Dynamics and control of spinning tethers for rendezvous in elliptic orbits

The dynamics and control of spinning tethers in elliptical orbits for payload rendezvous is studied. The required rendezvous conditions for the tether tip are derived for the case where the tether system center of mass and payload are in coplanar elliptic orbits. It is proposed that rendezvous control can be achieved by tracking the unique tip trajectory generated by propagating the rendezvous conditions backwards in time. The range of suitable combinations of tether system orbit eccentricity, tether length, and payload orbit eccentricity are studied numerically. It is shown that certain combinations of parameters lead to non-spinning capture requirements and slack tethers. Control of the tether motion through tether reeling is examined using a nonlinear model predictive control strategy. Numerical results illustrating the effectiveness of the controller are presented.