Development of Mercury Precise Orbit Determination Software and Application

We have developed the first Mercury precise orbit determination and geoscience parameters solution software system with independent intellectual property rights, MERGREAS, considering the great prospect of its future missions in China. The software simulates forecasting ephemeris, observations, and precise orbit determination (POD), and then results are compared with GEODYN-Ⅱ. The difference magnitude of the forecasting ephemeris is at 10^-7-10^-8 m in a day, and the speed deviation is at the magnitude of 10^-9-10^-12 m/s; besides, two-way range difference is 10^-4 m and two-way range-rate difference is 4×10^-6 m/s. In POD, the X direction error is 0.2 m, Y direction 0.7 m, Z direction 0.5 m, therefore, the simulation results show that the software precision of POD can reach the level of GEODYN-Ⅱ for MESSENGER. Meanwhile, we analyze the Mercury lander with simulation of same-beam very long base line interferometry(VLBI), with position error of 1 m for orbiter and 0.88 m for lander. With the errors combination from Mercury gravity models and Mercury rotation models taken into account, the position error is 13.6 m for orbiter and 250.3 m for lander. This software can provide reference for the Mercury tracking task in future. These research results have certain application value to China future Mercury exploration missions.