Exploration of the Moon

The preceding decade was a particularly productive time for studies of the Moon, and substantial progress is likely in the next decade. The primary goals for lunar science are threefold. First, the Moon preserves a record—lost on Earth—of the earliest history of the solar system, including the ongoing bombardment as life emerged on Earth. Second, the Moon retains a record of the key processes—for example, volcanism and impacts—that determined the diverse evolutionary paths followed by all the solar system’s rocky worlds. Third, the Moon hosts water and other volatiles in its interior, across its surface, and in ice deposits at its poles, providing a record that may, for example, constrain rival theories of the origins of Earth’s oceans.

Prior decadal surveys included two lunar mission themes in their lists of New Frontiers candidates: the deployment of a global network of long-lived geophysical monitoring stations (Figure 42); and the collection and return on samples from the Moon’s South Pole–Aitken basin (SPA). With a diameter of 2,500 km, SPA is the largest, oldest, and deepest impact structure on the Moon. It straddles the farside, and its southern rim reaches almost to the south pole. Both missions would address aspects of the first two goals mentioned above.

FIGURE 31 (Above) A panoramic view of one of the locations in the Moon’s Taurus-Littrow Valley visited by the Apollo 17 astronauts in December 1972.

The geophysical network and SPA sample return both appear on the list of candidates competing for selection as the New Frontiers 5 mission (see Table 2). However, the SPA mission is particularly challenging because it must return just the right samples from multiple specific areas to fully address all of its science goals.

Lunar Discovery and Exploration Program

NASA’s other near-term robotic lunar activities are organized under the Lunar Discovery and Exploration Program, whose primary components are the Commercial Lunar Payload Services Program and the Volatiles Investigating Polar Exploration Rover (VIPER) mission.

COMMERCIAL LUNAR PAYLOAD SERVICES

The Commercial Lunar Payload Services Program (CLPS) is intended to enable regular, reliable, and affordable access to the Moon and, simultaneously, jumpstart lunar commerce. NASA modeled CLPS on successful programs transporting crew and cargo to the International Space Station, so that rather than building and operating its own lunar spacecraft, the agency will pay contractors to deliver payloads to specific destinations on and about the Moon. Eight CLPS missions are currently planned for the period 2023–2025. The first of these, Astrobotic’s Peregrine (see Figure 32), will carry a variety of NASA and other payloads to the Sinus Viscositatis in 2023.

If the commercial landers prove to be reliable, frequent CLPS missions can be used to test new technologies, address focused science questions, and train new scientists and engineers. However, their short surface lifetime is currently a significant limiting factor. Nevertheless, the decadal survey was broadly supportive of CLPS, concluding that purchasing delivery services is a promising and innovative approach which, if successful, might be extended to the delivery of payloads to Mars and asteroids.

VIPER

VIPER is designed to characterizing the distribution and physical state of ice and other frozen volatiles that might exist in the permanently shadowed regions in the Moon’s southern polar region (see Figure 33). By doing so, VIPER will directly address the third science goal mentioned above and study the potential use of in situ resources to support future human exploration activities. It is designed to traverse some 20 km during a lifetime of 100 days. It will carry a neutron spectrometer to probe the subsurface for the presence of ice and it will be equipped with a drill that can penetrate to a depth of about 1 meter.

Human Exploration of the Moon

The decadal survey was not asked to make recommendations about human spaceflight activities in general or the Artemis program in particular. It was asked to consider how human space flight provides new opportunities for achieving science goals.

While there have been historic tensions between human and robotic exploration activities, astronauts can, with careful planning, address important space science goals. Humans bring intellectual flexibility and adaptability to tasks—as demonstrated, for example, during the Apollo program (Figure 31) and during shuttle missions to repair and upgrade the Hubble Space Telescope—but at a cost. Keeping astronauts alive and well is very expensive.

The committee noted that a robust science program is required to ensure the maximum value and longevity of a program like Artemis. The promise of a continuous stream of exciting discoveries is a core element of ambitious and enduring space programs, as evidenced by the success of sustained robotic programs such as the Mars Exploration Program (see later section).

ENDURANCE-A

As an example of how astronauts could enable high-priority science, the survey committee revisited SPA sample return. In fact, the decadal survey recommended removing the SPA mission from the list of candidates for New Frontiers 6 (it is still a candidate for New Frontiers 5) and replacing it with a new concept, Endurance-A, combining robotic and human capabilities (see Figure 34).

Endurance-A would be delivered near to the center of SPA aboard a CLPS lander and, over a period of some 4 years, would conduct a 2,000 km traverse, collecting samples en route. Once the traverse is completed, Endurance-A would rendezvous with and deliver its samples to Artemis astronauts at or near the south pole.

The retrieval and return to Earth of a substantial suite of samples collected from diverse locations across SPA represents an ideal synergy between NASA’s human and robotic exploration of the Moon. It would produce flagship-level science at the cost of a medium-class mission. Such a forward-looking, inspirational partnership would deliver groundbreaking science not possible through the collection of limited samples by astronauts working in the vicinity of an Artemis landing site.