NASA Gravity Probe B Mission Update January-February 2007
GP-B DATA ANALYSIS STATUS
Note: A more complete status overview of the GP-B data analysis process & results announcement is posted at the top of our GP-B Home page: http://einstein.stanford.edu. Following is a brief summary of our activities and accomplishments during the past few months, and a summary of our plans to announce the results of GP-B.
Since the meeting with our Science Advisory Committee last September (SAC meeting #15), we have been proceeding through Phase III of the data analysis, in which the data from all four gyros is being integrated over the entire experiment. During this final analysis phase, we are continuing to pursue both geometric and algebraic interpretations of the data, which is enabling us to make further improvements in the accuracy of the results. Now that the gyro polhode behavior is well understood (see our November 2006 Mission News Story at http://einstein.stanford.edu/highlights/hl_polhode_story.html), we have been able to shift our focus to identifying and addressing some subtle systematic sources of noise and interference that are buried in the data, along with the relativity signals. Identifying and removing as many of these subtle systematic effects as possible is critically important for reducing the margin of error in our final results–especially the frame-dragging result. While we have been making steady progress in these efforts, it has proven to be a slow and painstaking process, and it is now apparent that several more months of data analysis will be required to achieve the lowest possible margin of error.
At the SAC meeting #15 last September, committee members anticipated this situation and recommended that we ask NASA to create a contingency plan, and budget for an extension of the data analysis phase for several months past our scheduled results announcement at the American Physical Society (APS) meeting on 14-17 April 2007 in Jacksonville, FL. To this end, following a meeting with NASA in mid January, NASA has requested a proposal for extending the GP-B data analysis phase through December 2007, and this is in progress.
Consequently, we are now planning a two-phase announcement of the GP-B results. Our first announcement will be made at the April APS meeting, as planned for some time now. (For more information about our presentations at this meeting, see this month’s GP-B Mission News story below.) In conjunction with this announcement, NASA is planning a press/media event at NASA Headquarters in Washington DC just prior to the APS meeting. The experimental results in this first announcement will have been presented to and vetted by our Science Advisory Committee during SAC meeting #16, which is scheduled for 23-24 March 2007. These will be preliminary results, representing the lowest margin of error obtainable by that date.
Concurrent with this preliminary results announcement in April, we will be releasing an initial science data set to the National Space Sciences Data Center (NSSDC) at Goddard Space Flight Center in Greenbelt, MD. The remainder of our science data, along with a complete archive of GP-B documents, images, video, and related program information will be released to the NSSDC by the end of May. All GP-B data and information archived at the NSSDC will be publicly available.
Following the APS meeting, our science team is planning to spend several more months removing further systematic sources of noise and interference, with the goal of reducing the margin of error in the result to the lowest possible level. These results will still be relative to the position of our guide star, IM Pegasi, which changed continually throughout the experiment. This proper motion of the guide star has been measured on our behalf by the Harvard-Smithsonian Center for Astrophysics (CfA). Thus, the final step in the analysis will be to combine our gyro spin axis orientation results with data mapping the proper motion of IM Pegasi relative to the unchanging position of a distant quasar.
In late fall, 2007, playing the role of our own harshest critic, our science team will perform a careful and thorough final review of the analysis and results, checking and cross-checking each aspect to ensure the soundness of our procedures and the validity of our outcomes. We will then convene a final SAC meeting to obtain the committee’s independent review of the final results. Moreover, we will seek independent reviews from a number of international experts.
We intend to announce the final experimental results of GP-B through a NASA press/media event towards the end of 2007. At that time it is also our intention to have submitted a number of papers on the GP-B results for publication in peer-reviewed scientific and technical journals.
GP-B SPACECRAFT & MISSION STATUS
The GP-B space vehicle and payload continue to remain in good health. All active subsystems, including solar arrays/electrical power, Experiment Control Unit (ECU), flight computer, star trackers, magnetic sensing system (MSS) and magnetic torque rods, gyro suspension system (GSS), and telescope detectors, are performing nominally.
The spacecraft remains in a hibernation state. We are continuing to monitor the health status of the spacecraft on a weekly basis and archiving the status data, but we no longer performing any significant operations on the vehicle or its payload.
The United States Air Force Academy (USAFA) has begun conducting training for staff and cadets on the operation of the spacecraft. Members of our GP-B Mission Operations Team are continuing to support the USAFA to help them get their Mission Operations Center up and running.
GP-B MISSION NEWS
The GP-B Results Announcement & Presentations at the APS Meeting in April
GP-B will have a strong presence at the American Physical Society (APS) meeting in Jacksonville, Florida, on 14-17 April 2007. During this meeting, we will emphasize three main themes:
— Successful completion of most challenging space-based experiment in NASA’s history
— First scientific results from this historic mission
— Public release of Level2 science data (via NSSDC)
Four members of the GP-B team have been invited to speak at the APS meeting, beginning on Saturday morning, April 14th, with GP-B Principal Investigator, Francis Everitt, giving the plenary conference talk, entitled First Results from Gravity Probe B.
In addition, on Saturday afternoon, two papers related to GP-B will be delivered in Session C12: Experimental Tests of Gravity.
— C12.00004: “Lessons Learned from Gravity Probe B for STEP, LISA and other experiments” by GP-B team members Paul Worden and Sasha Buchman
— C12.00005: “Proper Motion of the GP-B Guide Star” by the Harvard-Smithsonian Center for Astrophysics Gp-B guide star tracking team: Irwin Shapiro, Daniel Lebach, Michael Ratner, Norbert Bartel, Ryan Ransom, Michael Bietenholz, Jerusha Lederman, and Jean-Francois Lestrade
On Sunday morning, April 15th, three members of the GP-B team have been invited to give special talks on three aspects of the GP-B program:
— H7.00001: “The Gravity Probe B Science Instrument,” by GP-B Co-Principal Investigator, John Turneaure
— H7.00002: “The Development Challenges of Gravity Probe-B–an ongoing partnership between Physics and Engineering” by GP-B Co-Prinipal Investigator, Bradford Parkinson
— H7.00003: “Gravity Probe B Data Analysis Challenges, Insights, and Results” by GP-B Co-Investigator and Chief Scientist, George (Mac) Keiser
Finally, on Sunday afternoon, April 15th, a large part of the GP-B team and associated scientists and engineers will present 22 poster sessions on a host of scientific and technology topics, as listed below.
Session L1: Poster Session II L1.00011: GRAVITATION
— L1.00012: “Radio Imaging of the Gravity Probe B Guide Star IM Pegasi” by Michael Bietenholz, Ryan Ransom, Norbert Bartel, Daniel Lebach, Michael Ratner, Irwin Shapiro, Jean-Francois Lestrade — L1.00013: “The ‘Core’ of the Quasar 3C454.3 as the Extragalactic Reference for the Proper Motion of the Gravity Probe B Guide Star” by Norbert Bartel, Ryan Ransom, Michael Bietenholz, Jerusha Lederman, Daniel Lebach, Michael Ratner, Irwin Shapiro, Leonid Petrov
— L1.00014: “Performance of the Gravity Probe B Inertial Reference Telescope” by Suwen Wang, John Goebel, John Lipa John Turneaure
— L1.00015: “Gravity Probe B Timing System and Roll Phase Determination” by Jie Li , Jeffery Kolodziejczak
— L1.00016: “The Gravity Probe B SQUID Readout Detector” by Barry Muhlfelder, Bruce Clarke, Gregory Gutt, James Lockhart, Ming Luo
— L1.00017: “SQUID Control, Temperature Regulation, and Signal Processing Electronics for Gravity Probe B” by James Lockhart, Barry Muhlfelder, Jie Li, Bruce Clarke, Terry McGinnis, Peter Boretsky, Gregory Gutt
— L1.00018: “Gravity Probe B Science Instrument Assembly (SIA)” by Saps Buchman, Barry Muhlfelder, John Turneaure
— L1.00019: “Polhode Motion of the Gravity Probe-B Gyroscopes” by Michael Dolphin, Alex Silbergleit, Michael Salomon, Paul Worden, Daniel DeBra
— L1.00020: “Evidence for Patch Effect Forces on the Gravity Probe B Gyroscopes” by Dale Gill, Saps Buchman
— L1.00021: “Gravity Probe B Orbit Determination” by Paul Shestople , Huntington Small
— L1.00022: “Simulator Technology of the Gravity Probe-B Mission” by David Hipkins , Robert Brumley , Yoshimi Ohshima , Thomas Holmes
— L1.00023: “Achievement of the Magnetic Environment Requirements for Gravity Probe B” by John Mester, James Lockhart, Michael Taber
— L1.00024: “The Gravity Probe B Gyroscopes” by Saps Buchman, Bruce Clarke, Mac Keiser, Dale Gill, Frane Marcelja, Robert Brumley
— L1.00025: “Gravity Probe B Gyroscope Electrostatic Suspension System (GSS)” by William Bencze, David Hipkins, Tom Holmes, Saps Buchman, Robert Brumley
— L1.00026: “The Gravity Probe B Relativity Mission (GP-B)” by C.W. Francis Everitt
— L1.00027: “Gravity Probe B Experiment Error” by Barry Muhlfelder, G. Mac Keiser, John Turneaure
— L1.00028: “Gravity Probe B Science Data Analysis: Filtering Strategy” by Michael Heifetz, Thomas Holmes, David Hipkins, Alex Silbergleit, Vladimir Solomonik
— L1.00029: “Performance of the Gravity Probe B Cryogenic Sub-System” by Michael Taber, David Murray
— L1.00030: “The Gravity Probe B Drag-free and Attitude Control System” by Michael Adams, Daniel DeBra
— L1.00031: “Features of the Gravity Probe B Space Vehicle” by William Reeve, Gaylord Green
— L1.00032: “Classical Torques on Gravity Probe B Gyroscopes” by Alex Silbergleit, G. Mac Keiser, Yoshimi Ohshima
— L1.00033: “Trapped Flux Mapping for the Gravity Probe B Gyroscopes” by Michael Salomon, John Conklin, Michael Dolphin, G. Mac Keiser, Alex Silbergleit, Paul Worden
NEXT SCHEDULED GP-B UPDATE AT THE END OF MARCH 2007
Our next regularly scheduled update will be towards the end of March, following SAC meeting #16. Of course, we will send out a timely update if noteworthy events occur here at GP-B in the meantime.
PREVIOUS GP-B UPDATES
If you wish to read any of our previous updates, our GP-B Web site includes a chronological archive of all the updates/highlights (with photos and drawings) that we have posted over the past 8 years: http://einstein.stanford.edu/highlights/hlindexmain.html
OTHER LINKS THAT MAY INTEREST YOU
– Our GP-B Web site, http://einstein.stanford.edu contains lots of information about the Gravity Probe B experiment, general relativity, and the amazing technologies that were developed to carry out this experiment.
– Video and/or audio of May 18, 2006 public lecture by Principal Investigator, Professor Francis Everitt, on GP-B. You can view a streaming video of the lecture in your Web browser: http://einstein.stanford.edu/highlights/hl_video_everitt051806.html. You can also download either a video or audio only copy of the lecture to an iPod from the Stanford University iTunes U Web site: http://itunes.stanford.edu, This Web page automatically launches the Apple iTunes program on both Macintosh and Windows computers, with a special Stanford on iTunes U “music store,” containing free downloads of Stanford lectures, performances, and events. Francis Everitt’s “Testing Einstein in Space” lecture is located in the Faculty Lectures section. People with audio-only iPods can download the version under the Audio tab; people with 5th generation (video) iPodfs can download the version under the Video tab.
– Visual tour of the GP-B spacecraft and payload from our GP-B Web site: http://einstein.stanford.edu/content/vehicle_tour/index.html
– PDF file containing a 1/20 scale, paper model of the GP-B spacecraft that you can download print out, and assemble: http://einstein.stanford.edu/content/paper_model.
– NASA’s Marshall Space Flight Center also has a series of Web pages devoted to GP-B: http://www.gravityprobeb.com
– The Harvard-Smithsonian Center for Astrophysics (Cambridge) and York University (Toronto), with contributions from the Observatoire de Paris, have been studying the motions of the guide star, IM Pegasi for over a decade. To find out more, visit: http://www.yorku.ca/bartel/guidestar/
– In addition, you’ll find information in the Guide Star FAQ on our Web site: http://einstein.stanford.edu/content/faqs/faqs.html#guidestar and on pages 18-20 of the Gravity Probe B Launch Companion: http://einstein.stanford.edu/highlights/GP-B_Launch_Companion.pdf
– The Einstein Exhibition at the Skirball Cultural Center in Los Angeles has closed.However, you can visit the American Museum of Natural History’s virtual Einstein exhibit on the Web at: http://www.skirball.org/exhibit/amnh_frame.html
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