Accession Number : ADA114640

Title :   Evaluation of an Advanced Gyro and Wheel Speed Modulation for Highly Accurate Azimuth Determination.

Descriptive Note : Final rept. 26 Jan-31 Dec 81,

Corporate Author : CHARLES STARK DRAPER LAB INC CAMBRIDGE MA

Personal Author(s) : Shearer,J

PDF Url : ADA114640

Report Date : 31 Dec 1981

Pagination or Media Count : 82

Abstract : This report presents the results of a feasibility study which evaluated the technique of Wheel-Speed Modulation (WSM) of a CSDL-designed Permanent Magnet ((PM) wheel gyroscope for measurement of true astonomic azimuth to state-of-the-art accuracy. The report describes a detailed performance model for WSM operation of the gyro, and a series of unique tests which were especially 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. 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. Some anomalous gyro torque data were observed whenever environmental changes (tilt and temperature) occurred. No conclusions can be reached at this time as to whether this anomalous behavior was the result of an inadequately or incorrect performance model, or the inability to accurately measure and compensate for tilt and tilt rate errors. The demonstrated performance confirms that WSM is a feasible alternative for the advancement of azimuth measurement technology.

Descriptors :   *GYROSCOPES, AZIMUTH, DETERMINATION, PERMANENT MAGNETS, ACCURACY, GYRO STABILIZERS, TORQUE

Subject Categories : Non-radio Communications

Distribution Statement : APPROVED FOR PUBLIC RELEASE