Abstract:
Objectives Tianwen-1 is the first independent interplanetary mission of China, and it was launched on 23 July 2020 and delivered directly into the Earth-Mars transfer orbit, which arrived at Mars in February 2021. It will complete orbiting, landing, and roving tasks in one operation. Exploiting tracking data from gathered during this science exploration and extended mission, this paper explores possible ways to improve the Mars gravity field model by simulation.
Methods We designed two types of orbits, including the polar orbits with near zero eccentricity and the near equatorial orbit with large eccentricity. Based on these two types of orbits, we recovered six gravity solutions considering various error sources, such as measurement noise, solar pressure error, rotation model error, and tracking time length. We used the power spectrum method to analyze and evaluate these recovered gravity models.
Results We find that a month of tracking data from the polar orbit or the combined polar and near equatorial orbit could be used to properly reconstruct the Mars gravity field model with orders and degrees of 42 under the 0.1 mm/s measurement noise. When 10% solar pressure error is added, the gravity model solution only suffers a slight influence showing in the power spectrum analysis. Furthermore, when Mars rotation model error is added, the degree variances of gravity models are affected only after the 35-order and degree.
Conclusions The results show that considering the influence of comprehensive error, the accuracy of gravity field solutions of the two types of orbits is similar. Nevertheless, the orbit with large eccentricity near the equator has a slightly stronger constraint on more than 35-order and degree coefficients. Besides, when the track tracking data collected from the near equatorial orbit phase are added in the recovering of Mars gravity model, the proposed model can improve the precise orbit determination accuracy of a spacecraft with near-equatorial orbit.
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