Relativity Revisited

The purpose of the telescope and the guide star is to help scientists keep track of four spinning spheres, or gyros, onboard the satellite. These gyros, which will be listed in a forthcoming edition of the Guinness Book of World Records as the roundest objects ever manufactured, are the heart of the experiment. In the beginning, their spin axes are aligned with IM Pegasus. If space-time around Earth is really twisted, as Einstein says, the gyros will wobble, slowly drifting out of alignment with the distant star during GP-B's one-year mission.

"One of the things all of us were terribly worried about was getting some dirt in the gyro housings," Everitt says. The gyros float a near-perfect vacuum, and only a thousandth-of-an-inch gap separates the spheres from their casings.

A spinning spherical gyroscope in Earth orbit should wobble in the whirlpool shaped space-time around our planet.

"The gyros were cleaned before they went up, but we gave this thing a tremendous vibration during launch. Wouldn't you expect a piece of dirt to come in through one of the pump-out ports, land right on one of the gyros and jam it?" he says. "That would be the end of that gyro."

This time all the worrying was for nothing. "The gyros have all been as clean as a whistle," he says. They're suspended in their casings, aligned with the guide star, and spinning thousands of times per minute. "Amazing, delightful."

Now the gathering of science data begins. The satellite's onboard computers should be able to handle this phase of the mission automatically. Still, at least one person will be on duty monitoring GP-B at all times throughout the year, Everitt says. "It should run itself, but you can never relax."

After more than 40 years of methodical planning and four months of intense troubleshooting, GP-B's scientists feel "a real sense of gladness," he says. "What a difference it makes to be up there and operating. How thrilling that is. We all feel that."

Gravity Probe B mission control at Stanford University.

"Some people," laughs Everitt, "are talking about taking a week or two of well-deserved vacation."