Somtaaw wrote:It's also the Fusion versus modern fission issue concerning power. We use fission, so X tonnage nuclear reactor mass stays at X tonnage it doesn't really change as you use the reactor. Honorverse ships are fusion powered, and they specifically use Hydrogen which being flammable = super dangerous.
Ditto with fusion. Strictly speaking, both fusion and fission fuel mass slightly more than their products, as the difference is the energy release. With fusion, that's about 1% reduction in mass only. You only get major mass reduction with a matter/anti-matter reactor, for which one of the fuels is extremely more reactive. If you meant that the fuels for fusion are more massive than for fission, I agree (U-235 and U-238 are far more energy dense than H-1, D-2 or He-3).
But note that "flammable" implies combustion with oxygen. If there's no oxygen for the hydrogen to react to, it won't. But that brings the point that the ship need not carry water, since it can simply burn a bit of its hydrogen supply to make water for the crew.
There's also a question whether the fusion fuel needs to be hydrogen. It could be Helium-3, which as a noble gas will not react chemically to anything. Even if it needs to be hydrogen, the hydrogen could be carried in the form of water or heavy water. You just electrolyse it to separate into oxygen and hydrogen before feeding into the fusion chamber (you need less energy to electrolyse than you will gain in fusion, so it's still net positive). In fact, water is a good shield against cosmic rays if you don't have armour or particle shielding, so it is one of the most likely ways we'll power our first interstellar ships.
Manticoran battlecruisers carry enough hydrogen for 6 MONTHS of usage, excluding any time spent in hyper with reactors turned off using their sails to produce power. 6 months supply for (at least) 3 reactors is a ridiculously huge amount of Hydrogen bunker storage required, and all of it needs to have space to be internally sealed which increases the overall dedicated space. Otherwise you get a "golden BB" that blows up that battlecruiser with 1 hit, because that laser dug deep and pricked a hole in the reactor mass bunker... and caused an electrical fire that causes that hydrogen to explode.
I don't think a hydrogen explosion is likely, as explained above. However, if the bunkers do store a compressed gas, whether it's deuterium, helium, rupturing the bunker could cause explosive decompression, which would further rip open the hole created by the projectile. That's considerable damage. A water tank wouldn't nearly as much damage, as I don't think it would store water under high pressure. However, it would sublimate when exposed to vacuum.