Advanced Propulsion for Fast Lunar Missions

Abstract

Half a century ago the Apollo missions carried 12 people to spend a short time on the Moon. After all this time, the space agencies of some countries and a number of private companies committed themselves to restart human lunar exploration, this time with the aim to establish a long-term human presence on our satellite and to start a lunar economy. Most of the planned lunar missions are based on the use of chemical propulsion, which allows to perform the one-way Earth-Moon travel in 3 or 4 days. Recently NASA and DARPA joined forces to develop a nuclear thermal rocket for planetary and lunar missions. In spite of the relatively small distance of the Moon from the Earth, carrying the required payload to the Moon is costly and there is some interest in using more advanced propulsion systems, with the purposes of reducing both the travel time and the cost. In particular, advanced propulsion devices will be developed for travelling to more distant destinations and, when they will be available, they could be used with advantages also for the Moon. The aim of the present paper is to discuss the perspectives which will be opened in the future by the possibility of using nuclear (both thermal and electric) or solar electric propulsion and, in a more distant future, nuclear fusion propulsion to travel to the Moon. A number of examples of lunar missions performed with different types of advanced propulsion show what are the conditions at which these advances can be achieved and which are the constraints that will limit these efforts. Keywords: Lunar Missions, Human Lunar Exploration, Advanced Propulsion, Trajectory Optimization, Specific Impulse Optimization