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

6.5 Final Integrated Testing, Launch & Science Mission(2002-2005)In November 2002, Gaylord Green became Program Manager. During 2001-2002, Green, who had considerableprior spacecraft operations experience—including working with Parkinson on the development anddeployment of the U.S. Air Force’s Global Positioning Satellite System—had been responsible for organizing theground support operations for GP-B at the Vandenberg Air Force Base launch site on the southern Californiacoast. At the time he assumed the job of Program Manager, the spacecraft was being prepared at LockheedMartin for a thermal vacuum test—a ground simulation of the conditions that the spacecraft would encounterin orbit.6.5.1 The Thermal Vacuum TestBefore the thermal vacuum test began, the LM mechanical team inadvertently left some unshielded wires restingagainst the spacecraft. Then, on the next shift, when the electronics team powered up the spacecraft for theelectronics test, four fuses blew, preventing heater strips from being powered. Thus, during the thermal vacuumtest at the cold temperatures of space, the associated heaters were not turned on and certain parts of thespacecraft were too cold. Also, a vent on the dewar's guard tank leaked into the thermal vacuum chamber,degrading the vacuum.With the launch date now set for December 2003, and what appeared to be yet another possible problem withthe spacecraft, NASA Headquarters convened yet another program review to determine whether to proceedtowards launch or cancel the program. Both the NASA Independent Review Team and the GP-B ScienceAdvisory Committee recommended that GP-B continue with launch preparations. To ensure minimal risk,NASA decided to repeat the thermal vacuum test following a spin balance test early in 2003. The second thermalvacuum test was performed in May 2003 without issue. Shortly thereafter, in July 2003, the spacecraft wasloaded aboard a special truck and driven to the launch complex at Vandenberg Air Force Base.Back at Stanford, throughout the latter part of 2002 and most of 2003, the GP-B Mission Operations Center andthe mission operations team worked very hard, preparing for launch. Under Green's management, a total ofseven procedural simulations were held to rehearse the GP-B mission operations team both for launch and foran unusually sophisticated initialization and orbit checkout period. Rehearsals for dealing with a number ofpotential anomalies that could occur on orbit were included in these simulations.6.5.2 Six-Month Launch Postponement for ECU RepairIn early November 2003, as part of a final spacecraft acceptance review, a grounding problem was discovered ina voltage converter on the Experiment Control Unit (ECU). The ECU was essential for gyro spinup and dewarmonitoring, but not for collecting experimental data. Stanford's recommendation was to turn off the ECUduring the actual science experiment, but LM recommended repairing it. NASA Headquarters then had to makea difficult go/no-go decision. This was the ultimate risk management decision, and not wanting to possiblyjeopardize the experimental results, NASA Headquarters reluctantly decided to postpone the launch for 5-6months so that the ECU could be returned to LM for correction of the voltage converter problem.6.5.3 Successful Launch and Flight MissionModifications to the ECU were completed in March 2004, and the ECU was then shipped back to Vandenbergand reinstalled on the spacecraft frame. A new launch date was set for mid April, and a pre-launch pressconference was held at NASA Headquarters at the beginning of April. The GP-B team, which at that timeincluded people from LM and NASA and totaled close to 200 people was primed and ready when GP-B finallylaunched on April 20, 2004. It was a flawless launch.Gravity Probe B — Post Flight Analysis • Final Report March 2007 163