Global UltraViolet Imager

Gyroless-extending the TIMED mission

The TIMED spacecraft is now it its eighth year of a two-year mission, amassing an unprecedented, uninterrupted collection of upper atmospheric data. Over the course of this time, degradation of the gyros has forced the need to allow operation without them. As a result, the attitude estimation algorithms have been enhanced to allow continued operation under gyroless conditions. This paper describes the algorithms implemented to perform attitude estimation with a tracker-only solution, as well as operational issues encountered with a gyroless spacecraft. On-orbit performance is presented, demonstrating the ability to maintain pointing performance requirements with these new algorithms.