THE INSTITUTE'S PROFESSIONAL FORUM

Contributor- J. D. Salisbury

Peer Reviewed

Abstract:	Comments on “lnfegrated Navigation Systems and Kalman Filfering: A Perspective” I was very interested in Dr. Brown’s article, “Integrated Navigation Systems and Kalman Filtering: A Perspective” contained in your Winter 1972-73 edition (vol. 19 no. 4). Although this article was mainly tutorial I feel that I should expand and discuss his statement about feedback and feed-forward corrections to the inertial system and its outputs. (See the second paragraph on p. 359.) Position Locator (GPL), which was an inertial naeigation system with a Kalman filter. The system was unaided; it used only its own velocity errors and heading-rate errors as filter measurements while it was at rest with respect to the earth. We tried both methods of system correction i.e., feedback correction to the INS and feedforward correction to the INS output data. We found that the INS performed considerably better with feed-forward correction. We also found that we could use this mode of operation for at least two days without any noticeable degradation due to the INS error buildup and its possible bad effect on the error modeling linearity assumptions. Our well-settled GPL built up errors due to gyro drift at a greater initial rate than when it had established a certain amount of oscillatory components of error. Our analysis and non-linear simulation indicated that the source of the trouble was static friction between the cases and floats of the gyros and primarily the vertical gyro and that the oscillations minimized the effect of this friction. (Since magnetically supported gyros, ours were not, should be free of static friction, we would expect this phenomenon to be absent or greatly reduced in INS’s using this type gyro.) On the basis of our work with the GPL we recommend that similar Kalman filtered inertial systems use the feed-forward mode and further that the INS should be allowed to develop oscillatory errors (which are well modeled in the filter) prior to the start of a mission.
Published in:	NAVIGATION: Journal of the Institute of Navigation, Volume 20, Number 2
Pages:	190 - 192
Cite this article:	Salisbury, Contributor- J. D., "THE INSTITUTE'S PROFESSIONAL FORUM", NAVIGATION: Journal of The Institute of Navigation, Vol. 20, No. 2, Summer 1973, pp. 190-192.
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