Deriving the spin rate and orientation from the quiescent spacecraft ABRIXAS using optical observations

With the power loss of ABRIXAS shortly after launch and consequent absence of telemetry, there was urgent need to determine ABRIXAS' spin rate and orientation to assess the possibility of re-establishing telemetry during periods of full-Sun orbits. We conducted optical and video observations of ABRIXAS passages, and later simulated the optical appearance of ABRIXAS based on a three-dimensional model of its reflectivity properties. Here we show (I) how the spin rate of ABRIXAS slowed down between June and December 1999 and (II) what information can be deduced on the temporal change of the orientation of the spin axis. We discuss the benefit of using ground based optical observation as a cost effective way to develop information about the orientation of a satellite when there is no telemetry.