Positioning Of High Orbit Spacecrafts Based On Multi-GNSS

High orbit satellites play an irreplaceable role in communication and meteorology because of their incomparable characteristics.For high orbit spacecrafts,the most important problem is the positioning of them.Traditional positioning method of high orbit spacecrafts is to use ground stations to measure,which will inevitably increase the complexity of ground stations with the development of high orbit spacecrafts.Besides,it is still impossible for China to build ground stations around the world.In a word,it is necessary to study the positioning of high orbit spacecrafts based on multi-GNSS.For navigation satellites were designed to locate ground users,their transmitting antennas are all pointing to the center of the earth.But for high orbit spacecrafts,the height of their orbits is greater than most navigation satellites,which causes high orbit receivers cannot receive navigation signals transmitted from satellites on the same side of the earth.Furthermore,the farther propagation distance will result in greater loss of signals,which cause the power of signals received by high orbit receivers is definitely lower than that of ground receivers.All of these will increase the difficulty of the autonomous positioning of high orbit spacecrafts based on navigation satellite system.This paper focuses on the autonomous positioning of high orbit spacecrafts based on GNSS navigation satellite system.The main research contents include feasibility study,positioning performance and environmental impact etc,which has important guiding significance for further development of autonomous positioning of high orbit spacecrafts.In this paper,the sensitivity of receivers will be studied firstly.Firstly,the model of high orbit spacecrafts and the model of GNSS navigation constellations will be built by STK.Based on this model,we will carry out simulation about the number of visible satellites of high orbit receivers.By comparing the number of visible satellites received by high orbit spacecrafts in different integrated systems and different receiving sensitivity respectively,we can get the minimum sensitivity of receivers.Besides,this paper will also simulate the Doppler shift and the relative acceleration between high orbit spacecrafts and navigation satellites,which can provide the parameters for the signal capture of receivers.Performance evaluation plays an important role in positioning and it is a guide to judge the positioning effect of a navigation system.Firstly,the positioning accuracy of high orbit spacecrafts positioning in all directions will be studied.Then,this paper will monitor the integrity of the receiver based on RAIM,analyze the availability of the receiver under different shielding angles and briefly describe the continuity.The propagation path of a navigation signal received by a high orbit spacecraft is different from that of ground receivers.So the existing atmospheric model for ground users is no longer applicable.In order to make the atmospheric error more accurate,we will study the atmospheric environment of high orbit spacecrafts.The keystone of the study is the tropospheric delay and ionospheric delay caused by atmosphere.Since signals received by high orbit receivers may not pass through the atmosphere,we need to study the proportion of signals passing through the atmosphere first.Then,the ionospheric delay for high orbit spacecrafts is analyzed.This paper innovatively established a ionospheric delay model for high orbit receivers and calculated the ionospheric delay of some typical satellites by this model.Finally,to visualize the simulation results,this paper will build a visual platform based on GUI under MATLAB.In this way,users can obtain the simulation results only through the GUI interface.Users can control STK through the MATLAB interface and easily get simulation results from the GUI interface.