| Gravity Probe B (GP B) is an ongoing joint project by Stanford, NASA, and Lockheed to test Einstein's general theory of relativity. The objective of the experiment is to detect and to measure the geodetic and frame-dragging effects exhibited by an Earth-orbiting spinning gyroscope. The general theory of relativity predicts that the first of these effects is 2.22 {dollar}times{dollar} 10{dollar}sp{lcub}rm -7{rcub}{dollar} deg/hr and the second is 1.43 {dollar}times{dollar} 10{dollar}sp{lcub}rm -9{rcub}{dollar} deg/hr. To attain the mission accuracy goal, gyroscopic precession due to Newtonian torques must not exceed 1.3 {dollar}times{dollar} 10{dollar}sp{lcub}rm -11{rcub}{dollar} deg/hr.; The time histories of these signals is used to obtain the spin vector motion in the laboratory. This motion is used to estimate the mass unbalance and the inertia ratios of the gyroscope, and to obtain information on the coefficients of the gyroscope's higher harmonics in shape. Biases in the SQUIDs were calculated, and the spin vector trace inside the gyroscope is estimated.; This research develops techniques to reliably measure the time history of the spin vector in the lab using two or three pick-up loops, using the signature of the magnetic trapped flux inside the gyroscope. Also described is the technique used to estimate the gyroscope's characteristics using precession information in the lab and in the body. Spinning at 1 H z, gyroscope 86-4 had a precession rate of 98 deg/hr, which represents a mass unbalance of 6.1 {dollar}mu{dollar}cm. This mass unbalance would result in precession of 1 {dollar}times{dollar} 10{dollar}sp{lcub}-12{rcub}{dollar} deg/hr or less than 0.03 m sec/year in orbit conditions. Therefore gyroscope 86-4 (based on mass unbalance estimated in the lab) is within science mission requirements in terms of precession due to Newtonian torques. This research also shows that we can estimate the coefficients of higher harmonics in shape of the gyroscope using the time rate of change of the spin vector in the lab. Decay of the trapped magnetic field was observed and recorded during this research, it was found to take place during the first few hours after levitating and spinning the gyroscope. |
