It has taken almost 50 years to conceive and build and has cost
$600 million, but now NASA's Gravity Probe B spacecraft could be
upstaged by telescopes on the ground. The craft is designed to
accurately test Einstein's general theory of relativity.
According to the theory, a gyroscope orbiting a massive object
such as the Earth should experience two forces that gradually
cause it to "precess", pushing its axis of spin out of
alignment. The stronger force, known as the geodetic effect, is
caused by the Earth warping the fabric of space-time. The other,
known as the gravitomagnetic effect, is caused by the rotating
Earth dragging space and time around with it. Gravity Probe B,
which carries ultra-sensitive gyroscopes, was conceived in the
1950s to measure these forces, but was only launched in April
2004. It has yet to take any measurements. Francis Everitt, the
physicist in charge of the project at Stanford University, US,
says the probe should produce results by mid-2006. Meanwhile,
astronomers have been stud