“If there is enough ice near the surface, then heat can be applied to the surface directly and the vapor captured under a dome called the capture tent,” says Sowers. The vapor is then collected in a chilly container called a cold trap , where it turns into usable ice.
Despite being one of the coldest places in the cosmos, the moon’s surface may one day have multiple heat sources. Reflected sunlight is one option. Alternatively, both the U.S. and China also plan to put nuclear reactors on the moon so that they aren’t reliant on using solar power—which can be somewhat fickle on the lunar south pole—to sustain their bases. The fission reactions that would split atoms to power those plants also produce excess heat that could be harnessed for water extraction.
In recent years, space agencies and industry partners have come up with different ways to use heat to retrieve lunar ice. One proposal would deploy a rocket engine, trapped under a pressurized dome, to carve out deeper craters and extract more water than other methods would allow. Although focusing more on Mars, NASA also has their own “dust-to-thrust” concept where autonomous robots would dig up extraterrestrial soil, transport to a processing facility, and heat it up with ovens to remove the water.
One of the most promising water extraction technologies comes courtesy of a European Space Agency project named LUWEX (short for Lunar Water Extraction)—and a working prototype already exists. Either autonomous mining robots or astronauts would dump icy soil into the contraption’s mouth. Zabel, the LUWEX project manager, explains that heating up frozen lunar rocks is quite difficult, because of the lack of an atmosphere on the moon and the already frighteningly low surface temperatures. That’s why LUWEX’s crucible stirs and rotates the lunar soil, which broils it more efficiently and removes the ice.
From there, a cold trap captures the liberated water and transfers it into a liquefier, ready to be used. Well, almost ready: At this stage, the water is still polluted by extremely fine, glassy-like pieces of lunar dust. “It has a kind of milky appearance—like grey milk,” says Zabel. Fortunately, engineers working on the project have also designed a purifier than seems to work wonders. “We achieved drinking water quality.”