The Research On The Key Technologies Of Ultra-Rapid Orbit Prediction

The satellite navigation and positioning technology has shown great research value and experienced unprecedented high-speed development in 1970s.It mainly includes two aspects:one is the navigation satellite constellation:the new Galileo and Beidou satellite navigation system is under constraction,the single medium Earth orbit is developed into multiple orbit forms,dual-frequency is replaced by three frequency or multi frequency signals,the old satellites is replaced by the new technology one and so on.The two is that the GNSS real-time high-precision service systems emerge in an endless stream.It can provide real-time,high-precision location,navigation and time service for users anywhere in the world.Thus,multi-GNSS real-time high-precision positioning is the development trend in the GNSS field.As the spatial dynamic refrences of GNSS positioning,real-time high-precision satellite orbit plays the most important role.Any satellite orbit error will directly affect the final results of GNSS positioning,especially the present real-time centimeter level PPP-RTK technology,real-time atmospheric monitoring and the emergence of earthquake and tsunami warning based on GNSS.As the most common real-time orbit of GNSS,ultra-rapid prediction orbit has very important research value and applicated prospect.Based on the development of the ultra-rapid prediction orbit,this paper analyzes and summarizes the shortcomings of the current research on ultra-rapid prediction orbit.Starting from the solution processing,mathematical model and some key problems of the ultra-rapid prediction orbit,the influence of the length of the observed orbit and the solar pressure model during the orbit-normal mode are studied.The following contents are included:1)First,it introduces the development status of multi-GNSS and the development process of GNSS positioning technology,and summarizes the importance of multi-GNSS ultra-rapid prediction orbit and the significance of this paper.Then the development of ultra-rapid prediction orbit at home and abroad and the research results of the key technology of ultra-rapid prediction orbit(the arc length and the solar pressure model of the observed orbit)are introduced.Then,we summarize some unsolved problems in the development of multi-GNSS ultra-rapid prediction orbit.2)Starting from the orbit prediction process,it introduced the common coordinate system and the ERP parameters used in their mutual conversion,then it introduced the satellite's motion equation.It is proved that the solution of the satellite orbit can be attributed to the initial state parameters of the satellite,and then the orbit fitting is introduced to estimate the initial state parameters of the satellite.The orbit prediction also involves the selection of dynamic models,it summarizes the types of solar pressure models,and introduces representative solar pressure models.Finally,the method of evaluating the performance of predicted orbit is introduced.3)It focused on impact of the fitting arc length of observed orbits and solar radiation pressure on orbit prediction performance for GPS,GLONASS,Galileo and BeiDou.The impacts are analyzed from three aspects,including orbit differences,Helmert alignment and stability of SRP parameters.As for orbit differences,the fitting arc lengths which have the smallest WRMS and median values are 40-45 h,40-45 h,42-48 h,40-50 h and 42-54 h for GPS,GLONASS,Galileo,BeiDou-IGSO and BeiDou-MEO,respectively.As for Helmert alignment parameters,the fitting arc length of 40-45 h,36-45 h,42-48 h,42-48 h and 39-54 h are more stable for each na,vigation satellite system.The results show that the performance of predicted orbit is closely related to the arc length of fitted orbits and stability of SRP parameters.In general,the fitting arc lengths of 40-48 h and 44-48 h have the smallest RMSs for GPS and GLONASS SRP parameters.When considering the joint solution of multi-GNSS for ultra-rapid orbits in the IGS.MGEX project,the optimal arc length interval is suggested as 42-45 h based on the above analysis.4)By using the data of BeiDou IGSO and MEO satellites during yaw-fixed mode,the effects of different solar radiation pressure models on orbit prediction were compared.There are four kinds of radiation model in comparison,which are ECOM 5 parameter model,ECOM 5 parameter ECOM model plus one additional constant acceleration in along-track direction,ECOM 9 parameter model and modified Adjustable Box-wing model.The results showed that ECOM 9 parameter model and the modified Adjustable Box-wing model was superior to that of the ECOM 5 model and ECOM 5 plus constant acceleration model.The modified Adjustable Box-wing model is slightly better than the ECOM 9 parameter model.Compared to the orbit prediction during yaw-string mode,the accuracy in along track and radial direction during yaw-fixed mode should be improved.