Gravity probe B, which has been proposed for a space shuttle launch in 1992, is a 2-ton spacecraft that has been under study for several years at the Marshall Space Flight Center, Huntsville, Ala. The heart of the spacecraft is a gyroscope, which consists o f a solid quartz golfball-sized sphere that serves as the rotor. Levitated in space by an electric field, the rotor would spin completely untouched at 170 cycles per second.
The rotor is so nearly perfectly round that if it were expanded from its golfball size to the size of the earth, the highest imperfection on its surface would be only about 1.8 m (6 feet). To give the ball superconductivity, Marshall has developed a niobium coating for the rotor and has been instrumental in the development of an isothermal barrier—a large vacuum-bottlelike container that would provide near-absolute-zero temperatures for the gyroscope.