| With the increasing variety of means for human understanding of the universe,human exploration activities continue to expand into outer space and even deep space environment,making the application of satellites in medium and high orbit increasing gradually.However,the precise orbit determination of satellites is the premise and basis for the successful implementation of the application mission.At present,the traditional ground-based measurement technology,by measuring angle,velocity and distance,is still the main technical means to achieve the orbit determination of medium and high orbit satellites.Due to the short tracking arcs,uneven distribution of stations,and the orbit determination accuracy of the ground-based measurement technology is only 100 meter level.It has been unable to meet the increasingly prominent navigation needs of medium and high orbit satellite missions.The onboard GNSS technology has the advantages of all-weather,high precision and low cost,and can realize continuous tracking of satellites.It has been successfully applied to loworbit satellites.The post orbit accuracy is of centimeter level,and the real-time orbit accuracy can reach the dm level.Further into outer space to expand the application scope of GNSS navigation system,then the mature spaceborne GNSS technology will be applied to the higher orbit satellites,which can effectively reduce the financial burden on the ground network,enhance the independent management ability of satellites,and then reduce the satellite dependence on ground system.Currently,the high-orbit GNSS technology is still in the research stage.Due to the long transmission path of the signal,which is about 2 to 3 times longer than that of the ground user,there is a certain systematic delay error in observations due to the influence of the plasma layer,resulting in a deviation between the geometric observation model and the observed data.Considering the signal acquisition sensitivity,high-orbit weak signal receivers are generally single-frequency GNSS receivers,so it is necessary to further study the error characteristics of single-frequency signals.In addition,the onboard GNSS applications of HEO,satellites can fly from above the navigation constellation to the low-orbit altitude,so further study is needed to refine the observation errors in low orbit;because the main perturbation power sources are not the same near the apogee and perigee,to obtain a more precise orbit dynamics,the perturbation force need to be fully considered,and thus the study of the efficient integral algorithm and the GNSS weak signal real time orbit determination method is one of the research difficulties.This thesis mainly studies the theory and method of precise orbit determination of onbornd GNSS weak signals.Around GNSS data quality analysis,geometric model of weak signals,orbit dynamics model and integral method,post and real-time precise orbit determination analysis,etc,we study the measured GPS data quality of weak signals of the TJS-2 satellite,and analyze the characteristics of errors,laying the foundation of the establishment of the geometric model and stochastic model;we also analyze the characteristics of the perturbation force of the gravity field in HEO varying with the orbit altitude,study the real-time orbit determination method of HEO based on weak signal GNSS,and develop the prototype software,to provide support for autonomous navigation of onboard GNSS spacecraft in high orbit.The details could be listed as follows:1)This paper systematically studies the theory and method of precise orbit determination of the onboard GNSS spacecraft in high orbit,analyzes the perturbation characteristics of the spacecraft,and studies the DOP characteristics of onboard GNSS observations,laying a foundation for precise orbit determination and error modeling of the measured data.2)The work analyzes the error characteristics of the GNSS weak signal observations in the high orbit environment,and it is found that there are systematic errors related to the sidereal period in the carrier phase observations of the TJS-2 satellite.Based on this,a sidereal correction model is established.Verifications showed that,adopting the correction model,the RMS value of posterior carrier-phase residuals was reduced from 245.8 mm to 82.1 mm,improved by 66.6%.In addition,we also found that in the process of tracking of the signals,the receiver could be influenced by occultation effects,and led to some deviation in the pseudo-range observations,causing the serious error adustment of the receiver clock,which would further damage the quality of other navigaion data at the same time.This finding could provide a reference for the improvement and upgrading of the domestic high-orbit GNSS receiver.3)This paper studies the method of signal error refinement of single frequency GNSS in low orbit,especially the reduction method of geometric error such as ionospheric delay and navigation ephemeris error.We introduce the modified germ-parameter approach,which can impose constraints on the domin of carrier-phase observations and thus separate the trend errors absorbed by the posterior carrier-phase residuals,making the residuals reducing to mm level.The simulation results showed that the single-frequency real-time orbit determination accuracy was improved from 0.68 m to 0.37 m,with an increase of 45%.4)The thesis studies the perturbation characteristics of HEO and the orbital dynamics integration method.There are different main perturbation force sources at different orbital altitudes for HEO.In the thesis,we proposed an adaptive variable-step integral and reduceddynamics method of real-time orbit determination based on GNSS,suitable for HEO,and the stability of orbit integral could be further improved through the error precorrection for the predicted values.This method overcomes the shortcomings of traditional one-step method in integration efficiency and multi-step method in step length fixation.At the same time,the adjustment strategy of the gravity order varying with the change of the orbit altitudes was used to enhance the adaptive ability of real-time orbit determination,and to improve the operational efficiency.Simulation results showed that the number of step length correction was reduced by 22.6%,and the average adjustment time was increased from 29.2minutes to 37.4 minutes.In addition,the 3D integral error was also reduced from 7.2 cm to less than 2 cm.5)The work studies the precise orbit determination method of the onboard GNSS weak signal of the high-orbit spacecraft,and the accuracy is verified with the measured data of the TJS-2 satellite and the Chang'E-5 experimental vehicle(CE-5T).For the long arc orbit determination of TJS-2,the accuracy of overlapping orbits with non-difference method is1.3 m,while the epoch-difference method can effectively reduce the influence of the slow geometric errors and the orbit determination accuracy is better than 0.7m.However,in the orbit determination of the short arc segment of the high-orbit spacecraft(CE-5T),the epochdifference method is highly sensitive to errors,and the orbit determination accuracy is only12 m,while the non-difference orbit accuracy can reach 7.1 m.6)On the basis of PANDA software,the prototype software of real-time orbit determination of spaceborne GNSS weak signal for HEO satellite was developed.The onboard GPS data of TJS-2 was used in real-time orbit determination,adopting GPS broadcast ephemeris.The errors in the phase observation of weak signals were corrected by the sidereal model.The convergence time of the along,cross and radial direction was 10 hours,6 hours and 16 hours respectively.After convergence,the orbit determination accuracy of the along,cross and radial direction was 0.51 m,0.37 m and 0.42 m respectively,and the 3D accuracy was 0.76 m.In the orbit determination of CE-5T for the return periods of the high elliptical orbit,the RMSs of the along-track,cross-track and radial-track of the real-time orbit determination were 8.40 m,4.56 m and 11.75 m,respectively,and the 3D accuracy was 15.14 m. |
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