In just the past month or so I’ve seen multiple items crop up about getting critical minerals from space. First, this hearing in the House Committee on Natural Resources. This could be chalked up to uninformed congressional aides who don’t know Uranus from, well…
And then Phil Metzger posted this pic of the company OffWorld presenting at Commercial Space Week:
A small handful of other new startups have raised rounds–albeit, mostly in 2021/22 with rates at zero–on the premise of returning rare treasures from space back to Earth for sale.
The only positive thing I can say about this is that there’s in theory a market for these goods with a known price point. But there’s two glaring issues I’ll claim are death knells for return-to-Earth’s-surface space resource architectures. The “surface” part is important because space-mined rocket propellant is likely to be economic all the way down to low-Earth orbit.
Ore grades and all-in sustaining cost
In mining, the all-in sustaining cost (AISC) is the cost it takes to produce a resource like lithium or iron and encompasses everything from exploration to mining equipment to site reclamation. It’s basically the cost of goods, to which profits are added to get the market price of a metal.
One way we could split up AISC is to isolate (1) just the cost of energy to extract a pure resource from the raw ore, then (2) everything else (labor, overhead, etc.).
In this 2-part AISC (energy + everything else), the energy term shouldn’t differ in space for an identical raw material–except energy itself will likely cost more–but it can change markedly if the material is different. On the other hand, the “everything else” term will be much higher for space mining than terrestrial mining and will likely remain so even for highly automated robotic approaches (remember that terrestrial mines are quickly being automated too).
If we plot the price of different elements versus their typical ore grade (or concentration), we get a power law that holds over 7 orders of magnitude in grade. The outliers here are elements like cesium and uranium that have special handling requirements (i.e., they kill you). Elements extracted from the atmosphere form their own offset trend with roughly the same slope.
The chart is backed up by well-known relations for single elements; for example, copper prices rise similarly for declining ore grades.
All this suggests it will only make sense to mine critical minerals in space if they have higher ore grades than on Earth. Likely significantly higher to make up for the higher costs of energy and space operations. The problem is that for basically every element on the periodic table, the opposite is true: terrestrial ore grades are higher than any material found in space (on the Moon, Mars, asteroids, doesn’t matter). Often the differences are staggering, with 10× better terrestrial grades for critical minerals like gallium and rare earths, 100× for lithium, and 40,000× for uranium. No future decline in terrestrial ore quality is going to flip this, and short of a total ban on new mines on Earth, the economics don’t make sense.
This is where people will point out that some elements like nickel and platinum group metals are more concentrated on metallic asteroids than the best ores we have here. This is true, as work I’ve led has shown in detail. But that’s where glaring issue #2 comes in.
Return mass
The amount of metals we mine is immense. Just look!
If we go back to the OffWorld chart and rattle some of these off:
Nickel: 2.7 million tons
Copper: 21 million tons
Cobalt: 170 thousand tons
Lithium: 106 thousand tons
That’s PER YEAR. How much mass can we bring back on a Starship, the largest and most capable rocket for the next 10+ years? SpaceX doesn’t publish this number, but internet forum folks have estimated it at 40 to 50 tons. So, for nickel alone we’re talking about 54,000 Starship loads per year to replace the terrestrial supply. 540 Starships to make a 1% dent. It just doesn’t add up.
At this point we’re left quibbling over a few things like osmium and rhodium that are mined in small amounts (1s to 10s of tons per year) and have ore grades in space that are marginally higher than Earth. Let’s check in on how these platinum group metals are doing:
Oops. That’s right, we’re replacing internal combustion engine vehicles with EVs, and in doing so getting rid of catalytic converters that make up most of the platinum group metal demand. On top of that, each year we get better at chemistry and can do a broader range of tasks with more Earth-abundant materials.
I understand that some space mining companies are having trouble finding customers and revenue, and appealing to critical mineral shortage fears may be a tempting place to turn. But it taints the more viable majority of the field. The basic premise of space resources does make sense for propellant for refueling, metals used in space for large apertures, and eventual Mars colonization. But most of the general public can’t separate this from return-to-Earth platinum asteroid bonanza nonsense.
Just as with every scarcity fear in the past, we’re not going to run out of critical minerals. We’ll substitute other more abundant elements, like the ramp up of sodium batteries out of CATL. We’ll get better at extracting from lower grades with increasingly green technologies. And yes, we’ll get them from seafloor nodules. Hell, if you throw enough energy at the problem you can pull elements from seawater or garden-variety rocks or soils. But critical minerals aren’t coming from space.