Research On Key Techniques Of Autonomous Orbit Determination Of User Spacecraft Based On Beidou Inter-satellite Link

Accurate space-time information plays an important role in the maintenance of spacecraft orbital position.Increasingly crowded orbits and ever-increasing operational accuracy lead to higher requirements on the accuracy of the spacecraft’s orbit determination.Although there are many orbit determination methods,each has its own advantages and disadvantages,and they cannot solve the problem of high-precision orbit determination for spacecraft at all times.The traditional model of determining the orbit on the ground and then injecting the orbit data to the satellite has the problems of high communication pressure and information lag,which cannot meet the increasing real-time requirements of aerospace applications.With the completion of the Beidou-3 system,orbit determination based on the Beidou inter-satellite link has become a feasible solution for autonomous orbit determination by user spacecraft.Beidou inter-satellite link system has strong extension application capabilities.Connecting the user spacecraft to the Beidou inter-satellite link system and regarding the user as an extended node of the Beidou inter-satellite link system can make full use of the unique characteristics and global coverage advantages of the satellite navigation system as a time and space reference.Using the on-board processor to process inter-satellite measurement data to obtain its own orbit can theoretically meet the real-time orbit determination requirements of the spacecraft.Because the Beidou inter-satellite link is tailor-made for cooperative users such as navigation satellites with accurate priori orbit and time synchronization information,the design implicitly requires users for precise prior information.At the same time,because the Beidou satellite adopts the time division system,a Beidou satellite can only establish one inter-satellite link at a time.How to use the limited inter-satellite link to achieve the orbit determination and communication requirements of users and Beidou itself is still a hard problem! This leads to the basic problem of this work:how to use the limited inter-satellite link signal to efficiently realize the autonomous orbit determination of the user’s spacecraft? Around this issue,the thesis focuses on the following key technical issues:1.The access strategy of user spacecraft.The Beidou inter-satellite link measurement equipment is designed according to the Beidou satellite measurement and communication requirements.Because the user’s spacecraft’s orbital parameters and prior information accuracy are very different from those of the Beidou satellite,the user’s access methods and access strategies may also differ from those in the navigation satellite.Therefore,it is the first key technical problem to be solved to clarify the boundary of the user spacecraft’s access with Beidou and determine a reasonable access strategy.2.Performance analysis of user orbit determination.The basic problem of precise satellite orbit determination is to use observation data with measurement errors to solve a dynamic process whose differential equations are not precisely known.On the basis of a given initial state with errors,the solution is in a certain sense "best" estimate of the satellite’s motion state.Since the measurement characteristics,measurement geometry,and measurement sampling frequency of the user are significantly different from the Beidou internal link,how to analyze the orbit determination performance of the user spacecraft based on the user’s orbital characteristics and prior information accuracy is the second key technical issue of this dissertation.3.Optimization of inter-satellite link contact planning.The finiteness of inter-satellite link resources makes us hope to occupy as few link resources as possible while meeting the precision requirements.From the perspective of computational complexity,the solution to the link allocation problem is an NP-hard problem.How to obtain a good inter-satellite link allocation at a relatively low computational cost is still a difficult problem.This problem is the third key technology of this dissertation.4.Optimization of autonomous orbit determination algorithm.The design of the autonomous orbit determination algorithm requires a reasonable design of the autonomous orbit determination algorithm to meet the index requirements under the given constraints and prior information.At the same time,autonomous orbit determination algorithms are strictly limited by on-board processing capabilities,thus ground orbit determination algorithms are difficult to implement on spaceborne platforms.When users use inter-satellite links for autonomous orbit determination,since the total number of links is limited,it is hoped that users occupy as few link resources as possible on the premise of meeting orbit determination accuracy.Reducing the sampling rate means that the accuracy of the orbit model needs to be relatively higher when designing an autonomous orbit determination algorithm.At the same time,a larger sampling period will aggravate the nonlinearity of the orbit model.Both of these aspects will cause an increase in the computational complexity of the orbit determination algorithm.How to reduce the calculation cost of the orbit determination algorithm as much as possible while meeting the measurement accuracy index is still a difficult problem.In order to solve the above key technical problems,the dissertation proposes a two-step data formalization algorithm combining itemized compensation method and observation data fitting method and proposes a user orbit determination performance analysis based on multi-epoch observation weighted geometric dilution of precision,proposed an inter-satellite link allocation algorithm based on covariance control strategy and graph matching algorithm,and analyzed the optimization method of orbit prediction module and nonlinear estimation algorithm from the aspects of computational complexity and computational accuracy.These technical methods can solve the four key technical problems mentioned above and have passed theoretical analysis and simulation verification.They can be used for the user’s spacecraft autonomous orbit determination program and other related applications of inter-satellite links.