Three-Dimensional Hinged-Rod Model for Elastic Aerobraking Tethers

Earlier analysiswith a rigid-rodmodel demonstrated thataerobraking tethers are feasible. In fact, the aerobraking tether may be superior to chemical retropropulsion when applied to exploration of the atmosphere-bearing planets of the solar system. Recent optimization studies provide even further advances in minimizing the tether mass with respect to propellant mass. Inasmuch as most of the work performed so far has modeled the tether as a rigid rod, it is clear that bending effects warrant investigation. An advanced model, consisting of a collection of hinged rigid bodies with springs and dampers at the hinges, is introduced. By using a matrix formulation the equationscan bemade very compact for any number of tether segments. The orbiter andprobe vehicles at the ends of the tether are also modeled as rigid bodies with the added feature of a movable attachment point. The forces include distributed gravitational and aerodynamic forces over the entire tether. A numerical example is presented that uses a prior mass optimization solution (based on the planar, rigid-rod model) for aerobraking at Mars. The example involves capture into an inclined orbit, which creates  exing in both out-of-plane and in-plane motions. The results indicate that the  exible behavior of a carefully designed tether is benign and does not exhibit large perturbations from the rigid-rod behavior. Because of its generality, the new model may prove useful to other investigators working with tethers in space.