New tracking modes and performance for Mars spacecraft orbit determination and lander positioning

Abstract Precise orbit determination and lander positioning are still a challenge for Mars exploration. In this paper, three positioning methods are proposed, including the same-beam differential Very Long Baseline Interferometry (VLBI), four-way orbiter-lander Doppler and three-way loop Doppler for Mars orbiter and lander. Measurement models and these three positioning methods are further analyzed and evaluated using simulation experiments. The results show that about 60-m level accuracy for the Mars lander can be achieved by a combination same-beam differential VLBI data at 10 ps noise level with two-way Doppler data at the 0.1 mm/s noise level. Since VLBI data are sensitive to the angle between two radio sources, the accuracy of the Mars orbiter was not improved. The geometry of four-way orbiter-lander Doppler is more sensitive than the geometry of ordinary two-way Doppler, and therefore, after adding the four-way orbiter-lander Doppler data, the accuracy of the orbiter and lander positioning can reach the meter and decimeter level. Furthermore, the three-way loop Doppler reduces the number of orbital repeater signals and improves the POD accuracy at the meter level as well as the lander positioning accuracy at the decimeter level. Therefore, the three-way loop tracking mode provides an important reference for future Mars missions.