Hi,
Here is the Gravity Probe B mission update report for Jan 21, 2005
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GRAVITY PROBE B MISSION UPDATE FOR 21 JANUARY 2005
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GP-B Status At a Glance
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Mission Elapsed Time: 276 days (39 weeks/9 months)
Current Orbit 4,075 as of 4:30PM PST
Spacecraft General Health Good
Roll Rate Normal at 0.7742 rpm (77.5 seconds per revolution)
Gyro Suspension System (GSS) All 4 gyros digitally suspended in science mode
Dewar Temperature 1.82 kelvin, holding steady
Global Positioning System (GPS) lock Greater than 96%
Attitude & Translation Control (ATC) See Mission Director's Summary below
Command & Data Handling (CDH) See Mission Director's Summary below
Telescope Readout (TRE) See Mission Director's Summary below
SQUID Readouts (SRE) See Mission Director's Summary below
Gyro #1 rotor potential -4.4 mV (before solar flare), -3.8 mV (after flare)
Gyro #2 rotor potential 6.0 mV (before solar flare), 6.6 mV (after flare)
Gyro #4 rotor potential -10.7 mV (before solar flare), -9.5 mV (after flare)
Gyro #3 Drag-free Status Backup Drag-free mode (normal)
Gyro #3 rotor potential 1.5 mV (before solar flare), 1.4 mV (after flare)
Mission Director's Summary
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We are in the process of recovering from the effects of 7 major solar flares that have erupted from the Sun's surface since 15 January 2005. These flares have resulted in extremely high levels of proton radiation and two multi-bit errors (MBE) in our SRE electronics. In addition, these high levels of solar radiation saturated the GP-B telescope detectors, causing the telescope to lose track of the guide star (IM Pegasi). We have now re-locked the telescope onto the guide star. We have determined that one of the MBEs in the SRE electronics is in a non-critical location, but the second one is in a location that is used for SQUID calibration. We are in the process of creating a work-around for the second MBE location. Our science team reports that the loss of data from these events has been minimal, and that it will have no significant effect on the experimental results.
Mission News
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Yesterday, the National Oceanic & Atmospheric Administration's (NOAA) Space Environment Center (SEC) issued the following advisory bulletin:
STRONG SOLAR FLARE AND RADIATION STORM
Active solar Region 720 produced a powerful X7 flare (R3 radio blackout) today at 0701 UTC (00:01 A.M. MST). This is the largest of seven major flares observed in this large and complex sunspot cluster since it emerged as a major flare producer on 15 January.
A strong (S3) radiation storm began soon after this flare. Radiation storms on the NOAA scale are based on proton measurements at >10 MeV. However, this radiation storm is particularly interesting because of the influx of high energy protons (>100 MeV). In fact, this radiation storm, based on the >100 MeV protons, is the strongest since October 1989. A rare, strong ground-level event (GLE) was also observed. GLEs are increases in the ground-level neutrons detected by neutron monitors and are generally associated with very high energy protons (>500 MeV). Elevated neutrons at ground level means there are high fluxes of energetic protons near Earth. High energy radiation storms can be particularly hazardous to spacecraft, and to communication, navigation, and aviation operations at high latitudes.
The 7-day graph of proton activity, displayed on our GP-B Web site, clearly shows the very large increase in proton radiation that has been detected over the past few days, as a result of this solar flare and the subsequent radiation storm. In particular, notice the huge increase in high-energy protons (>100 MeV), represented by the green line in the graph on 20 January 2005. This level of high-energy protons is almost 100 times greater than the high-energy bombardment that accompanied the solar storm of 7 November 2004 (shown for comparison in the adjacent chart on our GP-B Web site.)
This extraordinarily high level of proton bombardment saturated the GP-B telescope detectors, causing the telescope to become unlocked from the guide star. Also notable was a huge increase in single-bit errors (SBE)-81 in a 24-hour period, where the norm is around 9 SBEs per day. (SBEs are self-correcting; MBEs must be corrected by re-loading the affected memory location.) This is the first time that we can confirm an obvious correlation between solar activity and SbEs and MBEs in various electronic systems on-board the GP-B spacecraft. Moreover, NASA reports that other satellites were also affected by this event. As was the case last November, these solar flares triggered a severe geomagnetic storm here on Earth, and Norway has reported seeing a beautiful Aurora.
As of today, the solar activity is continuing, but the levels of proton bombardment appear to be decreasing. The GP-B telescope is now re-locked on the guide star, and the Attitude and Translation Control System (ATC) is once again performing nominally. Performance of the SRE electronics appears to be unaffected by the two MBEs sustained in its memory locations, and we are continuing to keep a watch on it. The net effect of this event on the experimental results appears to be negligible-although, it did keep a number of GP-B staff members very busy this past week.
For more information about this past week's solar storm, see the following Web sites:
National Weather Center Space Environment:
http://www.sec.noaa.gov/NASA/ESA SOHO-Exploring the Sun--Web site:
http://soho.nascom.nasa.gov/NASA Sun-Earth Real-time Viewer:
http://sunearth.gsfc.nasa.gov/sunearthday/media_viewer/flash.htmlNASA Exploring the Universe-Our Solar System, 19 January 2005 News:
http://www.nasa.gov/vision/universe/solarsystem/jan_flares.html.
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CLARIFICATION TO LAST WEEK'S UPDATE
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After reading last week's update, several people did some quick calculations and emailed us saying that there is no way that 185 MB of data, stored in the Solid State Recorder (SSR) on-board the spacecraft, could be transmitted to a ground station in 12 minutes at 32 Kbps. This is true. During ground passes, the on-board computer cannot write to the SSR, so the real-time telemetry data is interleaved with the stream of stored data from the SSR that is being downloaded to the ground station. The stored SSR data is downloaded at 5.12 dual-encoded Megabits per second (0.64 Megabytes per second), whereas the interleaved real-time data can only being transmitted at 32Kbps. Thus, the term "32K" refers to this 32Kbps rate at which the real-time data that is being streamed from the spacecraft's computer directly to the GP-B Mission Operations Center (MOC) here at Stanford.
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NASA - Stanford - Lockheed Martin
Gravity Probe B Program
"Testing Einstein's Universe"
http://einstein.stanford.eduBob Kahn
Public Affairs Coordinator
Phone: 650-723-2540
Fax: 650-723-3494
Email: kahn@relgyro.stanford.edu
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Regards,
LelandJ
