Exploring the Moon in the 21st Century

doi: 10.2113/gselements.15.5.360

Introduction

In 2019, we are celebrating the 50^th anniversary of NASA’s momentous Apollo expeditions to the Moon. The samples brought back by the astronauts, and the fieldwork those astronauts performed on the lunar surface, cemented the Moon’s status as the cornerstone of the solar system. It is not an exaggeration to say that the Apollo expeditions transformed our understanding of our solar system, and, in fact, most of the discoveries made in planetary science since the 1960s can trace directly, or indirectly, from the scientific results of those Apollo expeditions.

Although some erroneously proclaim that the Moon is “Been there, done that”, nothing could be further from the truth. After a long hiatus, beginning in the first years of the 21^st century, there has been a resurgence of interest in the Moon, including the Kaguya mission by the Japanese Aerospace Exploration Agency (JAXA); the Chandrayaan-1 mission by the Indian Space Research Organizations (ISRO); four Chinese missions:- 2 orbiters (Chang’E-1 and -2) and two landed missions with rovers (Chang’E-3 and -4); as well as four NASA missions: the Lunar Reconnaissance Orbiter (LRO), the Lunar Crater Remote Observation Sensing Satellite (LCROSS), the Lunar Atmosphere and Dust Environment Explorer (LADEE), and the Gravity Recovery and Interior Laboratory (GRAIL). Taken collectively, the results from these missions have shown that the Moon is a far more interesting, and far more valuable, destination for future exploration than was perceived even during the Apollo era. Results from recent lunar missions have only increased the interest in a vigorous program of lunar exploration and utilization.

The 50^th anniversary of Apollo 11 presents the perfect opportunity to take a look to the future. The Moon now presents an entirely new paradigm for planetary exploration through incremental, affordable investments in cislunar (i.e., between Earth and Moon) infrastructure. But how do we do that?

Roadmap to the Future

The Lunar Exploration Analysis Group (LEAG), the community group started in 2004 that organizes and leads the large and diverse lunar exploration community, has developed the Lunar Exploration Roadmap (LER) (LEAG 2016). Featuring inputs from engineers, planetary scientists, commercial entities, and policymakers, the roadmap presents a cohesive strategy to make concrete advances along the following three themes:

1. Science Use the Moon for scientific research by addressing fundamental questions about the Moon, our solar system, and the Universe around us. Like the four terrestrial planets (Mercury, Earth, Venus, Mars), the Moon has a crust, a mantle, and a core and is, therefore, one of the most accessible destinations to cohesively address questions about early evolution of planetary interiors. The Moon retains a record of the formation, evolution, and impact history of Earth and the inner solar system, as well as an otherwise inaccessible record of the Sun’s evolution and history. Finally, this is another area where the Apollo expeditions represent a strength: there are five decades worth of planetary science hypotheses that lunar geological fieldwork will address. The lunar surface could also provide a unique and stable long-term platform for astronomy. In particular, manned radio observatories or optical interferometers on the far side of the Moon could produce dramatic advances in astrophysics. The LER prioritizes science concepts and goals from the 2007 National Research Council Scientific Context for the Exploration of the Moon report (NRC 2007), which were subsequently affirmed and amplified by the LEAG’s “Advancing Science of the Moon” report (LEAG 2017).
2. Sustainability Use the Moon to learn how to live and work productively off-planet, for increasing periods, to enable extended off-planet human settlement. The Moon has abundant material and energy resources that can be used to decrease the costs and dramatically increase the capabilities of future solar system exploration. Lunar resources, in particular, offer an enduring opportunity for commercial investment and bringing cislunar space fully into Earth’s economic sphere of influence while building international partnerships. Commerce is a key aspect of ensuring the sustainability of future space activity. Public–private partnerships, growing from initial government-funded lunar resource extractions and utilizations, will provide the capabilities required for any future sustained human space operations.
3. Feed Forward Use the Moon to prepare for future missions to other destinations. The Moon is the only viable deep-space test-bed for testing technologies, systems, and operations to enable cost-­effective human operations beyond low-Earth orbit. The Moon’s combination of radiation, hard vacuum, and low-gravity provides a unique laboratory to study the physiological, biological, and biomedical aspects of long-duration operation on planetary surfaces. Irrespective of the innumerable ways in which lunar exploration is required for the success of future voyages to Mars and beyond, establishing a lunar outpost will establish the comprehensive workforce and industrial base required to successfully make voyages to Mars, dwarf planet Ceres, and beyond.

A Vision for Lunar Exploration in 2050

Successfully implementing the LER will result in a variety of benefits for the United States of America, and the world. While predicting events three decades hence is fraught with uncertainty, the LER offers a path for a dramatically altered landscape for planetary science and exploration by the year 2050. The Moon’s attainability offers intriguing possibilities where lunar surface operations are commonplace, with at least several hundred people living and working on the Moon full-time. Examples of the kinds of activities we foresee include:

Transformational Planetary Science Geology is a field science, and can best be done by humans, mapping and solving complex field problems to answer fundamental questions. By the 2050s, we anticipate that in-person fieldwork would be undertaken by academic institutions (in a similar way that NASA and the NSF support activities in Antarctica) yielding profound benefits for our understanding of the solar system. A lunar outpost, for example, could enable lengthy expeditions to geology field sites across the lunar surface using both humans and human-tended robots, depending on the science question to be addressed.

Enduring Commercial Growth Fueled by access to lunar resources, large-scale operations on the surface of the Moon and in cislunar space are commonplace and have expanded Earth’s economic reach and dramatically increased the human presence in cislunar space. From refueling assets in geosynchronous space to tourism to space-based solar-power, commercial activities in cislunar space are routine and profitable.

A New Paradigm Cislunar Infrastructure, powered by lunar resources, promises a dramatic increase in NASA’s capability, specifically in planetary science. Missions could be assembled at Lagrange point 2 and supplied using lunar resources, so dramatically lessening current mass constraints prior to routine departures to Mars and other destinations. As another example, return samples requiring complete isolation from Earth’s biosphere from other destinations (such as Mars, or outer planet moons) could be received and examined at completely isolated facilities on the lunar surface.

Following the Lunar Exploration Roadmap

There are near-term steps that must be undertaken to ensure that the breathtaking potential of lunar exploration is realized. The Lunar Exploration Analysis Group has developed a roadmap implementation strategy for the 2020s (LEAG 2011) designed from the outset to advance science and have viable on-ramps for commercial activity with objectives clearly traceable to the strategic knowledge gaps (Shearer et al. 2016).

Phase 1 – Prospect for Resources

Build upon the results of recent lunar missions to define whether the resources are actually viable reserves. Such prospecting needs to be a campaign (i.e., visiting several resource-rich locations) and should define the composition, form, and extent of the resources; characterize the environment in which the resources are found; define the accessibility of the resource; quantify the geotechnical properties of the regolith in which the resources reside; establish the capability of autonomously traversing several tens of kilometers to sample and to determine the lateral and vertical resource distribution on meter scales; identify resource-rich areas for targeting future missions; and establish capabilities such as automated cryogenic sample return and curation to facilitate the assay of potential resources.

Phase 2 – Demonstrate the use of Local Resources

Based on the results of Phase 1, the next step would be to carry out an end-to-end demonstration of resource extraction and utilization. This would address important science questions and validate key technologies, including feedstock acquisition and handling, resource storage, resource production system longevity, and dust mitigation strategies.

Phase 3 – Lunar Resource Production

Based upon the results of Phase 2, lunar resources could be utilized to enable increasingly complex operations on the lunar surface, including life-support for human outposts and propellant for reusable landers, all as part of a sustainable human-tended facility on the surface (Spudis and Lavoie 2011).

The Next Steps on the Moon

The Moon represents the fundamental underpinnings for understanding solar system processes and history. The Moon is also the critical enabling asset for any human exploration activity that the world may undertake in space, now and in the future. By the 2050s, creating the capabilities inherent in executing the Lunar Exploration Roadmap will enable us to go anywhere, and do things heretofore only imagined, throughout the solar system.

Building cislunar infrastructure does not require technologies wildly outside our experience base. Rather, it is facilitated with evolved versions of currently existing technologies, such as microwave power transmission, laser communications, solar power, nuclear fission power, regenerative life support, propellant transfer and storage, and telerobotics. In terms of new investments, the demonstration and flight qualification of presently well-conceptualized (but unflown) technologies for cislunar resource extraction and utilization would provide a capability required for any future sustained human space operations. At the time of writing, through Project Artemis, NASA is taking some of the first steps towards a sustainable human presence at the South Pole of the Moon (Fig. 1). With its easy access to benign illumination conditions (Mazarico et al. 2011; Speyerer et al. 2016) and proximity to potentially economic volatile reserves (Li et al. 2018), the South Pole of the Moon is the place where we will convert space from a wilderness, visited only briefly and tentatively, to a sustainable frontier of human activity where we answer fundamental scientific questions, grow a cislunar economy, and pave the way to journeys beyond.

References

LEAG (2011) Lunar Exploration Analysis Group (LEAG) Robotic Campaign Analysis Letter. https://www.lpi.usra.edu/leag/reports/RoboticAnalysisLetter.pdf

LEAG (2016) The Lunar Exploration Roadmap: Exploring the Moon in the 21st Century: Themes, Goals, Objectives, Investigations, and Priorities 2016. Version 1.3. Lunar Exploration Analysis Group (LEAG). https://www.lpi.usra.edu/leag/LER-2016.pdf

LEAG (2017) Advancing Science of the Moon. Report of the Lunar Exploration Analysis Group Special Action Team, held 7–8 August 2017, Houston, Texas, United States of America, 68 pp

Li S and 7 coauthors (2018) Direct evidence of surface exposed water ice in the lunar polar regions. Proceedings of the National Academy of Sciences of the United States of America 115: 8907-8912

Mazarico E, Neumann GA, Smith DE, Zuber MT, Torrence MH (2011) Illumination conditions of the lunar polar regions using LOLA topography. Icarus 211: 1066-1081

NRC (2007) The Scientific Context for the Exploration of the Moon. National Research Council of the National Academies. National Academies Press, Washington DC, 120 pp, doi: 10.17226/11954

Shearer CK and 10 coauthors (2016) Results of the Lunar Exploration Analysis Group (LEAG) GAP REVIEW Specific Action Team (SAT). Examination of Strategic Knowledge Gaps (SKGs) for Human Exploration of the Moon. Annual Meeting of the Lunar Exploration Analysis Group (2016), Abstract 5025. https://www.hou.usra.edu/meetings/leag2016/pdf/5025.pdf

Speyerer EJ and 5 coauthors (2016) Optimized traverse planning for future polar prospectors based on lunar topography. Icarus 273: 337-345

Spudis PD, Lavoie AR (2011) Using the resources of the Moon to create a permanent, cislunar space fairing system. AIAA SPACE 2011 Conference & Exposition held 27–29 September 2011, Long Beach, California, doi: 10.2514/6.2011-7185