A 30 year project to boldly go where no gravity probe has... well, anyway, you
get the point.
Gravity Probe B is a
satellite that should be launched near the end of 2000. It's a collaborative project between
Stanford University and
Lockheed-Martin, and it has been 30 years in production.
It plans to test one of the remaining untested predictions of
Einstein's theory of
General Relativity.
In layman's terms (which is how it was explained to me), a heavy spinning object (like the
Earth) will
twist spacetime around it, affecting
spinning objects near it. The effect is very small, even for things the size of Earth, but might be significant in some
galaxy-scale events like
quasars.
To measure this frame-dragging effect, the satellite will contain 4
gyroscopes. These gyroscopes, spheres of fused
quartz, are the
smoothest objects ever made by man. If one was magnified to the size of the Earth, the height difference between the
deepest valley and the
highest mountain would only be about 10 feet. The gyroscopes are
isolated from all external forces, cooled down by the surrounding
liquid helium, and spun to 10,000 rpm.
Superconducting shields eliminate all
magnetic and
electric fields, and complex stationkeeping systems eliminate effects of
solar wind and
micrometeorites. The gyroscopes are free-floating, and kept centered in their housing by electrodes. Their orientation is read with SQUIDS (superconducting quantum interference devices), which are extremely sensitive, and no, I don't know how they work either. A very sensitive
telescope, also made of quartz, keeps the satellite oriented in the right direction.
In the end, the satellite needs to be able to detect a change of rotation axis in the gyroscopes of about the width of a human hair seen from a mile away over the period of a year.
In short, it was a very
cool place to work for a
summer job.
2003 Update: No, it hasn't launched yet. But it's pretty likely that the current Fall 2003 launch plan will actually stick.
Update 2: Make that December 6, 2003.