Power conditioning unit for low-power arcjet flight application

A low-power (1600 watt class) power conditioning unit (F' CU) has been designed, developed, and qualified by Pacific Electro Dynamics. This PCU operates in conjunction with the low power arcjet thruster developed by Rocket Research Company for north/south stationkeeping and orbit modification applications on commercial satellites. General Electric Astro Space Division is the sponsor of the development work being performed by these two companies. An arcjet system consists of an arcjet thruster assembly, PCU and power cable. The PCU performs the principal function of convening direct current input power into a regulated, constant-power output to the arcjet thruster. To initiate the electrical arc in the arcjet, the PCU outputs a short-duration, 4000 to 5500 VDC start pulse. After the arc is initiated, a controlled current profile is applied to the thruster to ensure that the arc is sustained during the warm-up and stabilization period. During steady-state thruster operation, the PCU provides a constant power level of 1630 watts to the thruster despite stochastic variations in arc voltage. The overall power conversion efficiency of the PCU ranges from 91% to 94% depending on input and output voltage levels. The high efficiency and packaging density of the design results principally from the use of a push-pull power converter topology and custom-designed, power-hybrid microcircuits for the power switching function. This paper describes the electrical and packaging design of the PCU including the functions performed, performance specifications, and operating characteristics. The qualification and test status of the PCU design is also described. I" operate the axjet, a PCU is required to convert satellite bus power into conditioned output power at the appropriate voltage and current levels to maintain the electric arc. Other required PCU functions include start pulse generation and current control during arc stabilization. The PCU must monitor the satellite command interface for thruster start and stop commands and provide thruster system status data to the satellite telemetry system. A low power arcjet thruster and associated PCU are shown in Figure 1. Four thrusters and PCUs are typically required for a satellite north/south stationkeeping application. The thruster is produced by Rocket Research Company and the PCU by Pacific Electro Dynamics. The PCU provides approximately 1630 watts of conditioned power to the thruster which develops over 500 seconds of specific impulse. The block diagram of an arcjet thruster system is shown in Figure 2. The system components include the arcjet, PCU, power cable. The arcjet assembly incorporates the thruster, a catalyst bed to decompose the hydrazine propellant, a valve to control propellant flow, and a fluid resistor to control feed pressure. The satellite provides main and auxiliary power, and command inputs to the PCU. The PCU outputs analog status data to be processed and transmitted to ground stations by the telemetry system. As a principal component of the thruster system, the PCU must provide the electrical requirements of the arcjet in minimum weight and volume. The following sections of this paper describe the requirements, operating characteristics, and electrical and packaging design implementation of the PCU. Views of the PCU are shown in Figures 3 and 4. The use of arcjet thrusters for satellite stationkeeping applications provides significant system advantages due NCE CHARACTERISTlCS to high specific impulse (Isp) when compared to conventional thruster types. In order to efficiently To properly operate the arcjet thruster, the PCU is d * Pacific Elecm Dynamics: P. T. Skelly, Staff Engineer J. R. Fisher, Manager Mechanical Engineering C. M. Golden, Manager Advanced Development Member AIAA Copyright