Research On Differential GNSS Relative Positioning Technology For Spacecraft On-Orbit Service

For high-value spacecraft with failure or fuel depletion,on-orbit maintenance or life extension services have important economic and technical value.The relative positioning technology for guiding service spacecraft to approach and dock the target spacecraft is the key for such on-orbit service capability.The differential GNSS relative positioning technology based on Global Navigation Satellite System(GNSS)can provide high-precision,continuous and reliable relative position information,which is an important development direction in this field.At present,the intersatellite relative positioning technology based on differential GNSS plays an important role when the two satellites are several kilometers to one hundred meters apart.However,when the service spacecraft approaches and hovers or orbits observation target spacecraft,due to changes in the common view sky caused by the attitude movements of the two spacecraft,the differential GNSS relative positioning has the risk of interruption,and targeted research to enhance system reliability is required.The main work of this paper includes the following four parts:(a)Design of real time carrier phase differential relative positioning system.Analyzing main errors of navigation satellite signal in the transmission process,and constructing the double difference carrier phase observation equation;Linearizing the pseudo range observation equations and calculating the approximate position of differential GNSS receiver based on the principle of least square method;Using LAMBDA method to solve the integer ambiguity of double difference carrier phase observation equation and calculating the relative position.Finally,the basic positioning capability of real time carrier phase differential relative positioning system is verified by off-site test and semi physical simulation test.(b)Design of three antenna observation combination differential relative positioning method.Aiming at the problem that the number of common view satellites is less than 5 for a long time due to the attitude movement of service spacecraft and target spacecraft,which leads to the interruption of differential GNSS.Based on the principle of vector operation,a differential relative positioning method of antennas observation combination is proposed.This method can effectively increase the number of common view satellites between service spacecraft and target spacecraft,increasing the number of carrier phase observation equation,and improving positioning stability.The influence of antenna phase center offset for differential relative positioning method of three antenna observation combination is also analyzed.The results show that with the increase of the antenna phase center offset,the interruption rate and positioning error of the three antennas observation combination differential relative positioning method increase continuously.(c)Design of Multi-source GNSS Parallel Differential Relative Positioning Method.Based on the spatial-temporal unified space environment of BDS Navigation Constellation and GPS Navigation Constellation,designing three antennas parallel differential relative positioning method of dual mode combination of BDS and GPS,finding effective relative positioning output by searching between antennas.The results show that the method is less affected by the phase center offset of the antenna,but the stability of differential GNSS relative positioning is weaker than that of the three antennas observation combination differential relative positioning method in the orbit around phase.Based on the complementarity of the two differential relative positioning methods,the mechanism of multi-source GNSS parallel differential relative positioning is proposed,searching the effective relative positioning output between two differential GNSS relative positioning systems to further improve the stability of differential GNSS relative positioning for spacecraft on-orbit services.(d)Design of simulation analysis system.In order to meet the need of close observation of on-orbit service spacecraft,designing test scenarios for service spacecraft to hover,approach and orbit around the target spacecraft in close orbit.Building a semi physical simulation analysis system based on attitude orbit dynamics simulator,dual channel navigation star simulator and differential GNSS receiver to simulate on-orbit service test scenarios,navigation star signals and differential GNSS relative positioning data between two satellites,and using MATLAB,STK and other tools to assist the analysis system to analyze and verify the differential GNSS relative positioning algorithm.