Payload and Spacecraft Technology for GP-B

Abstract Gravity Probe B is an extremely precise space experiment which will test Einstein's General Theory of Relativity. The cryogenic probe, dewar and spacecraft provide the stable platform and the rigorous environmental conditions necessary for the science instrument to make its demanding measurements. This paper discusses payload and spacecraft technologies developed for Gravity Probe B which also have applicability to future cryogenic space missions. The technologies described include low-magnetic and ultra-high vacuum materials developed for use within the cryogenic probe. Also described are advances in the design of superfluid helium flight dewars including passive orbital disconnect struts (PODS), composite neck tube, honeycomb vapor cooled shields, light-weighted helium tank and vacuum shell, and a guard tank developed to simplify dewar servicing on the launch pad. Additionally, a high stability mount for the attitude gyros and star tracker, a proportional helium thruster for attitude and translation control, a thruster isolation valve, and a mass trim mechanism for precise on-orbit control of the space vehicle lateral center of mass and products of inertia are described.