The Projectile Challenge For GPS Guidance

Lawrence L. Wells

Abstract:	Advances in technology have enabled the use of GPS in smaller and smaller platforms. One current development is the application of GPS to projectiles. L3-IEC is currently involved in two such programs: the Extended Range Guided Munition (ERGM) projectile for Navy 5" deck guns and the Excalibur (formerly the XM982) projectile for Army 155-mm Howitzers. Raytheon Systems Corporation, Tucson AZ, is the prime developer of both projectiles. These projectiles are guided in-flight by GPS. While the use of GPS in a projectile generates a lengthy list of severe related requirements; the first and most onerous requirement is the ability of the GPS receiver to survive the 15,000-g+-setback shock of gunfire. Having survived the gunfire, the next problem is that the range and flight duration of a gunfire-propelled projectile is quite short compared to powered munitions. This means that very fast initial acquisition is required. High jamming conditions must be expected since the GPS is being used operationally by these tactical weapons in a battlefield environment. Collectively, this means the Projectile GPS receiver must have a jammer-tolerant very fast direct-Y acquisition and track capability. It must be tightly coupled with an on-board inertial measurement unit (IMU) for optimum jammer tolerance. The Projectile GPS receiver must be SAASM-based for battlefield security. It must draw minimal power to conserve limited on-board battery power. Finally, these guided projectiles will be manufactured in high quantities. The recurring cost of the Projectile GPS receiver for guidance is a major consideration. This paper describes L3-IEC's GPS receiver that is designed specifically to satisfy these projectile application requirements. The direct-Y acquisition issues, including the acquisition correlator and reference oscillator considerations are discussed. The jammer tolerance features and how they interact with acquisition and track are described. The SAASM design is described and the complete GPS receiver is described and illustrated.
Published in:	Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001) September 11 - 14, 2001 Salt Palace Convention Center Salt Lake City, UT
Pages:	850 - 854
Cite this article:	Wells, Lawrence L., "The Projectile Challenge For GPS Guidance," Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001), Salt Lake City, UT, September 2001, pp. 850-854.
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