Reduction of Missile Impact CEP Via Carouseling for a 2- or 3-Gimbaled Platform During Free-Fall

David Y. Hsu, Allan J. Brockstein

Abstract:	A typical ballistic missile flight has three mission segments: boost, free fall (zero-g) and re-entry. Specification requirements are usually given for impact position error in CEP. One of the major causes of this position error is the attitude error from the Inertial Measurement Unit (IMUJ developed during free fall due to the gyros. This paper describes a technique for reducing the gyro error effects in free fall of a 2-gimbaled IMU by a novel sequence of gimbal rotations, often called caroseling. The gyro error sources include bias, scale factor, scale factor asymmetry, misalignment angles, and trend. This technique applies equally well to a 3-gimbaled IMU, hence it is useful to many missile navigation systems. The attitude error accumulated before re-entry greatly affects the error at impact. During free fall the body experiences coning motion which causes the instruments in the 2-gimbaled IMU to precess. Before the proposed caroseling scheme can be applied, the IMU precession must first be sensed and then removed; a mechanizable procedure is included. In a 3-gimbaled system the body coning motion does not cause the IMU to precess due to complete isolation of the instruments by the gimbals. Simulation results are included to show the effectiveness of the caroseling procedure on reducing the attitude errors caused by the gyros during free fall and the subsequent reduction of impact CEP. The simulations are configured so that the effect of each gyro error source is considered independently. Thus the contribution of each individual source to overall performance is assessed.
Published in:	Proceedings of the 1986 National Technical Meeting of The Institute of Navigation January 21 - 23, 1986 Long Beach, CA
Pages:	115 - 115
Cite this article:	Hsu, David Y., Brockstein, Allan J., "Reduction of Missile Impact CEP Via Carouseling for a 2- or 3-Gimbaled Platform During Free-Fall," Proceedings of the 1986 National Technical Meeting of The Institute of Navigation, Long Beach, CA, January 1986, pp. 115-115.
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