Tethered planetary capture: Controlled maneuvers

A new concept for the application of space tethers in planetary exploration and payload transfer is presented. It is proposed that a payload be deployed on a spinning tether in a hyperbolic orbit in order to provide a sufficient delta-v such that it is captured in an elliptical orbit at the destination planet. Due to conservation of momentum, the main spacecraft gains a "momentum-enhanced gravity-assist". This concept is investigated by conducting numerical simulations of a simplified system. The mathematical model is derived using Lagrange's equations including tether mass, but neglects tether vibrations. The feasibility of the concept in the constant length case is demonstrated by numerically integrating the equations of motion. The required tether mass to prevent rupture is optimized using numerical and iterative techniques. These results are validated through mass and force contour plots. The optimum tether length, diamter and mass are determined for each of the major outer planets in the solar system. Finally, it is shown that controlling the tether length during the maneuver is preferable to maintaining the tether at a constant, length. The control problem is posed as one of minimizing a performance functional, and a solution method is proposed utilizing nonlinear programming with direct integration. (C) 2003 Elsevier Science Ltd. All rights reserved.