Evaluation of cryogenic power conditioning subsystems for electric propulsion spacecraft

The power requirement of vehicles designed to transport cargo supporting a piloted expedition to Mars is in the range of megawatts. Therefore, it is imperative that the megawatt class power processing unit designed for high-power nuclear electric propulsion vehicles using turboalternators and advanced magnetoplasmadynamic (MPD) thrusters should be such that the overall system efficiency is as high as possible with minimum system specific mass. This paper examines the use of cryogenic power conditioning subsystems to achieve that goal since they have very high efficiency. In the past, cryogenic power conditioning have shown complexity of design and implementation and were costly and somewhat uncertain. With recent advances in materials, devices used in power conversion and cooling methods, further improvements in efficiency and specific mass are realizable. Cryogenically cooled MOSFETs and MCTs are considered for power conversion and two configurations have been examined. It is found that a system efficiency of 92.67% and specific mass of 9.99 kg/kW_e can be realized using MOSFET-based cryogenic power conditioning systems for electric propulsion spacecraft using MPD thrusters. With cryogenically cooled MCTs, the specific mass decreases to 9.77 kg/kW_e, but the efficiency also decreases to 90.94%