THE MSX SPACECRAFT POWER SUBSYSTEM

The Midcourse Space Experiment (MSX) spacecraft is the fourth in a ser ies of APL spacecraft sponsored by the Ballistic Missile Defense Organ ization. Though similar to its predecessors in mission objectives, the MSX differs notably in the performance and environmental requirements that drive the design of the electrical power subsystem (EPS). Divers e modes of operation and autonomous fault tolerance over a 5-year miss ion having a near-polar, low Earth orbit provide challenging engineeri ng constraints to the EPS design. To meet these requirements, the MSX EPS consists of a 1200-W silicon solar array, a 50-ampere-hour nickel- hydrogen battery, and a microprocessor-based power management system. These components have been procured or fabricated by APL, integrated w ith the MSX spacecraft, and tested to assure successful mission perfor mance. The MSX EPS design demonstrates a viable concept in power syste m engineering to meet the requirements of highly diverse, high-power, low Earth orbit applications.