A Virtual Navigation System and Solutions of Extraterrestrial Disturbances

Guochang Xu, Xiaochun Lu and Xiaohui Li

Abstract:	A study on a virtual navigation system is conducted in GeoForschungsZentrum (GFZ) Potsdam in cooperation with the National Time Service Center (NTSC) of Chinese Academy of Sciences (CAS) to investigate a possibly alternative navigation system, which should be an unusual system without too much similarity with the exiting GPS, GLONASS and Galileo systems and which should be much economically to build and more efficient for use. The new system will be used to verify the standard theory and algorithms from a special view aspect. Emphasize is given to the use of the node geostationary satellites with small or large inclinations. Software has been developed to simulate the virtual navigation systems (and of course may be used to simulate the systems of GPS, Galileo and GLONASS). First step of study is concentrated in a regional navigation system (for Asia). An optimal constellation of the system is studied for a reasonable coverage to meet the requirement of positioning user. Then the concepts of orbits determination for maintaining the system and algorithms of positioning for applications are investigated. The virtual system needs fewer satellites so that the system may be built much more economically. The longer visibilities of the satellites lead to a greatly reduced size of problem in applications such as orbit determination or positioning. The instability of the traditional algorithm becomes obvious and stabilised measure has to be taken. A new algorithm of orbits determination is in developing, which does not need to solve the variation equation for forming the observation equation and to use the numerical integration for forecasting the orbits. A disturbance coordinate system is introduced to describe the model of solar radiation pressure. The traditionally used adjustment model has been found out that it is not reasonably formulated. A simplified model is reached by using the disturbance coordinate system to represent the problem. A theoretical solution of the solar radiation disturbance on the satellite motion is derived based on the nominal motion of the satellite. Numerical solutions of the disturbance of the Sun and the Moon can be derived similarly under simplification and approximation within the limitation of the accuracy requirement. The disturbance of the gravitational field of C20 is derived theoretically. However, the intension to derive the 6X6 orders and degrees of the gravity field disturbance seems to be much more complicated than originally estimated (cf., Xu 2008). An extension of the regional navigation system to the global system is made and has been resulted an excellent constellation of a virtual navigation system. In scientific points of view, we believe this virtual navigation system will be a true one in the future because of the enormous advantages. Further studies on different problems are necessary.
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	2668 - 2675
Cite this article:	Xu, Guochang, Lu, Xiaochun, Li, Xiaohui, "A Virtual Navigation System and Solutions of Extraterrestrial Disturbances," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 2668-2675.
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