Control of fluid mass center in the Gravity Probe B space mission Dewar

Gravity Probe B was a cryogenic, space-based mission that successfully measured two effects predicted by general relativity. The mission required a 2400 l liquid helium Dewar. In this paper we describe the design and performance of the approach taken to control the distribution of the liquid in the Dewar on-orbit. Such an approach may be applied to other spacecraft containing significant liquid mass.