Gravity Probe B
To ensure the accuracy of the gyroscope, "you have to make
the most perfectly spherical thing," said Rex D.
Geveden, who oversees the gravity probe work at the science and
applications project office at the Marshall Center.
As far as anyone knows, Stanford's quartz spheres are the smoothest,
roundest objects ever made. Polished within 40 atomic layers of a
perfect sphere, they are so smooth that if they were they the size of
Earth, the tallest mountain would be barely six feet high.
Stanford researchers - among them Sasha Buchman, who is responsible
for manufacturing and verifying the gyroscopes, and technician Thorwald
van Hooydonk - were so successful that the gyro rotors they
fabricated have been adopted by the National Institute of Standards and
Technology as the density standard for the quartz materials from which
they were sculpted.
Is this experiment manifestly
a totally crazy idea? The answer is that it became fairly obvious to us it
was not manifestly crazy. Francis Everitt
Each rotor is suspended within a near-perfect vacuum in a housing that
leaves only 5/10,000ths of an inch clearance. Jets of helium gas,
traveling at the speed of sound, puff the gyros up to a speed of 10,000
rotations a minute. At that scale, even the most minute contamination
would be disastrous to the experiment.
"If you get a particle of half a milli-inch, it can jam the whole gyro
and it will come to a screeching halt," says co-investigator John
Once in orbit, the four gyroscopes - two spinning clockwise and
two spinning counter-clockwise - are aligned with the star Rigel in
the constellation Orion.