Chang Shengqi

Local correlation and orbit determination for DOR signals in Chang’E-3

The X-band Delta-Differential One-way Range is first formally used in Chang’E-3 spacecraft, and will be continually used for other Chinese future deep space navigation. We have carried out researches on each DOR tone using local correlation method which is quite different from the conventional VLBI correlator. The CE-3 signal interferometry processing is completed with this method. High precision Delta-DOR group delay and radio source correction are obtained for orbit determination. The phase noise of local correlation is significantly smaller than that of the VLBI conventional correlator. The ephemeris from local correlation is about 20 m different from the precise ephemeris of CE-3 project, and the corresponding equivalent residual delay is about 0.4 ns. Experiment result shows that local correlation is more suitable for weak signal processing, and it can be used for the future Chinese lunar and other deep space exploration projects.

Mars spacecraft tracking and analysis of VLBI orbit determination

The Chinese Mars mission will be launched in 2020, which consists of an orbiter and a rover. Mars spacecraft tracking and precise orbit determination are very important for achieving engineering and scientific detection. This paper first analyzes the Mars spacecraft tracking technology, and then introduces VLBI orbit determination results used in the mission of Mars Science Laboratory. Further, for a Mars spacecraft launched in July 2020, we give the angular distance between the spacecraft and the sun from launch to disorbit, the solar plasma delay, and observation elevation, at Shanghai, Beijing, Kunming and Urumqi stations in the arc segments of trajectory correction maneuver, Martian orbit insertion, plane maneuver, and disorbit. Orbit determination and prediction errors in the arc segment of Martian orbit insertion are also presented. Three-dimensional orbit determination error is reduced from 45.7 km to 18.8 km, and the periareon height prediction error (1 sigma) is reduced from 28.2 km to 7.6 km when combined VLBI data with range and Doppler data.

Real-time orbit determination for transfer orbit and lunar orbit of the CE-5T1 probe

In order to meet the needs of autonomous capability for the lunar exploration, an analysis of real-time orbit determination is proposed in this paper for the CE-5T1 probe by using extended Kalman filter. For the lunar-Earth transfer orbit, compared with the least squares method, the accuracy of orbit determination result using 2.5 h satellite-based GNSS data is about 30 m in position, and 1 cm/s in velocity by using EKF method, as well as the velocity of convergence is better than 1 h. For the lunar orbit, the result shows that the EKF method is able to achieve the same level accuracy to the least squares method, furthermore, through a better orbit forecast algorithm design, the Earth-based observation gap caused by the shelter of the moon has little influence to the filter accuracy of the following observation arc.

The application of the seam beam VLBI techniquefor the orbit determination of CE-5 in the rendezvous and dockingphase

CE-5 will be launched in 2017 – 2018, and it is a lunar sampling return mission. It is the first time for China to carry out the rendezvous and docking in the Moon. How to achieve rendezvous and docking successfully in the Moon is very important for CE-5 project. When the ascender is about 70 km farther away from the orbiter, the ground based tracking technique including range, Doppler and VLBI will be used to track the orbiter and the ascender. Later the ascender will approach the orbiter automatically. Here the application of the same beam VLBI for the orbit determination of the orbiter and the ascender in the long range of the rendezvous and docking phase is discussed. The same beam VLBI technique can be used to track the orbiter and the ascender simultaneously when they are in the same beam. Delta delay of the two probes can be derived, and the measurement accuracy is much higher than that of the traditional VLBI data because of the cancelation of common errors. Theoretically it can result in a more accurate relative orbit between the two probes. The simulation results show that the relative position accuracy of the orbiter and ascender can reach about 1 m in CE-5 project with delta delay data of 10 ps.