A Clean Slate for Space Resource Extraction
Surprisingly, one has to make a case not to import coal to the Moon
Why does producing steel emit so much carbon? In 2023 the answer is no longer that it’s the only way we know how to make steel, because there are a host of green technologies ready to be deployed like hydrogen-based steel or the promising Helios Cycle.
Of course, the real answer is that coke-based steel production came about when we didn’t know any better, and there was plenty of coal being ripped from the Earth ready to be thrown into blast furnaces. Those immense furnaces had large facilities and long supply chains built up around them and a workforce trained to operate them. Even though we now have better technology, it will take decades to uproot the entrenched systems and transition to green steel.
The same is true for mineral processing and metal extraction: legacy technologies involve staggering amounts of acids and synthetic solvents, many of which are difficult to recycle or dispose of. Promising techniques are on the horizon that use just water, or brine, or biotechnology, but the baked-in status quo will continue to win out for the foreseeable future.
The beauty of space is not just that it represents the frontier of a techno-optimist future, but that it offers a clean slate. We can pick and choose the best practices and technologies available today to take with us into space, and leave behind the anachronisms we’re currently stuck with. There isn’t a trained workforce with standards of practice waiting on the Moon, or capital projects and sunk costs deployed on Mars. It’s a blank but regolith-dusted canvas that represents a fully fresh start. It’s in this vein I’ve written in the past about food production, where nobody would seriously propose bringing with us a system that cages billions of sentient and suffering animals for slaughter, even if they still regularly find themselves in a Chick-Fil-A drive-thru.
But I’m a bit worried when I look at some of the technologies being proposed for propellant and metal extraction on the Moon. These will be the first space resources produced at scale, and the lunar surface is where this will happen. Fortunately, the commercial sector in the US has zeroed in on a technology called Molten Regolith Electrolysis (MRE) that can extract oxygen, iron, silicon, and aluminum (possibly others) directly from raw regolith. It does this with no solvents or consumables. There’s been a strong recent convergence toward MRE: Lunar Resources did pioneering work and continues to play a leading role, NASA KSC and Honeybee Robotics have dabbled, it’s the method of choice for Blue Origin’s lunar resource technology (Blue Alchemy), and Helios has made important strides too.
At the same time though, other ideas are being moved forward. One is called “carbothermal reduction”, which is favored by Sierra Space and certain segments of NASA. Carbothermal reduction is not much different than coke-based steel production, in that it uses hydrocarbons as the reducing agent to separate metal from oxygen. Are there hydrocarbons on the Moon we could use for this? Not really. So, the idea is to import hydrocarbons from Earth at the current cost of $1M/kg, then combust them to generate the end products. Even with methane reformation there will be CO2 in the exhaust stream, necessitating a constant resupply. For now, there’s not really harm in emitting CO2 on the Moon, but why do this? Why ship what’s essentially coal from the Earth to the Moon and burn it to make propellant? It’s quite obviously a stupid idea, but it’s being funded and supported by NASA, and now DARPA through the LunA-10 program.
There are other ideas just as bad if not worse. Europe and ESA, in their unwavering effort to do things their own way, have honed in on molten salt electrolysis which would involve importing metric tons of salt to the Moon to use as an electrolyte. Can we resupply the salt with local materials in space? Nope. Endless shipments from Earth required, and nowhere to put the salt once it’s been degraded enough to no longer be useful. Other concepts include deep eutectic solvents and ionic liquids; things with names like 1-ethyl-3-methylimidazolium dicyanamide that speak for themselves. Local supply is untenable, these are difficult if not impossible to reform or reuse, and there’s nowhere to dispose of them.
Why are these technologies being proposed? Probably because they work (though not especially well), and because they vaguely resemble what we’re already doing on Earth.
But what I’m suggesting here is that this isn’t sufficient justification. We have one chance at a clean slate before practices get entrenched and we start doing things because “that’s the way they’ve been done”. Technologists, program managers, and funding agencies should take a step back and ask some really basic questions, like does it make sense to import salt and coal to the Moon to use as reagents in resource extraction? If not, then why keep throwing money at these technologies?
Space resource extraction should use consumables only when they can (now or in the near future) also be supplied from local materials. We should recognize the clean slate for what it is, and properly dispose of techniques and practices that have no future on our planet or beyond it.