HETE Satellite Power Subsystem

The HETE (High-Energy Transient Experiment) satellite a joint project between MIT's Center for Space Research and AeroAstro. is a high-energy gamma-ray burst/X-Ray/UV observatory platform. HETE will be launched into a 550 km circular orbit with an inclination of 37.7°, and has a design lifetime of 18 months. This paper presents a description of the spacecraft's power subsystem, which collects, regulates, and distributes power to the experiment payload modules and to the various spacecraft subsystems (radios, electronics, sensors, and actuators). The spacecraft uses four solar power arrays for primary power during orbit-day, and six rechargeable nickel-cadmium batteries during orbit-night. Two Power Point Trackers (PPT) are used to regulate the operating points of the solar arrays. The outputs from the PPTs provide the spacecraft's main power bus, which is used to recharge the batteries through three Battery Charge Regulators (BCR), and to supply power to distributed DC-DC switching converters for individual subsystems. The benefits gained by using a distributed-power scheme are improved regulation, electrical isolation of payload subsystems, simplified wiring, and fault tolerance. Each experiment subsystem can be powered on and off independently, with minimum disturbance to other subsystems.