Spudis, Paul - The Moon as an Enabling Asset for Spaceflight

Abstract: 
Unique among the accessible space destinations beyond low Earth orbit, the Moon possesses the material and energy resources in usable form to supply a space-based transportation infrastructure, thereby establishing a permanent presence in space. From nearly a decade of intensive robotic exploration, we now have a detailed understanding of the environment and deposits of the poles of the Moon. Because the Moon’s spin axis obliquity is low (1.5°), portions of the terrain near the poles are in either near-permanent sunlight or in permanent darkness. Areas in sunlight can support the generation of electrical power via solar photovoltaic arrays; infrequent and brief eclipse periods can be bridged with rechargeable fuel cells generating electricity. Permanently dark areas are extremely cold (25-40 K) and contain elevated quantities of volatile substances, including hundreds of millions of tons of water ice. Water is one of the most useful substances for spaceflight – it can support human life (as a consumable and as radiation shielding), it is a medium of energy storage, and in the form of liquid hydrogen and liquid oxygen, it is the most powerful chemical rocket propellant known. The proximity of the quasi-permanent sunlit areas to the cold trap volatile deposits allows a sustainable presence at the lunar poles, where nearly continuous harvesting of water can be conducted. Thus, the Moon is an “off-shore” logistics depot for deep space travel. Because of the Moon’s proximity to Earth (400,000 km or 3 light-seconds round-trip), it is possible to begin surface assaying, infrastructure emplacement and processing of lunar resources using teleoperated robots controlled from Earth. Robots can be sent to the Moon in small packages (1-2 tons) as individual missions and then operated as an integrated system to begin surface operations prior to human arrival. This technical approach makes lunar return affordable, as the robotic pieces can be delivered to the Moon on whatever schedule is permitted by budgetary considerations. These robotic systems will build outposts devoted to the extraction of water from the lunar poles. Eventually, this water will be exported to cislunar space. Individual pieces of a space transportation system, including fuel depots, cryogenic processing plants, orbital transfer vehicles, and lunar landers will be permanently based in various locales throughout cislunar space. After each journey, these vehicles will be re-fueled and refurbished for ongoing use. By using lunar resources to supply a transportation system to access all points between Earth and Moon (home to all of our satellite assets), we establish a permanent foothold in space. Such a transportation system will revolutionize the paradigm of satellite-based applications in cislunar space, including communications, navigation, national security and scientific observations. By going to the Moon and learning how to extract and use its material and energy resources, we enable human missions to the planets.