The telescope readout electronics for the gravity probe B satellite

dThe pointing and stability requirements for the Gravity Probe B (GP-B) Relativity Mission pose a number of challenges for the star-tracking electronics. Because the telescope-gyroscope assembly operates at 2.8 K, the detector circuit's Si JFETs at the telescope focal plane must be thermally isolated and heated to at least 50 K through self-heating or with the aid of heating resistors. We have designed a low noise, thermally stable photodetector circuit that meets the GP-B requirements as well as fabricated an isolator to give the required thermal isolation and mechanical stability. Test results of the detector - isolator assembly are presented.