The Moon’s polar regions are home to permanently shadowed craters. In those craters is ancient ice, and establishing a presence on the Moon means those water ice deposits are a valuable resource. Astronauts will likely use solar energy to work in these craters and harvest water, but the Sun never shines there.
What’s the solution? According to one team of researchers, a solar collector perched on the crater’s rim.
There’s abundant solar energy on the Moon. But not all the time and not everywhere. At the bottom of the deepest craters closest to the poles, there’s no Sun.
Researchers from the Texas A&M Department of Aerospace Engineering are anticipating future missions to the Moon’s permanently shadowed craters to harvest water resources. They’re working with NASA’s Langley Research Centre on reflectors that can be mounted on a crater rim. When paired with a receiver somewhere inside the crater, solar power can be delivered where it’s needed.
Dr. Darren Hartl is an associate professor of aerospace engineering at Texas A&M University. He’s leading a team of researchers working on solar reflectors. “If you perch a reflector on the rim of a crater, and you have a collector at the center of the crater that receives light from the sun, you are able to harness the solar energy,” said Hartl. “So, in a way, you’re bending light from the sun down into the crater.”
Though they’re still in the early stages of their research, computer models show that a parabolic reflector transmits the optimal amount of light to crater bottoms. Parabola designs are common in different types of things like telescopes, microphones, and car headlights. There are also solar parabolic reflectors at work here on Earth.
This is the Eurodish, a parabolic solar collector. The collector is mounted to the dish itself, but on the Moon, the collector would be in the crater where power is needed. Image Credit: Schlaich Bergermann und Partner and released into the Public Domain at http://wire0.ises.org/wire/independents/imagelibrary.nsf
Parabolic dishes are common on Earth. Here, we can make them any size we want and build them wherever we need to. But the whole endeavour is different on the Moon. Every pound we launch into space is expensive. Their goal is a reflector small enough to be transported to the Moon and large enough to harness enough energy.
The researchers are working with self-morphing material that was developed by Hartl and other engineers at Texas A&M. Self-morphing materials are based on natural materials that turn matter into complex surfaces. They can change shape in response to their environments. These include muscles, tendons, and plant tissue.
“During space missions, astronauts may need to deploy a large parabolic reflector from a relatively small and light landing system. That’s where we come in,” said Hartl. “We are looking at using shape memory materials that will change the shape of the reflector in response to system temperature changes.”
Dr. Hartl specializes in advanced multifunction materials. At Texas A&M, his team focuses on projects ranging from “… self-folding origami-based structures to self-regulating morphing radiators for spacecraft to advanced actuators for avian-inspired aircraft,” according to his bio. He also has over a decade of experience working with self-morphing structures and Shape Memory Alloys (SMA.)
One of the difficulties of operating on the Moon is the wild temperature swings between night and day. At the equator, the temperature can reach 121 Celsius (250 F), far hotter than anywhere on Earth. But at night, the temperature drops precipitously to -133 C (-208 F.) The permanent shadows in the Moon’s deep polar craters foster temperatures as low as -250 C (-415 F.)
Hartl has experience developing materials for these pronounced swings in temperature. He leads the Multifunctional Materials and Aerospace Structures Optimization (M2AESTRO) Lab at Texas A&M. “Our proposed solutions incorporate shape-shifting metals that adjust their own heat rejection based on how hot or cold they are, so it solves the problem for us,” Hartl said in 2019.
This video explains some of what they’re working on at M2AESTRO, though it’s a few years old.
The Moon is the next frontier for human habitation. Astronauts will live and work there, and water is a vital resource. Not just for drinking, but it can also be split into oxygen for respiration and hydrogen for fuel. Scientists aren’t certain how much water ice there is, but there’s enough to be useful.
Extracting and managing that resource will be critical for the success of Artemis and other lunar exploration efforts. Doing it effectively will require advanced solutions designed specifically for the lunar environment. Self-morphing materials could play an important role.