ABSTRACT
This chapter aims to cover gravity, centripetal force, the nature of an orbit and trajectories to the Moon. It explores space stations—Skylab, Mir and the plans for a new major international space station. With a large enough space station, or spacecraft, it is possible to use rotation to simulate the effects of gravity. At first the crews used to throw trash out of the airlock, but they have been dissuaded from doing that as the international space station is in a circular orbit. A spacecraft in orbit is in a continual state of free fall. In orbit the only force acting on all the objects is gravity, and as a result they all naturally follow identical paths. Factor that has to be taken into consideration when plotting the path of a satellite or spacecraft is the speed at which it is moving in the orbit.
