Iecec 95-306 Power Processing Unit Options for High Powered Nuclear El. Ectric Propulsion Using Mpd Thrusters

An electric proptdsion vehicle designm! to transport cargo in support of a piloted expedition to Mars will require electrical power in the range of megawatts. This paper summarizes an evaluation of various megawatt-class power processing unit (PPU) design and technology options for high-power nuclear electric propulsion (NEP) vehicles using turboalternators and a d v a n c e d magnetoplasmady namic (MPD) thrusters. A baseline system uses a low-voltage hsrboahernator, rectifiers and thrusters. However, there are other options. Four such design and technology options with the potcntia] of improving overall system efficiency and reducing cabling mass are analymd. The first option uses high-voltage AC from a wye-conncctcd turboalternator and a step-down transformer, the second option uses a six-phase star-comectcd turboal[emator inslcad of the wyc-conncctcd alternator in the baseline configuration, the third option uscs PPU rectifier electronics located near the thrusters with a remotely-located radiator, and the fourth option uses cryogenic power conversion electronics and cabling to reduce Iosscs. *Also a Professor of Electrical Engineering at California S[atc University, Long Ilcach, CA 90840. II is found that the third option has the potential of providing maximum overall power conversion efficiency and reducing mass. Prcscn[ly, the fourth option appears to have maximum complcxi(y of design and implementation, is costly, and is somewhat uncertain even though it can be the most attractive option in the future. INl RODUCTION Fi8ure 1 shows the schematic arrangement of the various components of a MW-class NEP vetilcle. An electric space pro}nrlsion system consists of a power source (e.g., nuclear reactor and thermal-to-electric power conversion system). a power processing unit (PPU) which converts the power sorrrcc’s power output (voltage) to the form required by the thrmslcrs, and the clc.ctric thrusters. In thk shrdy, PPUS for a 1.5 -MWC nuclear electric propulsion (NEP) vehicle using a dynamic power conversion systcm (e.g., Rankine) and highPov.’cr magnctoplasmadynarnic (MPD) thrusters. The baseline configuration for the NEP vchiclc considered here consists of three SP-I 00 category dynamic power conversion units, a power processing module (PPM) containing the PPU electronics, and two clusters of L1-propellant MPD thrusters with 8 thrusters in each cluster.