GPS BEYOND LEO:SIGNAL ENVIRONMENT SYSTEM DESIGN CONSIDERATIONS

摘要

The purpose of this paper is to present GPS signal environment prediction data that is useful in the design of GPS space navigation systems in MEO, HEO, and GEO orbits, and beyond.The President's Vision for Space Exploration, including a new manned vehicle that will operate from LEO to trans-lunar orbit, along with new user navigation accuracy and robustness requirements for GEO satellites, have spurred a new interest in developing GPS navigation systems designed to operate in the sparse measurement environment. Understanding that environment is key to designing a successful system.Several published papers have described the well understood geometric constraints of the GPS system when operating receivers near or above the GPS constellation. A select few operators have reported on actual data collected by receivers operating at or above the GPS constellation. Finally, several papers have been authored regarding proposed systems showing simulation results for high altitude GPS based navigation systems. These simulation results are based on modeling assumptions that are critical to the analysis. Visibility analyses are informative, but if the link margin is a few dB and uncertainty is a few dB, system success may be in doubt.This paper will (1) briefly summarize some earlier work in the use of GPS above the terrestrial and LEO regime, (2) discuss and present predicted GPS signal environment data in a manner that is useful to system designers developing GPS based or GPS augmented space navigation systems beyond the LEO regime, permitting trades to be conducted in system design.