Any astronauts reaching the surface of the moon will be greeted first by a plume of dirt, sent flying by the boosters of their spacecraft. They will emerge and put bootprints in the dirt, take samples and study the dirt, and eventually they may use the dirt to make the fuel and other supplies needed to maintain a long-term lunar presence. When it comes to exploring the moon, it’s all about dirt.
Planetary physicist In 2013, he cofounded a group of research labs at NASA’s Kennedy Space Center, Florida, where research teams spend their days working with artificial lunar regolith, like the sample pictured below, to learn how it behaves and what we will be able to do with it. With NASA’s Artemis programme aiming to put humans back on the surface of the moon in 2027 and eventually set up a permanent base there, that knowledge is becoming increasingly important.
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Regolith will be both a danger to astronauts as they land and a crucial resource as they build. Metzger works with scientists at a variety of labs who are figuring out how to protect astronauts and their dwellings from the pointy, perilous dust grains and how to use the dirt to make rocket fuel and radiation shielding.
He spoke to Â鶹´«Ă˝ about what a permanent human presence on the moon might look like, why regolith is so important to that vision and how understanding this thick layer of rubble could even unveil the secrets of Earth’s past.
Swapna Krishna: What first got you excited about working with regolith?
Philip Metzger: I was doing a field test of lunar robot prototypes in Hawaii, up on the volcano Mauna Kea, back in 2010. I was thinking about how it was so dry and cold on that mountain and there was very little vegetation, and that was kind of like the moon. That’s why we were testing on it, because it was similar to the moon. I got to thinking, you know, not much life can exist this high up the mountain naturally, but we’re creating these robots that serve other robots. We were testing robots that would make oxygen out of the soil, and then other robots would get the oxygen to be able to drive, and others could make fuel to launch rockets.
It’s kind of like we’re making a little ecology, like life that’s adapted to being in a waterless place. And, well, that’s really what it’s going to take. If we’re going to cross that ocean of space to these other islands, we need life to go ahead of us to prepare it.
Which is what we’re doing: developing an artificial life, an artificial ecology that can reproduce using local resources, but without water. That got me all excited thinking about it.
You have to land on it, drive on it, dig in it, build with it and study it
NASA is preparing to land astronauts on the moon with its Artemis III mission – what will they face on that landing?
There are problems with landing because the rocket exhaust is going to blow around the soil, and that can obscure your view. Your sensors can’t see the ground as well.
With a very big rocket, you could even create a hole. We didn’t produce any holes under the landers during the Apollo programme, but with these larger rockets, if you have nozzles that go close to the ground with a lot of thrust, it could dig a deep hole and could cause a direct tipping hazard for the rocket. When you shut your engine off, that hole is going to collapse. It will cave in and then your rocket can tip.
The second problem is, once you’ve shoved the soil down to create a deeper hole, the gas goes down in the hole and has to come back out again. You’re shooting sand and rocks and dust right back up at your rocket, so you can immediately damage your rocket with rock impacts.
What are some of the other things astronauts will have to figure out with regolith after landing?
I like to say you have to land on it, drive on it, dig in it, build with it, extract resources from it and study it.
Landing on it is first. Then comes driving on it – we want to make sure vehicles don’t get stuck. We dig in it to explore what’s under the surface and collect regolith as a resource. But we’re trying to dig in super low gravity, so how do you get enough force when you push a bucket through the soil? On Earth, the wheels of a rover on the ground will keep you from going backwards, but there isn’t much force on those wheels on the moon because the gravity is so low. This is why we’re working on techniques for low-gravity digging.
Then, you want to build with the regolith. Eventually, we want to start to build landing pads. We want to extract resources like oxygen and ice for rocket fuel. And of course, from the very beginning, we want to be studying it.
How do we figure out how to do all these things, with so little actual moon dust to work with on Earth?
Researchers at the Florida Space Institute’s Exolith Lab, which is one of the labs I visit frequently, went all over North America finding all the right mines to get the right minerals so they can crush them and mix them in the right proportion so that it’ll be just like the mineralogy of lunar soil. They’re crushing all these different kinds of rocks and mixing them in cement mixers. My team and I then regularly go into this giant arena where we have loads of simulated soil and test rocket exhausts blowing on it or robots driving on it.
One of the goals of all this research is supporting a long-term human presence on the moon. What do you think that will look like?
One problem is that because of the radiation, you’ll have to be underground. I don’t think people are going to want to live their entire life in a cave. I think people will live in space stations orbiting around the moon that rotate so there’s artificial gravity, and they will teleoperate robots down on the surface.
But people will be going down for short periods, maybe for a month at a time. So they’ll fly down to the moon and live in a habitat. The habitat is probably covered with regolith so that it is radiation shielded. And they’ll be able to go out on spacewalks to do geology or work on the robots.
After their week or month or however long on the surface, they’ll go back up to the space station, where they might stay for a year before coming back to Earth.
I think, eventually, when we have really large industry in space with a lot of robotics, then we’ll be able to build truly gigantic habitats in space where people can live long term. They’ll be large enough so that, psychologically, you won’t feel cramped. But it’s going to take decades, if not a century, of building robotic industry in space before we can build structures that large.
Is it really worth it or even feasible to mine resources and create rocket fuel on the moon?
Absolutely. I get frustrated by those people who claim it’s never going to be economically viable. They were saying, “[SpaceX’s] Starship is going to be so cheap to launch, we can just use it to send rocket fuel into space from Earth”. I would argue back, yeah, but if it’s so cheap to launch, that means the equipment for mining can also be launched very cheaply too.
The moon is 42 per cent oxygen by mass. It’s a great big giant ore body of oxygen up there in the sky. And the biggest cost of space flight is launching oxygen. When you launch a big tank of rocket propellant into space, 80 per cent of that weight is oxygen – if you can get that oxygen from the moon, that’s a huge saving.
The cost of making rocket propellant on the moon is going to go down faster than the cost of launching it from Earth. Now, it may take a few years before it’s cheaper to bring it from the moon all the way down to low Earth orbit. But it’ll immediately be cheaper to use rocket fuel made on the moon for spacecraft in lunar orbit.
What else can we use regolith for?
Another thing you can do is make metal for use in building habitats and other structures on the moon. You can make magnesium, iron, aluminium and titanium using some of the minerals in regolith. You can also simply scoop regolith up and use it as a building material.
As well as this, in the soil at the poles of the moon, there’s ice. We need water for a lot of things – we need it for life support, we need it for agriculture. Now, there are challenges there because regolith has a lot of metals in it and its grains are very sharp. That’s unlike the grains of soil on Earth, which are a lot more rounded thanks to natural weathering. We have people in our lab researching how to use lunar soil as a plant growth medium, because the angular, fine particles and the heavy metals are problems for that, as is the lack of organic material.
Another big use is just doing science.
What sort of science can we do with moon dust, aside from learning about the moon itself?
The moon is like Earth’s attic. If you go to an old house that’s been around for a couple hundred years, go up in the attic and there are all these antiques and the family history is up there.
Well, here on Earth, a lot of the history of the planet gets destroyed because of weathering and tectonics recycling the crust. But the moon has no water cycle to destroy the rocks, and it has no plate tectonics. So there’s a lot of history of our solar system stored in the regolith of the moon.
For example, we think the ice on the moon came from comets, and they may have been the result of a bombardment that occurred more than 3 billion years ago.We think that this bombardment may be crucial to understanding how life can exist on Earth, because that may be what brought water to our planet.
If we want to find out the history of what caused that bombardment, then we need to go to the moon, study that ice and study the craters there. If we can understand how Earth became a habitable planet, then that’ll help us to understand what fraction of other planets out there in the cosmos might also be habitable. Answering the question of whether there could be life elsewhere in our galaxy, that’s an answer that we’re going to get by studying the soil on the moon.
