What resources are suitable for firearm propellant in Jovian sci fi setting?

Question

I'm building a setting revolving around helium-mining space stations in orbit around Jupiter, and a war to control them. Currently I'm trying to work out weaponry for both light and heavy weapons in that setting. My goal is to design something that is plausible for that far out from Earth, but technobabble to handwave some aspects is acceptable.

The trouble with designing firearms is that coming by nitrocellulose or any other traditional solid propellants would be extremely hard to get in the atmosphere of Jupiter. The most plentiful resource out there is hydrogen. Jupiter is like 75% H.

I've done my research, and it seems hypothetically possible to use hydrogen combustion to propel firearms. You could use compressed hydrogen from the atmosphere, or you could even use water shipped from Ganymede or Europa to get the oxygen you need, and electrolyse it right there in the gun. But H is extremely inefficient, because you need the hydrogen to be REALLY dense to get enough energy out of its combustion. That's why the space shuttles' orange hydrogen tanks were so large - you need a lot of it.

I even got to wondering about the practicality of crossbows or other flechette technology - literally spaceships with ballistae on them, like Spelljammer. But they're too clean, they're not dirty enough.

That leads me to my next point: this setting is kinda gritty and awful. "We are all pawns in a corporate-controlled hellscape" level of awful. So if there's an option that's really nasty, dirty, pollutive, or the like, that's the best kind of answer.

So, does anyone have any thoughts on potential options here? Technobabbling a way to turn hydrogen into solid propellant (without having to freeze it to -260°)? Making guns (or bullet casings) literally just glorified gas compressors with ignition chambers? Helium lasers, cause there's no shortage of that? Or is there another way, whether a source of more practical resources that's flying under my radar, or a technology I'm failing to take into account?

Thanks for stopping by!

Answer 1

Frame challenge

They have "helium mining space stations in orbit around Jupiter". This means that they already have ginormous amounts of propellant for their engines; compared to the vast amounts of propellant guzzled by the enormous rocket engines of the helium mining space stations, the needs of firearms are _^tiny. Just use a very small fraction of the rocket fuel.

But the propellant was never the real problem. The real problem is the bullets.

The stereotypical AK-47 cartrige contains about 1.6 grams of propellant and fires an 8 gram bullet. The bullet is five times more massive than the propellant! Where do they get their bullets from? It would be strange if they brought the bullets with them but forgot to pack the powder...

Answer 2

Railguns with metal hydrogen (https://en.wikipedia.org/wiki/Metallic_hydrogen) slugs, shoved in diamond anvil cascades https://en.wikipedia.org/wiki/Diamond_anvil_cell.

On impact, the speed of the slug is transferred into the first anvil, which hammers into the metal hydrate slug creating a miniature sun, which then is squeezed, onwards into ever bigger, ever more denser squeezed anvils, all within split seconds... The fusion- is short lived, intense and very disproportional to the size of the slug.

Like having a sun shoved through your front window.. with the walls and atmosphere of your spacecraft, becoming part of the temporary containment vessel while the sun drives through it.

Answer 3

One option is simply to use hydrogen and oxygen. Check out this educational article, which explains:

At a first glance, this reaction seems strange. In some reaction conditions, the reagents may react extremely rapidly, resulting in explosion. In other conditions, they may react very slowly or not at all. The pressures that constitute the separation between those extreme behaviors are called the "explosion limits".

and has this graph:

In other words, one path to success to have the right combination of pressure and temperature to produce a hydrogen-oxygen explosion. This requires (and I personally think this is cool) a power source in the rifle that produces the appropriate pressure and temperature.

An alternative is to use Silane (SiH4). This one might be a challenge due to the somewhat dramatic lack of silicon in the Jovian atmosphere. However, when mixed with the appropriate products, it also produces a bang.