Hi,
Here is the latest update of the Gravity Probe B Mission.
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GRAVITY PROBE B MISSION UPDATE FOR 17 DECEMBER 2004
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As we near the end of 2004, the GP-B spacecraft has been in orbit for just under eight months and collecting science data for almost four months. It remains in fine health, and all subsystems are continuing to perform well. The spacecraft is beginning to experience brief periods of being eclipsed from sunlight by the Earth during each orbit, signaling that its recent full-sun season is waning. It is flying drag-free around gyro #3, maintaining a constant roll rate of 0.7742 rpm (77.5 seconds per revolution.) The temperature inside the Dewar is holding steady at just under 1.82 kelvin. Recent measurements indicate that approximately half of the superfluid has now been expended from the Dewar. All four gyros are digitally suspended in science mode. We are now approximately 40% of the way through the science phase of the mission. The data collection process is continuing to proceed smoothly, and the quality of the data remains excellent.
A GP-B RETROSPECTIVE OF 2004
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Looking back, 2004 has been a year of monumental triumph for GP-B. The year began with a re-work of the Experiment Control Unit (ECU), and its subsequent reinstallation into the space vehicle.
At the beginning of April, as the space vehicle was being readied for launch, the official GP-B pre-launch press conference was held at NASA headquarters in Washington DC. (You can view a streaming video of this press conference, which includes many technical details about the GP-B science experiment and technology, on the Web at:
http://www.ksc.nasa.gov/elvnew/gpb/index.htm.)
Three weeks following the press conference, at 9:57 am PST on 20 April 2004, a Boeing Delta II rocket carried the GP-B spacecraft, embodying over 40 years of dogged persistence in science and engineering, into a perfect orbit. That emotionally overwhelming day, culminating with the extraordinary live video of the spacecraft separating from the second stage booster meant, as GP-B Program Manager Gaylord Green put it, "that 10,000 things went right." The GP-B launch will long be remembered--not only by GP-B Principal Investigator, Francis Everitt, and the GP-B team, but also by thousands of people who have been associated with GP-B in one way or another over the years and countless others who have been following it.
The launch was the "end of the beginning" for GP-B. The ensuing 4-month IOC period demonstrated the exceptional preparedness and dedication of the GP-B team, from dealing with anomalies in orbit to spinning up the four gyros last August, which following the launch, was the second greatest milestone in the program.
Now, four months into the 10-month science phase of the mission, our whole GP-B team can reflect back on the past year with an enormous sense of pride and accomplishment. And, as we look forward to the coming year, we are keenly aware of our continued responsibility to see this once-in-a-lifetime experiment through to its final conclusion.
WEEKLY UPDATES SCHEDULE
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This is the last of our scheduled Weekly Updates for 2004. Stanford University--and most of our GP-B staff--is officially on holiday for the next two weeks. However, our Mission Operations Center (MOC) will continue to operate around the clock. Should an unexpected critical event occur during this period, we will post a special update. Otherwise, we will resume these regular updates on 7 January 2005.
THE MOC BEFORE CHRISTMAS
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We leave you with a GP-B twist on the poem, "The Night Before Christmas," composed by GP-B/Lockheed Martin Poet Laureate, David Spencer. (A jargon/names/acronym glossary follows the poem.)
T'was the night before Christmas, when all through the MOC
Not a creature was stirring, not even the clock
The pass plans were done by the console with care
Waiting for TDRS or GN so fair
The ARB was all nestled all snug in their beds
While visions of science danced in their heads
And Francis in his kerchief and Brad in his cap
We'd all settled in for a two-week lapse
When on RTWorks there arose such a color
I sprang from my chair to see what was the matter
Away to the console I flew like a flash
Popped open the screen and my face went all ash
The lights on the screens of the SGI stations
Gave the luster of satin to all variations,
When what to my wondering eyes should appear
But a red limit change, my heart grew in fear
With a number of limits going out of their way
I knew in a moment I'd need help on this day
More rapid than eagles I picked up the phone
And dialed and dialed the ARB at their homes
Now Benzce, now Mester, and Muhlfelder too
On Gaylord! On Surzyn and Shestople too!
To the top of the stairs, to the top of the MOC
Now dash away, dash away, dash, do not walk!
As old PPCRs before the wild ARB fly
When met with an obstacle, mount to the sky
So up to the MOC the ARB they did fly
With thoughts of a safemode, and no reason why
And then in a twinkling I heard on the stairs
The prancing and pawing at the lock with no care
As I drew up my head and was turning around
In came the ARB with almost no sound
They were dressed in their jammies, from their heads to their toes
And their hair was all tousled, that's how it goes
A bundle of papers were held tight in their hands
And they looked very nerdy, without any tans.
Their eyes didn't twinkle, their faces were gray
Their cheeks were all saggy, no dimples I say
Their mouths were drawn tight like a nice Christmas bow
And the hair on their chins had started to grow
A folder of plans they held tight in their arms
Was it answers I needed to fix the alarms?
No coffee was made; I'd drunk it all up
They were groggy at best, I said, "Wassup?"
They walked by me quickly, just like an elf
And I laughed when I saw them, in spite of myself
With that look on their faces and a nod of their heads
Soon gave me to know I had nothing to dread
They spoke not a word, but went straight to their work.
And filled out the forms, then turned with a jerk
They gave me THE PLAN, the guy who was there
And giving a nod, they said "Have a care"
The problem was solved; in my heart I was glad
That the ARB all came in, it wasn't so bad
And I heard them exclaim, ere they drove out of sight
This could've waited until morning's light!
Glossary of Jargon, Names & Acronyms Used in the Poem
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MOC Mission Operations Center
TDRS NASA Tracking & Data Relay Satellite
GN NASA's satellite telemetry Ground Network
ARB GP-B Anomaly Review Board
Francis Francis Everitt, GP-B Principal Investigator
Brad Brad Parkinson, GP-B Co-PI
RTWorks Computerized spacecraft status report
SGI Silicon Graphics Inc. computer workstation
Bencze Bill Bencze, Deputy Program Mgr. & ARB coordinator
Mester John Mester, Mission Director & ARB member
Muhlfelder Barry Muhlfelder, Deputy Program Mgr. & ARB member
Gaylord Gaylord Green, Program Manager
Surzyn Joe Surzyn, Lockheed Martin ARB coordinator
Sheltopl Paul Shestopl, Mission Director & ARB member
PPCR [Telemetry] Pass Plan Change Request
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CLARIFICATIONS & CORRECTIONS TO LAST WEEK'S UPDATE
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For readers who are interested, GP-B Deputy Program Manager, Bill Bencze, has provided a more detailed and technical explanation of the cause of the GPS anomaly reported last week.
The GPS system generated an extremely large velocity spike for a short period, due to a combination of bad constellation geometry and the internal dynamics of the satellite selection algorithm in the GPS receiver. This velocity information was then used by the ATC processing to generate an estimate of the orbital parameters of the spacecraft. These large velocity estimates were squared and then multiplied by other large numbers that ultimately exceeded the range of a "short floating point" number in the processor (roughly 3x10^38) -- generating a floating point exception. Multiple exceptions were generated because these large velocity estimates were used a number of times in the calculation. This sort of processor exception is an unexpected -- though not unplanned for -- occurrence since the software is very carefully tested; such exceptions may generally indicate a serious problem with the processor. A safemode was programmed to trigger on 5 events within 5 seconds, which it did in this case, to filter out a single, occasional exception. This is safe, conservative position to maintain the overall health of the vehicle while providing safing in the event of a large processor fault. The triggering of this safemode then led to a chain reaction triggering of three other safemodes.
Last week's update had a couple of typographic errors and a homonym error: Svalbard is the correct spelling of the town in Norway where one of our ground tracking stations is located. In the third paragraph, the word "it's" should have been "its," and our MOC was "teeming," not "teaming" with activity. Many thanks to subscribers who reported these errors.
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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
