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GP-B: More Than Just a Pretty Face
Questions about the ways space, time, light and gravity relate to each other have been asked for eons. Theories have been offered, yet many puzzles remain to be solved.

GP-B dewar No spacecraft ever built has required such extreme demands on technology and testing. Scientists and engineers have worked tirelessly for more than 40 years developing new technologies just for this mission.

Gravity Probe B is "the most challenging experiment that NASA will perform in this millennium," according to Dr. Frank McDonald, former NASA chief scientist.

Image to left shows the dewar. Among the biggest challenges for GP-B is keeping its Science Instrument Assembly constantly cooled to a temperature of 1.8 Kelvin, or minus 271.4 degrees Celsius (slightly above absolute zero), which will last 18 to 24 months. Credit:NASA

The GP-B spacecraft contains an assortment of cutting-edge equipment. One of the largest is the dewar, a 9-foot-tall, thermos-like vat that holds 645 gallons of superfluid liquid helium.

GP-B gyroscope Image to right shows a gyroscope out of its quartz block. It took years of research and development to produce the GP-B gyroscopes. Although only one gyroscope is needed to perform the necessary experimental measurement, the quartz block in the GP-B Science Instrument Assembly contains four gyroscopes to ensure reliability in the science measurements. Credit:NASA

Also, Gravity Probe B sports the world's most spherical gyroscopes. Measuring the curvature (geodetic effect) and "twisting" (frame-dragging) effect of local space-time demands the use of a gyroscope that is nearly perfect in two ways: every point on the surface must be exactly the same distance from the center, and its structure has to be identical from one side to the other.

Superconducting QUantum Interference Devices Image to left shows the Superconducting QUantum Interference Device (SQUID) magnetometers that measure the drift of the gyroscope's spin axis. A superconducting loop is embedded in one side of each gyroscope's housing and connected to one of the SQUIDs, which perform the task of monitoring the magnetic fields around the gyroscopes. A special electronic control box on the outside of the space vehicle is connected to the gyroscopes and keeps them levitated and centered within their housing. Credit:NASA

Each gyroscope is an almost perfect 1.5-inch sphere made of specially-fused solid quartz. The gyroscopes were painstakingly chosen and molded specially for this mission, and the spheres were polished to near-perfect roundness. If we were to enlarge these spheres to the size of the Earth, the highest peak or deepest trough would measure only 8 feet from sea level. They are the most spherical objects in the universe, aside from neutron stars.

GP-B quartz telescope Every component has gone through years of testing and construction. GP-B was built in a class 10 clean room, so the entire craft wouldn't be subject to particles larger than a single micron that could disturb the delicate components.

Image to right shows the astronomical telescope. This onboard telescope is able to pinpoint the center of the distant guide star to within 0.1 milliarcseconds. Credit:NASA

If Albert Einstein were alive today he'd be relaxing in his easy chair, pipe in hand, very calmly awaiting the results of this historic mission and probably marveling at the technology it takes to probe his 89 year-old theory.

On April 19, the GP-B spacecraft will launch from Vandenberg Air Force Base in California to take one of the most difficult experimental measurements in the history of science. NASA's Marshall Space Flight Center in Huntsville, Ala., manages the GP-B program and its partner, Stanford University in California is responsible for mission design and data analysis.

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Elaine M. Marconi, KSC Staff Writer
NASA's John F. Kennedy Space Center and Marshall Space Flight Center