How to Depict a Broken FTL Drive (and other Superscience)

[Fred Brackin]

Originally Posted by Daigoro

Also, reliable detonation after penetration seems like an easily solved problem by TL 10. Maybe just take a modern-day bunker buster's specs and boost them up appropriately.

Oh no. Contemporary bunker buster bombs strike at a subsonic speed. Maybe 600 miles per hour at most. The Delta-V on a light Spaceships missile is 10 miles per second (36,000 miles per hour) and double that for a heavy one. No subsonic munition design is at all relevant to such an impact.

I wonder if it might be possible to create a nuclear warhead that detonates because it's been blown to incandescent vapor but nothing that relies upon having a solid object survive impact is useful for any space combat but for very close range ones at very low speeds. Maybe two giant robots with handgeld autocannons at a thousand yards or so but nothing even vaguely realistic.

[Anthony]

Originally Posted by Fred Brackin

I wonder if it might be possible to create a nuclear warhead that detonates because it's been blown to incandescent vapor.

There's traveller-esque collapsing rounds, where the impact compresses a subcritical mass to supercritical, but I would expect it to rather unreliable (you could probably make it detonate properly if it hit a monolithic plate at a fixed angle, but an irregular surface or off-angle hit wouldn't collapse properly).

The other possibility is a tandem warhead, where you have a kinetic penetrator followed by a secondary explosive that goes through the hole created by the first.

[ericthered]

Originally Posted by Johnny1A.2

For power generation for internal 'hotel load', the basic life support systems and ordinary uses, a very little hydrogen is probably sufficient for a long time. A gram of fused deuterium yields (at perfect efficiency) something in the neighborhood of 20,000+ kilowatt-hours. A gram of ordinary 'light' hydrogen, perfectly fused, runs 6-7 times more. So most of your internal systems won't use much.

...

But that reaction drive, that's another barrel of piscine vertebrates. You call it a 'torch'. That usually implies high thrust over long periods, and it's expensive. You'll need to decide more or less what that torch can do, to make a good guess at fuel/reaction mass consumption and ship performance.

Looking at theoretical yields for fusion and the amount of energy needed to achieve that is a fantastic idea. Thanks.

The "Fusion Torch" is strait out of spaceships, and its the most common super-science reaction drive at TL10^, which is why I'm using it*. In this case the engine gives half a G of acceleration and has 15 mps of delta-v per fuel storage system (1/20th of the mass). I think that gives me 80 minutes of acceleration per system (and I'm packing 3).

I'm not sure If I'm doing the physics right, but I think that means that each second the torch needs to accelerate a hundred-thousandth of the ship (20th of ship's mass times 80 minutes times 60 seconds) to 500 km/s to balance the momentum of adding 5 m/s to the rest of the ship. For each ton of ship, that's 10 grams out the other side at speeds requiring 1 gigajoule of energy per second. 10 grams of Deutrium ... don't quite give 1 gigawatt-seconds of energy per second. If I did the math right. I suppose there is a reason that drive is marked as super-science.

*I looked at doing a custom set of numbers, but it really hasn't been that relevant to the expected use case.

[Anthony]

At TL 10, the fusion torch drive is 15 mps/tank, or an exhaust velocity of 300 mps. Power requirement is (300 mps)*thrust/2, or 240kW/N, or 2.2GW/ton thrust (as it as a T/W ratio of 10, 22GW/ton of drive).

That's ridiculous, which is why it's superscience, but its actually still pretty low compared to fusion. Max theoretical iSP for deuterium fusion is about 8% of c or 15,000 mps (50x higher); since energy per ton of fuel scales with the square of exhaust velocity, only one part in 2,500 of the fuel needs to be fused.

[johndallman]

Originally Posted by Fred Brackin

Making nuclear warheads that would survive impact at space velocities is soemwhere between extremely unlikely and actually impossible. If your missiles have miles per second of delta-V you're probably in impossible territory. Impact with solid objects at multiple miles per second causes meteoric explosions.

Actually, it isn't that that hard to get fission explosions at contact ranges. You put your warhead near the back of the missile, and use the inertia of the components to assemble a gun-style device as the missile is slowed down by the rearward thrust of its nose turning into plasma.

The timescale of nuclear chain reactions is very short, about a microsecond for the whole reaction. If the missile is hitting at 30 km/sec, that microsecond corresponds to about 3 centimetres of its movement.

A nuclear explosion may not be very useful under these circumstances, but it's not hard if you go about it the right way.

[PTTG]

@OP, I realize this is a bit late to the party, but my thoughts on the matter:

All kinds of high tech require energy, and for anything dealing with high-energy physics, it's almost certainly going to be electricity. Therefore, highly charged capacitors could be a threat in any damaged system.

The fact that a FTL drive is probably quite hot means that you can have dangerously hot environments the heroes have to brave, as well as having malfunctioning cooling equipment make rooms perilously cold. Plus, high temperature coolants can themselves be toxic.

Weird scientific equipment might need high intensity magnetic fields, vacuum vessels that can pop, and of course, intense EM radiation. Usually this is ionizing, but it could alternatively be infrared or microwave radiation at the very low end, which will mainly have subtle heat dangers.

Also possible is high-energy particle accelerators. Anatoli Bugorski accidentally got struck with a beam of protons that caused highly focused burning damage through his head in the '70s. He's still alive today, though he suffers some epilepsy. PCs might be lucky enough to be struck through the limbs, which may be quite treatable.

More exotic hazards might include antimatter vessel failure. Depending on the size, this could simply be a slow, fizzling gamma ray source as stray antihelium escapes a misaligned magnet bottle and pings off of a conventional aluminum spar.

Oh, and then there's regular piercing, slashing, or crushing damage that could be caused by heavy bits of metal shifting around following a collapse, or dumb robotics flailing around.

[lwcamp]

Originally Posted by ericthered

That's a really good question. As is how much fuel the reactors burn compared to the reaction mass of my fusion torch engine. Of course, that uses fusion too. I don't think I can justify a ship that's 15% hydrogen isotopes by mass, but it would be nice to have some heavy hydrogen in the mix. Spaceships doesn't distinguish between hydrogen and deuterium/tritium, so I'm not sure about the ratios. Does anyone have thoughts on how to set that up?


That's a nice detail. I am starting to think about how all of that hydrogen is stored. The liquid part sounds a bit tricky, because there is already a LOT of heat in this ship, but I'm not sure how feasible gaseous hydrogen on the ship is.

The ship probably has traps in each compartment that are designed to collect that seeping hydrogen and safely dispose of it in some way (whether its mostly gaseous or not). The easiest way is to burn it periodically, but if the entire compartment just got flooded with hydrogen, that's probably a very bad idea.



You can at least separate the warheads from the rocket fuel, And hopefully store them somewhere less likely to explode than on an armed missile. I'm leaning towards using chemical rocket fuel for the missiles right now, but I might use fusion torches like the main ship.


About half the warheads are probably going to be super-science devices designed to deplete enemy shields. I'm not sure how explosive those are yet. I'm actually not that confident that nuclear warheads will detonate successfully after penetrating ship armor: as I understand it nuclear explosions are tricky things. So there may be some armor-piercing conventional shells along with the nuclear weapons serving as the equivalent of high explosive rounds: fantastic for bombarding soft targets, and kind of meh for attacking other ships.

As long as you are willing to use superscience, here's some stuff that, while well beyond our ability to do today still has some physical justification:

Fusion fuel - use the proton-boron reaction. Have a store of boron enriched in boron-11. React this with ordinary hydrogen (no deuterium, no need to worry about tritium at all, which is radioactive). Boron is easy to store, since it is a solid. Also, you don't get any of those really annoying neutrons irradiating your reactor, posing a radiation hazard to everything around it, and activating the entire engineering section so that it is all radioactive. We know that the proton-boron fusion reaction is possible. It is hard to get going, and it is possible that it always loses more energy to bremsstrahlung x-rays than is produced by the fusion reaction (or maybe not, with spin polarized nuclei or high magnetic fields or something) - but maybe you can use tech related to your FTL to get the fuel to fuse (like having a space-time warp that mirrors the x-rays back into the fuel, helping to heat it up again).

Hydrogen storage - consider metastable metallic hydrogen. It's still pretty low density, but denser than liquid or gaseous hydrogen. It also remains solid at room temperature. Can hydrogen exist in a metastable metallic state at room temperature and pressure? No one knows, but it is at least still a possibility that has not been rules out by known science. Might as well use it. (Of course, if the metallic hydrogen is only marginally metastable, it could be very explosive stuff, releasing lots of energy if it decomposes back into normal diatomic hydrogen molecules.)

Luke

[lwcamp]

Originally Posted by Fred Brackin

Oh no. Contemporary bunker buster bombs strike at a subsonic speed. Maybe 600 miles per hour at most. The Delta-V on a light Spaceships missile is 10 miles per second (36,000 miles per hour) and double that for a heavy one. No subsonic munition design is at all relevant to such an impact.

I wonder if it might be possible to create a nuclear warhead that detonates because it's been blown to incandescent vapor but nothing that relies upon having a solid object survive impact is useful for any space combat but for very close range ones at very low speeds. Maybe two giant robots with handgeld autocannons at a thousand yards or so but nothing even vaguely realistic.

When a hypervelocity long-rod penetrator munition impacts, the front ablates away (while ablating away the target material in front of it), but this produces a force that slows down the part behind it. Eventually, the end state (of penetrating into a semi-infinite homogeneous medium) is a cavity eroded and blasted out by the penetrator with a plug of the penetrator's back end stuck into the bottom/back of the cavity. This rear plug area is still subject to fairly violent deceleration forces, but of similar magnitude to those experienced by, for example, launch of munitions by a modern howitzer. So it is conceivable you could put munitions in that back area that detonate on a fuse at a certain distance after impact.

Luke

[Fred Brackin]

Originally Posted by lwcamp

it is conceivable you could put munitions in that back area that detonate on a fuse at a certain distance after impact.

Luke

You won't be able to do this beyond a certain threshold of velocity. Probably when the created plasma is spewing out enough hard x-rays to ionize the whole back end before it can decelerate meaningfully.

[Johnny1A.2]

Originally Posted by Fred Brackin

You won't be able to do this beyond a certain threshold of velocity. Probably when the created plasma is spewing out enough hard x-rays to ionize the whole back end before it can decelerate meaningfully.

At that velocity, though, do you really need munitions at all?