Simulation of GPS Vulnerability During Launch of Space Vehicles with Interfering Inputs

V.J. Reid, D.J. Biezad

Abstract:	Space vehicles launched from the continental United States normally require two independent tracking sources to satisfy range safety requirements. To date, these two tracking sources have been radar and inertial measurement units (IMUs). Because of the cost of maintenance and operational support, the government has implemented studies concerning potential phase out of radars during the next several years. Global Positioning System (GPS) technology is a candidate source of tracking that could be used to replace radar. The next -generation Atlas and Delta launch programs are already investigating operational use of GPS receivers as the second tracking source. However, GPS can be vulnerable to interference; which, in turn, can cause the receiver to lose track of individual satellites. Under worst-case circumstances interference can cause complete loss of ability of the GPS receiver to estimate position. Fortunately, GPS satellite simulators can be used to verify tracking integrity throughout the mission. This paper will describe the simulation of received GPS signals during launch of a space vehicle when interfering inputs are present using an Interstate Electronics Corporation Satellite Constellation Simulator (SCS). The simulation employs a realistic operational trajectory and uses an omni antenna with uniform gain (zero dB gain: 360°). The simulation varies the amplitude levels of a broadband interfering signal source at three interfering ground transmission sites. Tabular data for the resulting performance using Geometric Dilution of Precision (GDOP) as a metric is presented. The primary objective is to show the limits of interference tolerance for a typical GPS receiver under simulated operational conditions. The paper also provides an introduction and theoretical background for the GPS simulation task. It describes and discusses the potential effectiveness of GPS simulators in this type of work.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	2070 - 2081
Cite this article:	Reid, V.J., Biezad, D.J., "Simulation of GPS Vulnerability During Launch of Space Vehicles with Interfering Inputs," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 2070-2081.
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