Research On Dynamics Control And Trajectory Optimization For Electric Sails

With the rapid development of Chinese aerospace industry, the deep space exploration, even the deep space resource utilization, will gradually become a research hotspot in the research field of aerospace. Finding an effective propulsion technology is the first step to complete the interstellar voyage mission. Because of its great potential in the field of deep space exploration, many European experts have paid attention to electric sails. However, there are few researches on the electric sail in China. Since electric-sail spacecraft can use dynamical pressure of solar wind to generate thrust without consuming any propellant, it is quite suitable for deep space exploration mission and non-Kepler orbit. In this paper, the dynamics, control and trajectory optimization of electric sail are studied. This thesis mainly includes the following several aspects:Since the attitude and orbit of electric sail-spacecraft is coupled, the coupled attitude-orbit dynamics are investigated in this paper, based on the thrust model of single charged tether. The mathematical model characterizing the propulsive thrust is first described as a function of the orbital radius and the sail angle. Based on the thrust model, the orbital dynamics and attitude dynamics is investigated respectively. Since the solar wind dynamic pressure acceleration is induced by the sail attitude, the orbital and attitude dynamics of electric sails are coupled, and are discussed together.For the trajectory optimization problem of electric sail, a hybrid Gauss pseudospectral, sequential quadratic programming and genetic algorithm optimization method is proposed. The initial guesses for the state and control histories of the nonlinear programming problem, which is transcribed from the continuous optimal control problem by using Gauss pseudospectral method, are interpolated from the best solution of a genetic algorithm with less Legendre-Gauss(LG) points. Through a random and global search, genetic algorithm can provide a reasonable initial guess. Based on the obtained initial guess, the nonlinear programming problem can be solved by sequential quadratic programming to obtain the optimal solution. To verify the effectiveness of the proposed optimization method, transfer problems from Earth to Mars, Ceres and the boundary of solar system are investigated. Simulation results show that the hybrid optimization method is capable of searching the feasible and optimal solution without any initial value guess. This feature is ideal for the orbital control problem of electric sails, which is generally without prior knowledge.For the attitude tracking control problem of electric-sail spacecraft, the feedback linearization and sliding mode variable structure control are proposed. Via state feedback linearization, the strong coupling and nonlinear attitude control problem can be transformed into linear problems, in which each channel is independent of others. Then, each channel can be controlled via the sliding mode variable structure control. To verify the effectiveness of the proposed control algorithm, several simulations are implanted. Simulation results show that attitude can’t achieve asymptotically stable under the proposed control algorithm, because of the existence of non-matching uncertainties. However, through the rational design of sliding surface and control parameters, the system can also be provided with strong robustness and expected dynamical performance.Since the acceleration of electric sail is more sufficient for high displacement orbits, electric sails are proposed to keep displaced orbits. Based on the coupled attitude-orbit dynamics of electric sail, the heliocentric displaced orbits are designed, and the necessary condition for keeping displaced orbits is also obtained. Then, the stability of the designed displaced orbits is analyzed. Analysis results show that only when inertia parameters of electric sails and orbital parameters of displaced orbits satisfy certain conditions, heliocentric displaced orbits with electric sail are balanced and stable. Based on the results of stability analysis, the linear quadratic regulator is implanted for the unstable displaced orbits. Numerica l simulation results show that the linear quadratic regulator is suitable for the stable control of electric sail in displaced orbit, and a small torque can make the coupled attitude-orbit system to be stable.