Why the Lunar South Pole?
NASA was recently directed to return to the Moon by 2024, an announcement first made in remarks given by Vice President Mike Pence at the 5th meeting of the National Space Council on March 26th. However, this huge announcement and acceleration in schedule also came with another set of exciting details. He stated, the “lunar South Pole holds great scientific, economic, and strategic value,” and that “when the first American astronauts return to the lunar surface, that they will take their first steps on the Moon’s South Pole.” But why the focus on the Moon’s south pole? He explored that as well, saying that we will “mine oxygen from lunar rocks” and “use nuclear power to extract water from the permanently shadowed craters of the South Pole”. These statements are exciting because they specifically include the use of in-situ resource utilization on the Moon, and select human landing locations near the South Pole due to proximity to those resources.
As mentioned, oxygen exists in lunar rock (regolith) and can be directly extracted. This would be done for many reasons, such as life support oxygen, propellant oxidizer, or even to facilitate plant growth. In samples of lunar material that have been tested, oxygen abundance is found to be between 42-45% by weight. Using lunar oxygen is important because of the high cost per kilogram of launching materials into space from Earth. There are many methods to extract oxygen that require a large amount of energy, but these still provide a cost savings in comparison. This cost savings provides the motivation to utilize in-situ oxygen resource utilization on the Moon, so that mission costs are lower and missions become more sustainable. A few tested methods to produce lunar oxygen include carbothermic reduction of regolith, hydrogen reduction of regolith, and molten regolith electrolysis.
In addition to oxygen in lunar rock, water is also known to exist in lunar permanently shadowed craters, many of which are found at the Moon’s South Pole. This water is found in the form of ices in the extremely cold temperatures found in the permanently shadowed regions (PSRs), which have been observed to reach as low as -238 C (-397 F). From current information, water presence is confirmed but quantity is highly varied. Information from the LCROSS mission in 2009 detected a water weight percentage of up to 5.6 ± 2.9% by mass. Following this, a 2018 paper that analyzed data collected from the Moon Mineralogy Mapper (M3) indicated many locations containing ice concentrations as high as 30% in the upper few millimeters of the surface of permanently shadowed regions. Many methods are being studied to extract Lunar water, such as using reflected sunlight or microwaves to melt ices.
All future planned robotic and human missions to the Moon will require a source of power. This is also true for future efforts to extract useful lunar resources, such as oxygen and water. There are multiple promising methods for producing this power. Peaks of high illumination are points on the Moon’s surface, often found on high crater rims, that provide near constant solar illumination. These locations can provide almost constant solar power (electrical and thermal), and often have direct line of sight to Earth for communications.
Another promising source of power for the Moon’s PSRs is nuclear fission. Like nuclear power plants on Earth, a small safely designed nuclear fission system on the Moon could provide a reliable, high output source of electricity and thermal energy. This is important for supporting operations on the Moon that will grow more power hungry over time. The recent mention of the need for a nuclear source of power for lunar ISRU by Vice President Pence is important as it is essential for a government agency to first develop and test nuclear fission systems for sustainable ISRU space deployment. Space resources and space development more generally will benefit greatly from space nuclear fission as it provides a reliable high output energy source at a relatively low cost, where alternatives such a solar would require a huge size system to provide the same power output. For locations in space without direct sunlight (underground, in shade, or farther from the Sun), having nuclear as an option will promote sustainability and provide cost savings.
While we have answered the question of why the Lunar South Pole, there are many other reasons to go back to the Moon in general. These include the Moon’s plentiful metal resources, such as Titanium which exists in large quantities. Metals provide additional targets for ISRU and enable a lunar based economy that can increase space sustainability through cost savings and commercial investments. In addition to resources, the Moon is seen as a good focus as a training ground for Mars, a financially conservative option, and close enough to allow possible abort to Earth that isn’t realistic for locations further away.
Returning to the Moon will be exciting no matter the destination, but the choice of the South Pole is an excellent option for the reasons we discussed. Unlike the first set of Apollo landings, this return will be targeting landing locations chosen for their available resources. With the intent to use these resources for producing needed fuel and oxygen, this new journey to the Moon shows promise to be sustainable. With the utilization of space resources, a sustainable space program and commercial economy is possible. This is why we will go to the Lunar South Pole.