Rock around the planets

Abstract

From a strictly dynamical point of view the difference between a natural and an artificial celestial body relies on the possibility that the latter has to follow trajectories chosen not only by gravitation but also according to human will. Spaceflight dynamics is a branch of celestial mechanics that has developed along with the advances in the astronautical sciences for controlling the motion of artificial satellites and interplanetary spacecraft. Orbital changes are obtained either by properly operating an onboard propulsion system or by exploiting gravitational perturbations, thus opening new and exciting perspectives for celestial mechanics. In particular, the direct exploration of all the major Solar System bodies has been made possible by deep-space probes following complex trajectories, where manoeuvres and close encounters with the planets play a deciding role in sending a spacecraft toward its target. This is why spaceflight dynamics should not be considered only a practical application of known principles, but also as a novel approach to orbital motion.