## Expanding Frozen Orbits with Rotating Tethers

The exploration of planetary satellites by robotic spacecraft is currently of strong scientific interest. One of the challenges of planning such a mission is the design of the science orbit, which is the orbit where the acquisition of scientific data takes place. Science orbits for missions to planetary satellites have, in general, low altitudes and near-polar inclinations so that the entire surface can be mapped, and the science requirements of the mission can be accomplished. However, designing such an orbit can be very difficult because the dynamical environment of many planetary satellites is highly perturbed with respect to an integrable two-body system due to their proximity to their central planet. One such example is the Moon.

High-inclination orbits around the Moon are known to be unstable, and thus emerges the problem of maximizing the orbital lifetime. At his concern, the so called frozen orbits offer an interesting starting point for the design of science orbits, for they have the peculiarity that the orbital elements (with the exception of the mean anomaly and longitude of the ascending node) remain constant. Therefore, the search for high inclination and low eccentricity frozen orbits is a very attractive research field.

SDG-UPM has recently pursued to give an insight into the potential applications of rotating space tethers for the exploration of celestial bodies. Particularly, the last end of this Thesis is the obtention of a semi-analytic model that permits to study the influence of a tether in the design of orbits of interest for science missions.