A Spacecraft Electric Propulsion System Using Hybrid Excitation Generator for Deep Space Missions

This study presents an in-space nuclear electric propulsion system integrating a multiphase hybrid excitation generator. In spite of the low amount of thrust of electric thrusters, their high specific impulse, high efficiency and constant thrust make them a perfect candidate for deep-space missions and allow spacecraft to operate for extended durations, enabling them to reach distant destinations and conduct long-term missions while conserving propellant resources. In the presented system, the generator rotor shaft is mechanically connected to a turbine that rotates by a heat power source, which is a nuclear reactor whose characteristics are adopted from NASA’s study on nuclear electric propulsion (NEP). The hybrid excitation machine converter mechanical rotation to electrical energy and provides electric power for the electric thruster. The hybrid excitation generator features an AC stator and a dual-part rotor with independent operation, facilitating adjustment of the machine’s air gap flux by varying the field winding current. The multiphase configuration enhances power density and minimizes DC voltage ripple, while a dual-rotor setup adds versatility to the machine’s control system. The machine has a wound field rotor and a permanent magnet rotor. For any fixed speed of the rotor, the permanent magnet flux is fixed while the wound field flux is adjustable. A local controller system manages the DC-DC converter outputs connected to the wound field rotor. A supervisory controller regulates local controller references in response to changing system power demands, ensuring efficient and precise power and voltage management for the spacecraft’s electric propulsion system. Simulation results are presented which effectively confirm the validity of the system and controller.