Navigation Performance in High Earth Orbits Using Navigator Gps Receiver

Ψ NASA GSFC has developed a GPS receiver that can acquire and track GPS signals with sensitivity significantly lower than conventional GPS receivers. This opens up the possibility of using GPS based navigation for missions in high altitude orbits, such as Geostationary Operational Environmental Satellites (GOES) in a geostationary orbit, and the Magnetospheric MultiScale (MMS) Mission, in highly eccentric orbits extending to 12 Earth radii and higher. Indeed much research has been performed to study the feasibility of using GPS navigation in high Earth orbits and the performance achievable. Recently, GSFC has conducted a series of hardware in-the-loop tests to assess the performance of this new GPS receiver in various high Earth orbits of interest. Tracking GPS signals to down to approximately 22-25 dB-Hz, including signals from the GPS transmitter side-lobes, steady-state navigation performance in a geostationary orbit is on the order of 10 meters. This paper presents the results of these tests, as well as sensitivity analysis to such factors as ionosphere masks, use of GPS side-lobe signals, and GPS receiver sensitivity. INTRODUCTION With recent advances in receiver capabilities, the Global Positioning System (GPS) is becoming an attractive alternative for satellites in geostationary or other high Earth orbits requiring improved orbit determination (OD) accuracies, reduced solution latencies, or accurate onboard state knowledge. The objective of this paper is to examine the sensitivity of GPS-based navigation performance to a number of important error sources or implementation assumptions. First, an orbit determination performance benchmark is established using the " best case " results for a geostationary user. These results utilize a GPS receiver with improved acquisition sensitivity, a high gain receiving antenna, and assume that measurements have been corrected to remove ionosphere and GPS ephemeris and clock errors. Subsequent analyses examine the sensitivity of the OD performance to factors including: receiver sensitivity and utilization of GPS side lobe signals, variations in transmitter antenna gain and transmitted power from different GPS satellites, ionosphere delays and mask settings, and GPS orbit and clock errors.