INTERPLANETARY MISSIONS PERFORMED OUTSIDE THE OPTIMAL LAUNCH WINDOWS

摘要

It is well known that the energy required for interplanetary travel depends on the launch and the arrival dates and that the launch windows are fairly narrow and depend on the particular launch opportunity. Usually the study of this dependence is concentrated on the periods in which the travel is easier, for a launch about 3 months before the opposition. This is true both for both impulsive and low thrust propulsion. However, there are essentially two reasons for launching a spacecraft to Mars (or to any planet) outside the launch windows characterized by a low-energy conditions: performing a mission which is longer than a 'short stay' mission but shorter than a 'long stay' one, and performing an emergency mission either to allow astronauts on Mars to get back to Earth or to deliver cargo to Mars. The aim of the present paper is studying these situations and to introduce a plot linking the two ways energy requirements with the duration of the forward and backward travel for a given stay on the planet.