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

simply stopping the timeline (halting execution of the command setcurrently loaded into the computer) to automatically rebooting thecomputer. These changes ensure that if the error occurs in a memorylocation that increments the error counter at 10 Hz, the computer willautomatically reboot immediately, rather than possibly freezing upand waiting for up to 8 hours for an “aliveness” test to trigger a reboot.13 MAY 2005—GRAVITY PROBE B MISSIONUPDATEMission Elapsed Time: 388 days (55 weeks/12.72 months)Science Data Collection: 259 days (37 weeks/8.49 months)Current Orbit #: 5,726 as of 5:00 PM PSTSpacecraft General Health: GoodRoll Rate: Normal at 0.7742 rpm (77.5 seconds per revolution)Dewar Temperature: 1.82 kelvin, holding steadyCommand & Data Handling (CDH): B-side (backup) computer incontrol, Multi-bit errors (MBE): 0, Single-bit errors (SBE): 9 (dailyaverage)Our telescope pointing and guide star capture times continue to beexcellent. The Experiment Control Unit continues to remain offduring most orbits, resulting in reduced noise in the SQUID ReadoutElectronics system (SRE). Once a week, we power the ECU back on fora few hours in order to obtain and check certain readouts, such as thedewar temperature, that are provided by the ECU.The NASA Distinguished Public Service Medal is awarded to anindividual whose distinguished accomplishments contributedsubstantially to NASA's mission. Contributions must be soextraordinary that other forms of recognition by NASA would beinadequate. This is the highest honor that NASA confers to anindividual who is not a government employee.Because the spacecraft has been in orbit for over a year now, we areable to conduct an analysis of the external temperature and solar arrayefficiencies by comparing current data from these systems with datacollected a year ago.In preparation for the end of the GP-B mission, which is fastapproaching, we have begun delegating tasks to complete our finalmission report, which we will deliver to NASA in July.GP-B PRINCIPAL INVESTIGATOR FRANCIS EVERITTHONORED BY NASAFollowing is a copy of the press release we sent out earlier this week,announcing this award.Stanford experimental physicist Francis Everitt has been awarded aNASA Distinguished Public Service Medal. NASA Deputy DirectorFred Gregory presented the medal to Everitt on April 27 at an awardsceremony at NASA Headquarters in Washington, D.C. Everitt isprincipal investigator of the Gravity Probe B (GP-B) experiment, acollaboration between Stanford University, NASA and LockheedMartin Corp. that is testing predictions of Albert Einstein's 1916general theory of relativity (his theory of gravitation) by means of fourultra-precise gyroscopes that have been orbiting the Earth in a satellitefor just over a year.Everitt obtained his doctorate at the University of London (ImperialCollege) in 1959 for research under Nobel laureate P. M. S. Blackett.He then spent two years at the University of Pennsylvania working onliquid helium. In 1962, Everitt joined William Fairbank and LeonardSchiff in the Stanford Physics Department as the first full-timeresearch worker on the GP-B experiment. His efforts advanced thestate of the art in the areas of cryogenics, magnetics, quantum devices,telescope design, control systems, quartz fabrication techniques,metrology and, most of all, gyroscope technology. His leadership asthe principal investigator for GP-B advanced the GP-B program fromthe concept and technology development stages to the experiment'slaunch on April 20, 2004, and its ensuing orbital operations.“None of us at the beginning had any idea how long it would take forthe GP-B spacecraft to fly and take the science data,” Everitt said whenasked about the long life of the project. “But speaking for myself, Ihave never been bored.”Gravity Probe B was developed on the Stanford campus in the W. W.Hansen Experimental Physics Laboratory (HEPL). The current onorbitGP-B mission operations center (MOC) is located in HEPL,where the science data is currently processed as well. From the MOC,the GP-B spacecraft is commanded with ground antennas in Alaska orGravity Probe B — Post Flight Analysis • Final Report March 2007 503