Abstract: The mechanical model of the platform of 3-DOF air-bearing spacecraft simulator is founded based on the method of kineto-elastodynamic analysis. According to the theory on the spacecraft attitude kinetics the formula for the platform structure mass-center displacement and for the counter-weight are deduced. Therefore, the calculation formula for unbalance torque arising from self-weight deformation of platform is obtained. It is calculated by FEM that the unbalance torque arising from self-weight deformation of platform with the platform design parameters combined by various numerical values. The influence of parameters change on unbalance torque when the stiffness in different directions of the platform structure is equal, is explored, and the concept of equilibrium point that makes the unbalance torque of platform structure become zero, is proposed. The relation between equilibrium sensitivity, i.e. the degree of influence of platform structure parameter change on the unbalance torque, and platform structure stiffness is analysis. The result shows there are many equilibrium points in a platform structure. At every equilibrium point, the influence of a slight change in structure parameter value on the unbalance torque arisen from the platform self-weight deformation may differ greatly. The higher the stiffness is, the lesser the influence of the structure parameter change on the unbalance torque will be.

Key words: Air-bearing spacecraft simulator, Mass-center, Rigidity, Satellite, Unbalance torque