An Angles-only Initial Orbit Determination Method For Space Objects

Most of the space objects orbiting the Earth are debris,which threaten the safety of in-orbit spacecraft.It is essential and fundamental to possess the accurate orbit information to prevent the collision of space objects.Space surveillance is mainly performed using optical,radar and laser ranging techniques.The geographical locations of ground-based optical tracking stations are a major factor affecting the maintenance of a space object catalogue,in addition to the tracking time limitation.By contrast,the space-based optical means can operate 24 hours a day and a well-designed Space-based Space Surveillance System(SBSS)can realize the global coverage.SBSS is a development trend,and an integrated system of ground-based and space-based systems is a better approach to the development of China's space warning system of independence,global coverage and timeliness,which is essential to the operational safety of strategically important space infrastructure.Space object cataloguing using the space-based optical space surveillance technique involves the design of the space-based satellite system,data collection and processing,and the catalogue design,etc.This thesis makes some preliminary study on a couple of problems.First,the visibility of debris to the space-based optical system is analyzed,and a SBSS constellation consisting of 12 satellites on 6 orbits is designed.The results show that the constellation has a good global tracking coverage.Optical observation to space objects can only generate a series of anglular measurements.Determining an object's initial orbit merely from angles data is one of the classical problems in the orbit dynamics.When a LEO space debris is optically observed from a LEO space-based telescope which operates in the scanning mode,only a very short orbit arc can be observed due to high relative velocity between the debris and the telescope.It is usually very difficult to obtain IOD(initial orbit determination)solution from such very short-arc angles by using traditional Gauss and Gooding methods.In this thesis,a new method is proposed to tackle this very short-arc angles-only IOD problem.Given a set of angular observations,the ranges at two chosen epochs are tested through a step-by-step search procedure,making the angles-only IOD problem the classical Lambert's problem.The solution to the Lambert's problem is examined by a quality control procedure where the angular observations at other epochs are used to judge the quality of the IOD solution.In this way,multiple solutions could be obtained,and an optimal solution is then determined.The method is applied to process simulated space-based angular observation of too-short arcs of LEO space debris.Comparisons with the results from using the Gauss and Gooding methods show that,the proposed method is significantly superior over the other two methods in both the solution success rates and accuracy.And the analysis of the errors of the numerical method indicates that the errors of IOD have a strong correlation the variation rates of observations.The method is also applied to process the ground-based angular data of LEO objects and the space-based angular data of GEO objects.The results show that the proposed method is also valid.The simulation results can be used in the design of both the ground-based and space-based optical space surveillance systems.