Abstract: In this paper, the heatshield separation trigger for Tianwen 1 lander is determined through analyzing the aerodynamic characteristics and relative rotation effect on separation distance. First the results of the simulation with different separation Mach numbers indicate that the higher separation Mach number has a higher recontact risk, and the heatshield descents faster than the lander due to the ballistic coefficient difference. In order to obtain the quantitative relationship between the separation distance and the motion of the lander at separation time, an analysis model for the heatshield and the lander system is established according to the characteristics of the attitude movement of the lander and the force of the parachute. By using the analysis model, the separation distances at variations of lander swing phase are evaluated to figure out the riskiest separation phase (RSP). The restriction on the peak of lander angle velocity and separation velocity is determined for heatshield separation by the simulation at the RSP. Furthermore, according to the fact that the peak of lander angle velocity decreases with the Mach number, the restriction on peak angle velocity is replaced by the upper limitation of separation velocity which provides a very low recontact risk to heatshield separation.

Key words: Tianwen 1 lander, Heatshield, Separation trigger, Aerodynamic characteristics, Relative attitude motion