Status of the cryogenic telescope and guide star for Gravity Probe B Original Research Article

We describe the status of the development and testing of the star tracking telescope for Gravity Probe B. The fused quartz telescope with an aperture of 14 cm and 3.8 m effective focal length is attached to the gyroscope housing and continuously points to a guide star. A star image divider assembly in conjunction with cryogenic photo detectors is used to provide quadrant pointing information which is used to maintain the attitude of the spacecraft. Development and testing of the flight telescope has been completed. The optical test results will be discussed.