Orbit Determination and Analysis for Chang’ E-2 Extended Mission

The Chang’E-2 spacecraft was sent to the Lissajous orbit around the L2 of the Sun-Earth for an extended mission in June,2011.During that mission,the maximum distance between the satellite and the Earth was about 1 700 000 km.With an increase in the Earth-Satellite distance,the noise level in three-way ranging increases significantly on the one hand,and the constraint of flight dynamic decreases rapidly on the other hand.Moreover,the geometry for POD deteriorates,therefore the calculation for orbit determination also gets correspondingly more difficult during the process.These factors present challenges to the tracking system.In this paper,the POD for the Chang’E-2 extended mission is described in detail,and the accuracy is assessed using several methods.The results show that the degree of accuracy is better than 1km in the escape phase,and as the distance increases,the required arc-length for POD increases correspondingly.In the late phase of a transfer orbit,orbit determination calculation executed with 20 consecutive days’ data and and orbital comparison using overlaps and prediction analysis,show that the orbital error as a root mean square is at the level of 2 km.