GPS Performance for GEOs and HEOs - The Equator-S Spacecraft Mission

Kurzfassung

The successfully usage of spaceborne GPS receivers for orbit- and attitude determination has in the past mainly been applied for spacecraft in near-circular Low Earth Orbits (LEO), e.g. TOPEX/POSEIDON, RADCAL. However, no experience exists of using GPS signals for Spacecraft navigation in altitudes above the GPS (20.000 km), such as the Geostationary Orbit (GTO). In this context, EQUATOR-S with it`s highly ellipitcal orbit offers a unique possibility in order to increases significantly the experience concerning GPS visibility, signal reception and GPS based navigation. The application of GPS based spacecraft navigation in GEO`s and GEO`s will bring advantages in many aspects. Besides orbit/attitude determination, GPS offers a potential for increasing command capabilities and decreasing ground station support. This will lead to a reduction of mission cost especially for LEOP phase of geostationary satellites. This paper describes first experiences in operating a GPS receiver in a highly elliptical orbit and presents first results of GPS visibilty and signal reception conditions within this orbit.