Performance of the relativity mission superfluid helium flight dewar Original Research Article

The worldʹs largest capacity helium flight dewar has been assembled for use on the Relativity Mission, also known as Gravity Probe-B (GP-B). Acceptance tests performed include (1) weight, (2) proof pressure and leak checks, (3) vacuum bakeout, (4) main tank fill with He I, (5) parasitic heat rate tests, (6) well fill with He I from both the main tank and an external supply dewar, (7) well depletion, (8) conditioning the main tank to He II, (9) porous plug tests, (10) heat pulse meter tests, (11) transferring He II from the main tank to the well with a fountain-effect pump, (12) guard tank fill with He I with a nonvented He II main tank simulating launch pad hold, and (13) guard tank emptying. The measured performance is compared to the previously launched IRAS, COBE, and ISO cryostats. The Relativity Mission spacecraft will be launched in the time span 1999 to 2000.