Gravity probe B is effectively dead, after having exhausted its superfluid liquid He and taking data for ~ 1 year. Current temperature now likely exceeds 10K and rising (beyond the superconducting critical temp of niobium) with drag-free orbit mode around the quartz gyros switched off. Data analysis begins now and is expected to be complete in one year.

Do anyone know what they are going to do with it?
Can that spacecraft help in anything different of its mission?
Thanks...

They addressed this question in an old weekly update. To quote that update:


My guess is, considering the noise NASA has made about dropping funding for missions like the Voyagers (where the continuing science value is IMHO much larger), an extended mission for GP-B is unlikely.

NASA Science News for November 16, 2005

NASA's Gravity Probe B spacecraft has gathered all the data physicists need to check a bizarre prediction of Einstein's relativity.

FULL STORY at

http://science.nasa.gov/headlines/y2005/16....htm?list161084

Check out our RSS feed at http://science.nasa.gov/rss.xml

Amendment
=================================================
AMENDMENT TO GRAVITY PROBE B MISSION UPDATE FOR 2 DECEMBER 2005
=================================================


STANFORD REPORT NEWS STORY & VIDEO ON GP-B NASA TEAM AWARD
==============================================
This week, Stanford Report, the print and Web publications of the Stanford University News Service, published a brief story, along with a nicely done Web Video about the special Group Achievement Award that was presented to the GP-B team by NASA last Wednesday--and which was the subject of our Mission News Story last Friday. Following are links to the Stanford Report story and video:


Story: http://news-service.stanford.edu/news/2005...gpb-120705.html


Video: http://news-service.stanford.edu/news/2005.../videos/79.html



CLARIFICATION TO LAST WEEK'S MISSION DIRECTOR'S SUMMARY
============================================
Because GP-B is perceived as the paragon of precision, it is always a bit embarrassing when I make incorrect or inaccurate statements in our GP-B updates--which was the case in my description last Friday of what our GP-B telescope experts have been investigating in recent weeks.


While our GP-B spacecraft has many extraordinary capabilities, it is not following in the footsteps of the NASA COBE (Cosmic Background Explorer) and WMAP (Wilkinson Microwave Anisotropy Probe) missions to measure dark energy and cosmic background radiation. I have been reading Brian Greene's book, The Fabric of the Cosmos, and the terms "dark energy" and "cosmic background" seem to be emblazoned in my mind (along with Muzak holiday tunes playing in all the stores these days). The correct terms describing our telescope team's investigation are "dark current" and "stellar background." Following is a more accurate version of the paragraph I wrote last week:


Over the past month, our telescope experts have been monitoring data from the telescope detectors, observing their performance as the telescope views the stellar background in the vicinity of our guide star, IM Pegasi. In part, the telescope team is looking for the presence of "dark current," a signal produced by the detectors due to due to infrared and ultraviolet light from the faint stars surrounding IM Pegasi. To this end, they have been periodically cycling the shutter on the spacecraft's sunshade open and closed to observe the difference between current generated by the detectors with no light entering the telescope (shutter closed) and stellar background light entering the telescope (shutter open).


Many thanks to those who brought this to my attention, along with the typo in Bill Fairbank's last name.

=======================================
NEXT SCHEDULED GP-B UPDATE ON DECEMBER 30, 2005
=======================================
Our final regularly scheduled update of 2005 will be at the end of this month. Of course, we will send out a timely update if there are any important changes in the spacecraft's status, or 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

Paper (*cross-listing*): gr-qc/0302026

replaced with revised version Thu, 15 Dec 2005 20:18:40 GMT (11kb)

Title: Resolving the Degeneracy: Experimental tests of the New Self Creation
Cosmology and a heterodox prediction for Gravity Probe B

Authors: Garth A Barber

Comments: LaTex, 15 pages. Correction of the prediction of the GP-B geodetic
measurement to 4.4096 arcsec/yr

The new theory of Self Creation Cosmology has been shown to yield a concordant cosmological solution that does not require inflation, exotic non-baryonic Dark matter or Dark Energy to fit observational constraints. In vacuo there is a conformal equivalence between this theory and canonical General Relativity and as a consequence an experimental degeneracy exists as the two theories predict identical results in the standard tests. However, there are three definitive experiments that are able to resolve this degeneracy and distinguish between the two theories. Here these standard tests and definitive experiments are described. One of the definitive predictions, that of the geodetic precession of a gyroscope, has just been measured on the Gravity Probe B satellite, which is at the present time of writing in the data processing stage. This is the first opportunity to falsify Self Creation Cosmology. The theory predicts a 'frame-dragging' result equal to GR but a geodetic precession of only 2/3 the GR value. When applied to the Gravity Probe B satellite, Self Creation Cosmology predicts an E-W gravitomagnetic/frame-dragging precession, equal to that of GR, of 40.9 milliarcsec/yr but a -S gyroscope (geodetic + Thomas) precession of just 4.4096 arcsec/yr.

\\ ( http://arXiv.org/abs/gr-qc/0302026 , 11kb)

============================================
GRAVITY PROBE B MISSION UPDATE FOR 30 DECEMBER 2005
============================================

GP-B STATUS AT A GLANCE
=============================
Mission Elapsed Time: 619 days (88.4 weeks/ 20.3 months)
--IOC Phase: 129 days (4.2 months)
--Science Phase: 352 days (11.6 months)
--Final Calibration Phase: 43 days (1.3 months)
--Extended Science Phase: 4 days
--Post Mission Phase: 91 days
Current Orbit #: 9,134 as of 4:00PM PST
Spacecraft General Health: Good
Roll Rate: Normal at 0.4898 rpm (2.04 minutes per revolution)
Gyro Suspension System (GSS): All 4 gyros digitally suspended
Gyro Spin Rates: ~0 rpm (spinning slightly due to spacecraft roll)
Dewar Temperature: ~170 K and rising ~0.9 K/day
Global Positioning System (GPS) lock: Nominal
Attitude Control System: Nominal for post-mission operation
Pointing Error: (XY/Pitch-Yaw Axes) 0.39 degrees RMS;
Roll Phase (Z Axis) Error: 7.6 degrees RMS
Telescope Readout: Pointing performance too low to lock onto guide star
Command & Data Handling (CDH): B-side (backup) computer in control
Multi-bit errors (MBE): 3 (Triggered reboot of CCCB Backup Computer on 12/21/05)

MISSION DIRECTOR'S SUMMARY
=======================
On Mission Day 619, the Gravity Probe B vehicle and payload are in good health. All active subsystems, including solar arrays/electrical power, Experiment Control Unit (ECU), flight computer, star trackers and magnetic torque rods, gyro suspension system (GSS), and telescope detectors, are performing nominally. We continue to communicate with the spacecraft regularly, monitoring the Dewar and probe as they continue to warm up, and collecting status data from various instruments on-board.

The temperature inside the Dewar has now warmed to ~170 kelvin, and its rate of temperature rise has slowed to ~0.9 kelvin per day. By comparison, various devices on the exterior frame of the spacecraft are registering average temperatures of ~0 centigrade (~273 kelvin). The temperature inside the Dewar will eventually reach thermal equilibrium with the outside temperature, but its rate of rise will continue to decrease so that it will approach the equilibrium temperature very gradually.

About two weeks ago, having caged and removed static charge from all four gyros, we re-suspended each of them digitally. The digital suspension mode, which was used throughout the flight mission, is computer-controlled and enables the gyro rotors to be positioned with great precision. When the gyro rotors were caged, they were basically spinning with the spacecraft's roll rate, and thus when they were re-suspended, they have continued to spin at that rate (~0.5 rpm). At present, we have no plans to do anything further with the gyros.

On Wednesday 21 December 2005, the CCCB backup computer that is controlling all spacecraft operations sustained three multi-bit errors (MBEs). This triggered an excessive MBE safemode response, which re-booted the backup computer. Having worked through similar scenarios a number of times during the Science Phase of the mission, it took our two-person mission operations team about a day to fully recover from this computer re-boot, eventually returning all spacecraft systems to nominal operation.

It is important to emphasize that at this point in the mission, we are only performing maintenance operations on the spacecraft. Our main focus is analyzing the science data we have collected and finishing our final report to NASA. In this regard, our final report to NASA, which is over 450 pages long, is now in the final stages of completion. Our science data analysis is proceeding according to plan. We are in the process of analyzing approximately 1 terabyte (1,000 gigabytes) of data collected from the spacecraft. Two independent analysis teams here at GP-B are working on the data, frequently comparing their results for both quality control and to ensure the validity of the data analysis algorithms.


The main part of the data analysis is expected to be completed late this summer (July-August 2006). At this point, the Harvard-Smithsonian Center for Astrophysics (CfA) will provide our science team with their ultra-precise measurements of the proper motion of the guide star, IM Pegasi. In the final step of the analysis, our science team will combine the gyroscope results with the CfA proper motion measurements of IM Pegasi to arrive at the final experimental results. These results will then be carefully and critically reviewed by international experts in general relativity and data analysis to ensure that our statement of the effects observed are as accurate as possible. Only after this review is complete--early in 2007--will we make a formal and public announcement about the results of this unprecedented test of General Relativity.


Best wishes from all of us here on the GP-B team for a very happy new year.


=======================================
NEXT SCHEDULED GP-B UPDATE ON JANUARY 27, 2006
=======================================
Our next regularly scheduled update will be at the end of January. Of course, we will send out a timely update if there are any important changes in the spacecraft's status, or 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.


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


Photo, taken through a telescope by Swiss physics teacher and amateur astronomer Stefano Sposetti, of GP-B spacecraft in orbit, passing near IM Pegasi: http://aida.astronomie.info/sposetti




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/....html#guidestar and on pages 18-20 of the Gravity Probe B Launch Companion: http://einstein.stanford.edu/highlights/GP...h_Companion.pdf


Track the GP-B satellite on the Web using NASA's Java-based J-Pass satellite tracking application at: http://science.nasa.gov/realtime/JPass/ Also, you can track the GP-B satellite on Personal Digital Assistants (PDAs) using either the Palm OS or Pocket PC operating systems with software from Big Fat Tail Productions: http://www.bigfattail.com


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


==========================
ABOUT THE GPB-UPDATE EMAIL LIST
==========================
The email distribution list for this GP-B Weekly Highlights update is maintained on the Stanford University email lists server.

To subscribe to this list, send an email message to "majordomo@lists.Stanford.edu" with the command "subscribe gpb-update" in the body of the message (not in the Subject line).

You can unsubscribe at any time by sending an email message to "majordomo@lists.Stanford.edu" with the command, "unsubscribe gpb-update" in the body of the message (not in the Subject line.)


--

**********************************
NASA - Stanford - Lockheed Martin
Gravity Probe B Program
"Testing Einstein's Universe"
http://einstein.stanford.edu


Bob Kahn
Public Affairs Coordinator


Phone: 650-723-2540
Fax: 650-723-3494
Email: kahn@relgyro.stanford.edu
**********************************

2006
============================================
GRAVITY PROBE B MISSION UPDATE FOR 31 JANUARY 2006
============================================

GP-B STATUS AT A GLANCE
=============================
Mission Elapsed Time: 651 days (93.0 weeks/ 21.3 months)
--IOC Phase: 129 days (4.2 months)
--Science Phase: 352 days (11.6 months)
--Final Calibration Phase: 43 days (1.3 months)
--Extended Science Phase: 4 days
--Post Mission Phase: 123 days (17.6 weeks/ 4.0 months)
Current Orbit #: 9,605 as of 5:30 PM PST
Spacecraft General Health: Good
Roll Rate: Normal at 0.4898 rpm (2.04 minutes per revolution)
Gyro Suspension System (GSS): Gyro #1 digitally suspended; Gyros #2, #3, & #4 in analog suspension
Gyro Spin Rates: ~0 rpm (spinning at spacecraft roll rate)
Dewar Temperature: ~195 K and rising ~0.6 K/day
Global Positioning System (GPS) lock: Nominal
Attitude Control System: Nominal for post-mission operation
Pointing Error: (XY/Pitch-Yaw Axes) 0.39 degrees RMS;
Roll Phase (Z Axis) Error: 7.6 degrees RMS
Telescope Readout: Pointing performance too low to lock onto guide star
Command & Data Handling (CDH): B-side (backup) computer in control
Multi-bit errors (MBE): 1 in CCCA Backup computer; 3 in GSS computer

MISSION DIRECTOR'S SUMMARY
=======================
On Mission Day 651, the Gravity Probe B vehicle and payload continue to be in good health. All active subsystems, including solar arrays/electrical power, Experiment Control Unit (ECU), flight computer, star trackers and magnetic torque rods, gyro suspension system (GSS), and telescope detectors, are performing nominally. We continue to communicate with the spacecraft regularly, though less frequently, monitoring the Dewar and probe as they continue to warm up, and collecting status data from various instruments on-board.

The temperature inside the Dewar has now warmed to ~195 kelvin, and its rate of temperature rise has slowed to ~0.6 kelvin per day. The temperature inside the Dewar will eventually reach thermal equilibrium with the outside temperature of ~0 centigrade (~273 kelvin), but this will occur very gradually, over a long period of time.

As a result of the CCCA backup computer re-boot on December 21, 2005, the attitude of the spacecraft shifted approximately 90 degrees, so that instead of pointing in the direction of its orbit, the spacecraft is now pointed broadside or perpendicular to its orbit plane (orbit normal orientation). Because we are no longer tacking the Guide Star, IM Pegasi, there is no need to maneuver the spacecraft back to its Guide Star orientation. Rather, we have been stabilizing the spacecraft in its orbit normal orientation, and we are preparing to reduce its roll rate to 0.04 rpm (25 minutes/revolution) in order to collect sample planet eclipse data from the two star trackers on-board. (See today's Mission News story below for more information about the planet eclipse data and other sample data we will be collecting over the next few weeks.)


Because the spacecraft has been in orbit normal orientation for the past month, its two antennae have been oriented less favorably for communication with the NASA TDRS (Tracking Data Relay Satellite) system and with the NASA ground network tracking stations. Even though the spacecraft's antennae are omni-directional, their optimal transmission/reception path spreads out like a cone towards the front and rear of spacecraft, and their gain is somewhat diminished in the orbit normal orientation. Over the 3-day Martin Luther King holiday weekend of 14-16 January, this diminished antenna communications link, coupled with reduced weekend/holiday monitoring from our Mission Operations center (MOC), triggered a safemode that automatically re-boots the on-board CCCA Backup computer if it does not receive any commands from our MOC within a 36-hour period. We have since recovered from this re-boot.


Another unsurprising consequence of the spacecraft's recent position changes, as well as thermal changes in the quartz block where the gyros are housed, is that the Gyro Suspension System (GSS) automatically transitioned gyros #2, #3, and #4 from digital (highest control) to analog (safe and secure) suspension after the computer re-boot two weeks ago. The ultra-sensitive GSS interprets spikes in rotor position due to thermal stresses during warm-up as excessive gyro motion, and it automatically transitions the suspension mode from digital to analog to ensure the safety of the rotors. In due course, we will return these three gyros to digital suspension.

All of these recent spacecraft behaviors--spotty communication, computer re-boots, gyro safekeeping transitions--are the expected results of the spacecraft operating outside the limits of its controlled experimental environment, along with reduced communications and monitoring from our MOC. As we've stated many times in recent status updates, our main focus now is analyzing the science data we have collected. However, we will continue to perform minimal maintenance on the spacecraft, so that it is ready and available for other post-mission experiments, as described in the Mission News story below.

GP-B MISSION NEWS--SPACECRAFT READY FOR OTHER EXPERIMENTSŠOR HIBERNATION
============================================================
Our GP-B team has now completed all planned, as well as some extended post-mission analyses on our spacecraft and its component systems. We are in the process of stabilizing the spacecraft in its current orbit normal orientation, and the spacecraft is now ready and available for use by other scientists to perform various types of experiments. The GP-B spacecraft is a state-of-the-art orbiting laboratory, and it has performed extraordinarily well throughout the GP-B mission and beyond. While it no longer maintains the cryogenic environment necessary for testing the geodetic and frame-dragging effects of general relativity, the on-board star trackers, magnetometers, and science gyros are still functioning perfectly, and they can be used individually or in combination for a number of other types of experiments.

Thus, we are actively seeking scientific partners around the world who would be interested in using this space borne laboratory to perform additional post-mission experiments. To this end, for the next few weeks we will be collecting sample data to demonstrate and validate the spacecraft's post-mission experimental capabilities in the following five areas.

1. Occlusion of Stars by Planets
Within the next few days, we will begin the process of slowing down the spacecraft's roll rate to 0.04 rpm (25 minutes per revolution). At this very slow roll rate, the on-board star trackers can be switched into a more sensitive tracking mode, in which the light from stars can be integrated over much longer time periods. By observing brightness variations of various star systems, the star trackers can detect the presence of orbiting planets in those systems.

2. Measuring Residual Drag on the Spacecraft
The four GP-B science gyroscopes can be used as 3-axis accelerometers that are capable of measuring solar pressure and upper atmospheric drag on the spacecraft to an accuracy of 5 x 10-12 g.

3. GPS Satellite Accuracy Measurements
Because the orbit plane of our GP-B spacecraft is very well established, we can use the four science gyroscopes as 3-axis accelerometers to determine the spacecraft's precise inertial position without GPS reckoning. We can then compare this internally-calculated spacecraft position information with corresponding position information generated by various GPS satellites to determine their level of accuracy.

4. Subtle Aurora Borealis Effects
Using a combination of the on-board magnetometers, the proton monitor, and the four science gyros as accelerometers, we can investigate what happens when the upper atmosphere heats up as a result of bombardment by charged particles. We can also measure the buffeting effects of the upper atmosphere as the spacecraft passes through a region containing charged particles.

5. Latitude Axis Gravity Gradient
As a complement to the GRACE mission that measured gravity gradients along a longitudinal axis between a pair of orbiting spacecraft, the GP-B science gyros can be used as 3-axis accelerometers to measure latitude-axis (cross-orbit) gravity gradients.

As noted earlier, for the next few weeks, we will be collecting sample data to illustrate the feasibility and limits of performing all of the above experiments with the GP-B spacecraft. Because the spacecraft is already in orbit and functioning, funding requirements for such "experiments of opportunity" will be minimal. The cost for using the spacecraft to perform any or all of these experiments amounts to the cost of a 4-5 person mission operations staff over the period of the experiments.


In summary, the GP-B spacecraft has performed exceedingly well to date. It has experienced no serious failures, and all the systems required for performing post-mission experiments are operational and ready for use. In a few weeks, after we have finished collecting the sample data, if there is no interest or funding for performing any of these experiments, we will place the spacecraft in a safe, hibernation configuration and reduce our maintenance monitoring of its health to once a week.


====================================
NEXT SCHEDULED GP-B UPDATE ON FEBRUARY 28, 2006
====================================
Our next regularly scheduled update will be at the end of February. Of course, we will send out a timely update if there are any important changes in the spacecraft's status, or 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.


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


Photo, taken through a telescope by Swiss physics teacher and amateur astronomer Stefano Sposetti, of GP-B spacecraft in orbit, passing near IM Pegasi: http://aida.astronomie.info/sposetti


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/....html#guidestar and on pages 18-20 of the Gravity Probe B Launch Companion: http://einstein.stanford.edu/highlights/GP...h_Companion.pdf


Track the GP-B satellite on the Web using NASA's Java-based J-Pass satellite tracking application at: http://science.nasa.gov/realtime/JPass/ Also, you can track the GP-B satellite on Personal Digital Assistants (PDAs) using either the Palm OS or Pocket PC operating systems with software from Big Fat Tail Productions: http://www.bigfattail.com


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


==========================
ABOUT THE GPB-UPDATE EMAIL LIST
==========================
The email distribution list for this GP-B Weekly Highlights update is maintained on the Stanford University email lists server.

To subscribe to this list, send an email message to "majordomo@lists.Stanford.edu" with the command "subscribe gpb-update" in the body of the message (not in the Subject line).

You can unsubscribe at any time by sending an email message to "majordomo@lists.Stanford.edu" with the command, "unsubscribe gpb-update" in the body of the message (not in the Subject line.)


--

**********************************
NASA - Stanford - Lockheed Martin
Gravity Probe B Program
"Testing Einstein's Universe"
http://einstein.stanford.edu


Bob Kahn
Public Affairs Coordinator


Phone: 650-723-2540
Fax: 650-723-3494
Email: kahn@relgyro.stanford.edu
**********************************

============================================
GRAVITY PROBE B MISSION UPDATE FOR 7 JUNE 2006
============================================

GP-B DATA ANALYSIS & RESULTS ANNOUNCEMENT STATUS
=========================================

Note: The complete status overview of the GP-B data analysis process & results announcement from last month's GP-B Mission Update is posted at the top of our GP-B Home page: http://einstein.stanford.edu.

PROFESSOR FRANCIS EVERITT'S MAY 18, 2006 LECTURE

"TESTING EINSTEIN IN SPACE: THE GRAVITY PROBE B MISSION"

Below is a 90-minute MPEG-4 streaming video of the complete public lecture and
subsequent Q&A period delivered by Gravity Probe B Principal Investigator, Francis
Everitt in the Hewlett Teaching Center here at Stanford on Thursday, May 18, 2006.

http://einstein.stanford.edu/highlights/hl...ritt051806.html

Here's a relatively recent update on Gravity Probe B. Lots of analysis, and more analysis to come. Expect a lot more in April at the APS meeting.

http://einstein.stanford.edu/index.html

first results!

http://news.bbc.co.uk/1/hi/sci/tech/6561391.stm

It's funny, I was thinking of GP-B this morning and even wanted to ask about if. With the geodesic effect within 1% of the Einstein's theory, many alternative theories can be put to rest now. That's probably "good news" for dark matter and dark energy.

We still have to wait 8 months for the results concerning frame dragging. That's a weaker effect, and I don't think it affects astrophysics too much, except maybe loss of energy by rotating black holes. Although if the general relativity's predictions are not confirmed, it could turn everything upside down.

What are the other "best claimed accuracy" measurements of the geodesic effect? I skimmed the GP team press release earlier today but didn't see a claimed "improvement" factor.

The Executive summary claims many firsts, not included in the list is the most accurate measurement of the geodesic;

http://einstein.stanford.edu/content/exec_...xecSum-scrn.pdf

According to Bob Kahn, the GP-B was plagued by two unexpected sources of error: A time varying viscous moment in the probes, and electrostatic patches in the housing.

They seem to be confident that they can isolate the signal from the error, but it will take another nine months to do so.

The press release calls this a 'spectacularly' successful mission. Given the cost overuns, the political and scientific delays, the harrowing calibration period; and now the delay in processing the data, 'grueling' might be a more definitive adjective. Space is never easy.

Particularly this mission. Getting those gyros to work at the required precision for the full mission duration and survive transportation and launch was nothing short of heroic.

Always amazing to see that Uncle Albert's still batting a thousand...what a mind!

God, I remember seeing the thing at Stanford in 1984. My buddy who was a grad student pointed to it as something to laugh at -- an out-of-control project that had already taken 20 years, largely due to trying to push the envelope in too many places at once.

So after all this wait, how much new info does it really give us?

I see that there are some really negative opinions out there:

http://www.misunderstooduniverse.com/Gravi...c_Money_Pit.htm

Ignoring the comments about "nude swimmers," I've seen the claim elsewhere that the LAGEOS experiments already confirmed Frame Dragging, never mind the geodesic effect. However, there's at least one plausible-looking argument that the LAGEOS error bars are as much as 200%.

http://www.phys.lsu.edu/mog/mog10/node9.html

Upshot: I guess we just need to wait a bit longer. On the bright side, I think they're planning to release all the raw data in July.

--Greg

I'm not sure about that first site you linked to. He makes some good points, but obviously has an axe to grind.

Having said that, I have been hearing the same sort of criticism from many sources for years, that the science return to cost ratio of GP-B is very poor, in comparison to other potential missions that were not funded. And that's without the continuing difficulties in extracting useful data from the heavily contaminated results. In my opinion, the main competition for poorest science return to cost ratio among NASA missions (that returned significant results at all, and allowing for the general increase in science return per mission as the decades pass) would be Deep Impact, but GP-B still handily "wins" that comparison.

Mongo: Yeah, that first site could be useful in a class on "how to minimize your credibility online." :-) Trouble is, I couldn't find a more credibile-looking site that raised the same issues, although I've certainly heard them verbally from better sources. I mainly wanted something to put the second link in context, since that one was new to me.

--Greg

I must respectfully disagree with criticism of the inherent value of this mission. Refining measurements of the least understood yet most pervasive force in our personal frame of reference and its effects in the Universe seems like an entirely worthy scientific objective. Solidifying constraints undoubtedly also allows objective filtering of various theories and models.

We only know gravity from its effects. We really don't know what it is, in the same sense that we understand that electromagnetism involves various permutations and exchanges of electrons and photons. There are many elaborate & often contradictory theories out there, too often out in Doug's tin-hat land (or more respected incarnations thereof: branes, string theory, etc.), and this is a rather obvious indicator that our actual knowledge is sketchy at best. Therefore, purely experimental work such as this does make a vital and fundamental contribution to science. There are already plenty of theories; let's see some data.

Here is a little more information from mission PR, Bob Kahn:



Yes and no...they are assuming, (I assume), that the patches were constant, or grew and migrated at a predictable rate. This is always an iffy assumption, when you learn during your calibration checking that the behavior of the system is not as expected. My experience with static effects tells me they are anything but static.

nprev: The criticism (the most credible kind, anyway) is that because it was so late, Gravity Probe B was unable to return any new information. That is, all of the results it produced are things scientists were already able to determine by other means. That's very different from saying the information wasn't worth the cost of collecting; it's says that they spent all the money and ended up with no new information.

Once they post their raw data, we ought to start seeing independent papers analyzing it. That'll probably give us the best indication of whether anything new was actually learned or not. That may take a few years, though.

--Greg

Rather than results-oriented grumbling, there's also the "opportunity cost" grumbling... what else could we have spent the money on? But given that it was such a long-lived program and the politics involved with funding sources, I don't know that such an argument is really valid.

Seems to have been a noble exercise to me... elegant in the way a mathematical proof has elegance. While the thing certainly collected a lot of data, it's not like data from an observatory, it's data that's part of a methodical process that started decades ago. Like the difference between knowing that Halley's comet was going to show up in 1758 can saying, "yup, there it is"" versus determining that it was white and fuzzy. Still I'd rather not think of the total price tag.

I see your point, Greg, and I suppose I'm a hopeless believer in serendipity. For example, I was thinking that GpB's data may indirectly refine the value of G by measuring trace effects like frame dragging with (presumably) greater precision than previous ground-based methods like torsion balances. It bothers me that the most directly experienced physical constant is also the most poorly known...

nprev: I don't think Gravity Probe B was trying to improve our estimate of G, although I suppose someone might find a way to do that with their data. It's hard for me to be sure, though; in General Relativity, G usually is set to 1, so it's possible that a more precise value in "normal" units just falls out of one of their results and I'm just too dense to see it.

Even so, your point is a good one; according to Wikipedia (http://en.wikipedia.org/wiki/Universal_gravitational_constant) there's a recent paper in Science giving G to within half a percent. Contrast, though, the precision for the Standard Gravitational Parameter for Earth (G times the mass of the Earth) which has an error of only two parts in a billion.

That said, it seems to me that if we spent $780M on an experiment specifcally to get a better measurement of G, we'd get a much better number.

--Greg

Thanks for the link, Greg; I'll check it out!

[EDIT] Ah. My personal value is still within the error bars! (puts on tin hat, runs like hell...)

The connection (if any) between quantum physics and gravity is one of the most profound mysteries in all of science, one of the few things that stumped Einstein. I find it amazing still that we can, for example, explain how a light bulb illuminates down to the last photon, but cannot really say why (actually, how in terms of nuts & bolts; there's that good old spacetime/geodesic/deterministic/worldline confusion again) a pencil dropped upon a desk just did what it did. I'm always interested in any bona fide research that might even indirectly shed some light on this issue.

I note that the Gravity Probe B folks have updated their site and have given a new status update:

http://einstein.stanford.edu/highlights/status1.html

Reading between the lines, one would conclude they currently have a 5% accuracy on the frame-dragging (which would be 2x as good as the 10% the LAGEOS folks claimed) but for some reason they don't come right out and say it. This seems completely consistent with the incredibly secretive policy that has attended the entire project.

They do think that 2% precision for the frame-dragging effect and 0.02% for the geodetic effect is achievable (more significant, they're sure that better than that is not achievable with the data they collected), but they think they may actually need until March 2010 to finish analyzing the data.

The most negative way to spin this would be to say that they have now returned one bit of information, and if things go well, they hope to deliver an additional bit in two more years. The most positive spin would be that this is literally infinitely better than what they reported in April last year. ;-)

--Greg

Another update from GP-B came out last week.

http://einstein.stanford.edu/highlights/status1.html

Looks like NASA may deny their request for an additional $3.8M to keep massaging their data until 2010, forcing them to wrap it up by October 2008.

I thought this line was particularly telling: "One of the Sr. Review Committee’s main arguments supporting its recommendation that NASA not fund the final extension requested by GP-B, was that the goals of GP-B have already been fulfilled by other measurements, and that GP-B is therefore no longer relevant."

Of course, GP-B is the quintessential lazarus project -- it has a long history of coming back from the dead -- so I won't be surprised if they end up getting their money anyway. I also won't be surprised if, late next year, they report they need about $5M more plus two more years.

--Greg

Do you hear that huffing, chuffing sound? See those locomotives pulling all those tank cars?

That's the Gravy Train, boys... best not let it pull out without you!



-the other Doug

The nasa review mentioned is here. Different missions really are competing for the same underfunded science budget, and compared to heavy hitters like Spitzer and Chandra the Gravity B proposal doesn't fare so well. With a really tight budget I can see where the committee is coming from: you can get more science for your dollar funding ongoing observations than massaging a single dataset.

It's so over. The relevant quote from the assessment:

"Theories that can be expressed in Post-Newtonian (PN) formalism in the weak-field limit are sharply constrained by spacecraft laser ranging, VLBI observations of light bending, lunar laser ranging and radio pulsar timing. In PN formalism, geodetic precession is proportional to 1 + 2γ and frame dragging to 1 + γ + ¼ α1. Taken together, these observations constrain γ to a precision of about 1 part in 10^5 and α1 by about 1 part in 10^4. These are about 2 orders of magnitude below the limits that might be achieved by GP-B in the team’s optimistic projection of what they can do. Hence, in the most optimistic case, they would fail by 2 orders of magnitude to improve the current constraints on these alternate theories."


I would be very surprised to see funding continue and they're right to cut them off. A pathetic end really for such a storied project. Everitt seems grossly in denial in this NPR piece http://www.npr.org/templates/story/story.p...toryId=91007322 .