No abstract

This paper presents an online ascent trajectory optimization algorithm based on optimal control and convex optimization without accurate initial guesses. Due to the high complexity of space systems, exceptional cases such as engine failures may happen during the flight. In these cases, the dynamical model greatly changes and the nominal trajectory is infeasible. Thus, online trajectory optimization and replan should be considered when accurate initial guesses cannot be given. In this paper, the ascent trajectory optimization problem of launch vehicles is formulated as a Hamilton two-point boundary value problem (TPBVP) according to the optimal control theory. The control vector is expressed as a function of costate variables and the terminal condition is given according to the orbital constraint of the launch mission. In order to solve the TPBVP rapidly and accurately without accurate initial guesses, a convex approach is presented. Firstly, the flip-Radau pseudospectral method is applied to convert the continuous-time TPBVP into a finitedimensional equality constraint. Then, successive linearization is applied to formulate the problem as a series of iteratively solved second-order cone programming (SOCP) subproblems. Considering the accuracy and robustness of the algorithm, trust-region and relaxation strategy are applied. The convex trajectory optimization can be solved by Interior Point Method (IPM) automatically. Simulation results in the case of thrust loss are presented to show the accuracy, efficiency and robustness of the algorithm.

No abstract

Featured Application: This work may be used to improve the accuracy of attitude stability of flexible meteorological satellites.Abstract: Periodic disturbance may cause serious effects on the attitude of meteorological satellites, and the attenuation of periodic disturbance is required. In this paper, a fundamental study on the optimal design of constant compensations against known-law periodic disturbance for meteorological satellites is investigated. An analytical solution for the relationship between the frequency and amplitude ratios and the response of a typical second-order vibration system is firstly derived. The compensation and disturbance torques are determined according to practical engineering. The criteria for designing the optimal compensations are based on the analytical and simulation results. Then, the criteria are applied to a flexible spacecraft actuated by constant control torque in the presence of sustained periodic disturbance. The optimal compensation torque parameters for spacecraft are acquired based on former criteria. The compensate effectiveness of the optimal compensation torque is provided and compared with results of other selections in the frequency and amplitude ratio domain. Numerical simulation results and experimental results clearly demonstrate the good performance of proposed criteria. This work provides a significant reference for the vibration attenuation of meteorological satellites in the present of periodic disturbance.

This paper presents an innovative application of a 6-DOF robot in the field of rehabilitation training. This robot operates in a parallel fashion for lower limb movement, which adopts a new structure that can help patients to carry out a variety of rehabilitation exercises. Traditional parallel robots, such as the Stewart robot, have the characteristics of strong bearing capacity. However, it is difficult to achieve high-speed, high-acceleration and long journey movement. This paper presents a new robot configuration that can address these problems. This paper also conducts an all-around characteristic analysis of this new parallel robot, including kinematics, dynamics and structure, to better study the robot and improve its performance. This paper optimizes an algorithm to make it more suitable for rehabilitation training. Finally, the performance improvements brought by optimization are verified by simulations.