Realistic space combat vehicles?

[Pds314]

Assuming realistically plausible midfuture technology, no magitech (no FTL travel or communication, thermodynamically impossible instant grey goo, computers with components smaller than subatomic particles, teleportations, sci fi shields, unrealistically efficient radiators, reactionless drives, etc), and no compact fusion torch drives (i.e. if fusion drives exist, they're either nuclear pulse, thermal engines rather than direct fusion with ISP of thousands not millions, milli-gee thrust, or just generally ginormous and impractical for smaller craft), what do you see space combat vehicles looking like. We will handwave that there are still people engaging in combat for some reason, although what reason exactly will clearly influence vehicle design, it is not the aim of this thread to argue over the fine details of the socio-political future of humanity.

 

In particular:

1. Will there be compact, maneuverable dogfighters? What sort of systems do they use.

2. Directed energy weapons, kinetic energy missiles, kinetic energy bullets, high explosive missiles and bullets, nukes? In what roles?

3. Armor? Will it exist?

4. Are combat spacecraft returnable or single use? Are they pilotted?

5. What are the objectives? Is it fighting over asteroids, orbits, ideology, rebellions, economic control? Is nuking it from orbit the only we to be sure? Are ships used for gladiatorial combat?

6. What does an actual engagement look like? Is it just a single intercept at many km/s and hope you disable them? Does boarding ever happen? Do ships slow down to engage? Does combat occur in orbit, or on suborbital, or hyperbolic trajectories? How close do ships get? Does combat occur near important objects or in interplanetary space?

Edited October 30, 2020 by Pds314

[kerbiloid]

Define the "space combat" range.

Interstellar? Earth vs Mars? Countries on the Earths?

 

[Pds314]

3 minutes ago, kerbiloid said:

Define the "space combat" range.

Interstellar? Earth vs Mars? Countries on the Earths?

 

Well I'm thinking mostly within a star system.

[Spica]

1 hour ago, Pds314 said:

1. Will there be compact, maneuverable dogfighters? What sort of systems do they use.

Compact, maneuverable spaceships may definitely exist, but they will almost certainly take the form of unmanned missiles. Realistic close-quarters space combat engagements are likely to happen too quickly for a human-in-the-loop to be useful. They may be powered by chemical rockets or high performance NTRs. Low performing nuclear pulse drives or even nuclear salt water rockets might be seen on larger drones with higher ∆v capability, assuming of course that riding a criticality accident can be made a useful form of propulsion.

1 hour ago, Pds314 said:

2. Directed energy weapons, kinetic energy missiles, kinetic energy bullets, high explosive missiles and bullets, nukes? In what roles?

Lasers, electron beams, dustguns, kinetic missiles, and nukes are all fair game, which ones in particular are used depends on the size of the spacecraft and the amount of power it has available. Even old-fashioned bullets are viable, again it all depends on the details. One thing that will probably not be seen is conventional chemical explosives, since inert matter travelling at orbital speeds can easily contain more kinetic energy than even the most theoretical high-power chemical explosives.

1 hour ago, Pds314 said:

3. Armor? Will it exist?

If non-relativistic kinetic weapons dominate the setting, armor in the form of whipple shields will almost certainly be useful. Actively cooled and reflective laser armor may also be useful depending on the laser wavelength and whether or not the beam is pulsed or continuous. Nukes in space are effectively x-ray flashbulbs which makes them very powerful against lightweight armor. A whipple shield with unusually thick and wide-spaced layers will be better than nothing. Good luck armoring up against weaponized electron beams.

1 hour ago, Pds314 said:

4. Are combat spacecraft returnable or single use? Are they pilotted?

The larger and more complex a given spacecraft is, the more likely it is to be reusable. It is hard to draw specific lines that separate what would be manned and unmanned vessels, since that is ever so dependent on the details of the setting.

1 hour ago, Pds314 said:

5. What are the objectives? Is it fighting over asteroids, orbits, ideology, rebellions, economic control? Is nuking it from orbit the only we to be sure? Are ships used for gladiatorial combat?

Now this is not knowable any more than the objectives of any earthbound war are. Any and all of the causes you listed may well be possible objectives, and they will all influence ship design.

1 hour ago, Pds314 said:

6. What does an actual engagement look like? Is it just a single intercept at many km/s and hope you disable them? Does boarding ever happen? Do ships slow down to engage? Does combat occur in orbit, or on suborbital, or hyperbolic trajectories? How close do ships get? Does combat occur near important objects or in interplanetary space?

Jousting is not a terrible analogy for how space battles may look. Relative velocity is your friend, as it increases the potency of any kinetic weapons you have and makes you vulnerable for less time. Just as in modern war, outranging your opponent provides you a tremendous advantage. If we're only concerned with engines with Isps on the order of thousands of seconds you may see hyperbolic engagements, but orbital mechanics are not totally irrelevant. I doubt boarding will be a likely occurrence, since any ship carrying cargo worth boarding for also has the capability to thoroughly destroy itself, and likely anything within boarding range of it.

Now, one major difference between terrestrial war and space war is the element of surprise. Since space is pretty empty and orbital mechanics keep things moving, there are exceedingly few places to hide. Additionally, any powerful weapons and/or propulsion systems will likely be detectable far beyond weapons range, making surprise attacks difficult and rare but not totally impossible. Current technology can detect cold rocks millions of miles away, bright radiators, exhaust plumes, and future imaging technology only make that task easier.

Just as modern war machinery takes a variety of forms (aircraft carriers, submarines, tanks, jet fighters, bombers, missiles, and more), so will military spaceships.

Edited October 30, 2020 by Spica
additions

[SOXBLOX]

9 hours ago, Pds314 said:

How close do ships get?

Here's the big question. Since the ships will not be getting close at all, and since sensor range is infinite, compared to a star system, space war will look like a missile and railgun slugfest. Since humans are bags of wet meat, and can't endure high g's, autonomous drones will be popular.

Ships will not need tactical maneuverability, but they may possess defensive maneuverability. (i.e. Closing for an attack vs. dodging) So space warfare might look like swarms of low ∆v budget drones screening a fleet, acting as sensor platforms, and shooting. You'll need a mothership for the drones, and a ship which can defend itself to carry humans.

Also, check out Atomic Rockets. I think it covers space warfare.

[Pds314]

25 minutes ago, SOXBLOX said:

Here's the big question. Since the ships will not be getting close at all, and since sensor range is infinite, compared to a star system, space war will look like a missile and railgun slugfest. Since humans are bags of wet meat, and can't endure high g's, autonomous drones will be popular.

Ships will not need tactical maneuverability, but they may possess defensive maneuverability. (i.e. Closing for an attack vs. dodging) So space warfare might look like swarms of low ∆v budget drones screening a fleet, acting as sensor platforms, and shooting. You'll need a mothership for the drones, and a ship which can defend itself to carry humans.

Also, check out Atomic Rockets. I think it covers space warfare.

So with range I think the question is at what range can your weapons reliably kill the enemy and not vice versa. I guess that puts an emphasis on being able to maneuver and control engagement range. If missiles need to actively evade anti-missiles or point defense, they probably have weaker ISP, much smaller size, and higher thrust to weight than ships themselves, with less delta-V. Is it possible to force a missile or a constellation of them to burn through it's finite delta-V by doing slow, stay maneuvers after it's launched? Likewise, is a constellation of missiles actually better for forcing an intercept than one missile?

 

If a missile is just a chemical rocket with a few km/s Delta-V, that makes for easily calculated minimum forced intercept radii against ships with lesser acceleration but higher delta-V. The question is, if you spam missiles that lead the target in different directions can they intercept further away than the one missile can. And can you ever force missile intercepts against more maneuverable opponents, or at least deny them a risk free intercept on you. With individual KKV missiles or salvos of them that aren't coordinated into constellations I can't see them actually extending the force intercept range and the range at high relative velocity should give the more maneuverable ship a free shot before breaking the intercept of the less maneuverable one. But if you start talking about dumping, e.g. 500 kkvs that each maneuver to lead the target, I'm not totally sure how that will affect the situation.

 

The trivial situation where ships joust at much higher relative speed than the delta v of the missile, and there is only one missile per target, gives the more maneuverable ship a completely safe undodgeable shot with parity missile specifications. If you plug some actual numbers you see that just burning through a 4 km/s missile's entire reserve of delta-V at 4 G (remember this is probably an NTR or something, so that's quite a strong engine) takes 100 seconds. So definitely inside that range, the missile can keep an intercept as long as we don't factor in evasive maneuvers for the missile.

Edited October 30, 2020 by Pds314

[Spica]

One thing to also be aware of is the surprisingly limited range of laser weapons. At visible light wavelengths and "sane" primary mirror diameters they're typically limited to a few tens to hundreds of kilometers at most. If you've played "Children of a Dead Earth" on Steam you'll get an idea of the implications of this. It forces engagement ranges down significantly enough that guns (be they electromagnetic or chemical) become useful as weapons.

2 hours ago, SOXBLOX said:

Also, check out Atomic Rockets. I think it covers space warfare.

This is a very good idea, Atomic Rockets is absolutely full of useful information for hard sci-fi spacecraft design.

[wumpus]

This thread had a lot about lasers.  I also included a calculation that for 60MW of power, you need heatsinks roughly the size of the ISS.  And this assumes E.E.Doc Smith levels of tech (4000K Carnot heat engines, 3600K radiators).  I assumed that any laser-based (or possibly neutron-beam based) combat would involve overwhelming those lasers.  Ideally you would have to attack from at least 3 orthogonal angles, and you would have to attack from 3 non-planar angles to have any effect at all.

[Terwin]

Modern air-to-air and ground-to-air combat seems to be more and more focused on missiles.  The smarter the missiles get, the the more scenarios where their performance envelope and disposability make them superior to a manned vessel.  Drones also seem to be largely functioning as missile platforms, giving them greater range and utility.

I see no reasons for this progression to change.

Anything in space is expensive enough that missiles and drones will clearly have a superior price-point  and performance envelope over anything that needs to cater to humans.

Drones would be a bigger thing if the long range engine is expensive enough to be worth recovering, otherwise a MIRV type weapon would work just as well and be less expensive. 

As such, I would expect in-system space combat to consist of mostly of long range missiles with terminal guidance.  Depending on the target type, the warheads could range from a payload of ball-bearings(to deny useful orbits to the enemy) to scatter-shot, to kinetic kill vehicles consisting mostly of a large solid shield hiding the guidance thrusters(protection from lasers and other anti-ordinance weaponry), or even nuclear warheads(probably mostly for dug-in targets like underground bases or basses hidden deep inside a reinforced asteroid).

 

 

 

[Nightside]

The point where humans (or some reasonable facsimile there of) need to in the loop is where speed of light delay is too long for strategic decision making, and no closer.

One-off attacks might be totally automated, but battles would still be in the vicinity of actual people.

[Spica]

5 hours ago, Terwin said:

Modern air-to-air and ground-to-air combat seems to be more and more focused on missiles.  The smarter the missiles get, the the more scenarios where their performance envelope and disposability make them superior to a manned vessel.  Drones also seem to be largely functioning as missile platforms, giving them greater range and utility.

I see no reasons for this progression to change.

The coming possibility of high-powered battlefield lasers might shift the balance away from missiles. The F-35B for example has a little over 21 MW of available shaft power that normally drives the lift fan, even 10% of that energy as a laser beam ought to be able to do significant damage to any incoming missiles. Remember, simply destroying any externally mounted sensors is enough to severely degrade or destroy the performance of any incoming missile, and that will certainly take less energy than outright destroying the incoming threat.

A collection of high powered pulsed lasers aboard a spacecraft should make a very potent missile-defense system.

[SOXBLOX]

11 hours ago, Pds314 said:

I guess that puts an emphasis on being able to maneuver and control engagement range...

Maneuverability is basically unimportant. It's great if you're engaging a target more than a few light-minutes away, but the "maneuverability" you would need in order to dodge there would be your normal RCS thrusters. No optimization required. 

More crucial is the issue of expanding your effective combat radius. You need to spread assets out over a large area volume, to control it. To do this, you should use attritable drone swarms, either functioning as glorified kamikaze drones or carrying missiles, railguns, etc.

One of the most interesting ideas I've seen is equipping a missile with a small one-shot railgun. The missile lofts the gun to a suitable position, from which it fires it's railgun, thus circumventing any point defenses. This has an equivalent in the Casaba-Howitzer missile on AR. Alternatively, use a missile, but put on a Sprint-esque second stage to do a high-g terminal phase.

The most crucial is having the maximum possible ∆v budgets, and survivability. So, lots of point defence grids spread between multiple platforms, sorta like Aegis, except most of those platforms are drones.

[Pds314]

59 minutes ago, SOXBLOX said:

Maneuverability is basically unimportant. It's great if you're engaging a target more than a few light-minutes away, but the "maneuverability" you would need in order to dodge there would be your normal RCS thrusters. No optimization required. 

More crucial is the issue of expanding your effective combat radius. You need to spread assets out over a large area volume, to control it. To do this, you should use attritable drone swarms, either functioning as glorified kamikaze drones or carrying missiles, railguns, etc.

One of the most interesting ideas I've seen is equipping a missile with a small one-shot railgun. The missile lofts the gun to a suitable position, from which it fires it's railgun, thus circumventing any point defenses. This has an equivalent in the Casaba-Howitzer missile on AR. Alternatively, use a missile, but put on a Sprint-esque second stage to do a high-g terminal phase.

The most crucial is having the maximum possible ∆v budgets, and survivability. So, lots of point defence grids spread between multiple platforms, sorta like Aegis, except most of those platforms are drones.

Right. I'm not talking about dodging a missile so much as expending thousands of Delta-V with the main engines minutes before a high speed pass, draining the missile's fuel to zero if it tries to follow that maneuver, regardless of thrust. Thus the emphasis on maneuverability in the sense of TWR, not angular maneuverability, as being able to do a safe attack during a pass. That way you can line up an intercept, drop your constellation of missiles, which outrange theirs because of your superior TWR, and get out before they can do much about it, as their missiles are still not able to individually force an intercept when yours can.

As for using Casaba Howitzers or other standoff weapons on a projectile, it still limits the range because you still need to miss by "only" a hundred kilometers or something. Also point defense may well consist of missiles or your own Casaba Howitzers that can take the thing out well before it is 100 km from a target which is like... practically knife-fighting range if everything else in this thread and on atomic rockets and such is accurate. I guess the other question is if 1 kg of solid material does the job with a direct hit, do you wanna put the cost and mass of a nuke and the vehicle to propel it. Also because defensive Casaba Howitzers are probably viable as well. You mention the Sprint ABM which I'm pretty sure just used a nuke to disable the incoming missile, not a direct hit, I guess the other question is with something like the sprint ABM, does it have the Delta-V efficiency to be meta? It's got a very high TWR but if you have to launch it from within, say, 2 minutes of intercept, to get it to hit some lightbulb core NTR or something, is it really better than a missile that can do 20 G of acceleration instead of 100 but has significantly better Delta-V?

Edited October 31, 2020 by Pds314

[Pds314]

2 hours ago, Nightside said:

The point where humans (or some reasonable facsimile there of) need to in the loop is where speed of light delay is too long for strategic decision making, and no closer.

One-off attacks might be totally automated, but battles would still be in the vicinity of actual people.

I mostly agree here. Also in terms of speeds being too fast for crew to react, distances should be enough that they aren't. If you start a light-second apart, and the difference in speed is 30 km/s, then that still takes 3 hours to finish the battle. Having humans at least in the general vicinity probably gives you an advantage for controlling vehicles, even if most of the vehicles are little more than RC drones. The other thing is that communication links can be jammed and moreso when engagements involve throwing thousands of missiles with Casaba Howitzers around like WWII FlaK.

7 hours ago, Terwin said:

Modern air-to-air and ground-to-air combat seems to be more and more focused on missiles.  The smarter the missiles get, the the more scenarios where their performance envelope and disposability make them superior to a manned vessel.  Drones also seem to be largely functioning as missile platforms, giving them greater range and utility.

I see no reasons for this progression to change.

Anything in space is expensive enough that missiles and drones will clearly have a superior price-point  and performance envelope over anything that needs to cater to humans.

Drones would be a bigger thing if the long range engine is expensive enough to be worth recovering, otherwise a MIRV type weapon would work just as well and be less expensive. 

As such, I would expect in-system space combat to consist of mostly of long range missiles with terminal guidance.  Depending on the target type, the warheads could range from a payload of ball-bearings(to deny useful orbits to the enemy) to scatter-shot, to kinetic kill vehicles consisting mostly of a large solid shield hiding the guidance thrusters(protection from lasers and other anti-ordinance weaponry), or even nuclear warheads(probably mostly for dug-in targets like underground bases or basses hidden deep inside a reinforced asteroid).

 

 

 

So one question is light lag. Another is whether you're launching this up through an atmosphere or gravity well at all, and another is whether you have assembly line style production of 3000 s ISP NTRs. I would not count on "every gram counts" being always the best answer.

Edited October 31, 2020 by Pds314

[SOXBLOX]

2 hours ago, Pds314 said:

I'm not talking about dodging a missile so much as expending thousands of Delta-V with the main engines minutes before a high speed pass, draining the missile's fuel to zero if it tries to follow that maneuver,...

Perhaps I'm not following you, but what I think you're proposing can be achieved just as easily with a small burst from the thrusters many minutes, or even hours, before collision. Unless you just want to wait until the last minute to dodge, which is silly. When it's that close, you can shoot it. (And if you can't, your warship + drone swarm should be resilient enough to handle it.)

2 hours ago, Pds314 said:

...is it really better than a missile that can do 20 G of acceleration instead of 100 but has significantly better Delta-V?

Depends on what you're trying to do. My idea was for a terminal phase high-g vector change, to make it difficult to hit. The high ∆v part would have been the first stage.

All that said, if you're working on worldbuilding or something, and you want space destroyers maneuvering hard to dodge huge swarms of missiles, totally go for it. As long as you're internally consistent, anything works.

[Pds314]

1 hour ago, SOXBLOX said:

Perhaps I'm not following you, but what I think you're proposing can be achieved just as easily with a small burst from the thrusters many minutes, or even hours, before collision. Unless you just want to wait until the last minute to dodge, which is silly. When it's that close, you can shoot it. (And if you can't, your warship + drone swarm should be resilient enough to handle it.)

Depends on what you're trying to do. My idea was for a terminal phase high-g vector change, to make it difficult to hit. The high ∆v part would have been the first stage.

All that said, if you're working on worldbuilding or something, and you want space destroyers maneuvering hard to dodge huge swarms of missiles, totally go for it. As long as you're internally consistent, anything works.

The reason I don't think you can dodge until the last minute is because pre-firing a missile an hour ahead or something is not super practical for exactly the reason you say. Because someone can just do low thrust high efficiency burns to evade the missile at that point and it's virtually guaranteed the missile doesn't hit because the ship can bleed it's fuel to nothing. As for being able to apply meters per second of delta-V and evade a missile with it, I don't see how this is the case. Up ahead, the missile can just as well track the spacecraft's maneuvers as it can up close, because as you say, tracking an exhaust plume from less than a light second is super easy.

If anything, this gives a reason for missiles to form a complicated constellation at a specific time and race out ahead of where the ship would go. Even maybe having several types of missiles, with multi-stage designs meant to sweep out sections of the spaceship's envelope and make them more dangerous while single or two stage missiles are used within a tight envelope.

Edited October 31, 2020 by Pds314

[N_Danger]

Interesting discussion.

 I think the real issue once you move away from the tactical level to the operational and strategic level is can you deplete the defender's resources faster than the attacker's?

 Given current and foreseeable tech, manned and unmanned vehicles will be very expensive (I think you would get more bang for the buck with unmanned). So you will be talking about just a few assets on each side.

 In the missile discussion, in the above posts, are there enough missiles available to the attacker to force the defender to run out of D/V during the engagement? They don't have to hit to have a measurable effect on the battle.

Is there a requirement for persistence in the engagement area from ether side? Are opponents passing through or is there an objective being fought over? 

 With a manned vehicle BINGO fuel will be an issue. How much D/V do you have before having to break off? With an unmanned vehicle, is it worth sacrificing to deplete the attackers supply so that follow on forces can enter the area?

And people's answers to those questions will lead to the ship designs chosen. With the very real possibility of the chosen design not working for a particular engagement.

It would be a bummer to travel at least several weeks if not months(depending on available drive tech) to an find out your chosen design is the wrong one for that fight.

 

[magnemoe]

16 hours ago, Pds314 said:

Right. I'm not talking about dodging a missile so much as expending thousands of Delta-V with the main engines minutes before a high speed pass, draining the missile's fuel to zero if it tries to follow that maneuver, regardless of thrust. Thus the emphasis on maneuverability in the sense of TWR, not angular maneuverability, as being able to do a safe attack during a pass. That way you can line up an intercept, drop your constellation of missiles, which outrange theirs because of your superior TWR, and get out before they can do much about it, as their missiles are still not able to individually force an intercept when yours can.

As for using Casaba Howitzers or other standoff weapons on a projectile, it still limits the range because you still need to miss by "only" a hundred kilometers or something. Also point defense may well consist of missiles or your own Casaba Howitzers that can take the thing out well before it is 100 km from a target which is like... practically knife-fighting range if everything else in this thread and on atomic rockets and such is accurate. I guess the other question is if 1 kg of solid material does the job with a direct hit, do you wanna put the cost and mass of a nuke and the vehicle to propel it. Also because defensive Casaba Howitzers are probably viable as well. You mention the Sprint ABM which I'm pretty sure just used a nuke to disable the incoming missile, not a direct hit, I guess the other question is with something like the sprint ABM, does it have the Delta-V efficiency to be meta? It's got a very high TWR but if you have to launch it from within, say, 2 minutes of intercept, to get it to hit some lightbulb core NTR or something, is it really better than a missile that can do 20 G of acceleration instead of 100 but has significantly better Delta-V?

That is an relevant point, it looks like who larger the ship who more efficient the engine. These efficient engines will not give you ships with fantastic TWR even if they are touchship tactically. 

[Spacescifi]

1 hour ago, magnemoe said:

That is an relevant point, it looks like who larger the ship who more efficient the engine. These efficient engines will not give you ships with fantastic TWR even if they are touchship tactically. 

 

That is the irony of rocketry. Larger vessels have more propellant to go farther than smaller vessels, but the problem is that the heavier a vessel becomes the lower thrust it's engines can operate under.

To be sure, if a ship is star destroyer huge and heavy, using any modicum of real physics and engines, it will do well to fight long range. Because the closer it is the more of a sitting duck is.

 

The heavier a vessel is, the less one can change course with it.

If anything, heavy vessels are best for travel to one destination with a refueling allowance, and then a turning back to wherever they will end up.

If small vessels run out of propellant, you can at least take solace in that they will also require less propellant to refuel shoud you come upon of source of resources or help.

[magnemoe]

On 10/31/2020 at 10:35 PM, Spacescifi said:

 

That is the irony of rocketry. Larger vessels have more propellant to go farther than smaller vessels, but the problem is that the heavier a vessel becomes the lower thrust it's engines can operate under.

To be sure, if a ship is star destroyer huge and heavy, using any modicum of real physics and engines, it will do well to fight long range. Because the closer it is the more of a sitting duck is.

 

The heavier a vessel is, the less one can change course with it.

If anything, heavy vessels are best for travel to one destination with a refueling allowance, and then a turning back to wherever they will end up.

If small vessels run out of propellant, you can at least take solace in that they will also require less propellant to refuel shoud you come upon of source of resources or help.

its worse, lots of the advanced designs as in pulse nuclear works better on larger ships, lost of realistic fusion ideas demand large engines. 
So it will be an minimum size for an high dV ship, this will be hundreds of tons, perhaps even 10.000 ton, and yes its also upper limits. 
But it might be a lot like in naval warfare its minimum size of warships for long range offences. 
Torpedo boats and later missile torpedo boats, are very nice but has an limited range and how long you can keep them at sea. 

[radonek]

On 10/31/2020 at 4:03 AM, Pds314 said:

I'm not talking about dodging a missile so much as expending thousands of Delta-V with the main engines minutes before a high speed pass, draining the missile's fuel to zero if it tries to follow that maneuver, regardless of thrust.

Outrunning a missile? I don't think that would work. Missile does not need to match target speed, it just need an interception. If you burn while missile is far away, correction would be small. If you wait for it to close in, you are essentialy trying to out-TWR it, which is a lost proposition.

[kerbiloid]

3 hours ago, radonek said:

Outrunning a missile?

SR-71