Abstract: 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.

Key words: Tethered subsatellite, Safe capture, Deployment, Optimal control, Legendre pseudospectral method