Gravity Probe B Completes a Year in Space |
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Written by spacetravel.org
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Sunday, 20 November 2005 21:56 |
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Gravity Probe B (GP-B), a NASA/Stanford physics experiment, has recently finished a year of gathering science data in Earth orbit. The results, which will take another year to analyse, should provide information about the shape of space-time around Earth.
GP-B utilises four gyroscopes in orbit around Earth, with their spin axes pointed toward a distant star as a fixed reference point. If there are no external forces on the gyroscopes, they should continue pointing at the star forever. However, if space is twisted, the axes of the gyroscopes should drift over time. The change in the direction of the gyroscopes axes relative to the star should enable scientists to measure the twists of space-time.
GP-Bs gyroscopes are the most perfect spheres ever made by humans. Made of fused quartz and silicon, they are 1.5 inches across and never vary from a perfect sphere by more than 40 atomic layers. If they were any less spherical, their axes would wobble, even without the effects of relativity.
Calculations indicate that the twists in space-time around the Earth should cause the axes to drift 0.041 arcseconds over a year. GP-B needs a precision of 0.0005 arcseconds to measure this. To make this possible, researchers developed a "drag free" satellite that could brush against the outer layers of the Earth's atmosphere without disturbing the gyroscopes, learned how to keep Earth's magnetic field out of the spacecraft, and created a device that can measure the spin of a gyroscope, without touching the gyroscope.
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