Autonomous Local Vertical Determination for Guided Artillery Shells

Donald E. Gustafson and David J. Lucia

Abstract:	Accurate local vertical (roll angle) estimates are required for guided artillery shells in order to correctly implement guidance commands. Although GPS and IMU data will typically be merged in the navigation filter to estimate local vertical as well as position and velocity, it is desirable to estimate local vertical in the absence of GPS data since this data will not be available at the start of flight and could drop out or be corrupted during flight. This study was undertaken to evaluate the performance of local vertical estimators which use only inertia1 sensors. More specifically, we consider local vertical estimation using gravity turn rate (flight path angle rate induced by gravity) information obtained using only on-board strapdown micromechanical gyros. A four state Kalman filter has been developed and tested using a Monte Carlo simulation and a typical micromechanical gyro error budget. The choice of four states depends strongly on the assumption that the spin rate of the navigation base will by relatively low (a few Hz) throughout the flight. At extremely low or extremely high spin rates, other filters would be required and performance may be quite different. Results were simulated for an Extended Range Guided Munition (ERGM) she11 over a planar ballistic path with a range of 6.4 nautical miles and a flight time of 60 seconds. It was found that local vertical can be acquired in less than ten seconds and can be tracked to within an rms error of less than ten degrees throughout the flight. Versions of the filter based on both known and unknown flight path angle rates were developed and tested. The results indicate that both versions perform well, but that the filter using known flight path angle rate tends to produce smoother error histories. Robustness of the filter was demonstrated in the presence of realistic disturbances. Estimation with large roll gyro errors was considered (biases as high as 0.5 rad/sec). An extended Kalman filter was used to estimate roll gyro error in a five state filter and retain good performance.
Published in:	Proceedings of the 52nd Annual Meeting of The Institute of Navigation (1996) June 19 - 21, 1996 Royal Sonesta Hotel Cambridge, MA
Pages:	213 - 221
Cite this article:	Gustafson, Donald E., Lucia, David J., "Autonomous Local Vertical Determination for Guided Artillery Shells," Proceedings of the 52nd Annual Meeting of The Institute of Navigation (1996), Cambridge, MA, June 1996, pp. 213-221.
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