Research On Orbit Determination For The Braking Lunar Explorer

In the soft-landing process, the thrust engine produces complicated thrust, the uncertainty ofthrust acceleration will cause enormous error to model. The soft-landing mission of lunarexplorer is in much demand of the real-time tracking and navigation along the descending flight.In order to realize the precise orbit determination of the maneuver process, this paper focuses onaccurately modeling the orbital maneuver process by on-line compensation to dynamicparameters. Taking the third lunar orbital brake process of CE-1as an example, the proposedmethod is validated with domestic VLBI network observations. Comparing with the post-result,the difference of semi-major axis is120m, and the difference of eccentricity is0.001. Mainconclusions of the paper are:1. Difference algorithm is proposed to detect the beginning and end of orbital control epoch.This paper analyzes the leaps of spacecraft acceleration during the maneuvering process,discusses the sensitivity of observation such as USB2-way Doppler and VLBI time-delay rate,constructs difference algorithm and eliminate the invalid result according to un-present ofcontinuous leaps, and detect the beginning and end of orbital control epoch. The proposedalgorithm is validated to detect the three brake process with domestic VLBI time-delayobservations.2．Statistical test algorithm is proposed to detect the orbital control and the attitude controlepoch. This paper applies residuals square as test statistic to form model fault diagnosis.However, the chi-square is insensitive to diagnose small model fault because of the slowingincrease of residuals; then this paper proposes multi-dimensional test statistic in open windowand double test confidences. The proposed method is able to enhance statistic sensitivity and alsokeep test solution reliable by adjusting two confidences, and can be used to detect attitudecontrol begin epoch accurately. In order to accurately detect orbital control epoch, this articlealso proposes linear attitude control force model and even orbital control thrust model tocompensate the maneuver process roughly. Taking the third lunar orbital brake process of CE-1as an example, the proposed method is validated to detect attitude control and orbital controlepoch real-timely with domestic VLBI network observations.3. The sensitivity of domestic VLBI baselines is analyzed in this paper. In view of differentdirection and length, the6baselines are different to monitor the spacecraft maneuver process. Inview of the mutual integral relationship, the sensitivity of different observation types aredifferent.4. Dynamic parameters compensation algorithm is proposed to realize the presise orbitdetermination of the maneuver process. This paper focuses on accurately modeling the orbital maneuver process by using linear attitude control force model and two kinds of orbital controlthrust models. An EKF filter with expended dynamic system is developed to estimate position,velocity and dynamic parameters precisely with consecutive high-precision observations. Due tothe compensation to the uncertainty of dynamic model, the precise and real-time orbitdetermination during the continuous maneuver process can be realized. Taking the third lunarorbital brake process of CE-1as an example, the proposed method is validated with domesticVLBI network observations.5. This paper summarizes the different descending modes and flight control programs oflunar soft-landing process, and analyzes the navigation and propulsion technology during thedescending flight.