The role of cryogenics in the gyroscope experiment

We discuss the design of apparatus being built to measure the general relativistic precession of gyroscopes in earth orbit, with emphasis on the role of cryogenics. Operation with a superconducting rotor is crucial in that it provides the only known way of attaining the required angular resolution of 0.001 arc-sec. Operation at low temperatures also provides the star tracker, to which the gyros are referenced, with excellent null stability. The boil-off gas from the large helium dewar is used to operate the vehicle in a drag-free mode which is expected to improve the gyro performance by a factor of ten. The dewar system is compatible with a wide range of experiments requiring temperatures as low as 2K in space.