Optimal Firing Attitude Design for Mars Probe “Tianwen-1” Braking and Capture

Abstract

To optimize ignition attitude design during Mars capture and braking of China’s first autonomous Mars exploration mission “Tianwen-1”, an analysis idea and a solution under the constraint of the whole vehicle were proposed. Firstly, the trajectory dynamics model in the capture phase was established. According to the pre-capture trajectory and the post-capture target trajectory, optimal thrust direction and ignition time in the orbit plane were solved by Newton iteration method with minimum fuel consumption as optimization objective, and thrust vector was obtained. Combined with illumination and measurement and control constraints of the detector, deflection range around thrust direction was determined. Finally, referring to the layout of star sensors, occlusion of star sensors by celestial bodies at different deflection angles during the whole process was analyzed, and the number of available star sensors and the available duration were calculated. The optimal ignition attitude was determined according to the principle of optimal available duration. The actual on-track braking capture results show that the semi-major axis deviation after track control is less than 947.122 km (semi-major axis variation of 102346.152 km), and the eccentricity deviation is less than 0.0021. At the same time, the whole process can meet the requirements of the whole device for measurement and control and illumination. During the whole acquisition process, at least two star sensors are available at any time, and compared with the telemetry results, the simulation error of the available duration of star sensors is less than 0.225 h.

Keywords

Mars probe / braking and capture / firing attitude