Gravity Probe-B is an interesting project, and I'd like to give you my take on it before you read the Press Release that follows. One of the elements of Einstein's work predicts a warping of timespace near objects with strong gravitational fields. Astrophysicists have known for some time that an orbit around the Earth is not what it should be. What I mean is that the time it takes for a satellite to make one orbit is shorter than it should be based on distance and speed.
Imagine being on a race track exactly one mile in circumference, in a car going exactly 60 miles per hour. It should take you one minute to go around the track, right? Not 55 seconds. This is what is happening to our satellites. In orbiting the Earth, satellites arrive at the starting point of their orbit a few fractions of a second sooner than they should. It appears that time is not only slightly warped by Earth's gravity, it is also being dragged by the rotation of the Earth.
Gravity Probe-B is an experiment to measure this phenomenon. In order to get a perfectly stable platform for measuring the degree of warp and drag, engineers and scientists at Stanford, Lockheed Martin, and the Marshall Space Flight Center created a satellite that holds four spinning gyroscopes. These gyroscopes are unique in that they spin the most perfectly round objects ever produced on Earth. The variation from "perfectly round" is so small that if these 2" Niobium coated glass orbs were expanded to the size of the Earth, variations would be less that a two foot sand drift. Having such precise gyroscopes allows the satellite to measure incredibly small variations in gravity, the passage of time, and the warp of spacetime that surrounds our planet.
April 20th was the one year anniversary of the launch of Gravity Probe-B, and the data collecting period of this project will be concluded late this summer. It will take a year of digesting the data before final results are released in the summer of 2006. Fascinating stuff for fans of SciFi, Space Exploration, and anyone who is excited by our growing awareness of how things really work.
NASA'S PRESS RELEASE
Is Einstein's general theory of relativity correct? Testing two extraordinary predictions of that theory is the goal of Gravity Probe B, or GP-B, a satellite that just marked its first anniversary in space. Published in 1916 and hailed as one of the most brilliant creations of the human mind, Albert Einstein's general theory of relativity weaves together space and time into a four-dimensional "fabric," called spacetime, and defines gravity as the warping and twisting of spacetime by massive objects.
Article comments
1 - Tom French
This is so cool. These are the kinds of questions that should make front page headlines.
2 - Duane
Thanks for the GP-B update, Bennett. However, you might be interested to know that the measurement of frame-dragging (the Lense-Thirring effect) has recently been measured to a precision of about 5% by the two spacecraft LAGEOS 1 and 2. LAGEOS is the acronym for Laser Geodynamics Satellite. The measured frame drag rate amounts to about 33 milli-arseconds per year, or about 1.9 meters per year at the orbit of the satellites. The agreement with Einstein's GR is 99 plus/minus 5 percent. GP-B will make a finer measurement, about 1% precision.
3 - Bennett Dawson
I agree Tom. Well it IS front page news here at BC. Thanks for the comment!
Bennett
4 - Bennett Dawson
Thanks Duane! Yes, I am interested to know about the confirmation by the LAGEOS satellites. Folks with the GPB project are holding off with any announcements until they have completed the data crunching.
I can understand this. Dr. Everette has over 20 years of his remarkable talent in this project, and wants to present the final results in toto.
What a great group of scientists and engineers we have doing this research!
Cheers,
Bennett
5 - Robert Edsall
A track with one mile _diameter_? Then the time should be pi (3.14159..) minutes. Or perhaps you meant to write "circumference" or, more generally, "perimeter."
6 - Bennett Dawson
Oh frickin' blush already! Thanks Robert, I'll go change it. Ya know, when I was writing this piece, I paused and thought "Diameter?" "not radius.... let's see, pipe is measured by outside diameter. Yeah, it's diameter."
BUT THEN, I emailed it to Marshal Space Center to make sure the facts were essentially correct, and the guy I talked to forwrded it to Stanford, they corrected a few things, added a few words, and sent it back to me.
How's that for scary?