基于直接配点法的绳系卫星系统变轨控制

讨论了不必回收子星的二体绳系卫星系统(TSS)的变轨方案。假设TSS质心运动满足经典的二脉冲Hohmann变轨,用未变形绳长加速率控制两次脉冲期间的TSS运动。利用直接配点法中的Hermite-Simpson方法将控制消耗最小的最优问题离散为大型非线性规划问题,然后用MATLAB的SNOPT软件包求解;针对初始偏差较大的实际情况,又结合直接配点法和滚动时域控制得到了解析的反馈控制律。仿真算例表明,得到的TSS变轨过程状态变化平滑,控制消耗较小,而且变轨之后TSS接近平衡状态;此外,反馈控制律对最优路径的跟踪效果较好,能够消除初始偏差的影响。

Orbit-transfer Control for TSS Using Direct Collocation Method

An orbit-transfer scheme of a tethered satellite system (TSS) without the retrieval of the sub-satellite is discussed. It is assumed that the mass center of the TSS moves along a classical trajectory of Hohmann orbit-transfer. The unstrained length acceleration of the tether is selected as the control input for the TSS motion between the two impulses. The control minimization is discretized into a problem of large scale nonlinear programming by means of Hermite-Simpson discretization, which is one of the direct collocation methods. Then it is solved using MATLAB software package SNOPT. As the initial states might have large errors due to practical constraints, a feedback control law using direct collocation and receding horizon control is introduced. Numerical simulation results prove that the optimal orbit-transfer of a TSS has smooth trajectory and the control consumption is very limited. The closed-loop feedback control works well, too, so that initial errors can be eliminated after a certain period.Key words: tethered satellite system; nonlinear programming; receding horizon control; direct collocation method; SNOPT software package