GPS Navigation for Use in Orbits Higher than Semisynchronous: A Look at the Possibilities and a Proposed Flight Experiment

The Global Positioning System (GPS) was originally designed for positioning and navigation uses on and near the Earth. Recent experiments have expanded the use of the GPS for orbit and attitude determination in low-Earth orbits. All of these uses are logical since GPS satellite broadcasts are always nadir pointing and the GPS orbit is higher than the receivers. This paper investigates using GPS signals for estimating satellite orbit parameters at altitudes above the GPS constellation of approximately 20,200km. Focus is given to the applicability of this technique to the United States Air Force Academy's (USAFA) lunar mission as a test bed for putting GPS receivers on future US military satellites orbiting at geosynchronous altitudes. Generic GPS navigation techniques for orbits above the GPS constellation are discussed. This includes an analysis of the expected geometry, required orbit-determination estimators, expected navigation error, and link budgets for geostationary-transfer orbits and geostationary orbits. The capabilities of both the Standard Positioning System (SPS) and the Precise Positioning System (PPS) is discussed. GPS receiver hardware and software options for the USAFA lunar mission are presented. Trade-offs are limited in scope to the monetary, power, and size budgets available to this mission. Similar analysis is accomplished for military geostationary satellites. A generic Defense Support Program (DSP) satellite is used to demonstrate the applicability and advantages of this tactic.