Graceful Degradation of GPS/INS Performance With Fewer Than Four Satellites

Zdzislaw H. Lewantowicz, Danny W. Keen

Abstract:	Precision first pass weapon delivery with exceptionally accurate navigation are vital to the operational survivability of attack aircraft. Systems such as the Global Positioning System (GPS) are currently being fielded and integrated with inertial navigation systems (INS) to support such a capability. It offers the potential for less costly weapon targeting systems if target coordinates relative to the GPS reference can be provided. The current standard GPS receiver requires simultaneous signals from 4 satellites (with good geometry) to calculate and output useful position and velocity information. However, signals from 4 satellites may not always be available, especially in and around heavily defended target areas protected by high power jammers. These high power jammers, even when recognized and appropriately nulled out by adaptive array GPS antenna, can result in large sectors of the sky surrounding these jammers no longer being monitored for any GPS satellite signals. This paper recommends changes to the existing GPS equipment and new aircraft Kalman filter algorithms which provide graceful degradation of aircraft navigation performance when only one, two, three, or intermittent satellite signals are available, and quantifies the level of relative performance expected for these conditions. This paper also analyzes the relative performance of various Kalman filter mechanizations as a function of filter size.
Published in:	Proceedings of the 1991 National Technical Meeting of The Institute of Navigation January 22 - 24, 1991 Sheraton San Marcos Hotel Phoenix, AZ
Pages:	269 - 276
Cite this article:	Lewantowicz, Zdzislaw H., Keen, Danny W., "Graceful Degradation of GPS/INS Performance With Fewer Than Four Satellites," Proceedings of the 1991 National Technical Meeting of The Institute of Navigation, Phoenix, AZ, January 1991, pp. 269-276.
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