How to turn moon dust into oxygen

Within a giant sphere, the engineers beckoned over their equipment. Before them stood a silvery metal contraption lined with colored wires—a box they hope will one day make oxygen on the moon.

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

Soon that regolith was Gloop. A layer of it is heated to temperatures above 1650 ° C. And with the addition of some reagents, molecules containing oxygen begin to escape.

“We’ve tested everything we can now on Earth,” said Brant White, program manager at Sierra Space, a privately held 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 deliver astronauts living on a future moon base.

Those astronauts will need oxygen to breathe, but also to make rocket fuel for a spacecraft that can launch from the moon and head for destinations beyond — including Mars.

Moonbase dwellers may also require metal, and could even harvest this from the dusty gray debris that litters the lunar surface.

A lot depends on whether we can build reactors capable of extracting efficiently or not.

“This could save billions of dollars in mission costs,” Mr White said, while explaining that the alternative – bringing lots of oxygen and spare metal to the moon from Earth – would be difficult 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, it is much more difficult on the Moon. Not least because of the conditions.

The huge 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 had to improve how the machine worked over time so it could better deal with the extremely jagged, abrasive texture of the regolith itself. “It goes anywhere, carries all kinds of gear,” says Mr. White.

And what’s crucial, which you can’t test on the ground or even in orbit around our planet, is the moon’s gravity — which is roughly one-sixth that of Earth. It might not be in 2028. or later that Sierra Space could 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 unless engineers design for it, says Johns Hopkins University’s Paul Burke.

In April, he and his colleagues published a paper Details of the results of computer simulations that show how a different process of extracting oxygen could be hindered by the Moon’s relatively weak gravitational pull. The process studied here was molten regolith electrolysis, which involves using electricity to split oxygen-bearing lunar minerals to extract the oxygen directly.

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

“These bubbles won’t rise as quickly—and may actually slow down from detaching from the electrodes.”

There may be ways to do this. One could be to vibrate the oxygen preparation device that can be impinged on the bubbles.

And the extra-smooth electrodes can facilitate the release of oxygen bubbles. Dr. Burke and his colleagues are now working on similar ideas.

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

Emphasizing 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 the astronaut’s fitness and activity levels.

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

The real use case for oxygen extraction technologies, Dr. Burke adds, is providing an oxidizer for rocket fuels that could enable ambitious space exploration.

Obviously, 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 that after each oxygen production cycle.

Along with colleagues, Palak Patel, a PhD student at MIT, came up with an experimental Molten regolith system for electrolysisto extract 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 delivery missions,'” she says.

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

Ms Patel says future lunar resource extraction machines could extract, for example, iron, titanium or lithium from regolith. These materials could help lunar astronauts make 3D printed spare parts for their lunar base or for replacement components for damaged spacecraft.

The usefulness of lunar regolith doesn’t stop there. Ms. Patel notes that in separate experiments, she has melted simulated regolith into a tough, dark, glass-like material.

She and his 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?