How to turn moon dust into oxygen

Inside a giant sphere, the engineers jumped on their equipment. In front of them stood a silver metal structure wrapped in colorful wires – a box they hope will one day produce oxygen on the moon.

After the team released the sphere, the experiment began. The box-like machine was now ingesting small amounts of a dusty regolith—a mixture of dust and sharp gravel with a chemical composition that mimics real lunar soil.

Soon, that regolith became unclear. One of its layers is heated to temperatures above 1650C. And, with the addition of some reactants, the oxygen-containing molecules began to bubble.

“We’ve tested everything we can on Earth right now,” says Brant White, a program manager at Sierra Space, a private company. “The next step is going to the moon.”

The Sierra Space Experiment unfolded at NASA’s Johnson Space Center this summer. It’s far from the only such technology researchers are working on, as they develop systems that could power astronauts living on a future lunar base.

These astronauts will need oxygen to breathe, but also to produce rocket fuel for spacecraft that can launch from the Moon and go to destinations further afield — including Mars.

The inhabitants of the lunar base may also need metal, and they can even harvest this from the dusty gray debris that litters the lunar surface.

Much depends on whether we can build reactors capable of extracting such resources effectively or not.

“It could save billions of dollars in mission costs,” says Mr. White explains that the alternative — bringing lots of oxygen and spare metals to the Moon from Earth — would be laborious and expensive.

Fortunately, the lunar regolith is full of metal oxides. But while the science of extracting oxygen from metal oxides, for example, is well understood on Earth, doing so on the Moon is much more difficult. Not least because of the conditions.

The large spherical chamber that hosted Sierra Space’s tests in July and August this year induced a vacuum and also simulated lunar temperatures and pressures.

The company says it has had to improve the way the machine works over time so it can better cope with the extremely sharp and abrasive texture of the regolith itself. “It goes everywhere, consumes all kinds of mechanisms,” says Mr White.

And the one essential thing you can’t experience on Earth or even in orbit around our planet is lunar gravity—which is roughly one-sixth that of Earth. It may not be until 2028 or later that Sierra Space can test its system on the Moon, using real regolith in low-gravity conditions.

The moon’s gravity could be a real problem for some oxygen extraction technologies if engineers don’t design for it, says Paul Burke at Johns Hopkins University.

In April, he and colleagues published a paper detailing the results of computer simulations that showed how a different process of extracting oxygen might be hindered by the moon’s relatively weak gravitational pull. The process under investigation here was electrolysis of molten regolith, which involves using electricity to split oxygen-bearing lunar minerals so the oxygen can be extracted directly.

The problem is that such technology works by forming oxygen bubbles on the surface of the electrodes deep within the molten regolith itself. “It’s the consistency of, say, honey. It’s very, very viscous,” says Dr Burke.

“Those bubbles won’t grow as fast—and may actually be delayed in detaching from the electrode.”

There may be ways around this. One could be the rocking of the machine’s oxygen production equipment, which can rock without bubbles.

And extra-smooth electrodes can make it easier to break off oxygen bubbles. Dr Burke and his colleagues are now working on ideas like this.

Sierra Space’s technology, a carbothermic process, is different. In their case, when oxygen-containing bubbles form in the regolith, they do so freely, and not on the surface of an electrode. This means there is less chance of them getting stuck, says Mr White.

Highlighting the value of oxygen for future lunar expeditions, Dr Burke estimates that, per day, an astronaut would require the amount of oxygen contained in approximately two or three kilograms of regolith, depending on that astronaut’s fitness and activity levels.

However, the life support systems of a lunar base would likely recycle the oxygen exhaled by the astronauts. If so, it would not be necessary to process so much regolith just to keep the lunar inhabitants alive.

The real use case for oxygen extraction technologies, Dr Burke adds, is to provide the oxidizer for rocket fuels, which could enable ambitious space exploration.

Of course, the more resources that can be made on the moon, the better.

Sierra Space’s system requires adding some carbon, though the firm says it can recycle most of it after each oxygen production cycle.

Together with colleagues, Palak Patel, a doctoral student at the Massachusetts Institute of Technology, came up with an experiment. molten regolith electrolysis systemfor extracting oxygen and metal from the lunar soil.

“We’re really looking at it from the point of view of, ‘Let’s try to minimize the number of resupply missions,'” she says.

In designing their system, Ms Patel and her colleagues tackled the problem described by Dr Burke: that low gravity can prevent the oxygen bubbles that form on the electrodes from breaking off. To counter this, they used a “sonicator”, which blasts the bubbles with sound waves to remove them.

Ms Patel says future lunar mining machines could mine iron, titanium or lithium from the regolith, for example. These materials could help astronauts living on the moon make 3D-printed spare parts for their lunar base or replacement components for damaged spacecraft.

The usefulness of lunar regolith does not stop there. Ms. Patel notes that, in separate experiments, she has melted the simulated regolith into a hard, opaque, glass-like material.

She and colleagues worked out how to turn this substance into strong, hollow bricks that could be useful for building structures on the moon – an imposing black monolithsay Why not?