Abstract：[Objective] Lunar and Mars exploration projects face the issue of autonomous spacecraft landing or taking off on the surface of the target celestial body in a low-gravity environment. Several mechanical problems arise when a spacecraft is flying in a low-gravity environment, which is different from Earth's gravity environment. To solve these problems, it is necessary to verify the key actions of spacecraft for soft landing on or taking off from the target celestial body.[Methods] Since the Chang'e-3 mission of the second stage of lunar exploration, the test system of the suspension low-gravity simulation technology has been studied via fast follow-up and multilevel compensation, and the real-time tracking technology for the spacecraft motion in large space has been developed to keep the pulling force applied in the entire process constant and the deflection angle of the force direction relative to the vertical direction sufficiently small. Through the technical improvement of the third stage of the lunar exploration mission and the technical upgrade iteration of the Mars exploration, a complete set of technical systems for the spacecraft has been successfully constructed to simulate the low-gravity landing and take-off test of extraterrestrial celestial bodies on the earth. A three-dimensional (3D) follow-up system adopts the two-level linkage driving technology of a large-scale follow-up and rapid and accurate tracking to construct a landing and take-off test method for simulating the low-gravity environment of a spacecraft on the ground, thus overcoming a series of technical difficulties, such as large test space and high control accuracy, and employing several key technologies, including multi degree-of-freedom linkage of the 3D follow-up system and high-speed and high-precision coordinated control of the large-inertia electromechanical equipment.[Results] The large-scale follow-up tracking of the spacecraft in the test process was achieved by controlling the movement of the rapid follow-up platform through the parallel-link system driving technology, and the requirement of the absolute inclination angle of the lifting rope was realized by applying a high-precision tension control to the spacecraft through the rapid follow-up platform device and following the movement of the spacecraft in the horizontal direction. Additionally, the horizontal stiffness of the fast follow-up platform was improved to overcome the adverse effects of the coupling shaking of the two-level linkage equipment in the spacecraft test.[Conclusions] The system has been successfully applied to a series of real ground test conditions, such as hovering, obstacle avoidance, slow descent, landing, and take-off of China's Chang'e-3 and Chang'e-5 in the lunar exploration project and Tianwen-1 spacecraft in Mars exploration. The test data which can support the research and engineering exploration of spacecraft are obtained, providing a key technical means for verifying and optimizing the comprehensive performance parameters of the spacecraft. With the continuous development of space missions, the mechanical environment simulation and ground test technology regarding spacecraft landing and take-off from extraterrestrial bodies pose new challenges. The 3D follow-up system for a low-gravity simulation will further develop toward a high-precision, large-load, and high-dynamic simulation technology, laying the foundation for the application of ground low-gravity simulation tests for manned lunar landing and deep space exploration missions.
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2023, Vol. 63 
