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General Relativity and Gravity Probe-B - Barry Muhlfelder (SETI Talks)



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GPS Technology and People Behind Gravity Probe B's Einstein Relativity Experiment

NASA's May 3 announcement that its long-running Gravity Probe B (GP-B) mission had confirmed two key predictions derived from Albert Einstein's general theory of relativity, mentioned GPS autoland techniques as one of the projects spinoffs.
However, the involvement of GPS technology and GPS experts in the mission was much deeper than the passing reference in a press release.

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Probe confirms Einstein effects

Nasa's Gravity Probe B has produced remarkable new confirmation of some key predictions of Albert Einstein.
The satellite's observations show the massive body of the Earth is very subtly warping space and time, and even dragging it around with it.
Scientists were able to see these effects by studying the behaviour of four perfectly engineered spinning balls carried inside the probe.

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NASA Hosts Science Update About Gravity Probe B Mission
 
NASA will hold a news conference at 1 p.m. EDT on Wednesday, May 4, to discuss the science results and legacy of the Gravity Probe B (GP-B) mission. The event will be in the NASA Headquarters Webb auditorium at 300 E Street SW in Washington.
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A NASA review appears to spell the end for Gravity Probe B, the project conceived in the 1960s to measure how the Earth warps the fabric of nearby space-time.

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MISSION UPDATE SEPTEMBER 2007

TIME-VARYING POLHODE MOTION IN THE GYRO ROTORS
The gyroscopes polhode motion is akin to the common "wobble" seen on a poorly thrown (American) football, though it shows up in a much different form for the ultra-spherical GP-B gyroscopes. While it was expected that this wobble would exhibit a constant pattern over the mission, it was found to slowly change due to minute energy dissipation in the spinning gyro rotors, caused by interactions of electrostatic patches on the rotor's surfaces and patches on the metallic surfaces inside the housings. The polhode wobble complicates the measurement of the relativity effects by putting a time-varying wobble signal into the data.

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It has been more than 90 years since Einstein put forward his theory of relativity. Physicists agree it is basically right, but they also suspect there is something deeper behind it.
Since the 1960s, scientists funded by NASA have been working on a project to precisely test Einstein's theory. The experiment, called Gravity Probe B, finally made it to orbit a few years ago, at a total cost of $750 million. The researchers gave a progress report at a conference in Florida last weekend, and said they have run into some snags.

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Lense-Thirring effect
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After 40 years of planning and hundreds of millions of dollars, NASA announced last week the first results from the Gravity Probe B experiment, which was designed to measure how Earth warps the fabric of space-time. The results may have been scooped, though, by astronomers bouncing lasers off the moon decades ago.
NASA launched Gravity Probe B (GPB) in April 2004. The satellite was equipped with precision-engineered gyroscopes to measure two effects predicted by Einstein's general theory of relativity. In one, called the geodetic effect, Earth's gravity dents space-time such that it should tilt each gyroscope by 0.0018 degrees over the course of a year. In a second, more subtle effect, called frame-dragging or gravitomagnetism, Earth drags space-time along with it as it rotates.

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A NASA mission that took 40 years to get off the drawing board has finally measured how the Earth dents the fabric of space-time.
The first result from the Gravity Probe B satellite confirms a prediction of Einstein's general theory of relativity to a precision of better than 1%.

"For the first time, we have seen one of Einstein's effects directly" - Francis Everitt, mission leader, of Stanford University in California, US.

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PRESS RELEASE: GP-B DATA ANALYSIS & RESULTS ANNOUNCEMENT STATUS

During the 50-week science phase of the GP-B mission and the 7-week instrument calibration phase, which lasted from August 2004 - Septermber 2005, we collected over a terabyte of experimental data. Analysis has been progressing through a 3-phase plan, each subsequent phase building on those preceding it.

In Phase I, which lasted from the end of September 2005 through February 2006, the analysis focused on a short term--day-by-day or even orbit-by-orbit--examination of the data. The overall goals of this phase were to optimize the data analysis routines, calibrate out instrumentation effects, and produce initial "gyro spin axis orientation of the day" estimates for each gyro individually. At this stage, the focus was on individual gyro performance; there was no attempt to combine or compare the results of all four gyros, nor was there even an attempt to estimate the gyro drift rates.

We are currently progressing through Phase II of the data analysis process, which began at the beginning of March and is scheduled to run through mid-August 2006. During Phase II, our focus is on understanding and compensating for certain long-term systematic effects in the data that span weeks or months. The primary products of this phase will be monthly spin axis drift estimates for each gyro, as well as refined daily drift estimates. In this phase, the focus remains on individual gyro performance.

In Phase III, which is scheduled to run from late August 2006 through December 2006, data from all four gyros will be integrated over the entire experiment. The results of this phase will be both individual and correlated gyro drift rates covering the entire 50-week experimental period for all four gyros. These results will be relative to the position of our guide star, IM Pegasi, which changed continually throughout the experiment. Thus, the final step in the analysis, currently scheduled to occur in January 2007, will be to combine our gyro drift results with data mapping the proper motion of IM Pegasi relative to the unchanging position of a distant quasar. The proper motion of IM Pegasi has been mapped with unprecedented precision using a technique called Very Long Baseline Interferometry (VLBI) by Irwin Shapiro and his team at the Harvard-Smithsonian Center for Astrophysics (CfA), in collaboration with Norbert Bartel at York University in Toronto and French astronomer Jean-Francois Lestrade.

Playing the role of our own harshest critic, our science team will then 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 turn the analysis and results over to our GP-B Science Advisory Committee (SAC), that has been closely monitoring our experimental methods, data analysis procedures, and progress for 11 years, to obtain its independent review. In addition, we will seek independent reviews from a number of international experts.

Throughout phases II and III, members of our team will be preparing scientific and engineering papers for publication in late 2006-2007. At the same time, we will be working with NASA to plan a formal public announcement of the results of this unprecedented test of General Relativity. We expect to make this announcement of the results in April 2007.

The next regularly scheduled update will be at the beginning of June. 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.

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