The flight software protects the StarLight Combiner and Collector spacecraft against fault conditions. The architectures of the guidance, navigation and control systems are identical for both the Combiner and Collector spacecraft to provide flexibility and reduce costs. Coarse sun sensors, star trackers, a fiber-optic rate sensor, and inputs from the automated formation flying sensor all contribute to determining the spacecraft's attitude. Each spacecraft includes a Ball CT-633 star tracker, which is the primary attitude reference for all phases of the mission. Three reaction wheels adjust the spacecraft's attitude when the interferometry instrument is not in use.
Momentum is managed in the background using thrusters, based on wheel speed limits.
The wheels are at zero speed during interferometer data collection. Small wheels provide low jitter operation while providing sufficient momentum to compensate for solar pressure torques during no-thrust periods. The Ball StarLight electric power subsystem is a direct energy transfer system with a battery clamped bus voltage. The system uses identical components for both the Combiner and Collector spacecraft, with the exception of the solar array shape and size. Power available in cluster checkout mode is derived from only the Collector solar array and must power both spacecraft.