4 ms·
The temperature of a gas is proportional to the average kinetic energy of its particles. So if you compare (e.g.) water vapor to hydrogen at the same temperatu
by p1mrx 3y ago
The temperature of a gas is proportional to the average kinetic energy of its particles. So if you compare (e.g.) water vapor to hydrogen at the same temperature, the hydrogen molecules are moving faster.
A hydrogen+oxygen chemical rocket propels H₂O, while a nuclear thermal rocket can use the lightest propellant (H₂) because the heat comes from elsewhere.
Smaller molecule, faster exhaust, better rocket.
- dgoldstein0 3y agoWouldn't we care more about the momentum of the exhaust rather than the mass? I'm not quite following why lighter particles are better
- p1mrx 3y agoAssume that total propellant mass is a constant (limited by the launch vehicle) and temperature is a constant (because melting the rocket would be bad.) With constant mass, you increase the total momentum by increasing the exhaust velocity. With constant temperature, you increase the exhaust velocity by making the molecules smaller.