ASCENDING NODE AND INCLINATION OPTIMIZATION OF SATELLITES CONSTELLATIONS IN MEDIUM EARTH ORBIT USING GPS

摘要

GPS navigation requires at least four GPS satellites to be visible at the same time. In standard terrestrial or LEO applications this requirement is always met. However, at MEO altitudes (Medium Earth Orbits with altitude ranging from 5000 km to 12000 km), the signal from four GPS satellites is seldom available. In great portions of the orbit only the signal from two or three satellites is received. In this paper the use of GPS for navigation in MEO is investigated. A Kalman filter is set up with the purpose of allowing accurate position and velocity determination even if less than four satellites are received. The configuration of the orbits of a MEO constellation is then studied. It is pointed out that GPS navigation is still possible at these altitudes and that the MEO constellation geometry can be set up to have the best coverage from the GPS.