How Moon Colonists Might Survive The Frigid Lunar Night

A “Last Quarter” Earth seen from the shadowed lunar landscape photographed by Japan’s Kaguya moon probe. During the fortnight-long lunar night, temperatures can drop to almost 300° below zero. The European Space Agency proposes to the heat retained by the lunar soil during the day to keep a future moon colony warm at night.  Copyright JAXA/NHK

Man, it can get cold on the moon. With virtually no air to speak of and a night that lasts just shy of two weeks, the surface temperature drops to around 275° below zero (–170° C). Dry ice or frozen carbon dioxide is toasty in comparison with a temperature of just –109° F (–78.5° C).

Picture the scene. You’re standing in darkness under a sunless sky, but you can still see look around and get your bearings. Even seeing crater rims and hills off in the distance. Why?  Not only does starlight provide lighting, but the Earth, four times the size of the full moon in our sky, casts a cool, blue light across the landscape.

Part of a panorama showing China’s Yutu rover and some of the tracks it made in the lunar soil. A small impact crater is visible at left. Click for the full, hi resolution view. Credit: Chinese Academy of Sciences, CNSA

Designers of future Moon missions and bases will have to contend with the lunar chill to make sure any habitats and machinery endure the long lunar night. Several robotic mission have suffered mishaps during the prolonged cold including China’s “Jade Rabbit” or Yutu rover, which landed on the moon in December 2013 and lost its mobility after about a month. Temperatures at the landing site plunged as low as –300° F (–184° C).

The Apollo manned missions stayed on the surface only a few days at a time, all during the early lunar morning when temperatures were moderating between bitter nighttime lows and daytime highs of around 250° F (121° C). One day, settlers will live day and night on the moon, but they’ll have to do so without vital solar energy and heat during 14 days of darkness.

This pellet of plutonium-238 dioxide is glowing red from the heat generated by radioactive decay. Pellets like this in the Cassini mission to Saturn and the Galileo mission to Jupiter produced about 62 watts of heat each. A device within the spacecraft converts the heat to electricity.

We could just use radioactive heat. Power cells that contain radioactive plutonium, like those featured in the movie The Martian, have been a staple on long-term missions to the outer solar system, where they’re used to not only keep electronics warm but also to provide power for  probes far from the sun. The heat from the decay of plutonium kept China’s Yutu warm and continues to power and warm NASA’s Mars Curiosity rover.

Unfortunately, this method may not be sustainable on a larger scale. That’s why folks at the European Space Agency (ESA) are looking for a better solution.

A future lunar base, perhaps constructed using 3D printing devices, will have to be heated during the long lunar night. Covering it with lunar soil, called regolith, would help to insulate the structure against extremes of heat and cold. Credit: ESA/Foster and Partners

“Up until now, radioactive heat and power sources have been the preferred solution for lunar habitats,” explains ESA’s Moritz Fontaine. “But these would multiply the cost and complexity of any expedition. “So we’re exploring a more sustainable solution, using the capacity of moondust to absorb and store energy when hit by sunlight, then releasing this energy during the lunar night.”

Driven by the temperature difference of night vs. day, this heat engine would keep things running during the day while storing excess heat for use at night.

Once night falls, the heat engine would be kept running in turn by the gradual release of the energy from the heated soil. Nice thing is, it’s workable in principle, so the next step will be to perform a simulation and then construct a demonstration unit to test it out. Moondust not only captures solar heat but can also be processed by future astronauts to extract oxygen, fuel and even water. Dead as the moon might appear to the eye, its dust may hold the key to making a future lunar outpost self-sustaining.