After the successful Apollo missions that put humans on the Moon starting 1969, the ongoing dream was that there would soon be a permanent human settlement on our only natural satellite. Best captured in science fiction works like the classic 2001: A Space Odyssey, colonization of the Moon was seen as somewhat inevitable. But as it turned out, the last time humans went beyond low-earth orbit (LEO) was the Apollo 17 mission in 1972. Sad times we live in.

Apollo 17 astronaut testing a lunar rover, in front of the landing module. Source: Wikipedia

The Soviet space program had some serious proposals for a permanent moon base, one of which was Zvezda. The plan was to use the super heavy-lift launch vehicle N1-L3 (the Soviet Union’s competitor to America’s Saturn V) to deliver tons of material for use in habitable modules on the lunar surface. Each of the modules were to be launched separately. The habitable modules were to be docked on a movable train-like platform, to allow exploration or repositioning of the moon base. The concept unfortunately died with the failed Soviet human lunar programs.

3D representation of the proposed Soviet moonbase Zvezda. Source: Wikipedia

NASA also had a lunar base concept in the 1980s which went nowhere due to fading interest in the idea and focus on other areas such as the Space Shuttle program.

Artist’s concept of a NASA lunar base in 1986. Source: NASA

Why the Moon is a great place to start

The Moon has no atmosphere and is basically a dead land. Mars definitely is a less hostile place better suited to colonization. Elon Musk’s SpaceX has its sights set on it too. But the Moon’s big advantages arise out of its proximity:

The Moon can be reached in a matter of days, allowing for faster development and use of fewer resources. Light takes only 1.3 seconds to reach the Moon, allowing for near real-time communications and remote control of machines, which would be impossible on any other major astronomical body. The short travel time to the Moon would allow for a quick emergency supply of materials or an urgent crew evacuation situation. Mark Watney from The Martian would have appreciated both of these.

Earth as seen by Apollo 8 in 1968. Being able to see their home planet could have an important emotional impact on future lunar colonists. Source: NASA

On the other hand, it takes months to reach Mars, which also has a round-trip communications delay of 8 to 40 minutes and doesn’t allow remote control of machines.

The Moon’s proximity makes it a stepping stone on our journey to becoming an interplanetary species. The question is, how? In such hostile conditions, how are we ever going to make a permanent home?

#1: Powering habitats on the Moon

The daytime temperatures on the lunar surface exceed 100° Celsius and nighttime temperatures can dip as far as -180° Celsius. Solar panels can be used to power moon colonies during lunar day; however powering the colonies during a lunar night — equivalent to 14 Earth days — is an issue that needs to be solved.

Enter the peaks of eternal light. The Moon’s equator is tilted only slightly by ~1.5 degrees to the orbit of the Earth around the Sun. Its orbital motion is such that some peaks near its poles are constantly facing the Sun, thereby making them peaks of eternal light.

Moon’s equatorial tilt with respect to Earth’s orbit. Source: Me, using Wikipedia

Well, eternal here means as long as the Sun shines or gobbles up the Moon when it becomes a red giant. The Japanese spacecraft SELENE identified four peaks near the lunar south pole which receive sunlight more than 80% of the time.

Four peaks of eternal light on the lunar south pole by JAXA’s SELENE spacecraft. Source: Wikipedia

NASA’s Clementine orbiter also discovered the nearby Malapert mountain was illuminated by sunlight nearly 90% of the time. Similar peaks are found at the lunar north pole. These areas will thus have near constant sunlight to power the moon colonies.

#2: Permanent shadow regions as a source of water

Similar to the regions of eternal light, there are regions near the poles which are permanently in the dark. This is usually due to the peaks shadowing those regions from sunlight or deep craters where the sunlight simply does not reach. These permashadow regions in the south pole have been observed by NASA’s Lunar Reconnaissance Orbiter (LRO).

Permashadow regions on the moon’s south pole as seen by the NASA’s LRO. Source: NASA

Discovery of water ice in the permashadow regions

Having not received any sunlight for nearly 2 billion years, these permashadow regions are an excellent trap for volatiles (chemicals which would vaporize in space if exposed to sunlight), including water. India’s Chandrayaan-1 spacecraft, using NASA’s Mini-SAR radar, found more than 40 craters containing water ice on the lunar north pole. It is estimated that there could be 100 billion kg of water ice in these regions. NASA’s LCROSS spacecraft detached the Centaur upper stage to deliberately impact one of the permashadow regions on the lunar south pole.