|
Post by AtomHeartDragon on Mar 5, 2019 19:36:15 GMT
First a disclaimer: By fighter I don't necessarily mean cramped (faux)aerodynamic piece of hardware with crew of 1-2 and no habitability to speak of. I also don't necessarily mean that any sort of fighters is necessarily a sound idea. However I can dismiss some of the criticisms and post some some reasons that may make small, low endurance, minimum crew combat spacecraft potentially a viable choice, at least given limited, COADE-like tech level.
First things first: - Fighters don't necessarily need 4x delta-v. They would in space battle between gravitationally unbound fleets, but I wouldn't expect this kind of space battle to actually be a battle in any meaningful sense, rather than few seconds of abject terror involving missiles and point defence (preceded by days to months of growing anxiety). If a fleet manages to successfully inject, fighter no longer needs 4x delta-v and probably shouldn't expect to waste most of its delta-v on orbital manoeuvres, but jinking. With primitive propulsion tech it is also likely that recovering fighters would be the job of their plodding, but much more efficient electric-nuclear mothership, so you could even risk making it 1x delta-v.
- There is a "horizon" of sorts in space. Both projected energy weapons and dumb kinetics work poorly at very long ranges, OTOH habitable volumes and large amounts of propellant are notoriously expensive to armour. Partitioning off only small amounts of propellant and habitability (if any) to armour and put in harm's way might be a sensible choice.
- Drones are generally going to be much more sensible option than fighters, but depending on EW, political climate and possibly ways to disincentivize enemy from trying to specifically target squishy motherships/tenders to disable the whole operation a case might possibly be made for autonomous, manned ships.
- For severely delta-v constrained designs, durability of meatsacks on board is not going to be particularly limiting. When using something like solid core NTR increasing acceleration immediately cuts painfully into combat endurance, so going above perfectly tolerable 0.5-2G is likely going to be pointless. Of course, just having a meatsack on board is going to be a delta-v and survivability hit, so additional incentive would be needed, but acceleration is not going to be the problematic part, at least not with early combat spacecraft.
Now, if on top of that you don't want to put all your eggs in a single basket, your essential combat technology scales down well enough, and the situation is murky enough to incentivize putting crews close to the action, you might have fighters - of sorts.
Maybe not X-wings (boo) or even Starfuries (half-hearted yay), but pieces of hardware well below kiloton, with crews in low single digits, minimum habitability (if still way higher than any atmospheric fighter) and able to spin on a dime.
|
|
|
Post by doctorsquared on Mar 6, 2019 4:03:36 GMT
I could see it being a viable option in a world where ECM/ECCM and other signal jamming and cyberwarfare systems exist that could jam the fly-by-wire systems of drones and missiles. In terms of wet-navy nomenclature, it'd be less of a 'fighter' and more something akin to a corvette or gun/patrol torpedo boat and either carry kinetic guns or some form of missiles (laser guidance would be nice and help remove the issues with the lackluster heatseeker AI we have now) with minimal power requirements.
The biggest argument against it is that a tiny (~5-10kg) conventional gun drone with enough thrust and dV to get a retrograde intercept trajectory can be carried in much greater numbers with much less mass.
|
|
|
Post by gyratron on Mar 6, 2019 10:39:10 GMT
I could see it being a viable option in a world where ECM/ECCM and other signal jamming and cyberwarfare systems exist that could jam the fly-by-wire systems of drones and missiles. In terms of wet-navy nomenclature, it'd be less of a 'fighter' and more something akin to a corvette or gun/patrol torpedo boat and either carry kinetic guns or some form of missiles (laser guidance would be nice and help remove the issues with the lackluster heatseeker AI we have now) with minimal power requirements. The biggest argument against it is that a tiny (~5-10kg) conventional gun drone with enough thrust and dV to get a retrograde intercept trajectory can be carried in much greater numbers with much less mass. It seems like if you make drones too small lasers can kill them very easily just by heating them up, plus the bullets they fire end up being so tiny and weak you might as well just make a micromissile instead. Anyway, I thought we were assuming a scenario where ewar made remote control ineffective? Are these drones piloted by highly trained mice?
|
|
|
Post by AtomHeartDragon on Mar 6, 2019 18:16:00 GMT
That a drone (of some sort) will outperform a manned ship is still a no-brainer, so you still need some good rationale for your zeroth law (which in the end is probably going to be political), and even then, you'll probably be mixing missiles and drones in quite liberally.
The point I want to make is that some of the most crippling perceived flaws of space fighters are not necessarily a thing and that some circumstances may favour small, nimble spaceships with reduced habitability and endurance, making some variant of a space "fighter" much less of a stupid contrivance.
|
|
|
Post by dragon on Mar 6, 2019 22:42:19 GMT
Also, a "space fighter" can be made a dual-purpose craft, if you accept a mass penalty of adding provisions for atmospheric flight (not necessarily wings, a high-speed lifting body might actually be better). I found that generally speaking, space weapons tend to be a poor choice for orbital bombardment. Lasers with reasonable aperture don't do that much damage and are heavily attenuated by atmosphere, while hypervelocity kinetic rounds tend to be too light and too fast to make it through atmosphere at all. This leaves missiles and low-velocity kinetics, the latter of which, again, don't do much damage unless packing explosive shells. Missiles are OK, but an atmospheric craft with a nuclear engine can be much more precise, harder to kill and much less predictable than an orbiting warship. They'd also need plenty of dV (even if using a nuclear ramjet, they'd still need enough to deorbit and then get back up), and while I suspect this would make such a fighter a pretty hefty vehicle, but this dV could make a group of them useful in orbital combat, as well.
|
|
|
Post by doctorsquared on Mar 7, 2019 1:25:06 GMT
I could see it being a viable option in a world where ECM/ECCM and other signal jamming and cyberwarfare systems exist that could jam the fly-by-wire systems of drones and missiles. In terms of wet-navy nomenclature, it'd be less of a 'fighter' and more something akin to a corvette or gun/patrol torpedo boat and either carry kinetic guns or some form of missiles (laser guidance would be nice and help remove the issues with the lackluster heatseeker AI we have now) with minimal power requirements. The biggest argument against it is that a tiny (~5-10kg) conventional gun drone with enough thrust and dV to get a retrograde intercept trajectory can be carried in much greater numbers with much less mass. It seems like if you make drones too small lasers can kill them very easily just by heating them up, plus the bullets they fire end up being so tiny and weak you might as well just make a micromissile instead. Anyway, I thought we were assuming a scenario where ewar made remote control ineffective? Are these drones piloted by highly trained mice? Now you say that but it's been done (kind of) and might be better than the current missile guidance systems we're using.
|
|
|
Post by AtomHeartDragon on Mar 8, 2019 19:07:51 GMT
Also, a "space fighter" can be made a dual-purpose craft, if you accept a mass penalty of adding provisions for atmospheric flight (not necessarily wings, a high-speed lifting body might actually be better). I found that generally speaking, space weapons tend to be a poor choice for orbital bombardment. Lasers with reasonable aperture don't do that much damage and are heavily attenuated by atmosphere, while hypervelocity kinetic rounds tend to be too light and too fast to make it through atmosphere at all. This leaves missiles and low-velocity kinetics, the latter of which, again, don't do much damage unless packing explosive shells. Missiles are OK, but an atmospheric craft with a nuclear engine can be much more precise, harder to kill and much less predictable than an orbiting warship. They'd also need plenty of dV (even if using a nuclear ramjet, they'd still need enough to deorbit and then get back up), and while I suspect this would make such a fighter a pretty hefty vehicle, but this dV could make a group of them useful in orbital combat, as well. I am getting strong F-35 vibes from that.
Aeroorbital fighter could be a cool idea, but I think it might need some beefier propulsion than solid core nuclear thermal (hybrid, ofc, airbreathing when in the atmosphere) to offset penalties from trying to do too many different things.
|
|
|
Post by dragon on Mar 9, 2019 22:26:25 GMT
It works on the same general idea as F-35. You either carry, say, 20 Harriers and 20 Hornets, or you can carry 40 F-35s, which can do what either of them does. The 20 extra birds more than offset the performance loss for either mission. It's inferior if you're trying to do both things the same time, but if you're doing one or the other, it's very much a better choice. Since you'd typically want orbital superiority before dropping onto a planet (since any resupply drops would also need to be delivered from orbit), an aero-orbital fighter could be an efficient choice even if powered with a solid core NTR.
This concept has an additional advantage of not needing any planetside infrastructure, which is good if you're using them to support an invasion. Even a VTOL needs some sort of surface base to fly from, not to mention it's deadweight until it's landed and unpacked from transport. With effective orbit-to-surface weapons being really hard to design, and usually of little use in space, such a fighter might, in fact, be an optimal choice on that basis alone.
|
|
|
Post by gyratron on Mar 10, 2019 2:56:28 GMT
I think space to atmosphere then back to space fighter would definitely be worth simulating to see how viable it is. Deorbiting can be handled with the help of aerobraking so that part is almost free, and when you go back up to space your only payload is one pilot so it's nowhere near as demanding as what we would normally think of for a launch vehicle where it's all about shoving as many tons of payload into orbit as possible. It might even be doable with chemical engines.
|
|
|
Post by doctorsquared on Mar 10, 2019 3:28:30 GMT
Also, a "space fighter" can be made a dual-purpose craft, if you accept a mass penalty of adding provisions for atmospheric flight (not necessarily wings, a high-speed lifting body might actually be better). I found that generally speaking, space weapons tend to be a poor choice for orbital bombardment. Lasers with reasonable aperture don't do that much damage and are heavily attenuated by atmosphere, while hypervelocity kinetic rounds tend to be too light and too fast to make it through atmosphere at all. This leaves missiles and low-velocity kinetics, the latter of which, again, don't do much damage unless packing explosive shells. Missiles are OK, but an atmospheric craft with a nuclear engine can be much more precise, harder to kill and much less predictable than an orbiting warship. They'd also need plenty of dV (even if using a nuclear ramjet, they'd still need enough to deorbit and then get back up), and while I suspect this would make such a fighter a pretty hefty vehicle, but this dV could make a group of them useful in orbital combat, as well. I am getting strong F-35 vibes from that.
Aeroorbital fighter could be a cool idea, but I think it might need some beefier propulsion than solid core nuclear thermal (hybrid, ofc, airbreathing when in the atmosphere) to offset penalties from trying to do too many different things.
I'm thinking some sort of hybrid NTR setup could be an interesting option: - NTR Core would have a thermocouple attached to it and generate primary power.
- While in orbit NTR works as usual to provide primary propulsion
- Outer coolant loop connects into a set of RCS nozzles to provide attitude control
- Atmospheric propulsion could either be handled by a nuclear ramjet (air acts as the coolant across the NTR core) or by electric turbofans powered by the thermocouple.
|
|
|
Post by bigbombr on Mar 10, 2019 7:03:03 GMT
It works on the same general idea as F-35. You either carry, say, 20 Harriers and 20 Hornets, or you can carry 40 F-35s, which can do what either of them does. The 20 extra birds more than offset the performance loss for either mission. It's inferior if you're trying to do both things the same time, but if you're doing one or the other, it's very much a better choice. Since you'd typically want orbital superiority before dropping onto a planet (since any resupply drops would also need to be delivered from orbit), an aero-orbital fighter could be an efficient choice even if powered with a solid core NTR. This concept has an additional advantage of not needing any planetside infrastructure, which is good if you're using them to support an invasion. Even a VTOL needs some sort of surface base to fly from, not to mention it's deadweight until it's landed and unpacked from transport. With effective orbit-to-surface weapons being really hard to design, and usually of little use in space, such a fighter might, in fact, be an optimal choice on that basis alone. It's hard to make a decent performing supersonic VTOL, which is one of the reasons the F-35 program took so much money. Making a vehicle that's good in orbital operations and atmospheric operations is much harder. Take a look at Skylon if you want to get a rough idea how much orbital capability will impact agility and size. Nuclear thermal propulsion would lessen this, but not eliminate it. In orbit, wings are parasitic mass, while in atmosphere the propellant used for reaching orbit is dead mass. This is not a jack-of-all-trades, master-of-none scenario. This is a jack-of-all-trades, crippled-at-all scenario.
|
|
|
Post by bigbombr on Mar 10, 2019 7:10:12 GMT
I'm thinking some sort of hybrid NTR setup could be an interesting option: - NTR Core would have a thermocouple attached to it and generate primary power.
- While in orbit NTR works as usual to provide primary propulsion
- Outer coolant loop connects into a set of RCS nozzles to provide attitude control
- Atmospheric propulsion could either be handled by a nuclear ramjet (air acts as the coolant across the NTR core) or by electric turbofans powered by the thermocouple.
- Bimodal nuclear cores (power generation/propulsion) are generally considered not worthwhile, because you typically need maximum thrust and power at the same moment, and the mass penalty is often comparable to using two separate reactors.
- Using the NTR to also power RCS seems interesting to me, but is the added mass of coolant lines and insulation worth it compared to using chemical RCS? Especially since routing the exhaust through most of the spacecraft will seriously decrease performance (due to pressure and temperature drop).
- The nuclear ramjet makes sense, the electric turbofan part doesn't. Your NTR core is likely much more powerful than your power generation core, and using a bimodal core to run electrical fans means Carnot slaps you in the face. Thermocouples IRL can't even come close to Carnot anyway, and they also tend to have a low power density.
|
|
|
Post by AtomHeartDragon on Mar 10, 2019 10:58:19 GMT
I think space to atmosphere then back to space fighter would definitely be worth simulating to see how viable it is. Deorbiting can be handled with the help of aerobraking so that part is almost free, and when you go back up to space your only payload is one pilot so it's nowhere near as demanding as what we would normally think of for a launch vehicle where it's all about shoving as many tons of payload into orbit as possible. It might even be doable with chemical engines. Your payload is one pilot AND the spacecraft. That's a lot.
|
|
|
Post by dragon on Mar 10, 2019 12:06:44 GMT
This is not a jack-of-all-trades, master-of-none scenario. This is a jack-of-all-trades, crippled-at-all scenario. Not true, who said anything about wings? You don't need wings to fly. Skylon is a really bad example, because it's a surface to orbit aircraft. The biggest dead mass tradeoffs involved in Skylon are involved with it landing. An aero-orbital vehicle, on the other hand, would come in at high speed and stay there, using a nuclear ramjet (it'd be operating well in scramjet envelope, but without scramjet's problems because there's no combustion) and a lifting body shape. It would not resemble a plane, but a hypersonic cruise missile like the X-51A. Which, incidentally, happens to be very close to the optimal shape for bouncing projectiles off your nose, in space. The only dead mass it'd have would be the ducting required to make the ramjet work. F-35 is a supersonic VTOL that has to operate in subsonic and supersonic envelopes. Aero-orbital fighter concept, meanwhile, has to operate in orbital and hypersonic envelopes. Nothing more. Skylon is a beast because it needs to go through all of them. It's also big because it uses liquid hydrogen, and it burns it through the flight, as opposed to just during the last stage. It stands to reason, the more environments you requires your vehicle to operate in, the more of a compromise it becomes. If you shed your preconception that an aircraft has to land on the ground and take off from it, a number of designs open up that were previously ruled out.
|
|
|
Post by gyratron on Mar 10, 2019 12:29:36 GMT
If you compare this idea to what is proposed for the skylon, that has to carry 15 metric tons and an 83m long spacecraft into low orbit. Assuming all your munitions have either been fired or jettisoned before reorbit this fighter has to carry a pilot, some cockpit systems and short term life support, maybe a radar if you think you need one (although it sounds like you are mainly aiming for a ground attacker) and whatever control surfaces and reinforcement you need for acceptable agility given the missions planned for this aircraft. To my untrained ear that sounds like it might actually be do-able with engine performance similar to that predicted for skylon in something not too much bigger than a regular fighter, the main obstacle seems to be that last one and what kind of compromises will be needed to make it viable for various altitudes and missions. Vulnerability during re-entry may also be a problem, not sure how much of a factor that might be. It will be handicapped compared to a regular fighter for sure, but you might just end up with something useful.
|
|