绳系卫星安全捕获策略下的释放最优控制

Optimal Control of Deployment with the Strategy of Safe Capture Using Tethered Subsatellite

安全捕获是绳系卫星系统空间应用的一个重要拓展。考虑系绳质量、系统质心变化及状态、控制约束,采用基于Lagrange方程的圆轨道条件下空间绳系网捕系统三维动力学模型。建立了安全捕获模型,推导得到零相对速度条件下的安全捕获末端条件。为保证方法的适用性,将基于Legendre伪谱法的连续时间最优控制问题离散为标准的非线性动态规划问题。最后在考虑释放控制前初始面外角偏差为5°的情况下,通过数值仿真验证了方法的有效性。仿真结果表明:对于远距离释放条件下的安全捕获,系统质心变化不容忽视;最小能量与绳长加速度约束下的控制响应相比最小时间与面内角约束要更平滑。

Safe capture is an important development of the application of tethered satellite system.Takeing tether mass,centroid drift and mission-related state-control constrains into consideration,the 3-D dynamics model of the tethered subsatellite in circular orbit is adopted for the rendezvous and capture of payloads on the basis of Lagrange equations.The safe capture model is established,and the end conditions of zero relative velocity rendezvous are derived.For the adaptability,the optimal control is solved by discretizing the problem based on the Legendre pseudospectral method.The initial error of the out-of-plane libration angle before deployment control is considered as 5 degree and the numerical results well demonstrate the performance of the proposed strategy.The numerical results show that,from the required long-term safe capture point-of-view,the excursion of the center of mass can＇t be ignored.Futhermore,the control response at constraints of minimum energy,and tether acceleration is better than that at constraints of the minimum in-plane angle and time.