Research on Asteroid Landing with a New Flexible Spacecraft

During soft landing on asteroids, the weak gravity and rugged terrain put the spacecraft at risk of crashing and bouncing, such that a safe and accurate landing is essential for the spacecraft. In this paper, a new flexible spacecraft, composed of three thrust units and connecting airbags, is designed for asteroid landing. To estimate the flexible deformation of the spacecraft, an equivalent system model consisting of three spring-damping components and three thrust units is developed. Based on this model, a control scheme including path planning, tracking control, and control allocation is proposed. Considering double-zero constraints and flexible connection constraints, the trajectories of three thrust units are planned with the Gaussian pseudospectral method and then fitted into the trajectory of the flexible spacecraft mass center. Then, a nonsingular terminal sliding mode control law considering flexible body disturbances and thruster saturation problems is designed. To solve the control allocation problem, an active set algorithm considering the time-varying installation matrix caused by the flexible deformation is applied. Two simulation cases are provided to demonstrate the effectiveness of the proposed control scheme.