it needs to be spread out over a radius of 13 miles. Finally, I am somewhat skeptical about the VLA being able to distinguish a 1 W probe at a million miles from the background of space.

Let's math! To simplify things, that 1 watt of power will all be emitted at 10 GHz in a perfectly isotropic manner. At 1 light second (3*10^8 m), that energy is spread over 4*pi*r^2 area, yielding 8.8*10^-19 W/m^2, way above the threshold of detection for the VLA. If we move to a (slightly) more realistic scenario where the object is blackbody emitting and we have a 1000 MHz wide channel to see it in (and assuming your temperature number is correct), then the VLA would be experiencing 7.8*10^-31 W/m^2, which is 5 or 6 orders of magnitude too low for the VLA to easily see.

[LordEntrails]

Not at all. But a lot of human war has been the more civilized combat then the more five year old ''I willz killz you 4evers!" A great many nations do go by the Rules of War with things like don't use poison gas and don't attack medical people and things.

And remember, for the first century or more of Life in Space, the only ones that will be around are the civilized nations and ones that otherwise agree with the civilized out look. The ''others'' won't really have any sort of ready space access.
...
So for a long while, Space will only be open to nations that did sign the Geneva Convention, and would sign a similar one for Space. So, again, a much more civilized space war.

No, wrong. I guess you don't know the historical references I made earlier or because of your patriotic views you don't believe the historical facts? (Or you never looked into history more than the politically correct parts taught in your school?) I mentioned Dresden and Hiroshima. Both were primarily civilian targets, both were utterly destroyed. Acts that were against the rules of war at the time of the incidents. Both acts committed by the Unites States of America in order to win WWII.

Want to go farther back in history? We will skip the Vietnam War and the other American ones since those are too easy to find atrocities from your "civilized" nations. How about we go back to before the USA was formed? Want to talk about the atrocities during the Crusades? You know, the crimes commuted by the European soldiers as they invaded a civilization for no other reason than "God said so"?

Or we could go farther back to the Romans or Greeks. Or the tales told by Homer?

So, these "civilized" nations that you say will be first to space, will probably go there under some treaty or governance with rules of war. But they WILL NOT follow those rules when adhering to those rules means they lose and breaking them means they win and suffer minimal consequences (as the winner).

[jayem]

The VLA might be able to resolve things 0.2 Arc seconds apart if it is operating at 10 GHz in the widest configuration. At about 2.4 GHz it can resolve things about 1 arc second apart, and resolution should scale inversely with frequency (so higher frequencies have tighter resolutions). It is also composed of 27 dishes each 25 meters in diameter. Also, to do that it needs to be spread out over a radius of 13 miles. Finally, I am somewhat skeptical about the VLA being able to distinguish a 1 W probe at a million miles from the background of space.



Let's math! To simplify things, that 1 watt of power will all be emitted at 10 GHz in a perfectly isotropic manner. At 1 light second (3*10^8 m), that energy is spread over 4*pi*r^2 area, yielding 8.8*10^-19 W/m^2, way above the threshold of detection for the VLA. If we move to a (slightly) more realistic scenario where the object is blackbody emitting and we have a 1000 MHz wide channel to see it in (and assuming your temperature number is correct), then the VLA would be experiencing 7.8*10^-31 W/m^2, which is 5 or 6 orders of magnitude too low for the VLA to easily see.

The temperature I got by black bodying in reverse (after all that 1 Watt has to go somewhere), and seems to get one watt out. But I did assume a more peaky peak than was sensible for something so cold, although if you've taken radio wave measurements off the infra red peak then that's a bit unfair (unless actually looking to use the VLA) the other way.

I wasn't thinking of directly using the VLA but an infra-red space equivalent which has several advantages.
1 we're selecting for lukewarm objects so the relevant background is a lot less.
2 infra-red is higher frequency so we need a shorter baseline (which allow some crude preprocessing and help the ships filter what data to share to managable levels)
3 some practical implementation issues don't count, also we can upgrade it with a reasonable level of future tech.
4 we're on ships 13 miles is trivial (the data connection isn't. Also you'd have similar issues as the ear with locating high frequency sounds. Is ship 1, 1004.15 wavelengths further than ship 2 or 1005.15. If we're dealing with countable numbers of photons, does phase even mean anything?)

The point of the VLA reference was more a sanity check as to whether the location could be measured accurately enough to aim by. If/as we can almost do it now then it seems reasonable that it might be possible to do it in the future (albeit under different and almost certainly under less favorable conditions). Had the outcome been hundreds of miles then the case would have been much weaker.

[Darth Ultron]

So, these "civilized" nations that you say will be first to space, will probably go there under some treaty or governance with rules of war. But they WILL NOT follow those rules when adhering to those rules means they lose and breaking them means they win and suffer minimal consequences (as the winner).

Well, of course, the Good Civilized nations won't War with each other in space. All that will be left back on Earth.

Again, I'd point to the more honorable parts of history...not ''every war ever".

So it will more like Space Base One will surrender, and the attackers will allow then to leave the base in peace.

Even space pirates, once they existed, would capture ships and crews....and then ransom them back.

Space War, for the first century or so, would be a different more honorable type of war.

[LordEntrails]

Well, of course, the Good Civilized nations won't War with each other in space. All that will be left back on Earth.

Again, I'd point to the more honorable parts of history...not ''every war ever".

So it will more like Space Base One will surrender, and the attackers will allow then to leave the base in peace.

Even space pirates, once they existed, would capture ships and crews....and then ransom them back.

Space War, for the first century or so, would be a different more honorable type of war.

You really need to put your text in blue so we know you're not serious. Because certainly you are writing these things is sarcasm because you wouldn't be so rude as to not actually consider the points someone is making before dismissing them with such ridiculous statements.

[Rockphed]

The temperature I got by black bodying in reverse (after all that 1 Watt has to go somewhere), and seems to get one watt out. But I did assume a more peaky peak than was sensible for something so cold, although if you've taken radio wave measurements off the infra red peak then that's a bit unfair (unless actually looking to use the VLA) the other way.

I wasn't thinking of directly using the VLA but an infra-red space equivalent which has several advantages.
1 we're selecting for lukewarm objects so the relevant background is a lot less.
2 infra-red is higher frequency so we need a shorter baseline (which allow some crude preprocessing and help the ships filter what data to share to managable levels)
3 some practical implementation issues don't count, also we can upgrade it with a reasonable level of future tech.
4 we're on ships 13 miles is trivial (the data connection isn't. Also you'd have similar issues as the ear with locating high frequency sounds. Is ship 1, 1004.15 wavelengths further than ship 2 or 1005.15. If we're dealing with countable numbers of photons, does phase even mean anything?)

The point of the VLA reference was more a sanity check as to whether the location could be measured accurately enough to aim by. If/as we can almost do it now then it seems reasonable that it might be possible to do it in the future (albeit under different and almost certainly under less favorable conditions). Had the outcome been hundreds of miles then the case would have been much weaker.

The VLA has 2 things going for it: total area, and long baselines. To get the same sensitivity on IR stuff you would need shorter baselines, but similar collection area. On the other hand, the radiometer approximation breaks down somewhere in the IR.

On the other hand, an IR interferometer has the problem that IR cannot be sampled coherently, so you have to interfere the original light. This leads to needing all your telescopes to have connections to eachother that can be swapped out.

On the gripping hand, looking for active, 1 watt, systems with a telescope is probably not the best way to find them. A radar system might be more effective, but then you have r^4 losses instead of r^2. At this point, I am just spitballing based on what I know about the VLA from doing a little work with it.

[Excession]

The gold standard for IR telescopes, with current tech and budget, is WISE (https://en.wikipedia.org/wiki/Wide-field_Infrared_Survey_Explorer). It achieved a lot, including finding 33,500 new asteroids and comets. It might provide a starting point for what a space based civilisation would be able to build in the way of telescopes. If they were expecting a war I imagine they would have thousands of much better scopes, fully supplied with new coolant as required; WISE was cooled with a block of solid hydrogen.

[redwizard007]

Why is it laughable? Missiles to shoot at satellites, satellites with cannon aboard are real world things.

Have been. If by satellite, you mean manned space station. That hasn't been a thing for almost 40 years. (Admittedly, I don't have access to classified material so this may have changed.)

Laughable because even minor damage to a ship is a catastrophic failure. The whole concept of fighting in a vacuum is sillier than frogmen dueling underwater.

[BlacKnight]

Lasers are the weapon to go with in space.
The problem with any sort of kinetic weapon is that the energy needed to increase speed scale exponentially, because E = M * V^2.
On the other side lasers already travel at the speed of light, their problem being concentrating enough energy on a spot to cause damage. The formula for calculating the radius of a beam is: RT = 0.305 * D * L / RL.
Where D is the distance, L the wavelength and RL the radius of the lens.
So to reduce the diffraction of the beam and thus the energy per square inch and thus the effective range we can use a shorter wavelength or a bigger lens.
The former has limits, but the latter can be increased to ridicolous sizes because there is no limit on how big things can be in space (well, there's gravity, but if you are building Death Stars things have gone out of hand).

The catch is that laser improvements scale linearly, so past a certain point kinetic weapons are unable to compete.
To add on this there is a limit on the heat that any material can take. You can't use too much energy on a single rocket or railgun without making them explode and making them bigger has trade offs.
But if you use a giant mirror the energy would be distributed on a large surface, so not only lasers use energy in a more efficient manner, they also can use more of it.

[Sean Mirrsen]

Lasers are the weapon to go with in space.
The problem with any sort of kinetic weapon is that the energy needed to increase speed scale exponentially, because E = M * V^2.
On the other side lasers already travel at the speed of light, their problem being concentrating enough energy on a spot to cause damage. The formula for calculating the radius of a beam is: RT = 0.305 * D * L / RL.
Where D is the distance, L the wavelength and RL the radius of the lens.
So to reduce the diffraction of the beam and thus the energy per square inch and thus the effective range we can use a shorter wavelength or a bigger lens.
The former has limits, but the latter can be increased to ridicolous sizes because there is no limit on how big things can be in space (well, there's gravity, but if you are building Death Stars things have gone out of hand).

The catch is that laser improvements scale linearly, so past a certain point kinetic weapons are unable to compete.
To add on this there is a limit on the heat that any material can take. You can't use too much energy on a single rocket or railgun without making them explode and making them bigger has trade offs.
But if you use a giant mirror the energy would be distributed on a large surface, so not only lasers use energy in a more efficient manner, they also can use more of it.
Large mirrors have their own problems (how do you suppose to armor them against... anything?), and exceptionally powerful lasers run into the same issues of heat. Plus with lasers you not only need to track the target's movement, but also properly range it, otherwise your focusing will be off. I don't know about how efficient either weapon system really is, but at least with a physical projectile, every joule of energy you manage to stuff into it as forward motion is going to stay with it and, if it hits, get delivered to the target. With lasers, even though the hitting part is more reliable, you're prone to losing that energy to scatter and poor focusing. In other words - if you can guarantee a hit, say against a planet or station, a kinetic weapon will be far more effective.

And if you're already building large, you can build long instead - a longer accelerator rail is harder to aim quickly, but can deliver more power to a slug for no increase in forward profile or material wear/heat increase. If you're building artillery ships, some manner of railgun will let you make them more compact and defensible than large laser reflectors.

(I mean. Granted, at a certain technological point a 'laser' may just be superior. I.e. if you go for broke and build a FEL for hard X-rays. That will pretty much outshoot any projectile weapon system short of true RKKVs.)

[BlacKnight]

Large mirrors have their own problems (how do you suppose to armor them against... anything?), and exceptionally powerful lasers run into the same issues of heat. Plus with lasers you not only need to track the target's movement, but also properly range it, otherwise your focusing will be off. I don't know about how efficient either weapon system really is, but at least with a physical projectile, every joule of energy you manage to stuff into it as forward motion is going to stay with it and, if it hits, get delivered to the target. With lasers, even though the hitting part is more reliable, you're prone to losing that energy to scatter and poor focusing. In other words - if you can guarantee a hit, say against a planet or station, a kinetic weapon will be far more effective.

And if you're already building large, you can build long instead - a longer accelerator rail is harder to aim quickly, but can deliver more power to a slug for no increase in forward profile or material wear/heat increase. If you're building artillery ships, some manner of railgun will let you make them more compact and defensible than large laser reflectors.

(I mean. Granted, at a certain technological point a 'laser' may just be superior. I.e. if you go for broke and build a FEL for hard X-rays. That will pretty much outshoot any projectile weapon system short of true RKKVs.)

Armor in space is... tricky. A kinetic or nuclear weapon would have so much energy that any form of armor would be useless. Lasers at short enough range would be the same. On the other side lasers operating outside their killing range would have way less energy, to the point that armor could be feasible.
But would it also be useful ? For that to work you need to have a weapon that can hit the enemy spacecraft once you have closed the distance, before you enter the killing range.
That weapon could be only another laser. But maybe it would be better to make a bigger laser instead of an armored one. No need for armor if you can kill anything before it shoots you.
Either way if you are considering armor you are in a laser dominated environment, because you can't tank kinetic rounds or nukes.

About targeting you have to consider that laser lens can be used as... lens. Not only that, you can use the laser beam as Lidar. And it goes even better: given that it's all the same system you don't have to worry about your gun being misaglined with your targeting system.
If you can see it you can target it, and if you can target it you can hit it.
Another advantage is that if you have targeting problems you would notice it in a matter of seconds. If your kinetic weapons have targeting problems you would notice it after hours or days.

You can build longer magnetic accellerators, that's true. But the heating problem is present also in the round and you can't make it too big. And even if you make it bigger you reduce the surface that receive acceleration while increasing the mass and thus the energy to accelerate it. So you hit diminishing returns.
Now, I don't know too much about the subject, but I remember reading that the maximum acceleration possible with optimal conditions is around 50 km/s. Which is impressive, but pale in comparison to certain lasers.

Let's use this good calculator for an example https://web.archive.org/web/20170412014001/http://www.5596.org/cgi-bin/laser.php
A 1 GW laser that works in the ultraviolet wavelength (400 nm) with a lens radius of 50 meters can hit at 100,000 km with a beam radius of 0.4 meters, melting 1 mm of carbon per second.
At 10,000 km it melts 1 meter of carbon per second.
Accellerating a 10 kg round at 50 km/s requires 12 GJ and it would require half an hour to cross 100,000 km, during which it would be melted with ease.

Notice that I'm considering only the energy that the weapons actually use, ignoring wastes.
But considering that lasers today achieve 33% efficiency (compared to 10% for railguns) even if future magnetic accelerators could hit 99% efficiency they would lose to lasers with modern efficiency.

[wumpus]

More thoughts:

Stealth: As noted, every craft is visible. The only possible means of being stealthy is to be mistaken for a natural rock or other space flotsam (expect Earth military sensors to carefully track satellite debris: that's a great way to hide a satellite). Assuming the cost to launch a "nanosensor space weapon detector" << "a stealthy space weapon", then stealth will likely be impossible as sooner or later it will get picked up by orbiting nanosensors. This only increases when you assume that "stealthy space weapons" need to launch missiles powered by nuclear-powered missiles that require at least one critical mass.

Unguided barrages. Any craft relying on this will lose to something long distance guided missiles. Drone/missile/shell ideas will merge into one basic "long distance weapon".

Nuclear missiles: as mentioned above, nuclear warheads might not be as effective (except as EMP devices). Of course, "Orion missiles" might make this moot: they hit hard and are difficult to evade. And I doubt that the speed will give them any disadvantage in course corrections (even if they use chemical means).

Lasers: don't underestimate how lasers disperse. Also remember that you need 1 square meter for each megawatt of laser (that's with unobtanium tech where your heatsink temperature==your Carnot engines Tc...). This means that anyone who can direct fire from at least 3 different locations can use their lasers to shut down your heat sinks, making lasers probably an ineffective weapon. I posted the math for this here: http://www.giantitp.com/forums/showsinglepost.php?p=23373139&postcount=2
I'd expect "orion missiles" to be vastly more effective than lasers in space battles for the foreseeable future.

Shields: assuming no magic sci-fi "shields" are invented, real "space shields" are a thing. Basically you build a thin layer away from your craft and any micrometeorites blazing by at escape velocity are vaporized on contact and are sufficiently dispersed when they impact the spacecraft (this is why a single hole in the Soyuz craft didn't rule out a meteor, you only get one hole anyway). How this would be used for warships isn't entirely clear, but would certainly give a "Dune" feel (you have to penetrate shields "slowly") and require high mass weapons (don't count on using tiny shrapnel from a nuke at long distance).

[halfeye]

On Earth in WW2 hitting aircraft in flight was difficult because you had to aim at where they were going to be when the shot got there, not where they were when the shot was fired.

In space, at long range, that will go from difficult to impossible.

All unguided weapons, including lasers, will miss 99.99% of the time at long range (where the range is greater than the diameter of the target by maybe a million). All manouvering targets will be missed, and most targets are moving and due to gravity nothing moves in a straight line in space. If you know exactly how a target will move you can maybe compute a shot, but any mistakes at all will mean a miss, and military targets ought not to be static that long on principle.

At a range of a thousand miles (which is really close for long range) a shotgun blast of projectile weapons with 10, 000 projectiles and a spread of one degree will have an average gap between projectiles of something like a mile (can't be bothered to work it out, but I doubt I'm high), and those projectiles will be hostile for infinity years, to everything and everyone.

Nukes not in contact with a surface will only do damage due to radiation sure, but if close enough will vapourise metals and cause severe shockwaves to any remaining unvaporised matter. Planetoids may be able to survive this, lesser objects generally not.

Drones drifting to an expected target area and waking up on arrival is my best guess for space weapons.

[BlacKnight]

Lasers: don't underestimate how lasers disperse. Also remember that you need 1 square meter for each megawatt of laser (that's with unobtanium tech where your heatsink temperature==your Carnot engines Tc...). This means that anyone who can direct fire from at least 3 different locations can use their lasers to shut down your heat sinks, making lasers probably an ineffective weapon. I posted the math for this here: http://www.giantitp.com/forums/showsinglepost.php?p=23373139&postcount=2
I'd expect "orion missiles" to be vastly more effective than lasers in space battles for the foreseeable future.

So you are saying that lasers won't be effective because bested by... lasers ?


Shields: assuming no magic sci-fi "shields" are invented, real "space shields" are a thing. Basically you build a thin layer away from your craft and any micrometeorites blazing by at escape velocity are vaporized on contact and are sufficiently dispersed when they impact the spacecraft (this is why a single hole in the Soyuz craft didn't rule out a meteor, you only get one hole anyway). How this would be used for warships isn't entirely clear, but would certainly give a "Dune" feel (you have to penetrate shields "slowly") and require high mass weapons (don't count on using tiny shrapnel from a nuke at long distance).

Whipple shields are completely ineffective against the weapons that could be used in space. They only work for micro impacts in a specific range of velocity.


On Earth in WW2 hitting aircraft in flight was difficult because you had to aim at where they were going to be when the shot got there, not where they were when the shot was fired.

In space, at long range, that will go from difficult to impossible.

All unguided weapons, including lasers, will miss 99.99% of the time at long range (where the range is greater than the diameter of the target by maybe a million). All manouvering targets will be missed, and most targets are moving and due to gravity nothing moves in a straight line in space. If you know exactly how a target will move you can maybe compute a shot, but any mistakes at all will mean a miss, and military targets ought not to be static that long on principle.

Physics doesn't care about military principles: spacecrafts can't have the propellant to randomly dodge all the time.
Furthermore the acceleration that can be imparted by realistic rockets is very low (efficient rockets necessary for long voyages are very bad at providing immediate thrust).
Dodging lasers would require to be at multiple light seconds as minimum. But to house the lasers necessary to fight at those ranges warships would have to be gargantuan , which would hamper dodging even more.

[jayem]

On Earth in WW2 hitting aircraft in flight was difficult because you had to aim at where they were going to be when the shot got there, not where they were when the shot was fired.

In space, at long range, that will go from difficult to impossible.

For linear movement I think that is something that has basically been solved a long time ago. Now you aren't doing the maths in your head. Similarly really for constant acceleration (or known gravity wells).

It does of course mess with the detection system though, especially if it has to scan. I'm pretty sure it's not quite as bad as it seems at first sight.

Maneuvering movement is of course easier in air that in space. In space you need to throw away mass (signaling the intent) and you only change the position from the predicted one by that movement alone, you don't change direction like a plane does.

To dodge by 10m from a predicted path in 60 seconds using 1% of your mass uses about 0.5kJ per kg which is pretty trivial but obviously can't be done 100 times. For 0.01% (<10,000 dodges) I make it about 6MJ per kg (which is comfortably less than petrol contains), if you can use the entire mass as energy you are good for about a billion.

[wumpus]

So you are saying that lasers won't be effective because bested by... lasers ?

No, I expect them to be bested by missiles. Ideally the "Orion missile", if available.



Whipple shields are completely ineffective against the weapons that could be used in space. They only work for micro impacts in a specific range of velocity.


It covers plenty of "shotgun" type attacks, many of which were proposed for SDI (aka "Star Wars" under Reagan). The specific range of velocity also covers most attacks moving in orbit or counter orbit. In other words, expect to use big missiles and you need to either directly hit the target or get close enough that you hit with significantly large shrapnel (little micro bits can be shielded).

[Anonymouswizard]

A handful of thoughts:

-In any realistic nearish future situation (say in the next 500 years assuming no known laws of physics are broken, potentially the next few millenia before humanity finally dies out) ships probably aren't meeting in deep space all that much. In this case battles will mostly be near points of interest, such as in orbit around planets or near known, useful asteroids, and other such things. Therefore we can assume that one side will generally have stationary defences.

-Long ranged weaponry in this situation will mostly be useful in the opening stages of the battle, and potentially the closing stages if the attacker isn't intending to spend the delta-v to stop at the target (and hasn't been destroyed). Depending on defences against these weapons and the exact ranges involved it might mean that one side is destroyed by drone missiles before it can launch a counterattack.

-Dumb weapons are likely to be short ranged only, and might never be employeed if both sides don't want to damage what they're fighting over. They might also form anti-missile countermeasures, although these will be a different scale to the 'weapon' types.

-The number of smart weapons carried will depend on how much delta-v the ships are willing to sacrifice in order to carry them and the amount of delta-v in the weapons (more delta-v means either a bigger missile or less mass to impact with/weapons to use). It's no use carrying so many missiles that your ship can't dodge any incoming fire. But it's also entirely possible that you might not have enough to actually destroy your target.

-An alternative to your smart weapons trying to ram your opponent you might give them their own weapons, although these weapons will each deliver less energy to your target than just ramming it might. It depends on how good your opponent's AMCM are.

-Unless there's a massive leap ahead in AI it's likely that there will have to be an actual human involved to make the high level decisions, possibly mere light-seconds away from where the actual battle is. This means we might see a ship which has a small habitat module containing a handful of people, a lot of remass tanks, and either a number of smart weapons or a number of drones designed to accelerate away from the ship and then launch their smart weapons (possibly by itself, possibly on command). Note that your opponent can likely see every weapon and drone ship you launch and launch countermeasures.

-The defending side likely has a delta-v advantage, if only because the attacker has to carry the delta-v to slow down if they intend to actually take the point of interest or defend it against others.


Now the big things that'll change this is the development of high-acceleration high-delta-v low volume drives, which will allow for (at least some) effective dodging, a lot if we assume true reactionless drives, and 'dark' drives that don't give a radiation signiature (which means if you shut down your radiator array you become a lot harder to track).

The question is, as people have said, what is worth fighting over? As other people have pointed out there seems to be nothing in space that'll cause significant resource shortages, which means that most wars are lightly to be philosophically or politically motivated, which also means that a long-distance war isn't terribly likely. The most likely war I can think of is 'homeworld versus colonies', which means that either the colonies are heavily outmatched technologically or the communication lag works against the homeworld.

Of course space battles are cool, so I'm still going to be writing stories and playing games about them. But they're not overly realistic.

[monomer]

:smallconfused: The ships in World of Ptavvs (along with pretty much every other Larry Niven Known Space work) use fusion drives, not chemical rockets? Oh, and their ultimate target is Pluto, which, in the backstory of the novel, was a moon of Neptune that got knocked out of orbit when an alien spacecraft rammed it at near-lightspeed.

Thanks for the clarification. It has been a while since I've read this and I was thinking that this was still early enough in the timeline where chemical rockets were still being used.

The point stands, though, that spaceships are dependent on reaction mass and acceleration budgets to get anywhere, and still have to decelerate for half the trip even if they can burn the whole way there.

Any kinetic weapon that is fired in space combat, even if it has a reasonably smart guidance system, is still beholden to inertia, as course corrections can only get you so far when you're travelling at ridiculous speeds and have a tremendous amount of momentum in the direction you started in. Missiles can be subjected to huge acceleration, but will be limited to how much propellant they store, while spaceships are limited by what the pilots and crew can withstand for extended periods.

[Rockphed]

The point stands, though, that spaceships are dependent on reaction mass and acceleration budgets to get anywhere, and still have to decelerate for half the trip even if they can burn the whole way there.

That actually depends on the speed of the exhaust. If you are using an exhaust with speed less than 1/2 light speed, you have a theoretical maximum speed of twice your exhaust speed. I say theoretical because actually getting to twice your exhaust speed is hard and is likely to get you wherever you were trying to go in system.

[halfeye]

That actually depends on the speed of the exhaust. If you are using an exhaust with speed less than 1/2 light speed, you have a theoretical maximum speed of twice your exhaust speed.

Eh? That sounds like complete rubbish, unless you're building in some fuel tank limits into that, which might work maybe?

Speed is relative, so the speed of the exhaust doesn't tell you much. If you start from Earth orbit, then you have the orbital speed of the Earth around the Sun extra for free.

[factotum]

No, it sounds like relativity--if your exhaust is 1/2 light speed, then double that is lightspeed, which we know you can't travel faster than (or even reach). Really not sure what relevance it has, though, especially since achieving an exhaust velocity that high is way beyond anything we could do in the near future. Even typical ion thrusters we have don't exceed 50km/sec exhaust--you'd need a massive linear accelerator and enormous amounts of power to achieve 0.5c, which is impractical to carry aboard a spacecraft.

Something that does occur, though: since there's really nothing to take or hold in deep space, the only things people would fight over would be space stations, planetary colonies, etc. Now, if the attacking party really doesn't care about capturing these and just wants to destroy them, they can just fire a black-painted projectile from long range at high speed. Chances are the target won't even notice the thing until it hits, and even if they do, space stations and colonies are not easy things to move.

[Forum Explorer]

Something that does occur, though: since there's really nothing to take or hold in deep space, the only things people would fight over would be space stations, planetary colonies, etc. Now, if the attacking party really doesn't care about capturing these and just wants to destroy them, they can just fire a black-painted projectile from long range at high speed. Chances are the target won't even notice the thing until it hits, and even if they do, space stations and colonies are not easy things to move.

See that is exactly why I don't think stealth in space will ever be a thing. Right now we can pretty much detect anything in our solar system, and we are barely looking. When there is an actual chance for their to be foreign powers to bombard you with whatever, and your only defense will be detecting them early enough to intercept it? The amount of eyes in the sky watching everything is going to skyrocket.

[halfeye]

See that is exactly why I don't think stealth in space will ever be a thing. Right now we can pretty much detect anything in our solar system, and we are barely looking. When there is an actual chance for their to be foreign powers to bombard you with whatever, and your only defense will be detecting them early enough to intercept it? The amount of eyes in the sky watching everything is going to skyrocket.

We didn't spot Oumuamua until it had already missed us.

https://en.wikipedia.org/wiki/%CA%BBOumuamua

[Rockphed]

We didn't spot Oumuamua until it had already missed us.

https://en.wikipedia.org/wiki/%CA%BBOumuamua

Please tell me we managed to at least ping it with the Arecebo radar.

On the other hand, if it is an imperial probe droid, I don't want it waking up after being hard pinged by planet ranging radar.

[Excession]

We didn't spot Oumuamua until it had already missed us.

https://en.wikipedia.org/wiki/%CA%BBOumuamua

But we did spot it, which counts for something. There are very few telescopes looking for objects like that right now, though the numbers are slowly increasing. A military budget would change things.

[LordEntrails]

Chelyabinsk with about a 20 meter diameter was completely undetected until it entered Earth's atmosphere on February 15, 2013. Where it detonated with energy in excess of 400 kilotons of TNT. Fortunately the detonation was around 20 miles high, resulting in only ~1,500 people injured.

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

This is an example of two thing;
1) Inert masses are hard to detect.
2) Fixed platform defenses are extremely vulnerable to "space combat".

Both points I think highlight the viability of inert KKVs at extreme range, especially for an attacking force. Yes, KKVs mean you probably will not be taking possession of the target intact. But I have yet to see a viable argument that in war capturing a target in a usable manner, rather than simply destroying it or denying it's use to the enemy, is of more tactical and strategic importance, and value.

[Darth Ultron]

The amount of eyes in the sky watching everything is going to skyrocket.

Simply put once you have a couple of space stations(maybe at Lagrangian points) and ships in space, you will really need to keep track of things. This will require space based objects to scan the solar system.

[factotum]

Simply put once you have a couple of space stations(maybe at Lagrangian points) and ships in space, you will really need to keep track of things. This will require space based objects to scan the solar system.

There are limits to how much you can see, though, and also which parts of the sky you check out. For instance, most natural asteroids and other space objects are roughly in the plane of the solar system, and we still don't see them all the time, as the examples above show. A military kinetic impactor could be coming in from any direction, which massively increases the amount of sky you have to look at; plus, a black-painted object at the same temperature as the background would realistically only be detectable if it was either hit by a radar pulse, or passed in front of something bright like the Moon or the Sun. (It's actually surprising how small those objects are--they occupy around half a degree in the sky, which means there's approximately half a million times as much empty sky as there is Moon).

[BlacKnight]

No, I expect them to be bested by missiles. Ideally the "Orion missile", if available.

Your plan to make lasers ineffective involve using lasers to heat the radiators. Which requires a more powerful laser than the opponent has. At that point you have already won and don't need any other weapon.


It covers plenty of "shotgun" type attacks, many of which were proposed for SDI (aka "Star Wars" under Reagan). The specific range of velocity also covers most attacks moving in orbit or counter orbit. In other words, expect to use big missiles and you need to either directly hit the target or get close enough that you hit with significantly large shrapnel (little micro bits can be shielded).

It doesn't cover electromagnetic radiation or jets of plasma. So useless agaisnt lasers, nukes and casaba howitzer style weapons. Which are the one that actually matters.



There are limits to how much you can see, though, and also which parts of the sky you check out. For instance, most natural asteroids and other space objects are roughly in the plane of the solar system, and we still don't see them all the time, as the examples above show. A military kinetic impactor could be coming in from any direction, which massively increases the amount of sky you have to look at; plus, a black-painted object at the same temperature as the background would realistically only be detectable if it was either hit by a radar pulse, or passed in front of something bright like the Moon or the Sun. (It's actually surprising how small those objects are--they occupy around half a degree in the sky, which means there's approximately half a million times as much empty sky as there is Moon).

A military attack can't come form any direction, it can come only from a spacecraft.
Spacecrafts are hot and leave an hot stream of propellant behind them, so they are way more visible than asteroids.
Any decent surveillance system will give particular attention to the routes that an inert object could have taken detaching from a spacecraft.

[Mechalich]

A military attack can't come form any direction, it can come only from a spacecraft.
Spacecrafts are hot and leave an hot stream of propellant behind them, so they are way more visible than asteroids.
Any decent surveillance system will give particular attention to the routes that an inert object could have taken detaching from a spacecraft.

You could launch a kinetic kill projectile from an asteroid or any other fixed point without an atmosphere, but it really doesn't matter. The thing is, firing a kinetic projectile will be visible even if the projectile itself is largely invisible. You're going have a massive burst of electromagnetic energy and/or heat when you shoot, so the railgun equivalent of a muzzle flash could be detected from a vast distance and potentially avoided very easily.

Now, the use of asteroids as weapons of long-term terrorism is very hard to defend against, at least if you have any sort of free-roaming of persons (or even drones) throughout the system rather than tracking them all closely. Putting some engines on an asteroid, adjusting the orbit using engines and then removing the engines and allowing the asteroid to cool back down would allow the motivated to throw something large and fast-moving at a fixed position.

[Knaight]

At a range of a thousand miles (which is really close for long range) a shotgun blast of projectile weapons with 10, 000 projectiles and a spread of one degree will have an average gap between projectiles of something like a mile (can't be bothered to work it out, but I doubt I'm high), and those projectiles will be hostile for infinity years, to everything and everyone.

1000 miles * sin(2*pi/360) = 17.45 miles, which here is the radius of the circle these projectiles are in at a thousand miles. That works out to an area of 957 square miles (rounded). As an admittedly imperfect approximation those 10,000 projectiles can be treated mathematically as if they were in a 100 x 100 square, here 30.9 miles on a side to fit the 957 square miles. Taking into account them being in the center point of said squares in this approximation that works out to .99*30.9/100, or 0.306 miles. Call it 0.3, taking into account significant figures.

That's a pretty dense coverage, with a pretty decent chance to hit just about any hypothetical war ship. Of course, it's also point blank range in space. The average gap scales perfectly linearly with distance (neglecting the volume occupied by the actual projectiles). At a light second this works out to 5.7 miles, at which point it's already looking pretty sad.

[Lord Torath]

There are limits to how much you can see, though, and also which parts of the sky you check out. For instance, most natural asteroids and other space objects are roughly in the plane of the solar system, and we still don't see them all the time, as the examples above show. A military kinetic impactor could be coming in from any direction, which massively increases the amount of sky you have to look at; plus, a black-painted object at the same temperature as the background would realistically only be detectable if it was either hit by a radar pulse, or passed in front of something bright like the Moon or the Sun. (It's actually surprising how small those objects are--they occupy around half a degree in the sky, which means there's approximately half a million times as much empty sky as there is Moon).According to Atomic Rockets (http://www.projectrho.com/public_html/rocket/spacewardetect.php), you can scan the entire sky every 4 hours. Today.
A full spherical sky search is 41,000 square degrees. A wide angle lens will cover about 100 square degrees (a typical SLR personal camera is about 1 square degree); you'll want overlap, so call it 480 exposures for a full sky search, with each exposure taking about 350 megapixels.

Estimated exposure time is about 30 seconds per 100 square degrees of sky looking for a magnitude 12 object (which is roughly what the drive I spec'd out earlier would be). So, 480 / 2 is 240 minutes, or about 4 HOURS for a complete sky survey. This will require signal processing of about 150 gigapizels per two hours, and take a terabyte of storage per sweep.

That sounds like a lot, but...

Assuming 1280x1024 resolution, playing an MMO at 60 frames per second...78,643,200 = 78 megapixels per second. Multiply by 14400 seconds for 4 hours, and you're in the realm of 1 terapixel per sky sweep Now, digital image comparison is in some ways harder, some ways easier than a 3-D gaming environment. We'll say it's about 8x as difficult - that means playing World of Warcraft on a gaming system for four hours is about comparable to 75 gigapixels of full sky search. So not quite current hardware, but probably a computer generation (2 years) away. Making it radiation hardened to work in space, and built to government procurement specs, maybe 8-10 years away.

I can buy terabyte hard drive arrays now.

I can reduce scan time by adding more sensors, but my choke point becomes data processing. On the other hand, it's not unreasonable to assume that the data processing equipment will get significantly better at about the same rate that gaming PCs get significantly better.

Now, this system has limits - it'll have trouble picking up a target within about 2 degrees of the sun without an occlusion filter, and even with one, it'll take extra time for those exposures.

It won't positively identify a target - it'll just give brightness and temperature and the fact that it's something radiating like a star that moves relative to the background.

On the other hand, at the thrusts given above, it'll take somewhere around 2 days of thrust to generate the delta v to move from Earth to Mars, and the ship will be in transit for about 1-4 months depending on planetary positions.

[monomer]

That actually depends on the speed of the exhaust. If you are using an exhaust with speed less than 1/2 light speed, you have a theoretical maximum speed of twice your exhaust speed. I say theoretical because actually getting to twice your exhaust speed is hard and is likely to get you wherever you were trying to go in system.

Speed is really barely a consideration. Acceleration and reaction mass are what matters. Sure, you may be able to go somewhere at ridiculous speeds, but if you don't start decelerating long before you get there, all you'll see is a short blur before you're long past it. And unless we have some basically fantasy-ish technology like inertial dampeners or gravity wave generators, your acceleration is limited to what a body can handle for an extended period.

Missiles don't have to worry as much in regards to maximum acceleration, but say you are moving at 0.1c, and you fire a missile. That missile starts out with that 0.1c of velocity in the direction you are traveling. It now needs to shed a large amount of that velocity to be able to maneuver enough to hit something, unless your original trajectory was pointing almost perfectly exactly at your target, and your target is basically stationary.

[pendell]

So ... what will people fight over in space?

The first things that come to mind are:

1) Position. If you can prevent people from getting too close to a gravity well, for example, that means no gravity-assisted slingshot maneuvers for them; they'll have to burn more fuel and possibly take longer to get places. If you control the lagrange points, that means no one else can build something there.

2) Resources. An ice comet, for example, would mean hydrogen , which means fusion fuel. And of course there's access to the mother planet proper. Earth is so far unique in the galaxy as the only planet that can support human life without technological assistance. I suspect we'll still need things from it for centuries that we can get nowhere else, so the person who controls access to the planet will be in a position to dictate terms to spacefaring humans for quite some time.

Anything else?

Respectfully,

Brian P.

[wumpus]

We didn't spot Oumuamua until it had already missed us.

https://en.wikipedia.org/wiki/%CA%BBOumuamua


But we did spot it, which counts for something. There are very few telescopes looking for objects like that right now, though the numbers are slowly increasing. A military budget would change things.

"We" [humanity] are looking for asteroids in our spare time from the wrong spot. The right spot would be in orbit around the Sun from well within Earth's orbit (so all the potential asteroids would be bright, especially when they are in past Earth's orbit and easiest to spot [although moving fastest]).

https://asteroidday.org/

[factotum]

The thing is, firing a kinetic projectile will be visible even if the projectile itself is largely invisible. You're going have a massive burst of electromagnetic energy and/or heat when you shoot, so the railgun equivalent of a muzzle flash could be detected from a vast distance and potentially avoided very easily.


Seeing where the projectile was fired from doesn't help you if you don't know what it was fired *at*. If the projectile itself is near-invisible then you're boned--you just have to either wait for a lucky detection, or the thing to hit its target, or else move every possible target the projectile could theoretically hit out of its way--a pretty much impossible operation.

[pendell]

Seeing where the projectile was fired from doesn't help you if you don't know what it was fired *at*. If the projectile itself is near-invisible then you're boned--you just have to either wait for a lucky detection, or the thing to hit its target, or else move every possible target the projectile could theoretically hit out of its way--a pretty much impossible operation.

Given the distances involved, couldn't you evade with just about a second's worth of burn without screwing up your overall trajectory? Then, if someone fires again, earn the second back by thrusting the other way?

That's why I put maneuvering jets on my projectiles to account for just such problems, as well as computational errors. At long ranges, it seems to me that an unguided projectile would have trouble hitting even an unmaneuvering target, let alone one capable of evasion.


Respectfully,

Brian P.

[BlacKnight]

Now, the use of asteroids as weapons of long-term terrorism is very hard to defend against, at least if you have any sort of free-roaming of persons (or even drones) throughout the system rather than tracking them all closely. Putting some engines on an asteroid, adjusting the orbit using engines and then removing the engines and allowing the asteroid to cool back down would allow the motivated to throw something large and fast-moving at a fixed position.

To deviate an asteroid you need to put some rockets on it or just vaporize a part of it with a laser. The total energy expenditure of energy would probably be lower than the one used to put it on the collision route.


Seeing where the projectile was fired from doesn't help you if you don't know what it was fired *at*. If the projectile itself is near-invisible then you're boned--you just have to either wait for a lucky detection, or the thing to hit its target, or else move every possible target the projectile could theoretically hit out of its way--a pretty much impossible operation.

This is assuming that you can fire straight at anything. But orbital mechanics are complicated and in reality you are very limited in movement.
For any spacecraft in a certain position there are only a few routes that a projectile fired from it can take, and only a minority of these would hit something.
So the defender just need to concentrate on these with his scanning power, or just sweep them with a laser beam powerful enough to vaporize small projectiles.
Another advantage of laser is that they can be focused less than their maximum capacity, resulting in a wider beam with lower energy density. So the same weapon can act as long range anti-ship gun or point defense system.

[Darth Ultron]

There are limits to how much you can see, though, and also which parts of the sky you check out.

Yes, you'd need a whole network. This would really be part of the first wave of space colonization as each rest spot would also have a watcher too.




1) Position.
2) Resources

Well, it is what people on Earth fight about...

[LordEntrails]

You could launch a kinetic kill projectile from an asteroid or any other fixed point without an atmosphere, but it really doesn't matter. The thing is, firing a kinetic projectile will be visible even if the projectile itself is largely invisible. You're going have a massive burst of electromagnetic energy and/or heat when you shoot, so the railgun equivalent of a muzzle flash could be detected from a vast distance and potentially avoided very easily.

The magnetic profile of a railgun could be shielded from detection. For every measure, their is a countermeasure developed, eventually. So it depends just what tech is available as to if KKV projectile launch can be detected.


According to Atomic Rockets (http://www.projectrho.com/public_html/rocket/spacewardetect.php), you can scan the entire sky every 4 hours. Today.

As demonstrated, with examples, we can NOT EFFECTIVELY scan the entire sky. And once active measures are made to hide the projectiles or mask the enemies, things get harder.


Given the distances involved, couldn't you evade with just about a second's worth of burn without screwing up your overall trajectory? Then, if someone fires again, earn the second back by thrusting the other way?
Only if you know what the target was. And only if a single target was selected. Just like you can predict where they will fire at, the enemy can predict your possible reactions, and fire multiple weapons to cover each of your probable reactions. Again, why I talked of firing 1000 KKVs. Only a coulple would need to be fired at any one location. They could be tactically fired to cover many the positions the target might be at.


That's why I put maneuvering jets on my projectiles to account for just such problems, as well as computational errors. At long ranges, it seems to me that an unguided projectile would have trouble hitting even an unmaneuvering target, let alone one capable of evasion.

Except maneuvering weapons are not stealthy, and hence the enemy can see them coming in. Now, if they run cold and silent until terminal phase, maybe that would be more effective than multiple inert KKV's. That is going to depend upon a detailed analysis of the tactical situation and the actual technology capabilities involved. (i.e. how good can the missles detect and manuever, how fast can the targets react, how good is detection, armor, damage, etc).

[pendell]

Again, why I talked of firing 1000 KKVs. Only a coulple would need to be fired at any one location. They could be tactically fired to cover many the positions the target might be at.


That sounds expensive. I wouldn't want to spend more than a couple of dozen long range shots on an individual target, not thousands.

Respectfully,

Brian P.

[Gnoman]

More importantly, there's no backstop in space. Any of those 1000 projectiles that don't hit a target are probably going to wind up in an unstable orbit around the sun, and eventually will either hit the sun or plow into something else. Hitting the Sun isn't a big deal, but there's a real chance that the "something else" that gets hit decades or centuries from now is going to be something that you don't want to destroy, even if you personally won't be around to see it.

[pendell]

More importantly, there's no backstop in space. Any of those 1000 projectiles that don't hit a target are probably going to wind up in an unstable orbit around the sun, and eventually will either hit the sun or plow into something else. Hitting the Sun isn't a big deal, but there's a real chance that the "something else" that gets hit decades or centuries from now is going to be something that you don't want to destroy, even if you personally won't be around to see it.

I thought of that, but then I thought just how big space is. Even a couple thousand stray ... pebbles? ... would probably go off into never-never land and never actually hit anything. Not unless the solar system got as crowded with space junk as earth orbit is currently. I'm not sure why it would, however, when we always have the sun to sling our junk into.

Respectfully ,

Brian P.

[jayem]

That sounds expensive. I wouldn't want to spend more than a couple of dozen long range shots on an individual target, not thousands.

Respectfully,

Brian P.

They could be slow, but then you have more time to avoid them, so in turn the target saves even more KE.

My guess is regardless of speed unless detection ranges are really poor compared to ship sizes and mass then non-guided shots will use more energy than evasion.

Also if at non-trivial ranges (I.E unless you let them get nearer you than you are spaced out). Once your basic detectors go, "something fired". You also have a pretty narrow arc when it's far away to keep tracking the missiles. For each target time combination you know where it has to be.

Where it will be different is:
a) You use them to add obstacles when your real attack comes
b) Some of them can be guided (but the guided ones are expensive and not perfect as else you could use them alone)
c) You really go for the long game and aim the collision for 2 orbits time with sling-shotting (so your initial movement is really tiny)
d) Under a false flag or something you can get really close

[Forum Explorer]

The magnetic profile of a railgun could be shielded from detection. For every measure, their is a countermeasure developed, eventually. So it depends just what tech is available as to if KKV projectile launch can be detected.



As demonstrated, with examples, we can NOT EFFECTIVELY scan the entire sky. And once active measures are made to hide the projectiles or mask the enemies, things get harder.


Except maneuvering weapons are not stealthy, and hence the enemy can see them coming in. Now, if they run cold and silent until terminal phase, maybe that would be more effective than multiple inert KKV's. That is going to depend upon a detailed analysis of the tactical situation and the actual technology capabilities involved. (i.e. how good can the missles detect and manuever, how fast can the targets react, how good is detection, armor, damage, etc).


How so? If it gives off even 1 degree of heat it'll be shining like a friggin lighthouse.


The examples were all of rocks that are close to absolute zero in temperature. The Atomic Rockets calculations is for scanning for objects that have heat and or light. Detecting asteroids and stuff is much much harder, because you basically need them to be blocking a different object to see them. Anything that isn't absolute zero is going to be dead easy to spot.


Problem is how can any ship run cold? People need heat to live, so even if you didn't have engines running, you'd still shine brighter then a neighboring star.

[Gnoman]

I thought of that, but then I thought just how big space is. Even a couple thousand stray ... pebbles? ... would probably go off into never-never land and never actually hit anything. Not unless the solar system got as crowded with space junk as earth orbit is currently. I'm not sure why it would, however, when we always have the sun to sling our junk into.

Respectfully ,

Brian P.

Deliberately slinging junk into the sun is extremely energy intensive. Any technology we have on the horizon wouldn't be able to do it.


That's also why stray impactors would be a very real problem. It is very unlikely that you're going to expend all the energy needed to get way above or below the ecliptic plane, and you certainly aren't going to accelerate them to system escape velocity, so your impactors are going to be sharing the same orbital space as everything else in the system.

[Rockphed]

How so? If it gives off even 1 degree of heat it'll be shining like a friggin lighthouse.


The examples were all of rocks that are close to absolute zero in temperature. The Atomic Rockets calculations is for scanning for objects that have heat and or light. Detecting asteroids and stuff is much much harder, because you basically need them to be blocking a different object to see them. Anything that isn't absolute zero is going to be dead easy to spot.


Problem is how can any ship run cold? People need heat to live, so even if you didn't have engines running, you'd still shine brighter then a neighboring star.

As I showed up thread, a small 64 kelvin object is impossible to detect in reasonable time with the current best hardware. Well, it is impossible to detect with a radiometer. Other detector types might be able to do it, I just don't feel like mathing it out.

[jayem]

Problem is how can any ship run cold? People need heat to live, so even if you didn't have engines running, you'd still shine brighter then a neighboring star.

Robots&Machines? It will still be shining like a torch, but that's a bit better.
Even fully active you'd probably be a bit better than people (about 1.4kW/sq meter of outside wall ??), though not be much.
I'd imagine you'd want at least the equivalent of a Raspberry Pi (~1 Watt) to monitor things and start the wakeup procedures. (The 64k case)
But I suppose it ought to be possible to have a purely passive on switch, in which you could really run cold (as long as batteries still work).

A human occupied ship would be at 300 odd K. Which would be outputting serious amounts of energy and on conspicuous wavelengths.

[Gnoman]

The requirements to keep humans alive wouldn't make much difference to the temperature of a ship. Waste heat from all the weapons, sensors, and propulsion systems would be most of it.

[Forum Explorer]

As I showed up thread, a small 64 kelvin object is impossible to detect in reasonable time with the current best hardware. Well, it is impossible to detect with a radiometer. Other detector types might be able to do it, I just don't feel like mathing it out.

64 kelvin is what -200 degrees or so? A little less I think. That's still incredibly cold. Could we actually move anything at that temperature? It's certainly way too cold for any ship with humans in it to operate.


Robots&Machines? It will still be shining like a torch, but that's a bit better.
Even fully active you'd probably be a bit better than people (about 1.4kW/sq meter of outside wall ??), though not be much.
I'd imagine you'd want at least the equivalent of a Raspberry Pi (~1 Watt) to monitor things and start the wakeup procedures. (The 64k case)
But I suppose it ought to be possible to have a purely passive on switch, in which you could really run cold (as long as batteries still work).

A human occupied ship would be at 300 odd K. Which would be outputting serious amounts of energy and on conspicuous wavelengths.

Hmm, I hadn't considered robots. Advances in AI could move all space combat to being done by computers. But again, how cold can we run them? Modern computers run very hot, though I hear google keeps a super computer in a room at basically absolute zero. But that's the room itself, not the computer

[jayem]

Hmm, I hadn't considered robots. Advances in AI could move all space combat to being done by computers. But again, how cold can we run them? Modern computers run very hot, though I hear google keeps a super computer in a room at basically absolute zero. But that's the room itself, not the computer
They have a better sleep mode.
If they are smaller then the thermal power output (any radiation from the actual operation is a different matter) is a lot smaller even if they are half as hot again (however they will really stand out as being artificial)

Also if you get the hot part relatively small compared with the rest of the ship. You can do proportionally more to direct some of the heat away from the target at least, and absorb some of the light (which will get re-emitted but as a lower temperature).
Perhaps ending up with a giant thermos flask with a metal lid (at the back). You could of course do something similar with a human filled ship, but the total energy is greater (unless you are firing the gun or accelerating) and you have to surround a greater volume

[BlacKnight]

A thing that hasn't be touched yet is the laser mirror web, composed of multiple mirrors that reflect a laser beam.
This allows to generate a beam on a planet or asteroid, without worrying about mass or heat management, and then use the mirrors chain to bring it where needed.
The issue with lasers at long range is diffraction, which in this case is solved by having a mirror refocus the beam to the next mirror in the chain, which in turn refocus it to the next mirror and so on until the target.
The last mirror can make the necessary aim adjustments to hit the target.
The advantages are numerous: the mirrors are light and cheap, while the expensive equipment necessary to generate the energy and the beam are far from the frontline. The system allows the use of the energy of an entire planet, which is basically impossible for a fleet of spacecrafts to match.

This web is useful not only for military purposes, but also for moving energy or even spacecraft (using the solar sail technology).
A space civilization could have thousands of mirrors transmitting energy across the solar system like a power grid/railway mix.

[Gnoman]

Even the best mirrors only have around 99.9% reflectivitiy, meaning that they absorb 0.1% of the beam energy. That doesn't sound like a lot, except that you need a hundred kilowatts (at least - that's the minimum target for short-range terrestrial projects against very fragile targets) to make a serviceable weapons-grade laser. That means that, at minimum, your first laser platform would have to be capable of absorbing 100 watts of laser energy without damage, which is not exactly trivial. To make matters worse, you'd be losing a kilowatt every ten bounces, which would thus require a higher output laser to compensate - which would also raise the amount of energy your mirrors have to absorb.


This, combined with the complex systems you'd need to be able to focus the beam as desired (a static mirror won't work, because it could have only one focal point), means that your mirrors would not be cheap. They would also require regular replacement as environmental effects degrade the quality of the optical coating, greatly reducing the reflectivitiy.



Or, to put it simply, the "laser web" simply wouldn't work. The mirrors would not be light or cheap, and the maintenance cost of the system would be enormous.

[halfeye]

1000 miles * sin(2*pi/360) = 17.45 miles, which here is the radius of the circle these projectiles are in at a thousand miles. That works out to an area of 957 square miles (rounded). As an admittedly imperfect approximation those 10,000 projectiles can be treated mathematically as if they were in a 100 x 100 square, here 30.9 miles on a side to fit the 957 square miles. Taking into account them being in the center point of said squares in this approximation that works out to .99*30.9/100, or 0.306 miles. Call it 0.3, taking into account significant figures.

That's a pretty dense coverage, with a pretty decent chance to hit just about any hypothetical war ship. Of course, it's also point blank range in space. The average gap scales perfectly linearly with distance (neglecting the volume occupied by the actual projectiles). At a light second this works out to 5.7 miles, at which point it's already looking pretty sad.

Oops, so I was high after all. I'm not convinced that that is a useful spread, it's longer than a sea-going destroyer, cruiser, or even battleship and sea ships are much longer than they are wide or deep, I would expect space ships to be wider but shorter.


They would also require regular replacement as environmental effects degrade the quality of the optical coating, greatly reducing the reflectivitiy.

Environment effects in space? micrometeorites are bad, but they would make a small hole, not affect coatings. I agree the idea probably wouldn't work though.

[BlacKnight]

Even the best mirrors only have around 99.9% reflectivitiy, meaning that they absorb 0.1% of the beam energy. That doesn't sound like a lot, except that you need a hundred kilowatts (at least - that's the minimum target for short-range terrestrial projects against very fragile targets) to make a serviceable weapons-grade laser. That means that, at minimum, your first laser platform would have to be capable of absorbing 100 watts of laser energy without damage, which is not exactly trivial. To make matters worse, you'd be losing a kilowatt every ten bounces, which would thus require a higher output laser to compensate - which would also raise the amount of energy your mirrors have to absorb.


This, combined with the complex systems you'd need to be able to focus the beam as desired (a static mirror won't work, because it could have only one focal point), means that your mirrors would not be cheap. They would also require regular replacement as environmental effects degrade the quality of the optical coating, greatly reducing the reflectivitiy.



Or, to put it simply, the "laser web" simply wouldn't work. The mirrors would not be light or cheap, and the maintenance cost of the system would be enormous.


Absorbing 100 w (on which surface ?) is trivial: modern military lasers already do it. The US Navy LaWS has an output of 33 kw and a lense of 1 m or less (can't find the exact size).
Mirrors in space can be arbitrarily big and distribute the energy on a large surface.

Obviously the mirrors would need some moving capability, but it won't have to be comparable to that of a spacecraft.
And that's the point about cheapness: they are not cheap in absolute, they are in comparison to the alternatives.

[Gnoman]

Environment effects in space? micrometeorites are bad, but they would make a small hole, not affect coatings. I agree the idea probably wouldn't work though.

Solar wind is a thing. For that matter, mere solar energy would have a degrading effect.


Absorbing 100 w (on which surface ?) is trivial: modern military lasers already do it. The US Navy LaWS has an output of 33 kw and a lense of 1 m or less (can't find the exact size).
Mirrors in space can be arbitrarily big and distribute the energy on a large surface.

Obviously the mirrors would need some moving capability, but it won't have to be comparable to that of a spacecraft.
And that's the point about cheapness: they are not cheap in absolute, they are in comparison to the alternatives.

You're obviously thinking that your mirror will just be a big flat disc in space.

That will not work. To do what you are wanting to do, the mirror will have to have a fully articulated surface, able to form any concave shape as dictated by the target range. This is because a beam calibrated for three light-minutes will do absolutely nothing at five, so you have to have the ability to adjust the focal point. This is expensive to build, and would require regular maintenance.

That is independent of the necessity of moving the lens itself, not only in small targeting arcs, but it would also need to regularly boost to maintain the proper orbit around whatever body you've placed it around.

The LaWS is not just a prototype well below the strength needed for an actual weapon, but has the enormous advantage of operating in air. This means that the mirror can dump all waste heat into the atmosphere. A space-mounted mirror will not be able to do that. Taking 100 Watts of energy may not seem like much, but you'll be radiating much less than that - and it is a per "shot" buildup. If you have to fire a dozen times in an hour, you've now dumped 1200 watts into the thing, and probably dumped less than 100W waste heat.

Then, we run into the same problem discussed earlier - your entire defense system is dependent on effectively immobile and extremely visible relays. Even if you managed to overcome all the technical hurdles, a single kinetic strike would vaporize any mirror, and render this immensely expensive system completely inert.

[BlacKnight]

You're obviously thinking that your mirror will just be a big flat disc in space.

That will not work. To do what you are wanting to do, the mirror will have to have a fully articulated surface, able to form any concave shape as dictated by the target range. This is because a beam calibrated for three light-minutes will do absolutely nothing at five, so you have to have the ability to adjust the focal point. This is expensive to build, and would require regular maintenance.

That is independent of the necessity of moving the lens itself, not only in small targeting arcs, but it would also need to regularly boost to maintain the proper orbit around whatever body you've placed it around.

The LaWS is not just a prototype well below the strength needed for an actual weapon, but has the enormous advantage of operating in air. This means that the mirror can dump all waste heat into the atmosphere. A space-mounted mirror will not be able to do that. Taking 100 Watts of energy may not seem like much, but you'll be radiating much less than that - and it is a per "shot" buildup. If you have to fire a dozen times in an hour, you've now dumped 1200 watts into the thing, and probably dumped less than 100W waste heat.

Then, we run into the same problem discussed earlier - your entire defense system is dependent on effectively immobile and extremely visible relays. Even if you managed to overcome all the technical hurdles, a single kinetic strike would vaporize any mirror, and render this immensely expensive system completely inert.


Or you can use an optical phased array to steer the beam. No need of moving parts.

Obviously the mirror will need radiators to manage the heat. Nothing different from any other spacecraft.
I also notice that you are still not providing any surface data. 100 watts alone means nothing.

You still think that kinetic strikes can penetrate a laser defense ? They can't, not without expenses way higher than the laser system they are supposed to beat.
I've already provided an example in an earlier post, but the best way to see that is to play with the numbers by yourself with this tool https://web.archive.org/web/20170412014001/http://www.5596.org/cgi-bin/laser.php

And if you think that a swarm of small projectiles is invisible: no, it isn't.
The defender knows that an enemy spacecraft has shot something at it. Thanks to orbital mechanics it knows when and where the projectiles will be in order to hit.
So it just has to sweep a laser beam in that spot. A beam that can be kilometers wide. Even ignoring the Lidar uses if there are pebbles there they will heat, revealing their presence.

[Rockphed]

Or you can use an optical phased array to steer the beam. No need of moving parts.

Phased arrays typically are less energy efficient than traditional (i.e. rotated conic section reflector) electromagnetic systems. Lasers are incredibly inefficient, so the added inefficiencies from the phased array might not matter.

That said, I think the problem was the moving parts in the mirrors, not in the broadcast system. I don't feel like doing the math, but I am fairly certain that your proposed laserweb will need to put the beam-waist of the lasers half-way down each transit path. If you have a cloud of mirrors, transit paths will not remain constant length, resulting in a need to change the focal length of every mirror constantly.

And to disrupt your laserweb, I don't need to destroy every mirror. I just need to destroy enough mirrors so your critical path has at least 1 leg where the laser cannot maintain a spot size smaller than the mirror on the other end. True, putting a single 25 kg slug through the center of a mirror will probably not reduce its laser transmission enough to matter, but if I sufficiently pit the surface such that it cannot focus, it needs repair or cleaning. If I am incredibly lucky, the pitting will go unnoticed and the mirror will vaporize as it absorbs the entire energy of the laser.

[jayem]

You're obviously thinking that your mirror will just be a big flat disc in space.

That will not work. To do what you are wanting to do, the mirror will have to have a fully articulated surface, able to form any concave shape as dictated by the target range. This is because a beam calibrated for three light-minutes will do absolutely nothing at five, so you have to have the ability to adjust the focal point. This is expensive to build, and would require regular maintenance.
Another option would be to make the mirror a bit bigger and have the focal length change smoothly across the laser. With a known gradient, I'm sure a second mirror could even be shaped to cancel some of [the errors] that [would cause] out. (at least this way the spread of the out-of focus components is halved)

The movement of two mirrors alone ought to do some good, although that might either need movement in the km range or for the other mirrors to have really tiny focal lengths.

With a decent set of mirrors, and having a pretty well defined beam coming in, and with the apparatus covering such distances I reckon it ought to be possible to create a much finer beam anyway. Two parabolic mirrors, one large (with a hole in the centre) to focus the pretty near parallel incoming light onto the focus. The other tiny to return the beam to parallel. would work apart from the fact that the final mirror is getting the full force of the laser.

[Rockphed]

With a decent set of mirrors, and having a pretty well defined beam coming in, and with the apparatus covering such distances I reckon it ought to be possible to create a much finer beam anyway. Two parabolic mirrors, one large (with a hole in the centre) to focus the pretty near parallel incoming light onto the focus. The other tiny to return the beam to parallel. would work apart from the fact that the final mirror is getting the full force of the laser.

Fun fact: the divergence rate of a laser beam depends only on the radius of the beam at its narrowest point. Alternatively, how narrow a beam can get is dependent on the rate of convergence. This plays merry chaos with things like optical fiber.

[Lvl 2 Expert]

Bouncing lasers through mirrors, lenses or even (speculative) artificial gravity lenses does have a cool effect though. Aside from it potentially reducing the heat problems of your laser it makes the main costly part of your weapon system very hard to counter attack. They'd either need to use their own lasers very precise, or they'd need to find some unexpected angle of attack.

[jayem]

Fun fact: the divergence rate of a laser beam depends only on the radius of the beam at its narrowest point. Alternatively, how narrow a beam can get is dependent on the rate of convergence. This plays merry chaos with things like optical fiber.

Too much thinking about light as a nice beam for me to pay attention to the wave aspects (it doesn't look like a narrow gap!).

I also assumed the light was collimated because it was so far away which is kind of true but only if you throw a lot of it away or the system was already good.

That seems a pretty fundamental limit that I think scotches any plan to use the long distances of space to improve our laser beam, in any other way than to reset it (Unless there's some arcane non-gaussian distribution, perhaps sinc like.).
It even has implications for the focusing methods.

My back of the envelope with the equation says for a 1mm burn, with Reddish laser and the focuser about 1m wide, you need the focuser about 3km away. Which is very close.

But with a 10cm burn (compensated by 10,000 timesing the power), a 100m focuser and X-rays you're back in light minutes (with the main ship at that far again).

So I think there is still potentially room, but it does limit the options considerably (unless there's a clever trick to be discovered).




Bouncing lasers through mirrors, lenses or even (speculative) artificial gravity lenses does have a cool effect though. Aside from it potentially reducing the heat problems of your laser it makes the main costly part of your weapon system very hard to counter attack. They'd either need to use their own lasers very precise, or they'd need to find some unexpected angle of attack.

That was observed by the OP, and is one of the things that I do like more and more about it.

Also combining the two, while you have a meter radius beam you can have low divergence (though at laser wavelengths still not low enough to be truly useful, and I can't think of any way to exploit it)

[wumpus]

This https://www.youtube.com/watch?v=bL5GN5OLmtc video came up in the "Chinese artificial moon thread" and while he didn't explain the reasoning behind "can't get a mirror to resolve better than .5 degree", I expect that is not only true for mirrors but any other laser blast (Scott Manley does have a great deal of training as an astronomer, although I think he bailed on his PhD program to work for Napster).

I doubt this interferes with US Navy warships using lasers to blast things (especially incoming missiles), but it certainly makes it much harder to attack targets across the vast reaches of space.

[Rockphed]

This https://www.youtube.com/watch?v=bL5GN5OLmtc video came up in the "Chinese artificial moon thread" and while he didn't explain the reasoning behind "can't get a mirror to resolve better than .5 degree", I expect that is not only true for mirrors but any other laser blast (Scott Manley does have a great deal of training as an astronomer, although I think he bailed on his PhD program to work for Napster).

I doubt this interferes with US Navy warships using lasers to blast things (especially incoming missiles), but it certainly makes it much harder to attack targets across the vast reaches of space.

I have decided that youtube videos are a very poor way of discussing things. Their discussion proceeds at speaking pace, which is slower than reading pace, they are hard to navigate through to find the specific thing being said, and they are hard to quote from.

[LordEntrails]

That sounds expensive. I wouldn't want to spend more than a couple of dozen long range shots on an individual target, not thousands.


No, 1kg inert KKV would be cheap. All the expense would be involved in the firing system. The only "expense" is their mass, in terms of conservation of mass within the mass limit of the space ship. So, these small KKV's would have a negligible dollar cost, and you could fire 1000 of them for the "cost" of a single guided and powered missile.


How so? If it gives off even 1 degree of heat it'll be shining like a friggin lighthouse.
...
Problem is how can any ship run cold? People need heat to live, so even if you didn't have engines running, you'd still shine brighter then a neighboring star.
You quoted me on this, but I was never talking about a ship. I was talking about an inert mass of 1 kg with perhaps a cross section of less than 5cm (more like 1-2cm).

OK, let's do the math, osmium is over 22g/cm^3. So 1kg is 45.5 cm^3 and would be a sphere of about 3.3 cm. And if you shaped that into an easier to launch and harder to detect projectile, the detection cross-section would be smaller.

So, such a mass could easily run cold, and not be detectable by heat/IR. And radar or lidar etc would still be hard to use. One possibility someone mentioned was to sweep the sky with lasers to heat up the objects and then use IR to detect them. But I doubt if you do the math you would be able to heat up such a dense object with such a 'laser sweep'. See the quote below from Rockphed.


As I showed up thread, a small 64 kelvin object is impossible to detect in reasonable time with the current best hardware. Well, it is impossible to detect with a radiometer. Other detector types might be able to do it, I just don't feel like mathing it out.

[BlacKnight]

Phased arrays typically are less energy efficient than traditional (i.e. rotated conic section reflector) electromagnetic systems. Lasers are incredibly inefficient, so the added inefficiencies from the phased array might not matter.

That said, I think the problem was the moving parts in the mirrors, not in the broadcast system. I don't feel like doing the math, but I am fairly certain that your proposed laserweb will need to put the beam-waist of the lasers half-way down each transit path. If you have a cloud of mirrors, transit paths will not remain constant length, resulting in a need to change the focal length of every mirror constantly.

And to disrupt your laserweb, I don't need to destroy every mirror. I just need to destroy enough mirrors so your critical path has at least 1 leg where the laser cannot maintain a spot size smaller than the mirror on the other end. True, putting a single 25 kg slug through the center of a mirror will probably not reduce its laser transmission enough to matter, but if I sufficiently pit the surface such that it cannot focus, it needs repair or cleaning. If I am incredibly lucky, the pitting will go unnoticed and the mirror will vaporize as it absorbs the entire energy of the laser.

Forgive me, but I seriously don't understand what the bolded sentence means. Putting down the beam-waist ?

Regarding throwing slugs at the mirrors: again, how do these slugs manage to reach the mirrors ?


This https://www.youtube.com/watch?v=bL5GN5OLmtc video came up in the "Chinese artificial moon thread" and while he didn't explain the reasoning behind "can't get a mirror to resolve better than .5 degree", I expect that is not only true for mirrors but any other laser blast (Scott Manley does have a great deal of training as an astronomer, although I think he bailed on his PhD program to work for Napster).

I doubt this interferes with US Navy warships using lasers to blast things (especially incoming missiles), but it certainly makes it much harder to attack targets across the vast reaches of space.

The Hubble telescope can resolve 0.07 arcsecond, so either that astronomer is talking of completely different things or he's lying.

[factotum]

and while he didn't explain the reasoning behind "can't get a mirror to resolve better than .5 degree", I expect that is not only true for mirrors but any other laser blast

The reason for the 0.5 degrees is because that's how big the Sun is at this distance, and a flat mirror can only reflect that--he does specifically say this is a flat mirror. A concave mirror would be able to focus the beam more narrowly, at the expense of having a very precisely defined focus distance. In addition, mirrors reflecting sunlight also have another critical difference to a laser, namely, the light is not coherent. I am absolutely 100% certain that a laser has far less than 0.5 degrees of variance.

[Mando Knight]

The Hubble telescope can resolve 0.07 arcsecond, so either that astronomer is talking of completely different things or he's lying.

The Hubble telescope isn't trying to concentrate sunlight into a death-ray pointing at the Earth, and it's not a single mirror, either, both of these being relevant conditions to the "can't focus the sun into a beam narrower than 0.5°" statement.

[Rockphed]

Forgive me, but I seriously don't understand what the bolded sentence means. Putting down the beam-waist ?

The minimum size of a laser is sometimes called the beam-waist. There are probably other names for it, but that is the one I remember. Lasers diffract such that if you know where the beam waist is, how big it is, and the wavelength you can determine the beam width at every other point. The relationship is, generally, that the smaller you make the beam waist, the faster the beam diffracts. If you want to send a laser a light minute away, you could do it by having a really big mirror with a focus 1 light minute away, which would result in the laser being minimum size at the far point, or you could do it by having a focus .5 light minutes away and having the 2 mirrors be the same size (the beam waist of a collimated laser going through a lens occurs at the focus of the lens). If I damage mirrors such that the minimum beam waist required for your longest jump is at least as large as your mirrors, then instead of focusing down at the mirror, you just have a flat mirror, which results in significant energy loss.

[Gnoman]

Regarding throwing slugs at the mirrors: again, how do these slugs manage to reach the mirrors ?


A KKV thrown at a essentially immobile, highly visible target will hit. Even if you detect it coming in, trying to deflect or intercept it will be essentially impossible due to the extreme velocity and small size. A ship can "dodge" it by irregularly making small trajectory changes that prevent accurate prediction information. Your mirrors can't.


To use an analogy, you're asking "How are the bullets from a sniper rifle going to manage to reach my giant searchlight?"

[Excession]

No, 1kg inert KKV would be cheap. All the expense would be involved in the firing system. The only "expense" is their mass, in terms of conservation of mass within the mass limit of the space ship. So, these small KKV's would have a negligible dollar cost, and you could fire 1000 of them for the "cost" of a single guided and powered missile.

Most of the cost of a bullet in space is likely to be getting the mass into space, and to the target, in the first place. If that cost is high enough, you may as well spend a bit more on the bullet to add some sort of terminal guidance. Something like the ability to explode into shrapnel before it hits the mirror, or do one jink to turn an obviously missing projection into a hit. That would force the point defences to engage further out, and target more projectiles, making it easier to overwhelm them.


So, such a mass could easily run cold, and not be detectable by heat/IR. And radar or lidar etc would still be hard to use. One possibility someone mentioned was to sweep the sky with lasers to heat up the objects and then use IR to detect them. But I doubt if you do the math you would be able to heat up such a dense object with such a 'laser sweep'. See the quote below from Rockphed.

Getting the launched projectile cold is an interesting challenge. A rail gun will heat up the projectile, as will just about anything else. You might need a liquid helium or solid hydrogen filled sabot or something. You would then need a mirror finish to minimise heating from the sun, which has the added bonus of making laser point defences much less effective.

[Forum Explorer]

No, 1kg inert KKV would be cheap. All the expense would be involved in the firing system. The only "expense" is their mass, in terms of conservation of mass within the mass limit of the space ship. So, these small KKV's would have a negligible dollar cost, and you could fire 1000 of them for the "cost" of a single guided and powered missile.


You quoted me on this, but I was never talking about a ship. I was talking about an inert mass of 1 kg with perhaps a cross section of less than 5cm (more like 1-2cm).

OK, let's do the math, osmium is over 22g/cm^3. So 1kg is 45.5 cm^3 and would be a sphere of about 3.3 cm. And if you shaped that into an easier to launch and harder to detect projectile, the detection cross-section would be smaller.

So, such a mass could easily run cold, and not be detectable by heat/IR. And radar or lidar etc would still be hard to use. One possibility someone mentioned was to sweep the sky with lasers to heat up the objects and then use IR to detect them. But I doubt if you do the math you would be able to heat up such a dense object with such a 'laser sweep'. See the quote below from Rockphed.

Ah, I was thinking about the ship firing the shot to begin with. Yeah, I suspect detecting the shots themselves will be incredibly difficult. So evasion is going to be mostly moving around quickly and unpredictably. At extreme ranges that should prove sufficient, even if the enemy is using a shot gun approach.

I also don't think immobile defenses will be much of a thing. Unless you want to count immobile sensors as defenses.

Honestly, I could see railgun shots being designed to be small enough to burn up in atmosphere, allowing them to fire willy nilly without worrying about collateral, while still being a threat to ships and satellites.

[factotum]

Most of the cost of a bullet in space is likely to be getting the mass into space, and to the target, in the first place.

I believe it was Arthur C. Clarke who pointed out, when the whole "Star Wars" program was a thing back in the early 80s, that all the Russians had to do to neutralise the billion-dollar laser satellites the Americans planned to build was to put up a two rouble bucket of nails in the same orbit but opposite direction. Combined orbital velocity at impact would easily destroy the satellite even if only one of the nails hit, and a bucket of nails would be far lighter, cheaper and easier to put into orbit than the big laser satellite.

[halfeye]

I believe it was Arthur C. Clarke who pointed out, when the whole "Star Wars" program was a thing back in the early 80s, that all the Russians had to do to neutralise the billion-dollar laser satellites the Americans planned to build was to put up a two rouble bucket of nails in the same orbit but opposite direction. Combined orbital velocity at impact would easily destroy the satellite even if only one of the nails hit, and a bucket of nails would be far lighter, cheaper and easier to put into orbit than the big laser satellite.

That would be true, however, on any one orbit the number taken down would be low, and one takedown would presumably be taken to be a prelude to a first strike, so a first strike in response is a possible outcome. That's supposing all your own satelittes in nearby orbits are expendable.

I think there are a bunch of nails in LEO now more or less, the way people talk about all the trash flying about up there.

[Excession]

I believe it was Arthur C. Clarke who pointed out, when the whole "Star Wars" program was a thing back in the early 80s, that all the Russians had to do to neutralise the billion-dollar laser satellites the Americans planned to build was to put up a two rouble bucket of nails in the same orbit but opposite direction. Combined orbital velocity at impact would easily destroy the satellite even if only one of the nails hit, and a bucket of nails would be far lighter, cheaper and easier to put into orbit than the big laser satellite.

If you're on Mars, putting a bucket of nails into low Earth orbit is not cheap. And if you throw the bucket from Mars they will spread out too much before getting there. The interplanetary nail-bomb is still a strong option, but it probably needs to get near the target before exploding. While you're spending all that reaction mass to launch the thing, you can add extras like decoys and terminal guidance for only a small relative cost increase.

[BlacKnight]

OK, let's do the math, osmium is over 22g/cm^3. So 1kg is 45.5 cm^3 and would be a sphere of about 3.3 cm. And if you shaped that into an easier to launch and harder to detect projectile, the detection cross-section would be smaller.

So, such a mass could easily run cold, and not be detectable by heat/IR. And radar or lidar etc would still be hard to use. One possibility someone mentioned was to sweep the sky with lasers to heat up the objects and then use IR to detect them. But I doubt if you do the math you would be able to heat up such a dense object with such a 'laser sweep'. See the quote below from Rockphed.

The energy to accelerate a 1 kg round to 10 km/s is 50 MJ. That doesn't seem particularly cold and stealth.
Furthermore a 1 GW laser beam with a radius of 5 meters applies an energy of 1 kJ per cm^2 per second. This is more than 7000 times the energy per surface of sun light reaching Earth atmosphere.



A KKV thrown at a essentially immobile, highly visible target will hit. Even if you detect it coming in, trying to deflect or intercept it will be essentially impossible due to the extreme velocity and small size. A ship can "dodge" it by irregularly making small trajectory changes that prevent accurate prediction information. Your mirrors can't.


To use an analogy, you're asking "How are the bullets from a sniper rifle going to manage to reach my giant searchlight?"

You should really make some numbers to understand the magnitudes we are talking about. For example to cross 1 million km at 10 km/s you need 27 hours. That's not exactly extreme speed.

The correct analogy would be "How is a WW2 aircraft penetrating the defense system of a modern carrier group ?"

[LordEntrails]

The energy to accelerate a 1 kg round to 10 km/s is 50 MJ. That doesn't seem particularly cold and stealth.
Why would any of the energy used to project the KKV actually heat the KKV? Their is no atmosphere to cause friction to heat it, their is no thermal explosion in a railgun to heat the projectile...

Does a magnetic railgun heat the projectile in some way I'm not familiar with?

And yes, hours and days for projectile transit time is understood (and goes hand in hand with the engagement ranges I've talked about, which lasers would not be able to handle). And it may sound untenable coming from our frame of reference and experience with sci-fi movies where everything is instant and in visual range, but this discussion is in part about dropping preconceptions and discussing possibilities.

[pendell]

With regard to hitting things with a KKV, just how hard is it to hit a target in space that is completely inert from across a solar system?

I ask, because every flight plan I've ever seen had a 'course corrections' phase with a certain amount of fuel allocated for the purpose. I believe at present people still need to take observations to compare actual vs. planned track, and if they diverge due to an error in calculations or a thruster cutting off a second too late, then they need to make a corrective burn or miss completely.

I assume that's why unmanned space probes have maneuvering engines and fuel, as opposed to simply being fired in the appropriate direction with a really large cannon such as the planned Iraqi super gun.

So my question: Is a KKV still going to need course correction, even against an inert target? If they are, then you're going to have to pay for engines, fuel, and a guidance computer anyway. So you might as well hang on an additional subroutine or two in case the target maneuvers. Your KKV becomes a smart projectile.

And if that happens, you're looking at a few thousand dollars per unit at minimum, which means you'll want to shoot dozens at a target, not thousands.

Respectfully,

Brian P.

[Mando Knight]

Why would any of the energy used to project the KKV actually heat the KKV? Their is no atmosphere to cause friction to heat it, their is no thermal explosion in a railgun to heat the projectile...

Does a magnetic railgun heat the projectile in some way I'm not familiar with?

All energy transfers have inefficiencies that generate waste heat, and there is also friction between the projectile and the rails of the gun.

[Rockphed]

Why would any of the energy used to project the KKV actually heat the KKV? Their is no atmosphere to cause friction to heat it, their is no thermal explosion in a railgun to heat the projectile...

Does a magnetic railgun heat the projectile in some way I'm not familiar with?

And yes, hours and days for projectile transit time is understood (and goes hand in hand with the engagement ranges I've talked about, which lasers would not be able to handle). And it may sound untenable coming from our frame of reference and experience with sci-fi movies where everything is instant and in visual range, but this discussion is in part about dropping preconceptions and discussing possibilities.

Railguns heat their projectiles by friction, ohmic losses in the projectile, and, probably, induction heating in the projectile. There is also heating from going through an atmosphere, but if we put the gun in space, that wouldn't be an issue. You might be able to put enough maneuvering in your laser web to avoid the shot, but every time the laser web is improved, it costs significantly more, while it just takes a couple extra shots to disable a mirror.

Now, to apply some further cold water to the laser web idea. If the closest mirror to the target is 1 Gm (1 million km) away, and we are using 600 nm light (because I feel like having a number), and we want a spot size of 5 meters, we have a divergence angle of 3.8197e-08 radians. Doing some trigonometry, this means that we need a 76 meter reflector. For comparison, the Greenbank Telescope, the largest fully steerable dish in the world, is 100 meters in diameter. You could get a smaller dish by going with a longer wavelength, or by putting your mirror closer to the target. If you want a UV laser, you will need a larger (potentially much larger) reflector.

[halfeye]

All energy transfers have inefficiencies that generate waste heat, and there is also friction between the projectile and the rails of the gun.

There are no rails. It's called a rail gun because it's like a small version of a mag-lev train, but the train is the gun, and stays still, and the rail is what is fired, so there is no contact between the gun and the shot, it's all moving magnetic fields. There probably is quite a lot heating.

Hm, thanks Rockphed. Seems that's a "coil gun/gauss gun" and a rail gun is something else. I think they changed the definitions when I wasn't looking, but whatever.

[Rockphed]

There are no rails. It's called a rail gun because it's like a small version of a mag-lev train.

You are not talking about the same kind of railgun other people are talking about. (https://en.wikipedia.org/wiki/Railgun) The version I am talking about is a linear motor that creates a loop involving the 2 rails and the projectile. The projectile moves freely along the rails, propelled by the magnetic force created by current running through the loop.

You might be thinking of a coil gun, which is the other magnetic launcher. I don't know as much about them.

[DaedalusMkV]

Does a magnetic railgun heat the projectile in some way I'm not familiar with?

Clearly yes, and it's actually one of the biggest hurdles to railgun design right now. Neither the rails nor the projectile being accelerated by the railgun are perfectly conductive, and for the most part the more ideal the projectile is as a weapon the less conductive it is. Take something with a fairly high electrical resistance and run an absolutely massive electrical charge through it and you get a very, very large amount of energy being converted to waste heat. In addition, even a flawlessly designed railgun requires the projectile to make contact with the rails during acceleration, which means a little bit of friction. And when you're talking about a projectile leaving the rails at kps values, a little bit of friction amounts to a huge amount of waste heat as well. Most of this heat winds up on the rails (which is why military railgun tests ended up with a whole bunch of melted guns), but the projectile is still going to come out of that gun hot enough that detecting it with IR sensors will not be any issue at all, for weeks after it leaves the accelerator. At least, unless you can build both the rails and the projectile out of a superconductor capable of handling the stresses of magnetic acceleration, which sounds like a pretty cool material that any engineer would love to work with.

Put it all together and, in atmosphere, the principal limitation on how quickly a railgun can fire is heat dissipation, not capacitor recharge. In space, that issue is going to be compounded dramatically. And that's assuming you can even build a railgun capable of firing thousands of projectiles at kps speeds; current designs need to replace their rails every 20 shots or so thanks to erosion from friction firing projectiles with orders of magnitude less energy, so you'd need to build your rails out of something that makes Titanium look soft if you didn't want to store an extra 50 sets of rails as well.


Obviously, coilguns get to avoid most of these problems, and are in general a much more practical choice as kinetic accelerators for space combat. That is, assuming you can solve the magnetic saturation problem (and current science says the answer to that is 'seems hard, just make the accelerator longer') and don't mind needing a hundred-meter-long plus accelerator tube. Oh, and accept that you'll need twice as much energy to accelerate each projectile as a railgun, so I hope you have some really good energy storage systems and a reactor that can provide some serious output.

[Gnoman]

You should really make some numbers to understand the magnitudes we are talking about. For example to cross 1 million km at 10 km/s you need 27 hours. That's not exactly extreme speed.

The correct analogy would be "How is a WW2 aircraft penetrating the defense system of a modern carrier group ?"

I think you need to do some caclulating.

A KKV massing .2 kg (a little heavier than a baseball, but much smaller) at 10 km/s would, by your figures, cost 10 MJ. Very little of this energy would necessarily be transmitted to the projectile as heat (instead of kinetic energy), because you can use driving sabots to push it out. This would result in a very bright launch signature, but after that you're looking for a pencil-sized chunk of metal that's essentially at background temperatures. When this projectile makes contact, it will impact for around 10 MJ - a little more than two kilograms of TNT (techically, the energy would be a bit different depending on how the mirror itself is moving in orbit - you'd have to either add or subtract the mirror's orbital velocity). That's more than enough to render any mirror non-functional even if it doesn't outright destroy it.


The long flight time of this projectile doesn't matter, because it is completely invisible. Calculating the exact path of your orbital mirrors is, while not trivial, extremely straightforward.

You'd see a series of really bright flashes from outside laser range, then a little over a day later your mirrors are exploding. You'd never have a chance to shoot at the incoming projectiles, because you'd never see them.

[halfeye]

I think you need to do some caclulating.

A KKV massing .2 kg (a little heavier than a baseball, but much smaller) at 10 km/s would, by your figures, cost 10 MJ. Very little of this energy would necessarily be transmitted to the projectile as heat (instead of kinetic energy), because you can use driving sabots to push it out. This would result in a very bright launch signature, but after that you're looking for a pencil-sized chunk of metal that's essentially at background temperatures. When this projectile makes contact, it will impact for around 10 MJ - a little more than two kilograms of TNT (techically, the energy would be a bit different depending on how the mirror itself is moving in orbit - you'd have to either add or subtract the mirror's orbital velocity). That's more than enough to render any mirror non-functional even if it doesn't outright destroy it.

This assumes that the KE is all absorbed by the mirror. Depending on the mirror's construction, the projectile might just make a small hole, and keep 99% of the KE while keeping on going.


The long flight time of this projectile doesn't matter, because it is completely invisible. Calculating the exact path of your orbital mirrors is, while not trivial, extremely straightforward.

Nothing ever has been, and nothing ever will be completely invisible.


You'd see a series of really bright flashes from outside laser range, then a little over a day later your mirrors are exploding. You'd never have a chance to shoot at the incoming projectiles, because you'd never see them.

You're talking about sniping from a range of millions of kilometres. Depending on the size of the targets that is somewhere between highly unlikely and utterly ridiculous.

[Rockphed]

You're talking about sniping from a range of millions of kilometres. Depending on the size of the targets that is somewhere between highly unlikely and utterly ridiculous.

Well, the 5 meter spot size mentioned earlier at a range of a million kilometers corresponds to a mirror diameter of about 75 meters for a red laser. How hard is it to get a bullet on a balistic trajectory that passes within 37 meters of a target position?

[Gnoman]

This assumes that the KE is all absorbed by the mirror. Depending on the mirror's construction, the projectile might just make a small hole, and keep 99% of the KE while keeping on going.



Nothing ever has been, and nothing ever will be completely invisible.



You're talking about sniping from a range of millions of kilometres. Depending on the size of the targets that is somewhere between highly unlikely and utterly ridiculous.



1. A valid point. I don't think it's likely that a functional mirror would be that flimsy, but it could happen.


2. In absolute terms, you're correct. In practical terms, the odds of detecting a strike of this sort is so extremely low that it might as well be. The projectiles would be completely inert (generating no heat, so the only signature would be whatever residual it picked up from launch), would be too small for radar to easily pick up, and would be extremely hard to spot visually. It might be giving off hard radiation, but I don't think that these projectiles would be moving fast enough for that.

3. I'm not saying "one shot per mirror". That's why I specified "several" flashes - put a few dozen on course for each target with a slight course variation, and you will get a hit. I think you're also overestimating the difficulty a bit, as this is an entirely deterministic scenario. The mirrors would be in a fixed orbit (trying to play maneuvering games would make coordinating the system extremely difficult, and thus render it useless without any hostile action), so all you'd have to do is calculate. Against a ship, or even a self-contained weapons satellite, you'd be entirely correct - there's no reason why those would not be able to alter course enough to make prediction impossible, but a mirror can't "dodge" this way.

[Sean Mirrsen]

Well, the 5 meter spot size mentioned earlier at a range of a million kilometers corresponds to a mirror diameter of about 75 meters for a red laser. How hard is it to get a bullet on a balistic trajectory that passes within 37 meters of a target position?

In order to hit a target 100 meters to a side, from a distance of 1 light-second, your shot needs to be accurate to within 0.00001 degrees, a couple hundredths of an arc-second. This is assuming your projectile is shot at a perfectly predictable velocity, and your calculation of the target's future position is perfectly accurate.

So, I'd say it is at least nontrivial.

[Mando Knight]

How hard is it to get a bullet on a balistic trajectory that passes within 37 meters of a target position?

Depends on the range. At a million kilometers, your firing solution would need a margin of error of around... 350 nanoradians.

To be fair, the laser needs that kind of targeting accuracy to be used against you at that range, too.

[Rockphed]

In order to hit a target 100 meters to a side, from a distance of 1 light-second, your shot needs to be accurate to within 0.00001 degrees, a couple hundredths of an arc-second. This is assuming your projectile is shot at a perfectly predictable velocity, and your calculation of the target's future position is perfectly accurate.

So, I'd say it is at least nontrivial.

Well, considering that we are talking about a mirror that is positions such that a 5 meter spot is hitting the right spot at that range, I suspect that a million kilometers (or 1 gigameter) is much farther out than we are really going to go.

edit: Going even further, our million kilometer away mirror needs to have a focal length of a million kilometers, plus or minus about 130,000 km. In other words, it is ever so slightly not flat.

[Knaight]

You'd see a series of really bright flashes from outside laser range, then a little over a day later your mirrors are exploding. You'd never have a chance to shoot at the incoming projectiles, because you'd never see them.

This is known as a cue to dodge; you don't need to shoot at the incoming projectiles. Of course, given the aim necessity you probably also don't need to dodge (though with a long enough gun barrel you can get the necessary accuracy; it comes down to if the barrel length is short enough to be manageable).

[factotum]

This is known as a cue to dodge; you don't need to shoot at the incoming projectiles.

Because the mirrors are the only possible target your enemy could be firing at, of course. :smallsigh: We've been through this already--seeing where the projectile was fired from does not magically give you insight into what it was fired *at*, especially in a target rich environment like a planetary satellite orbit.

[Knaight]

Because the mirrors are the only possible target your enemy could be firing at, of course. :smallsigh: We've been through this already--seeing where the projectile was fired from does not magically give you insight into what it was fired *at*, especially in a target rich environment like a planetary satellite orbit.

That target rich environment almost certainly has particular targets disproportionately likely to get shot at, starting with anything capable of shooting back - so you move those. Meanwhile outside of those target rich environments knowing to dodge is even easier. The issue with the mirror system is less the potential to break it with a KKV and more laser dispersion being generally a problem in space, where actual discrete objects do a much better job staying together.

[BlacKnight]

The long flight time of this projectile doesn't matter, because it is completely invisible. Calculating the exact path of your orbital mirrors is, while not trivial, extremely straightforward.

You'd see a series of really bright flashes from outside laser range, then a little over a day later your mirrors are exploding. You'd never have a chance to shoot at the incoming projectiles, because you'd never see them.

Orbital mechanics don't work that way. You can't shot straight at your target (unless you are using a laser :smallbiggrin:)
You need a lot of energy to change your orbit, and a prohibitive amount of energy to completely cancel your actual orbital speed and going freely where you want.

What does it means ? It means that your spacecraft trajectory is known by everybody, as well as the trajectories of any object that separates itself from it.
So the moment the enemy sees the spacecraft firing is going to calculate the possible orbits of the rounds, based on their possible speed. These trajectories are going to be quite close to that of the firing spacecraft. The speed imparted by a realistic railgun is not going to change that significantly.
Given that space is empty (and it would be so even with a lot of stuff around) only and handful of these are going to impact into something.

And the best thing is that the defender knows where the projectiles are at any moment. How ?
Because everything is moving in space. Immobile stuff are just things that are on a fixed orbit, but they are moving nonetheless.
So in order to hit the target the enemy rounds need to be at the right spot at the right time, which means that for any possible trajectory the projectiles must have a precise speed.
So the defender just has to concentrate its search on certain spots (which are no bigger than the target) where the projectile must be at a certain time.
Even without considering the heat imparted by the railgun itself the laser can heat the projectiles.

P.S.
I would advice everyone interested in understading how much of a bitch orbital mechanics are to try the PC game Children of a Dead Earth. It's very hard to get your missiles to connect with the enemy, even when it's on a fixed orbit. You need to get on the right orbit with your spacecraft first.
Unfortunately the railguns and lasers and targeting systems in the game are broken, so don't think it's realistic apart from the depiction of orbital mechanics.

[jayem]

That target rich environment almost certainly has particular targets disproportionately likely to get shot at, starting with anything capable of shooting back - so you move those. Meanwhile outside of those target rich environments knowing to dodge is even easier. The issue with the mirror system is less the potential to break it with a KKV and more laser dispersion being generally a problem in space, where actual discrete objects do a much better job staying together.

And (depending on their range) the energy cost to move the mirrors is roughly comparable to the cost of the bullet. You only need to move 1km in the time it takes to move X km.

If we stick with the million km lasers [handwaving the problems] then against slow (10km/s) missiles tiny perturbations would confuse them. In addition we have 100 seconds where they are within 1000km (if in a solar system they will be reflecting or warmed, and almost in the theoretical capacity of commercial satellites, albeit not that fast). Which still gives some time for some very quick shooting/moving.

Slow clever missiles then are not running cold, in which case we can't evade but really ought to be able to take it out.

A ludicrously faster missile say 0.1C would over-ride any realistic reaction. A single bullet also wouldn't use 'that' much energy (we'd need to steal the worlds electricity for a day). Actually implementing this, with a passable accuracy would almost certainly have more issues than the laser. If nothing else if you could throw that much power at it, then you don't need to worry about the beam waist issues (and we should probably compare against even more magic lasers).

In between you have lots of orders of magnitude one of which is a similar level of magic. Especially if you want them to fire cold.

Going the other way and taking away the magic from our lasers
For almost-current lasers (~100km), then the ballistic bullets if fired accurately enough easily win. Of course regardless of whether guns fire more accurately or lasers are used you'd expect stuff to happen at that scale.

For obtainably-futuristic somewhere in the middle (10,000km) then the slow hot missiles are well out (even if you spam them), while slow cold missiles are probably struggling (at least unless used in conjunction, or really good at being cold), and even ones a bit faster (obtainably futuristically so) have issues