The Visibility and Usability Research of Navigation Satellites for HEO

The application of global satellite navigation system to the user satellite at high elliptical orbit can overcome the disadvantage that the equipment of the ground control system is complex and high cost. But with the increasing of the altitude of user satellite, the number of usable satellites reduces, even less than four. In order to achieve navigating and positioning using the global satellite navigation system, this paper puts forward the concept of the transmission time demodulation threshold and the concept of ephemeris data demodulation threshold. We make full use of the navigation message information and analyze these new concepts to discuss a new method. The simulation result demonstrates that the new method improves the number of navigation satellites and period of navigating autonomously.