Evaluation of an advanced gyro and wheel speed modulation for highly accurate azimuth determination

The technique of wheel-speed modulation (WSM) of a permanent magnet wheel gyroscope for measurement of true astronomic azimuth to state of the art accuracy is evaluated. A performance model for WSM operation of the gyro, and a series of unique tests which were espcially designed to evaluate: (1) the repeatability of the gyro torque across repeated speed changes, (2) the long term stability of the known error parameters associated with LWSM, and (3) the accuracy of the WSM technique as compared with traditional four position gyrocompassing is described. The test data demonstrated that true azimuth can be measured to a precision of at least 0.75 arc seconds (one sigma) in an hour or less for a period of at least four consecutive days during quiescent conditions. The data also confirmed that the torque bias shift which arises from changing the gyro wheel speed is very repeatable. Thus, once this bias is calibrated, the gyro can be operated automatically using WSM to accurately track the azimuthal motions of the test article without interruption for extended periods.