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Gravity has long been a mystery to man. Seeking to unlock the secret of the force that drew objects to one another, 18th-century physicist Issac Newton first formally proposed a theory that would be applied as a matter of course over the next two centuries--until Albert Einstein. In 1910, Einstein shook the scientific world with his postulation of the General Theory of Relativity. In his complex description of the physical universe, he saw a cosmos in which space was curved, and time and speed inexorably related. Since that momentous day when Einstein turned the traditional laws of physics upside down, scientists around the world have sought to prove--or disprove--his theory. At NASA, a special team of engineers and scientists have joined with members of a prestigious academic community to advance a design for a machine that would test part of Einstein's famous pronouncements. Called GRAVITY PROBE B, the two-ton spacecraft has been under study at NASA's Marshall Space Flight Center in Huntsville, AL, in concert with scientists at Stanford University in CA. Proposed for launch in the 1990s aboard the Space Shuttle, Gravity Probe B would employ super-accurate gyroscopes to test a portion of Einstein's general theory of relativity. The heart of the spacecraft is the gyroscope, a solid quartz golf ball-sized sphere called a "rotor." Levitated in space by an electric field, the rotor would spin completely untouched at 170 cycles per second. The primary ability of this highly advanced gyroscope would be its extreme stability in its spin axis. Using a highly accurate reference telescope, the Gravity Probe B would sight on a particular star. In its orbit of about 325 miles above the Earth, the spacecraft would then measure the drift of the gyroscope from its aim at the star over a given period of time. In classical Newtonian physics, an ideal gyroscope--undisturbed by any other influences--would not drift from its aim more than a single milli-arc-second in a year. (A milli-arc-second is the angle of view a person would have of a single human hair placed ten miles away.) But in recent years, scientists using Einstein's theories have predicted that if an orbiting gyroscope were placed near a large body of mass, like the Earth, it would drift because of the gravitational field. That something would drift because of gravitational pull sounds like common sense, but in Newtonian physics that is not supposed to happen to a gyroscope. Einstein's theory implied that it would. Furthermore, the theory predicts that if the large mass near the gyroscope were spinning, as the Earth does, an additional drift would occur. The Gravity Probe B is designed to measure both drifts. It demands enormous accuracy in the gyroscope, but the Gravity Probe B will have that. And if the drift due to the Earth's rotation is 44 milli-arc-seconds, as the relativity theory predicted it would be, then that portion of the theory will have been proved. The idea of an experiment like the Gravity Probe B was conceived in 1959 by the late Dr. Leonard Schiff, a Stanford University professor. The precision called for in the experiment at that time was such, however, that technology literally had to catch up to Dr. Schiff's idea. It has taken years to be ready to attempt such a project, but the technology is now available, and the Marshall Center is ready to proceed toward the test of Einstein's theory. The Center has a contract with Stanford to carry out much of the research for the project. Marshall has developed in-house the rotor, which is so nearly perfectly round that if it were expanded from its golf-ball size to the size of the Earth, the highest imperfection on its surface would be only about six feet. To give the ball a quality of superconductivity, the Center has developed a niobium coating for research for the project. Marshall has developed in-house the rotor, which is so nearly perfectly round that if it were expanded from its golf-ball size to the size of the Earth, the highest imperfection on its surface would be only about six feet. To give the ball a quality of superconductivity, the Center has developed a niobium coating for the rotor and has been instrumental in the development of a dewar, a large vacuum bottle-like container that would provide near-absolute-zero temperatures for the gyroscope. With this superconductivity given by the niobium and the extreme cold, the rotor creates a magnetic field that allows the drift of the rotor, if any, to be detected by sensors without disturbing its motion. The extreme cold is also necessary to help provide as stable environment for the rotor as possible. That the gyroscope will change its pointing direction because of the nearness and spinning of mass is, of course, a theory. But it is believed that Gravity Probe B will be capable of determining the existence and magnitude of these non-Newtonian drifts. ---- NASA Fact Sheet, GRAVITY PROBE B, Dec. 1984 (64F1084) MSFC