Reluctant to identify a viable path forward, U.S. space policy continues adrift while yet another country has identified the Moon as a target of value and set out on a course of action. The (South) Korean Aerospace Research Institute (KARI) plans to send an orbiting spacecraft to the Moon in late 2018. In addition to carrying scientific and technological experiments, KARI is offering a portion of their payload space to foreign investigators. By doing so, they’ve increased the possibility of obtaining new strategic information critical to the ultimate success of a permanent return to the Moon.
The orbiter (KPLO, for Korean Pathfinder Lunar Orbiter) is a relatively small spacecraft (about 500 kg), similar in size to some previous lunar orbiters, such as Clementine (425 kg). It will launch on a procured, foreign launch vehicle, although it is planned to launch the follow-up soft lander mission on a Korean booster. The spacecraft will orbit the Moon in a 100-km-high, polar orbit for one year, permitting a complete survey of the lunar surface.
This mission has several objectives. In addition to developing the technology for future deep space missions, the orbiter will carry several scientific instruments. A polarimetric camera will globally map the Moon in three colors and determine the polarization properties of the lunar soil. Color wavelengths are selected to map the concentrations of the element titanium (Ti), a common element on the Moon but one correlated with high concentrations of solar wind gases. A high-resolution (better than 5 meters/pixel) camera will take images of the surface to characterize possible landing sites for the future soft-lander mission.
While the Moon has no global magnetic field, local areas of high field intensity exist. A magnetometer will measure the locations, and the extent and magnitude of these surface anomalies on the Moon. Finally, the spacecraft will carry a gamma-ray spectrometer to measure the concentration of several major rock-forming elements, including magnesium, iron, aluminum and calcium. The spectra from this instrument can also detect hydrogen, which will increase the size of the database we need to characterize the volatile content within the lunar poles. And an engineering experiment will test a means by which disruptions of space communication can be mitigated.
The instruments on KPLO will produce data on the Moon’s shape, composition and processes. In addition, there are opportunities to conduct additional measurements, as the Republic of Korea has graciously offered to host payloads provided by NASA, an accommodation for as many as four additional experiments. NASA’s Advanced Exploration Systems Division (a part of the Human Spaceflight Directorate) is sponsoring these instruments, with the aim of reducing the size and number of “Strategic Knowledge Gaps,” those areas of knowledge about the Moon’s composition and physical state that are critical to the success of future missions.
We’ve learned much in the last decade from the fleet of international spacecraft sent to the Moon, but key pieces of data remain elusive. For example, the Chandrayaan-1 mission in 2009 found evidence in near-infrared spectra for the presence of hydroxyl (OH), or water molecules (H2O), on the lunar surface. Concentration of these molecules varies with time and space, and they are more abundant toward the poles (i.e., at latitudes poleward of ~65°) in early morning and late afternoon.
An instrument specifically designed to map the water absorption feature globally across the lunar surface, is an example of what I’d identify as a “knowledge gap” payload. One idea for the creation of this spectral feature is that solar wind protons (hydrogen ions) constantly hit the sunlit side of the Moon, implanting themselves on the dust grains of the surface. In the presence of heat, such as that produced during the impact of a micrometeorite, these solar wind protons can chemically reduce iron oxides in the lunar soil, producing native metal (Fe0) and an OH molecule.
Hydroxyl molecules are unstable in the extremes of the lunar environment and will rapidly hop around the surface, becoming more active as the surface temperature rises. Considering this activity on a global scale over millions of years, these properties could result in a net movement of hydroxyl and water molecules toward the poles (the coldest regions of the Moon). If these materials “hopped” into one of the “cold traps” located near the poles (i.e., areas of permanent darkness), they would remain there forever. This process could be a mechanism that is adding water to the polar regions of the Moon, but we do not understand the magnitude or the details of such a process.
A small imaging spectrometer tuned to the “water band” and globally monitoring the formation and movement of these molecules is a useful instrument that could be flown on KPLO. In addition, a complementary mass spectrometer could detect water and other volatile species above the surface and monitor their movement to polar sequestration. Such detection may have already occurred with the CHACE experiment on the Moon Impact Probe released by India’s Chandrayaan-1. That spacecraft was sent to a hard impact near the south pole where, at about 82° latitude, it flew through a water vapor “cloud” with a density at least two orders of magnitude greater than found over the Moon’s equator. This water vapor may have been solar wind-produced water, migrating to the poles.
Understanding the water cycle on the Moon is critical to our mapping and use of its volatile resources. The two simple experiments described above won’t answer all our questions concerning this problem, but their data would constitute a major advance in our “strategic knowledge” of the Moon’s polar processes. Because the guest payloads are to be proposed by the lunar science community, we do not yet know which instruments will be selected and flown. I mention the water creation and migration problem as an example of an experiment that could yield not only strategic data for future exploration and utilization, but new science as well. For now, the lunar science community anticipates KPLO’s mission to the Moon and their selection of payloads proposed in response to KARI’s announcement of opportunity.