The reference telescope will focus on a star to calibrate results. It is hoped that the behaviour of the gyroscopes will verify Einstein's theory that space, time and matter merge into a continuum, which he called space-time, that curves around massive bodies, such as stars and planets. For example, it is known that light is bent when it passes close to a massive body.
Two consequences of Einstein's theory will be checked by the GP-B: firstly, that, as a large body such as the Earth rotates, space-time spins in the immediate region, a process called time dragging, and secondly, that the spin direction of a gyroscope will change as it moves through curved space-time, in a so-called geodetic effect.
The gyroscope payload will provide a near-perfect time reference system to measure how time and space are warped by the Earth. Minute motions of the gyroscopes will alter their electrical fields, allowing movements thousands of times smaller than the width of a human hair to be measured. The spacecraft will measure time-dragging to an accuracy of 1% and the geodetic effect to better than 0.01%.
The gyroscopes will have to operate in a pressure 10 times lower than vacuum pressure in space and will have to be provided with the lowest and most stable magnetic field imaginable, to achieve stability and freedom from outside forces.
Many scientists have lobbied NASA to cancel the Gravity Probe mission, claiming that it has little scientific value. This claim is based on earlier research, including the sub-orbital flight of a craft, called the Gravity Probe A, in 1979.
The 107kg package was launched on a Scout booster to 10,000km altitude on a 116min mission over the Atlantic Ocean. It carried a hydrogen maser clock, which was compared via telemetry with a terrestrial duplicate, to test the equivalence principle of general relativity.
Source: Flight International
