Concepts for Replacing Shipboard TACAN With Differential GPS

A. J. Van Dierendonck

Abstract:	The Tactical Air Navigation (TACAN) System is scheduled to be phased-out in the future. The NAVSTAR Global Positioning System (GPS) has been designated by the Department of Defense (DOD) as its replacement. However, it has not been specified how GPS will be used as that replacement, especially when it comes to shipboard applications. In land-based relative navigation (RNAV) applications, the airborne GPS receivers can be programmed to operate with fixed waypoints from which to navigate, in which case GPS can replace TACAN, an interrogating system, in a passive manner. In shipboard applications, however, the airborne receiver does not necessarily have knowledge of ship locations, making it impossible for it to navigate with respect to the ships. Thus, the receiver must be augmented in such a way to eliminate this deficiency, and provide a means for navigation relative to a ship or multiple ships. This paper presents methods for making GPS an adequate replacement for shipboard TACAN, using it in a differential mode in conjunction with a data link, which may either be a conventional communication system, or one that is implemented at one or two of the GPS frequencies. In the latter case, the data link becomes a pseudolite (PL) system, which could also provide ranging measurements to the ships. Whether or not a conventional data link or a PL system is used, the ship locations (and possibly, velocities) are broadcast to the airborne receiver, providing that knowledge and making it possible for the receiver to navigate with respect to the ships. Solutions of problems for the Differential GPS (DGPS) data transfer are also presented. If a conventional communication system is used, airborne and shipboard integration issues must be resolved. If PLs are used, no airborne integration may be required, but possible interference issues must be resolved. In either case, data encryption is a must, since the information being transferred is sensitive.
Published in:	Proceedings of the 3rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1990) September 19 - 21, 1990 The Broadmoor Hotel Colorado Spring, CO
Pages:	679 - 688
Cite this article:	Van Dierendonck, A. J., "Concepts for Replacing Shipboard TACAN With Differential GPS," Proceedings of the 3rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1990), Colorado Spring, CO, September 1990, pp. 679-688.
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