Electric/LH2

Electric/LH2 propellant. Liquid hydrogen used as the propellant in an electric arcjet or resistojet motor, where it is heated rather than ionized. The power source can be a nuclear reactor, thermal-electric generator, or solar panels. Liquid hydrogen had big drawbacks, however - it was highly cryogenic, and it had a very low density, making for large tanks, and making long-term storage difficult. Its use in electric engines, which by definition were low-thrust and long-duration, meant that no electric engines reached the operational stage using this propellant.