Attitude control challenges and solutions for Hayabusa spacecraft

Hayabusa attempted to touch-down two times in November, 2005 after two years of cruising and two months of proximity observation around ITOKAWA. One of three reaction wheels failed in late July of 2005, and the second wheel failed in early October. While the attitude stabilization logic with two wheels was inherent in the onboard system, the stabilization with one wheel required the use of onboard re-programming function and special ground support operations. This paper describes how the attitude control system and operation were adapted to cope with the loss of reaction wheels, along with the introduction of attitude control system that was designed to realize various attitude functions with minimum onboard resources.