Study Of The Dynamics Coupling Between The Two-axis Gimbal And The Satellite Bus

Dynamics coupling between the two-axis gimbal and the small satellite bus is oneof the problems that the ATP(Acquisition, Tracking and Pointing) technology mustsolve. The kinematics and dynamics coupling between the gimbal and the bus becomeeasier to take place due to the high mass ration between them, and in the microgravityspace environment, both of the these two parts can float freely. On the one hand, themovement of the gimbal may throw the satellite attitude angle off, or even cause thebus to be out of control. On the other hand, disturbance of the bus may cause apointing error in the gimbal, making it more difficult to keep tracking or imaging. Thekinematics and dynamics coupling between the spacial two-axis gimbal and the smallsatellite bus is discussed in this thesis through theoretical analysis, modeling andsimulation.Firstly, kinematics analysis of the gimbal is performed when it is in orbit with thebus. A model of the gimbal is established when it keeps pointing to an earth surfacetarget, while the bus is in its earth-oriented mode. The angular motion information ofthe gimbal is obtained through the computer simulation.Secondly, dynamics of the gimbal is discussed. The flat-topping phenomenonshowed in the angular tracing process and the zero-crossing distortion showed in theangular velocity tracing process are studied based on the LuGre friction model. Thegyroscopic effect is also presented in this section. A model of the gimbal is establishedto analyse its characteristics.Thirdly, different methods are used to establish the dynamics formula of thegimbal and the bus system. Dynamics coupling between the two-axis gimbal and thesmall satellite bus is then analyzed. Different spacial disturbance are taking intoaccount. Both the bus’ attitude angular error caused by the movement of the gimbaland the pointing error caused by the bus attitude angular deviation were analysed.Finally, simulations are applied to analyze the dynamcis coupling between thegimbal and the bus using the ADAMS (Automatic Dynamic Analysis of Mechanical Systems). Based on ADAMS and Simulink, a mechanical system of thetwo-dimensional gimbal was established to perform a combined simulation. Both therigid multi-body model and the rigid-flexible multi-body model simulation results areillustrated. The driving speed obtained from the kinematics simulation of the two-axisgimbal is used in the mechanical model. The satellite attitude angular deviationcaused by the movement of the gimbal is studied in the ADAMS/Postprocess module.