The measurements were made by observing the rotational axes of four ultraprecise gyroscopes inside the satellite. Each gyroscope consists of a tiny quartz ball, which is covered in a superconductive material and rotates 5,000 times per minute. The satellite telescope pointed at the IM Pegasi star in the Pegasus constellation, and because the direction was constant, magnetic quantum detectors could measure small changes in the gyroscopes’ rotational axes. It was therefore possible to confirm the existence of two kinds of effects.

Albert Einstein described the first effect: The Earth’s gravity bends space — a phenomenon called the geodetic effect. Space can be seen as a kind of rubber membrane, in which Earth — and all other massive objects — causes a dent. Consequently, the rotational axes of the gyroscopes are displaced, and calculations estimate the displacement to be 0.0018 degrees each year. Gravity Probe B has now confirmed this within 0.3 percent accuracy.

The other effect, predicted using Einstein’s theories, was detected in 1918 by Austrian physicists Josef Lense and Hans Thirring. The Earth’s rotation twists space; the twist has been calculated to be 0.000011 degrees annually. But because of technical problems with the satellite, this number has an uncertainty mar- gin of 19 percent, a considerable increase over the expected 1 percent.