GP-B Post-Flight Analysis—Final Report - Gravity Probe B - Stanford ...

Figure 13-45. A Bottom View of the GMA Showing the Supply Tanks and Outlet Valves13.5.2 Pre-Launch Ground SupportThe GMA was built by Moog, Inc. in Buffalo New York. The latch valves had a gas leakage specification of < 1x10 -7 std cc/second. Most of the latch valves met this requirement, though some valves leaked at as high as 1x 10 -4std cc/second. Some of the valves that did not meet the specification were the four vent valves that vented theGMA to space. The concern of these valves leaking on the ground was that “air” could leak back into the GMAthat would contribute cryogenic contamination into the science probe during spin-up. A mitigation plan wasdeveloped by Stanford to back fill the GMA with 300 psia of ultra pure helium (See Figure 13-46 below) up tothe pressure regulators to ensure a minimal risk of cryogenic contamination of the SIA (science instrumentassembly). Fill and Drain valves, as shown in Figure 13-48 below, were installed between the GMA and theProbe inlets to minimize cryo contamination from entering into the Probe.392 March 2007 Chapter 13 — Other Payload Subsystems Analyses