Abstract: A rocket motor and rocket motor feed system are disclosed. The rocket motor feed system includes a sonic choke which passively regulates the mass flow rate of gaseous propellant passing through the sonic choke. An injector is provided and isolates the upstream feed line of the rocket motor feed system from a combustor. Regenerative cooling circuits are disclosed. Self-pressurised gaseous propellants may be used with the rocket motor and rocket motor feed system. Suitable propellants are disclosed. Bi-propellants may be used. The sonic choke may provide a ratio of oxidiser:fuel to a combustor. Rocket motor feed systems with separate fuel and oxidiser branches are also disclosed. A rocket motor utilising such a feed system is disclosed.