Design of a power management and distribution system for a thermionic-diode powered spacecraft

The Electrical Systems Development Branch of the Power Technology Division at the NASA Lewis Research Center in Cleveland, Ohio is designing a Power Management and Distribution (PMAD) System for the Air Force´s Integrated Solar Upper Stage (ISUS) Engine Ground Test Demonstration (EGD). The ISUS program uses solar-thermal propulsion to perform orbit transfers from low Earth orbit (LEG) to geosynchronous orbit (GEO) and from LEO to Molnya. The ISUS uses the same energy conversion receiver to perform the LEO to high Earth orbit (HEO) transfer and to generate on-orbit electric power for the payloads. On-orbit power generation is accomplished via two solar concentrators heating a dual-cavity graphite-core which has thermionic diodes (TIDs) encircling each cavity. The ISUS power system is to provide 1000 W_e at 28+/-6 V_dc to the payload/spacecraft from a maximum TID generation capability of 1070 W_e at 2200 K. Producing power with this quality, protecting the spacecraft from electrical faults and accommodating operational constraints of the TIDs is the responsibility of the PMAD system. The design strategy and system options examined along with the proposed designs for the flight and EGD configurations are discussed herein