Navigating by Twilight: Autonomous Orbit Determination Using Solar Occultation Detection on the AIM Spacecraft

摘要

The Aeronomy of Ice in the Mesosphere (AIM) mission is a NASA Small Explorer observatory that was launched on April 25, 2007. Due to its coarse on-board orbit knowledge requirements, AIM was not designed with any orbit determination sensors or software except for an orbit propagator which was to be re-seeded by ground command at regular intervals. Several days after launch the spacecraft's communications receiver began to suffer from an intermittent failure. The uncertainty in performance of the spacecraft's receiver created a desire to develop, with urgency, a way for the spacecraft to navigate for very long periods of time without ground-provided updates. This paper presents the solution that was developed, loaded, and has been successfully operating in flight. A ground-loaded set of parameters define the orbit elements which are readily predictable over the long term (such as orbit plane evolution and radius) while an on-board observation of a discrete event -occultation of the Sun behind the Earth each orbit - provides the final in-track location fix. This unique software satisfied the on-board navigation requirement of ＜ 73 km error through several years of nominal and extended mission operations without the operations team needing to send a single additional navigation command.