How to cook up asteroids on Earth for space mining gear tests
The OSIRIS-REx mission to return samples from an asteroid will cost nearly $1 billion, and to make sure it's up to the job, NASA needs practice material. Belinda Smith chats to the scientist who will deliver the goods.
All aboard the asteroid mining bandwagon! In November, US president Barack Obama signed into law that citizens own whatever resources they mine from asteroids.
In February, the tiny European nation Luxembourg announced it will pioneer mining of gold, platinum and tungsten on asteroids. And in September, NASA plans to send its OSIRIS-REx spacecraft to asteroid 101955 Bennu and return with samples in 2023.
Having plans is all well and good. But like all mining equipment, OSIRIS-REx must be tested to make sure it's up to the task. The mission will end up costing nearly US$1 billion, and any organisation interested in off-Earth mining will need to run their gear through a gamut of tests before (expensively) sending it out into the field.
So how do you test machinery to mine an asteroid hurtling through space?
You build asteroids on Earth.
"And it's a lot easier than you might think," says Dan Britt, a planetary scientist at the University of Central Florida.
Britt should know. This month he landed a grant to build asteroid material for NASA and other organisations to play with – up to five tonnes if they want it.
"Basically, asteroids and meteorites are composed of pretty common compounds that you find fairly abundantly on Earth,” he says. “So we use meteorites as guides for mineralogy and texture we'd expect to see on asteroids."
After grinding and mixing compounds, they're mixed with water, dried and crushed with a press to make clumps of different size and shape. It feels dirty and dusty.
Britt has, so far, created one type of asteroid material. Its recipe is based on a meteorite called Orgueil, which plunged to Earth on the evening of 14 May 1864 in the southwest of France.
It broke apart and scattered across paddocks. But one fragment, which weighs around 14 kilograms, is one of the most studied meteorites in the world.
It's a carbonaceous chondrite – a type of asteroid rich in clay and ancient compounds from the birth of the Solar System. (There are three types of asteroid: chondrites, stony and metallic.) But even though carbonaceous chondrites aren't the most prevalent asteroids – they comprise less than 5% – they are the most interesting, Britt says.
"They're water-rich and carbon-rich – stuff asteroid miners are interested in." Water can be split into hydrogen and water and burnt for fuel, or turned into methane. Asteroids, in this way, can be used as fuel stations for spacecraft.
Rocks are out of this world
When meteorites blast through our atmosphere, they burn – that's what a shooting star is. So can Britt be sure he's working from untouched material? Or does this cooking change the rock's chemistry?
"It actually has very little effect," says Phil Bland, a geologist and meteorite hunter at Curtin University in Perth, Western Australia.
As the outer layer of a meteorite burns, it strips away. But a combination of freezing space conditions plus only a small time in the heat of the atmosphere – around 10 seconds at most – means only a small amount of the asteroid is burned away.
So sorry, Hollywood: a flaming meteorite hurtling to the Earth’s surface is just a myth. The interior is kept pristine and still ice cold – a bit like deep-fried ice cream. "It's counterintuitive," Bland says, "kind of bonkers, really."
Regardless, working with meteorites isn't without its risks. The asteroids most attractive to miners – carbonaceous chondrites – happen to be full of minerals called serpentines, that could also turn out to be toxic.
"Most serpentines are just fine," Britt says. "But you can get some serpentine that contains asbestos." Tweaking his recipe slightly, and using serpentines without asbestos, still produces "close enough" asteroid material.
Hardware? That's hard work
Even with Earth-made asteroid material, engineers certainly have their work cut out for them when it comes to testing their mining hardware.
Asteroids have an average surface temperature of a chilly -70 ºC. But they spin as they hurtle through space. Sun-facing regions can shoot up to 400 ºC while shadowed regions plunge to -220 ºC.
And asteroids, having low mass, don't have much gravity either. A drill, if it doesn't successfully pierce rock, might simply push itself off the asteroid surface.
Some scientists are conducting tests in drop towers, which simulate microgravity for a few seconds at a time, or in special chambers that emulate the vast swings in temperature.
Britt's taken his samples off Earth and has an experiment on the International Space Station called Strata. From May, samples of his asteroid material will be subjected to microgravity for the best part of a year then returned to Earth for analysis.
He plans to create four more recipes for different types of asteroids. And they won't only be used to test drill bits – rovers and other machinery will also be put through their paces on what Britt calls his “really dirty" material. It's dusty and grubby and sticks to everything.
He points to the Chinese lunar rover Jade Rabbit that got stuck in dust almost immediately after landing on the Moon in 2014. While it might’ve worked on Mars, the ultra-fine Moondust was its undoing.
Overcoming hurdles such as dust and microgravity are going to be major challenges even before equipment is launched. But, Britt says, that’s not his problem: "I can't solve them all!"