Since the movement of planets and space ships are governed by ordinary differential equations derived from the laws of Physics, it was thought that it could be appealing to the students to show, in somewhat simplified terms, what equations are those in two moments of a space ship that has been launched from the Earth and returns to it later. In each case, besides the presentation of the appropriate equation, the corresponding solution is also presented. In both cases the solution can be derived by using the techniques that the students should learn along the study of the chapter.