How scientists tested the supersonic dynamic characteristics of Tianwen-1 Mars Entry Capsule?

The Tianwen-1 Mars entry capsule successfully landed on the surface of Mars in southern Utopia planitia on May 14th, 2021 at 23:18 UTC. One of the biggest challenges is that a typical blunt body such as Tianwen-1 Mars entry capsule suffers dynamic instability in supersonic regime. To investigate the unstable Mach range of flight and to confirm the design of aerodynamic shape and mass properties is key to achieve the Mars entry of Tianwen-1. In a research paper recently published in Space: Science & Technology, Haogong Wei from Beijing Institute of Spacecraft System Engineering conducted a ballistic range test aiming at capturing supersonic dynamic characteristics of Tianwen-1.

The blunt body entry capsule of Tianwen-1 was programmed to unfold a trim tab at Mach 2.8 to trim the angle of attack towards 0° before parachute deployment at Mach 1.8. However, transonic and supersonic dynamic characteristics of blunt body entry vehicles are difficult to calculate by numerical methods, because transient and unsteady flow phenomena such as separation, reattachment, wake, and time-delay are hard to capture accurately. Therefore, researchers prefer studying flight dynamics via ground testing methods. There are three types of tests, including forced oscillation, free oscillation, and free-flight. However, it is difficult to capture accurate dynamic characteristics by forced oscillation tests since this method induces considerable disturbance to the flow field unavoidably. The free oscillation method can only be used to obtain the dynamic response in a single degree of freedom, which is considered as a simplified free-flight method. Thus, the free-flight method, which reflects the real dynamic characteristics of the dynamical model, .is an appropriate alternative.

In this work, the authors conducted a free-flight ballistic range test in order to obtain the static and dynamic aerodynamic characteristics of Tianwen-1 in trimmed and untrimmed configurations under typical supersonic conditions and to verify the numerical calculation results of supersonic static and dynamic aerodynamic characteristics of the capsule. The tests were carried out in the 200m Free-Flight Ballistic Range of China Aerodynamics Research and Development Center. The test medium in the chamber was air. The binocular measurement stations were installed besides the room along the model flying direction, which would be calibrated and aligned to the global base reference coordinate system before the test. There are two configurations of scaled test models: trimmed (with trim tab deployed) and untrimmed (with trim tab folded).

The identification algorithm of the aerodynamic parameters for the free-flight ballistic range test is established first: The aerodynamic coefficients of free-flight scaled models were derived by modified linear regression method based on position and attitude data. The Static and dynamic coefficients are established under the assumption of small angle linearization. Afterwards, the analysis of the position and attitude, attitude oscillation, aerodynamic force, static and dynamic stability of the capsule are made and the results demonstrated that the ballistic range test captures the attitude behaviors and aerodynamic characteristics of Tianwen-1 Mars entry capsule. The obtained pitch and yaw moment coefficients are used to discuss the aerodynamic characteristics of the capsule. The capsule in trimmed configuration is dynamically unstable in the pitch and yaw directions, whereas the untrimmed configuration is dynamically stable. In both cases, the capsule is statically stable in pitch and yaw directions.

Reference

Author: Haogong Wei,¹ Xin Li,² Jie Huang,² Qi Li,¹ and Wei Rao¹

Title of original paper: Ballistic Range Testing Data Analysis of Tianwen-1 Mars Entry Capsule

Article link: https://spj.sciencemag.org/journals/space/2021/9830415/

Journal: Space: Science & Technology

DOI: 10.34133/2021/9830415

Affiliations:  

¹Beijing Institute of Spacecraft System Engineering, Beijing, China

²China Aerodynamics Research and Development Center, Mianyang, Sichuan, China

About Haogong Wei

Haogong Wei, achieved his Master of Science degree at Purdue University in 2014. Since then he participated in China’s deep space exploration programs at Beijing Institute of Spacecraft System Engineering, focusing on flight dynamics and aerodynamics.