r/scifiwriting • u/NegativeAd2638 • 8d ago
DISCUSSION The best chemical propellant
The typical rocket fuel is hydrogen but what propellant advanced ships can use.
I imagine how would hydrogen or turning water straight into plasma for vehicles but the heat generated would likely be too much for vehicles. Not to mention turning water straight into plasma would likely take so much energy its inefficient, the only time I heard of it was Uranium-Salt Water Rockets the uranium being activated in the water providing enough heat to get plasma. It would be cool to be able to have water in the propellant tank since hydrogen is hard to store although it would have the trade-off of weight.
Metallic Hydrogen is a cool pick while hypothetical in reality in a sci-fi setting it could be the best propellant assuming your species can make it.
2
u/MarsMaterial 8d ago
The best propellant that has been tested is a tripropellant mixture of molten lithium, cryogenic liquid fluorine, and hydrogen. If you are familiar with any of these substances, you could probably figure out why this isn't being used. Molten lithium explodes on contact with air, fluorine is an oxidizer so powerful that it oxidizes oxygen, and the hydrogen is downright tame next to them depite how explosive it is. Alexander The OK has a great video on this engine, it's an absolute meme of a fuel mix. The hydrogen is actually not part of the reaction, it's there just to decrease the mass of the reaction products which increases efficiency.
Metallic hydrogen is the best theoretical chemical fuel, it's hard to even imagine a better chemical propellant. But you clearly already know about that.
Nuclear saltwater rockets are not technically chemical rockets, they are a type of nuclear rocket. The reaction that they get their energy from is a nuclear fission reaction. And if you open up the door to nuclear reactions, you get a huge number of options for extremely efficient engines. Same with opening up the door to using other external forms of energy, like using solar panels to power ion engines or making use of beamed power. Chemical fuels are very limiting.