Abstract: According to the needs of China's first autonomous Mars exploration mission, combined with the mass characteristics of the orbiter and the layout of the propulsion system, the influence of jet unloading on the angular momentum of the detector was analyzed. On the basis of the analysis, the angular momentum variation of the detector was calculated by the change law of the rotating speed of three axes before and after the flywheel unloading, and the impulse generated during each jet was solved, as well as the thrust direction deviation. Coordinates of the detector's center of mass were solved through disturbance of each axis from the thrusters within the same group. The jet unloading of China's Mars probe Tianwen-1 in its cruise phase using different thrusters for six times was analyzed with in-orbit data. Calculation results of the thrust vector deviation and the centroid coordinates were highly consistent with design values. The measured thrust vector deviation was not more than 06, and the absolute deviation of the center of mass was less than 18mm, proving that the calculation method was effective and correct which can be used to set the direction of ignition and propellant budget in subsequent orbital control tasks.

Key words: Mars probe, center of mass, jet unloading, deviation of thruster vector, disturbed torque, angular momentum