This paper investigates the use of relative attitude sharing between two spacecraft. The first, sharing, spacecraft, has an inertial attitude sensor. The second, receiving, spacecraft lacks an attitude sensor. The sharing spacecraft is able to sense relative attitude, enabling determination of the inertial attitude of the receiving spacecraft composed with the inertial attitude of the sharing spacecraft. Relative attitude is assumed to be available only under certain alignment conditions consistent with proper orientation of a passive relative attitude sensor on the sharing spacecraft and attitude fiducials on the receiving spacecraft. It is shown that an uncertainty-based metric derived from the Extended Kalman Filter can be used to autonomously determine when the spacecraft should modify their pointing objectives to accommodate resource sharing. This uncertainty-based decision parameter enables the spacecraft to share information more efficiently than a fixed-measurement update schedule, by switching the tracking objective from a target mode to a sharing mode, only when needed. It is shown that a star tracker, or equivalent attitude determination system on the sharing spacecraft can accommodate the attitude measurement requirements of multiple spacecraft.
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