Huo Mingying

Design and control of a position servo system in the zero gravity simulation of space manipulators

For the zero-gravity simulation of space manipulator, a position servo system is designed in this paper. The position servo system is composed of five servo platforms, which are used to track the joints of space manipulator, to ensure the slings keep vertical when the space manipulator is moving. Each servo platform consists of two CCD cameras, two servo motors, two orthogonal linear motion systems and a control computer. Using CCD cameras, the relative distance between manipulator joint and servo platform can be measured with no contact. Based on the measured distance information, platforms are controlled using PD controller to track the joints of space manipulator. In order to verify the tracking accuracy of servo platform with certain measurement error, numerical simulations are implemented. Simulation results show that the designed servo system can satisfy the zero-gravity simulation requirements of space manipulator.

Hybrid Genetic Algorithm Gauss Pseudospectral Method for the Electric Sail Trajectory Optimization

The electric sail is an innovative propulsion concept which uses the solar wind dynamic pressure to produce a thrust without the need for reaction mass. The electric sail is consisted by many tethers which are connected to a solar-powered electron gun. The electron gun emits electrons to maintain the tethers at a high positive potential. The electric field generated by the tethers reflects the solar wind ions to generate a thrust. In this paper, a hybrid genetic algorithm Gauss pseudospectral method is proposed to optimize the trajectory of the electric sail. The initial guesses for the state and control histories used in the Gauss pseudospectral method are interpolated from the best solution of a genetic algorithm. The proposed hybrid approach effectively includes global search ability of genetic algorithm and the high convergence rate of sequential quadratic programming. The numerical results show that the hybrid optimization method has the capability to search the feasible and global optimal solution of the electric sail trajectory without any initial value guess.