Gravity Probe B

In 1993, NASA dropped a space shuttle mission that might have helped check out the equipment in space, but the gyros have proved themselves so far in more than 90,000 hours of ground tests.

The perfection of the spheres is only a first step, however.

Bradford Parkinson“When they conceived this project, they thought it was a five-year deal, not a 30-year deal. When you are exploring the unknown, you can’t predict how long it will take.” ­ Bradford Parkinson

The quartz rotors pose a second, equally daunting test of ingenuity: How can researchers measure the direction of spin of an unblemished sphere without disturbing it or being able to see it? For that matter, how can they keep the spheres from expanding as internal temperatures fluctuate, or protect them from variations in the surrounding magnetic fields?

To do so, the researchers have taken advantage of how materials behave at low temperatures.

Each sphere is coated with superconducting niobium and chilled to 2.5 degrees Kelvin, within a few degrees of absolute zero (minus 456 degrees Fahrenheit). That permits the balls to be suspended electrically.

Any changes in the tilt of the gyroscopes' spin axes can be measured indirectly by detecting changes in the direction of the magnetic field surrounding the spheres with superconducting sensors that do not exert any unwanted force on the rotors. The low temperatures also help to stabilize the onboard telescope and shield the entire experiment from outside magnetic interference.

To keep the gyroscopes at the proper temperature in space, the entire package of instruments will ride inside what essentially is a thermos bottle, called a dewar, brimming with 640 gallons of some of the coldest liquid known to

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