The MSX power management system - A charge control system for a NiH2 battery in a low earth orbit

The Midcourse Space Experiment (MSX) spacecraft electrical power system utilizes a secondary nickel-hydrogen (NiH2) battery. The power management system (PMS) is being designed to monitor and control the state of charge of the spacecraft (S/C) battery. This design employs the use of a linear dissipative shunt, numerous digital nondissipative shunts, an electronic coulometer, and microprocessor-based electronics to control the charging of the battery. The microprocessor-based design allows versatility in the charge control algorithm implemented. For this spacecraft, the algorithm relies on an electronic coulometer, with secondary voltage, temperature, and pressure measurements. Interfaces to the S/C command and data handling system allow post-launch tailoring of the parameters used in the charge control algorithm. The design and operation of the PMS are discussed.