An idea: Firing lines in space?

[Admiral Valdemar]

You can also collect the matter again so that it's basically a very efficient, non-solid radiator surface. Or, if being attacked by beam weapons, you can disperse the material in the direction of the attack and help dissipate the weapon's energy.

[Sky Captain]

Missiles will always have higher delta-v than your ships. They don't have squishy organics and can accelerate alot more than 10 gs if they need to.

I think you misunderstood me. Small missile with chemical engine will never have as much delta-v as large nuclear powered ship. That`s right, missile will accelerate faster than ship, but it will also burn out it`s fuel even more faster. Chemical powered missile will have delta-v of about 10 km/s whereas nuclear engine equipped ship can have delta-v of about 200 km/s. Think about it, enemy fires missile spam on my ship from 200 000 km distance, missiles approach at about 10 km/s, it would take about 5,5 hours for them to reach me. All I have to do to avoid that missile spam is to do a comfortable 1 G burn for little more than dozen minutes and my ship is out of reach.

Of course if technology is advanced to the point small cheap fusion torch engines for missiles no longer is a problem then this tactic won`t work.

[Admiral Valdemar]

You can get chemical rockets from the Cold War that performed 10,000 gee burns. They'd be essentially impossible to avoid at close range.

[Starglider]

Something small and not needing a load of life support equipment, which can deliver munitions or act as a jammer or anything required with a small high thrust powerplant to give you 40 gees, but also more versatile than a basic missile.

40 gees? Standard Confederation tech only makes 25. Clearly I am going to have to set the Voidhawks on your illegal antimatter-powered ass.

[Admiral Valdemar]

40 gees? Standard Confederation tech only makes 25. Clearly I am going to have to set the Voidhawks on your illegal antimatter-powered ass.

Yes... well... Oh, I need to go to a meeting and I can't take this large sack of money with me. I shall leave it here, with you, and hope it is in safe hands.

[frogcurry]

You can also collect the matter again so that it's basically a very efficient, non-solid radiator surface. Or, if being attacked by beam weapons, you can disperse the material in the direction of the attack and help dissipate the weapon's energy.

If you are going to try to use the Joule-Thomson effect to cool your systems, then re-compressing the fluid back up again is going to re-heat it even more than the benefit of the cooling, so you'd have to wait until after the battle to do so to have any benefit (plus find somewhere to store all the fluid at the discharge pressure in the meantime, like a giant balloon). Also the effectiveness has an upper limit in terms of mass density achievable, push your fluid up into supercritical/ dense phase regions (60 - 200 bar + depending on fluid composition and properties) and the extra cooling relative to the extra pressure is negligible (although you do get more mass). Theres a hard limit to the cooling that this gives, as its dependent on the pressure drop, but at a high enough inlet pressure the J-T constant isn't very negative and it gives next to no cooling per bar of pressure lost.

Another idea for heat management would be to power laser weapons using an anti-matter one-shot fuel cell. Put into a "bullet" consisting of AM fuel, laser assembly and basic manouvering thrusters, launch it away, then let the bullet fuel cell do its thing, giving a burst of energy for one or at most a few shots before it melts. Aiming and sensor assemblys can be in the main ship. Because the heat is generated remotely, you aren't being heated by the weaponry, so you don't need to be radiating energy substantially as a result. The only downside is the extra cost and mass required.

[Admiral Valdemar]

If you are going to try to use the Joule-Thomson effect to cool your systems, then re-compressing the fluid back up again is going to re-heat it even more than the benefit of the cooling, so you'd have to wait until after the battle to do so to have any benefit (plus find somewhere to store all the fluid at the discharge pressure in the meantime, like a giant balloon). Also the effectiveness has an upper limit in terms of mass density achievable, push your fluid up into supercritical/ dense phase regions (60 - 200 bar + depending on fluid composition and properties) and the extra cooling relative to the extra pressure is negligible (although you do get more mass). Theres a hard limit to the cooling that this gives, as its dependent on the pressure drop, but at a high enough inlet pressure the J-T constant isn't very negative and it gives next to no cooling per bar of pressure lost.

It's not a system I would use in combat, or even on a warship, to be honest. It's another way of cooling a vessel, but since you'll be needing to perform manoeuvres and worry about other matters, the use of propellant or armoured radiators and retractable radiator wings would be better. Of course, with these systems you're going to be making more heat running the coolant around and diverting heat via Peltier or other processes, but the benefit is you're buying time in the now to expel more heat later on.

Another idea for heat management would be to power laser weapons using an anti-matter one-shot fuel cell. Put into a "bullet" consisting of AM fuel, laser assembly and basic manouvering thrusters, launch it away, then let the bullet fuel cell do its thing, giving a burst of energy for one or at most a few shots before it melts. Aiming and sensor assemblys can be in the main ship. Because the heat is generated remotely, you aren't being heated by the weaponry, so you don't need to be radiating energy substantially as a result. The only downside is the extra cost and mass required.

Sounds like a variation of Teller's ideas for X-ray lasers, only not one-shot-one-kill kinds like Excalibur. Again, refer to my Combat Wasp mention. Smart munitions that can react quicker, be made cheaper and divert firepower from the capital ships is far more preferable than broadsides a la age of sail warfare.

[Skgoa]

i've been wondering for a while now, wouldn't it be possible to "recycle" the heat? we know how to turn the heat from the reactor into electrical energy, why not dumb a little extra energy from the lasers/whatever into the steam turbine? or is this totally unrealistic?

[Formless]

Meet the second law of thermodynamics. You can't beat entropy, no matter how hard you try. You can try to recycle some of that heat, and you probably will. But whatever you use that waste heat for, it will actually create more waste heat as a result. Thus, you will always have more unusable heat than you started. That's the whole problem. The waste heat is, by definition, unusable. This is precisely the reason perpetual motion machines are impossible.

[Admiral Valdemar]

The best you'll get is improving efficiency a bit, like with a supercharger in a car. But in the end, you will always have waste. The benefits of some mentioned systems is that they delay the need to radiate it during battle, which can make your ship especially vulnerable and cook your crew and systems if not careful.

[Beowulf]

Missiles will always have higher delta-v than your ships. They don't have squishy organics and can accelerate alot more than 10 gs if they need to.

Delta-v and acceleration aren't the same thing - the missile will almost certainly have the acceleration and probably the mass-fuel ratio wins over the spacecraft, but the spacecraft might have a much more efficient engine that is able to win by being slow and steady over a long time.
<snip>
What might be interesting is something I said was unsuitable above: long range missiles with ion engines. Low acceleration but more delta-v - due to the missile's smaller mass, it may still out accelerate the spacecraft, winning at short range, and have the specific impulse to do the long haul too.

So I take that statement back - they aren't necessarily unsuitable and are worth looking into.


Active defenses change the whole game. A chemical powered anti-missile missile might be a good call; they are shorter range, so acceleration can give them the win. Might the offensive missiles have an electric first stage and a chemical terminal stage to dodge the defense missiles? Maybe. And then there is the fun of lasers. So consider the above to be just an idealized illustration.

That's all well and good analysis, but it leaves out a vital point: your payload on the missile is about 500 kg at most, not the ~120 metric ton Apollo mission stack. Delta-V is dependant on both mass ratio and specific impulse. The smaller design may result in a lower specific impulse due to complexity issues and the fact it's getting thrown away, but the mass ratio intensely favors the missile. Going with a more realistic size, and with a engine design that scales down that far, gives us a MITEE (Nuclear Thermal Rocket) powered 2-stage missile with about 21 metric tons of liquid hydrogen. It reaches top speed in less than 6 minutes. Exact values change depending on how you allocate the delta-v between stages.

You can also collect the matter again so that it's basically a very efficient, non-solid radiator surface. Or, if being attacked by beam weapons, you can disperse the material in the direction of the attack and help dissipate the weapon's energy.

If you are going to try to use the Joule-Thomson effect to cool your systems.

Droplet radiators do not operate under the Joule Thomson effect. Nothing evaporates. What you're doing is using a liquid with a low vapor pressure to absorb the heat, then spraying it into space. While there, the liquid rejects heat. It's then collected back up with a collector arm. If you're really clever, you can possibly end up with a phase change from liquid to solid, it changing back when it hits the warm collector arm. At this point it ends up recirculated into the heat exchanger, and warmed back up to get sprayed again.

This method has some limitations. For one, it must operate in the direction of thrust. Otherwise you lose a lot of coolant. A second is that manuevering will cause it to cease to operate in the direction of thrust. Thus you lose coolant. Stopping the radiator during manuevering will cause a drop in your thermal output, telegraphing your manuevering.

[Sky Captain]

The problem is on a realistic space warship there probably won`t be enough space to carry lot of big, potent missiles (although that might be solved with attachable missile pods), also large number of big missiles are going to be a lot of mass to haul severely reducing performance of a carrier craft. Second problem if your missiles are large with big fuel tanks you obviously won`t be able to carry as many as you could if your missiles were smaller. Also relatively few but big missiles will be easy targets for enemy point defenses (this might be somehow solved by designing a missile with large first stage carrying several smaller missiles as a second stage which separate from main booster when entering enemy point defense range).

Also opening fire from long range will have the risk of enemy choosing to outrun your missiles.

If warships have engines capable of several G acceleration while still having very high specific impulse like some sort of thermonuclear pulse or fusion torch drive then shooting missiles from long range could be totally pointless because it would be easy to outrun them.