MERcury Gravity REcovery and Analysis System (MERGREAS) and its performances from simulated four-way Doppler measurements.

The exploration of the planet Mercury requires software applications that can execute Precise Orbit Determination (POD) and estimate dynamic parameter solutions. In this paper, we present MERcury Gravity REcovery and Analysis System (MERGREAS), a new software product that is designed to support the future Chinese Mercury explorations. To validate the software we crosschecked the MERGREAS functionalities against the GEODYN-II. Simulated orbit determination experiments show that the differences between MERGREAS and GEODYN-II in the X , Y , and Z directions were 0.2, 0.7, and 0.5 m respectively with the arc length of 24 h. The integration interval for both software platforms was 10s. The MERGREAS software can utilize four-way Doppler measurements for spacecraft orbit determination as well as precise positioning of a Mercury lander. In simulations, we show that when the four-way Doppler data are included, the accuracy in Mercury spacecraft orbit determination can reach the centimeter level and the lander positioning accuracy can be refined to decimeter level. Furthermore, when we considered the influence of the Mercury gravity errors, measurement bias, and Mercury orientation model errors in POD with MERGREAS, the errors in the orbiter position ranged as high as 300 meters with a lander position deviation of about 10 meters. The Mercury gravity field solution was improved and the accuracy of the Mercury tidal Love number k 2 increased by an order of magnitude when simulated four-way Doppler data were added. The more precise k 2 value enhanced the accuracy of the constraints used in internal physical parameters estimation for Mercury. These results provide a reference for future Chinese Mercury exploration missions. [ABSTRACT FROM AUTHOR]