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A.J. Bradley, M. Wenz (AlliedSignal Guidance and Controls), E. Nelan (STScI)
HST Astrometry is presently conducted with Fine Guidance Sensor #1, having recently transitioned from Fine Guidance Sensor #3. During the Shuttle Servicing Mission SM3A the flight computer which controls the Astrometer will be replaced. Commanding changes were necessitated to transition from a fixed-point assembly language architecture to a floating-point C language. This paper describes the validation process of the commands and the controlling algorithms; a description of the test setup to conduct end-to-end testing with the hardware; an enhancement to the Astrometry TRANS mode to remove the Coarse Track/Fine Lock transition error; addition of an Astrometry MAP mode to facilitate tying the Star Tracker reference frame and the Fine Guidance reference frame to the spacecraft.