Orbit determination for Chang’E-5 mission in rendezvous and docking
Abstract
<p indent="0mm">In the Chang’E-5 (CE-5) mission, the orbiter and ascender are tracked by ground stations to realize high-precision orbit determination and control before reaching the handover point. Herein, the orbit determination accuracy of the CE-5 rendezvous and docking section is analyzed. The long-arc overlapping results of the orbiter show that for a 200-km-high lunar orbit, the position accuracy of 12-h orbit determination is <sc>18 m,</sc> and the accuracy in the radial direction is <sc>0.4 m.</sc> Furthermore, because of the frequent orbit control, short-arc orbit determination is necessary to predict the position and velocity for the next orbit-control point. The short-arc orbit determination results of each arc segment of the ascender show that using combined VLBI and ranging data for 5-min short arc orbit determination, predictions can be conducted for <sc>4 h</sc> and the differences in the position and velocity are <sc>3 km</sc> and <sc>2.5 m/s,</sc> respectively. When using the ranging data of two stations for 0.5-h orbit determination, predictions can be conducted for <sc>6 h</sc> and the differences in the position and velocity are <sc>1 km</sc> and <sc>1 m/s,</sc> respectively; when these two-station ranging data are combined with VLBI data, the maximum difference in the position is less than <sc>250 m</sc> and the maximum difference in velocity is <sc>0.223 m/s.</sc> If the arc length for the orbit determination is less than <sc>2 h</sc> (one circle), convergence is not achieved using only range data. In this case, using VLBI data additionally, the position difference is approximately <sc>150 m</sc> for a 3-h orbit determination prediction. Moreover, for 3.5-h (nearly two circles) orbit determination arc predictions for <sc>6 h,</sc> the orbit difference is less than <sc>30 m,</sc> and with the additional use of VLBI data, the orbit accuracy can be improved to <sc>10 m.</sc> The analysis results show that the long-arc orbit determination accuracy of the Chang’E-5 200-km lunar orbit is better than <sc>18 m,</sc> and the VLBI data significantly contribute to improving the accuracy of short-arc orbit determination and prediction results.</p>
