Orbit determination of CE-5T1 in Earth-Moon L2 libration point orbit with ground tracking data

Abstract

CE-5T1 is the pilot probe of China’s lunar exploration project phase 3, which is mainly used to verify CE-5’s orbit and reentry technology. CE-5T1 extended mission is the first of China to fly spacecraft in the Earth-Moon L2 region. It stayed at the L2 region for about 40 d from Nov. 2014 to Jan. 2015. The Shanghai Astronomical Observatory (SHAO) team utilizes the SODP (SHAO Orbit Determination Program), using a batch least squares method, to process range, Doppler and VLBI tracking measurements from ground stations. The orbit characteristics determine that L2 probe needs to use long arc data to improve the orbit accuracy. The effect of VLBI systematic errors on the orbit is bigger than that of range measurement because of the geometry difference between the probe and ground stations. For CE-5T1 in Earth-Moon L2 libration point orbit, the tracking accuracy for range, Doppler, VLBI delay and rate are typically 1 m, 1 mm/s, 1 ns and1 ps/s, respectively. The typical accuracies of orbit determination solutions are on the order of several hundred meters in position and several mm/s in velocity with 5-7 d tracking data. The combination of VLBI data with range/Doppler data can improve the orbit accuracy in the L2 region comparing with the range/Doppler data only. The technique and analysis method used can provide a baseline for future Earth-Moon libration point spacecraft mission, including CE-4 relay satellite in the L2 region.