Gravity Probe B

The Gravity Probe B satellite is designed to measure the geodetic and motional effects on four gyroscopes in a polar orbit at an altitude of 650 km. The magnitude of the precessions predicted by the General Theory of Relativity are 6.6 are sec/yr for the geodetic effect and 42 milli-arc-sec/yr for the motional effect. The goal of the experiment is to measure the geodetic effect to several parts in 10(5) and the motional effect to better than 1%. A significant decrease in the drift rates due to classical torques may be made by placing the gyroscopes in a drag-free satellite. To take advantage of this improvement in the accuracy careful attention must be paid to support independent torques, gyroscope and telescope readout errors, and the uncertainty in the proper motion of the reference star. The experimental approach, potential sources of error, and progress toward reducing potential sources of error in the construction of flight hardware are described.