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

[Fred Brackin]

Originally Posted by Johnny1A.2

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

At even 10 miles per second the whole attack vehicle explodes as if it werte a 40x its' own weight in TNT. That's not just the warhead either. Your guidance system explodes as 40x its' own weight in TNT. Double velocity and you're 4x energy.

So, no I wouldn't go to much trouble at all to add explosives to a kinetic energy weapon. I really wouldn't bother trying to engineer a contact nuke much less an armor-piercing nuke.

[Daigoro]

Originally Posted by Fred Brackin

At even 10 miles per second the whole attack vehicle explodes as if it werte a 40x its' own weight in TNT. That's not just the warhead either. Your guidance system explodes as 40x its' own weight in TNT. Double velocity and you're 4x energy.

So, no I wouldn't go to much trouble at all to add explosives to a kinetic energy weapon. I really wouldn't bother trying to engineer a contact nuke much less an armor-piercing nuke.

Are we talking about spaceships here or real world bunker busters?

By that calculation, for a 1 ton missile, that would yield a 40 ton TNT explosion. But bunker busters supposedly need a kilo- or megaton yield to bring down a whole underground complex, such as a hardened ICBM launch facility.

[Fred Brackin]

Originally Posted by Daigoro

Are we talking about spaceships here or real world bunker busters?

There are no real world "bunker busters" comprised of kinetic energy munitions that impact at 10 miles per second or higher.

However, the calculation I used does not derive from Spacships but rather a well-established rule of thumb that comes from meteoric impacts and proposed orbital KE munitions from the 60s such as Project:Thor.

On the other tentacle there are no "Real World" bunker busters with a kt or mt explosive yield either to my knowledge. There was some talk about a "ground penetrating" nuclear warhead back in the 80s but I don't believe any practical tests much less a deployed weapon system came of that.

I don't actually know of a larger bunker buster than a 5000 lb streamlined thick-cased delayed action fuse bomb that he USAF developed after the first Iraq war. Befoe that the RAF in WWII had the 12,000 lb Tallboy and the 22,000 lb Grand Slam but they and their like and have not been seen in the world in a long time.

[ericthered]

Originally Posted by Anthony

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.

I followed you (and my numbers agree with yours roughly) up until you say that deuterium fusion can provide x2500 the energy we need. Earlier in the thread the energy for a gram of deuterium was given as 20 MegaWatt hours, or 72 gigawatt-seconds. We're throwing about 10 grams of hydrogen out a second, and we require a few gigawatts a second, so I'm getting we're using around 700 to 300 as much hydrogen for propellant as we need. Which I suppose in the grand scheme of things really isn't that far off of x2500. The fused hydrogen is dwarfed by propellant weight, but its still used in an appreciable amount.

Originally Posted by lwcamp

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

Ok, this is cool stuff, and the kind of thing that makes science fiction cool. I'm not quite sure what metastable metallic hydrogen would be like. Are we talking pressurized bottles of propane, or are bricks of the stuff feasible? What sort of stresses would destabilize the stuff, how would you suggest storing it, and does anyone have practical names for the stuff* ?

*You don't live surrounded by something and refer to it by its 10-syllable technically correct name

Originally Posted by Johnny1A.2

Burning it uses up valuable oxygen. Granted you might theoretically collect the resulting water, but that doesn't strike me as very practical.

I ran the numbers on how much water I needed to pack to have two backup atmospheres for the ship sitting around in reserve. Its a pitifully small number, especially when compared to the drinking and toiletry water, and even more so when compared the coolant systems in the works.

I'm also under the impression that you want water reclamation on pretty much any spaceship, and given that this one has gravity on it, it shouldn't be terribly hard.

****************************************

On the warhead front, I'd like to lean away from nukes, but I'm keeping an eye on the possibility. I have super-science shields, but It'd be nice to know how the ship does without them.

[lwcamp]

Originally Posted by ericthered

Ok, this is cool stuff, and the kind of thing that makes science fiction cool. I'm not quite sure what metastable metallic hydrogen would be like. Are we talking pressurized bottles of propane, or are bricks of the stuff feasible? What sort of stresses would destabilize the stuff, how would you suggest storing it, and does anyone have practical names for the stuff* ?

*You don't live surrounded by something and refer to it by its 10-syllable technically correct name

No one has ever made any, so we're not sure about a lot of that. If it was metastable at room temperature, it would be a very lightweight silvery metal - lighter than aluminum, but with a very high strength-to-weight ratio. And yes, metastable at room temperature means you can have bricks of the stuff. Although for a lot of applications, powders, or cast or machined shapes, might be more practical.

What sort of stresses destabilize it depends entirely on just how metastable it is. Diamond is the metastable form of carbon, and it is metastable enough that smacking it around or putting it in a torch flame doesn't make it explosively turn into graphite. On the other hand, there are other metastable substances where a slight bump can make it nucleate a transition that violently turns the stuff into its more stable form. Since the properties are unknown, you can go ahead and decide what works for your setting.

If it is only marginally metastable, store it in well-insulated, shock-proofed, vibration dampened, refrigerated containers. If it is highly metastable, you can just have the coal hands shoveling chunks of it out of the bunkers into the furnace (at least, if you are going for that retro-feel - in actuality, ingots or powders would probably be more practical). Whatever form it is, it will burn, and unlike a lot of other metals you don't get a passivated oxide layer on the surface (since the oxide of hydrogen is - well - water. Either that or hydrogen peroxide. Neither of which make a very good barrier between a metal and the oxygen itching to react with it), so storing it in an inert atmosphere (such as argon or nitrogen) could be a good idea.

Since we don't have a name for the stuff yet, you get the joy of coming up with one yourself!

Luke

[Anthony]

Originally Posted by ericthered

I followed you (and my numbers agree with yours roughly) up until you say that deuterium fusion can provide x2500 the energy we need. Earlier in the thread the energy for a gram of deuterium was given as 20 MegaWatt hours, or 72 gigawatt-seconds.

Well, someone did the math wrong.

The reactions that occur in D-D fusion are:
D+D -> T + p + 4.03MeV.
D+D -> 3He + n + 3.27 MeV.

Total 4D -> T + 3He + p + n + 7.3 MeV; D has a mass of 1875 MeV so conversion is 0.097%, sufficient for exhaust velocity of 3.1% of c. Total conversion is 8.99e+13J/g so this is 8.75e+10J/g or 87 GJ. The 72 GJ figure above might come from this plus rounding.

However, tritium in a nuclear chamber hot enough for D+D fusion will almost instantly also fuse with another deuterium:
D+T -> 4He + n + 17.6 MeV.
This gives us a total of 5E -> 4He + 3He + p + 2n + 24.9 MeV or 0.265% conversion, sufficient for 7.2% of c or 238 GJ/g.

Now, there's a chance the reactor is also hot enough for the 3He + D fusion:
D+3He -> 4He + p + 18.3 MeV.
and the full reaction boils down to:
3D -> 4He + p + n + 21.6 MeV, or 0.383% conversion, sufficient for 8.75% of c or 345 GJ/g.

On reflection, I should probably have assumed a reactor that cannot burn 3He, as if you can burn 3He you probably do, so it's only about 2,000x as much energy as you need.

[Johnny1A.2]

Another potentially plausible hazard: subtle air contamination.

By 'subtle', I mean that ship's air is still breathable, but there's fumes and gunk in it that make it problematic over time. That could come from volatized chemicals in the damaged machinery, or heat exposure to ordinarily harmless shipboard materials, or any number of places. There would not necessarily be any smell or other indication, though there might be.

The subtle part could be something like a -1 to all IQ and DX rolls after breathing the contaminants for a few hours. It might take a while for the PCs to realize they were impaired, esp. because their own faculties are impaired (it's often the drunkest person who thinks he or she is the least impaired).

Maybe for every six hours of breathing it, another -1 on IQ and DX, and for every 24, -1 on HT. This could go on until somebody realizes that there's an issue or somebody passes out or commits a lethal mistake.