Science Instrument Support Electronics Systems for the Relativity Mission Satellite, Gravity Probe B

The Relativity Mission, Gravity Probe B (GP-B), uses four redundant high precision electrostatically suspended mechanical gyroscopes for measuring the relativistic precessions of the frame of reference in a 640 km polar orbit. The two precessions to be measured are predicted in General Relativity are the geodetic effect, 6.6 arcsec/year, and the frame dragging effect, 0.042 arcsec/year. The Science Instrument Support Electronics or Payload Electronics Package enables this measurement to be performed by providing the necessary control and monitoring functions for the Science Instrument Assembly that contains the four gyroscopes and reference star tracking telescope. This paper describes the overall architecture of the Payload Electronics system and the design and operation of its component parts: 1) the SQUID Readout electronics (SRE) for gyroscope orientation measurement, 2) The Gyroscope Suspension System (GSS) for gyroscope electrostatic suspension and spin axis alignment, 3) the Telescope Readout Electronics (TRE) for measurement of the reference star location, 4) the Experiment Control Unit (ECU) for heater, valve, and rotor electrostatic charge control and thermometry, 5) the custom GPS receiver for orbital position determination and time reference generation, and 6) the Gas Management Assembly (GMA) that controls and routes the gaseous helium used for initial gyroscope spin-up. Contingent upon a successful launch of Gravity Probe on April 17 2004, preliminary performance results will be presented along side the predicated performance estimates derived from system analysis and test on the ground prior to launch.