Multiple Star Trackers: Processing, Pitfalls, and Performance

Equipping spacecraft with multiple star trackers offers significant benefits for the attitude control engineer. Multiple aperture systems reduce the performance impact of roll-axis imprecision and reduce the likelihood of sun-inclusions causing loss of attitude lock. These benefits have been understood for some time. The wider availability of compact, low power star trackers makes multiple sensor systems increasingly attractive. That said, deriving the full benefit from a multiple star tracker system requires considerable attention to detail.This study examines the practical challenges of multiple star tracker systems. We present a comparison of different architectures for fusing measurements from multiple instruments and outline the key tradeoffs encountered during design. Additionally, using orbital data obtained from an Earth-Observing spacecraft, we examine and show how overlooking even minor factors can lead to significant performance degradation. Diagnosing the sources of increased error can be a challenge because different phenomena can introduce qualitatively similar errors. We highlight the outcome of our orbital study and present a series of insights that will allow designers to make the most effective use of their available sensors.