When you’re out in space, water is the most precious resource you can get your hands on.
It can be used for air, water, to grow food, radiation shielding, and most importantly,
as the propellant for your spacecraft.
Exploration of the Moon has revealed that there’s a tremendous amount of water ice
locked into the regolith, but it’s probably very difficult to access.
But there are also permanently shadowed craters at the Moon’s poles that could have more
than enough water to support a permanently inhabitable station on the Moon.
But it’s going to be tricky to get at, considering the fact that temperatures in the shadows
plunge to -240 degrees Celsius, just 30 degrees above absolute zero.
Just over a decade ago, India’s Chandrayaan mission entered lunar orbit, with the goal
of completely scanning the surface over the course of two years.
In 2008, the spacecraft released an impactor that smashed into the Moon’s south pole,
releasing a plume of regolith into space.
The spacecraft analyzed the composition of the plume and detected water ice.
At the same time, NASA’s Moon Mineralogy Mapper instrument onboard Chandryaan also
detected the presence of water ice across the surface of the Moon and concentrated towards
its poles.
This was surprising, but it was believed that the inner Solar System should be largely dry.
The radiation and the Sun’s solar wind should be sublimating away any water ice into space.
There are crater peaks that are in perpetual sunlight, and there are the floors of craters
near the South Pole which sunlight can never reach.
It’s believed that these craters are “cold traps”, which have been accumulating water
and other molecules for billions of years.
They could come from water-rich comets and asteroids impacting the lunar surface, throwing
debris into orbit, a fraction of which snows into these craters.
While the rest of the Moon experiences blazing days and then frigid nights over the 29-day
lunar day, these crater floors have never seen the Sun, and any water down there could
be permanently frozen as hard as rock, ready to be mined by future astronauts.
Here’s how the world’s space agencies plan to explore it.
The first and only mission to visit the region is China’s Chang’e-4 lander, which touched
down at the Moon’s south pole in January 2019.
Located on the Moon’s far side, the lander deployed Yutu-2 rover which crawled around
the surface of the Moon, studying the environment.
Over the course of its year and a half on the Moon, the rover has driven hundreds of
meters, photographing rock and studying the layers of regolith with ground-penetrating
radar.
Every two weeks, the mission goes into sleep mode, surviving the brutal lunar night, waiting
for the Sun to return to go to work again.
But the rover didn’t dare crawl into the permanently shadowed craters.
In order to understand them better, NASA recently announced the plans for its new Lunar Flashlight
mission.
This is a briefcase-sized Cubesat mission that will probably fly to the Moon in the
next couple of years as part of a series of science and commercial missions heading to
the Moon.
Over the course of two months, the spacecraft will follow an orbit that takes it over the
lunar South Pole, again and again.
It will be equipped with four separate lasers that shine at different near-infrared frequencies
and shine this laser light into the permanently shadowed craters
The spacecraft will examine the light returning from the surface of the Moon as it bounces
off the crater floor.
If it’s highly reflected and bounces back up, that means it’s hitting bare rock.
If it’s absorbed, that means water ice, and the better the absorption, the more widespread
the ice is at the surface.
Each laser will fire for a couple of milliseconds in sequence, and the illuminated region will
be about 35 meters in diameter.
And so, over time, the Lunar Flashlight will help build up a detailed map of the quantity
and locations of water ice deposits on the Moon.
Once scientists know where the water ice is, they’re going to want to explore it close
up with a rover.
But that has its own set of challenges, which we’ll talk about in a second, but first
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With detailed maps of water ice deposits on the Moon, the next step is to sample them
directly.
Drill into them, analyze their chemicals, find out how useful they’ll be for thirsty
astronauts.
And that means a rover.
But a rover working in these permanently shadowed craters will be unable to use any kind of
solar electricity, which it will need to power its instruments, rove around, and keep itself
warm enough to operate.
The normal solution for this is to use a nuclear-based radioisotope thermoelectric generator, like
what’s onboard NASA’s Curiosity Rover.
The problem is that the rover will need to get close to the ices it’s trying to study,
and if it’s generating tons of heat, that’s bad for the ice.
So how do you power a rover, in the dark, without a nuclear battery?
The answer should be obvious.
Lasers.
The answer is always lasers.
The European Space Announced recently funded plans for a laser-powered rover that would
receive a constant beam of energy from a nearby lander, giving it all the energy it needs
to carry out science in eternal darkness.
The mission would involve a lander and a rover.
The lander sets down on one of the nearby mountains which are in permanent sunlight,
and uses its solar panels to generate electricity.
It then fires a laser at the rover, up to a distance of 15 kilometers, hitting a modified
version of a solar panel, which converts this laser light to energy for the rover.
The rover would be able to crawl down a 10-degree slope to the crater floor, always remaining
within a direct line of sight of the lander.
In addition, this laser can be used as a two-way communications system.
The lander can transmit instructions to the rover while sending it power.
And then the rover can modulate a retroreflector on the collection panel to reflect laser light
back to the lander and transmit data.
The lander would then relay its discoveries back to Earth.
ESA engineers have already carried out a series of tests, including operating a rover in the
darkness through Moon-like terrain in Tenerife.
The next steps will be prototypes and testing of actual hardware that could fly to the Moon
in an upcoming mission.
We’re fortunate to have a large Moon so close to Earth.
It’s a stepping stone to help us explore the rest of the Solar System.
And now we’re learning there could be vast reserves of propellent sitting on the surface,
ready for us to take advantage of future missions.
It’s time to enter the darkness and search for water.
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These missions will help future explorers access to water on the Moon, for fuel, water,
and atmosphere.
But what will human missions to the Moon look like?
Here’s a video that talks all about it.