Not all rocks are created equal. It’s a mundane but inescapable fact that turns out to be particularly problematic if you’re designing a drill for a robot that will be poking holes in Mars.
When it’s millions of miles away from Earth, the new rover will not only need to search for signs of ancient life, it will need to be prepared for all the alien rocks it meets. Especially because, unlike its cousin Curiosity, this next-gen robot won’t just be drilling holes in those rocks: It will also be collecting rock cores and stashing them in various spots on the planet’s surface. If all goes well, the rock samples will be picked up and returned to Earth by a future rover, kind of like an interplanetary golden retriever. It’s a complicated strategy that forms the next step in NASA’s long-term plan to explore our small reddish neighbor, a plan that could eventually add human footprints to the rover tracks already pressed into the dusty, formerly wet Martian surface.
But first things first. The Mars 2020 rover needs to be able to drill, extract, store, and deposit all those cores.
“We don’t quite know what we’ll encounter when we get to Mars,” says JPL’s Matt Robinson, deputy product delivery manager for the rover’s sampling and caching subsystem. “We need to have a range of rocks we’re going to test.”
Robinson and I are standing in a cavernous lab on the JPL campus, in a place appropriately called the Rock Room. Somewhat ominously, there’s a sign on the door warning against the dangers of inhaling pure nitrogen gas. “Two breaths of 100% nitrogen can cause immediate unconsciousness with no warning,” it says in all-caps, which seems a bit out of place, considering that Mars wears a thin, gassy veneer of carbon dioxide. But no matter.
As its name suggests, the rock room is filled with baskets and baskets of rocks, mostly collected from sites in southern California. There are hard rocks and soft rocks and in-between rocks, and they’re all the geological equivalent of guinea pigs for the drill prototypes Robinson and his colleagues are developing. Like these rocks, some of the Martian targets will be hard and less likely to yield to the machinations of a nosy robot, while others will easily crumble under pressure. As evidence of the team’s ongoing experiments, there are piles of rocks bearing numerous cylindrical gouges.
“It’s somewhat of a design-by-test,” Robinson says. “You do the mechanical design, you build a prototype, then you come into the test bed and you test it.”
Opposite the rock piles are illuminated racks of clear plastic tubes, each holding a 4-inch-long cylindrical rock core. These dozens of tubes are the handiwork of the 2020 drill prototypes, and are almost exactly the type of thing the rover will be stashing on the Martian surface. The various cores are different colors and consistencies, and there’s more material in some tubes than others.
It occurs to me that it would be bad for the rover to accidentally cache an empty tube for future retrieval.
“Will the tubes on the rover be clear? Could you see into them?” I ask.
“It’s going to be a metal tube so you can’t really see into it, but there’s a camera that will look in and see how much sample there is,” Robinson assures me. He pauses, thinking. “But it would be nice to – like in Star Trek IV — have transparent aluminum…that would be really cool.”
Whales on Mars would also be nice.
Alien humpbacks aside, the plan right now is for the 2020 rover to retrieve as many as 42 rock cores and distribute them in strategic sites that are still TBD. That way, a future rover will only need to visit several locations to retrieve the cached samples instead of inefficiently retracing 2020’s path.
“This is our ambient robotic coring station,” Robinson continues, showing me one of the three drill prototypes the team is currently working with. As imagined, the 2020 drill would have a variety of bits available for tackling rocky obstacles; when the rover encounters an enticing rock, all it needs to do is shove its arm into a tool carousel and select the bit that’s best for the task. When it’s done with one tool, the rover can easily swap it out for another.
Right now, the retinue of options being tested includes a brush that will help smooth rock surfaces pre-drilling, as well as a dozen different bit prototypes. The team is also experimenting with stabilizing legs so the rover can achieve maximum rock-punch, as well as having the rover collect loose material from the surface, called regolith.
“The great thing about this test bed is it’s got a drill press that’s easy to set up and operate,” Robinson says, before the clamor of an ongoing test drowns out the rest of his sentence.
We move into the space where the third prototype lives, and it looks like I’ve stepped into a concert hall. On a small stage, the proto-arm is surrounded by multiple rocks, each with multiple lights and cameras aimed at it. The stage, it turns out, is hydraulic powered – and when the team wants to test the drill under Mars-like conditions, the whole platform can be launched upward until it docks with a pressure chamber hovering overhead.
“We actually raise it up and there are clamps up there which it clamps onto,” Robinson says. “You can pump down to Martian pressure and Martian temperature.”
On Mars, the surface pressure is about
60 0.6 percent that of Earth’s, and temperatures range from a wintry day in Ithaca, NY to somewhere you absolutely wouldn’t want to be. Robinson says the team runs roughly half its tests in the Mars-chamber, under the watchful eye of all those cameras.
But there are more differences between Mars and Earth than simply temperature and pressure.
“Does the different Martian gravity have any effect on the drill?” I ask.
“Gravity actually does affect the robotic arm quite a bit,” Robinson says. He explains that the team has to factor in weaker Martian gravity when teaching the rover where to retrieve bits and stash tubes. “If you were to go to those same joint angles on Mars, it would not work,” he says. “So we have to compensate for that in software. On the flipside, we’re now more capable because we carry less weight. So it’s both tricky and it’s good.”
All of this means that when NASA’s next rover arrives on Mars, expect the red planet to be poked, prodded, zapped and drilled into with all the precision that a wheeled, nuclear-powered robotic surgeon can offer – courtesy of these piles of geologic guinea pigs collected from spots on Earth.
In other words, as Albert Markovski astutely notes in the movie I Heart Huckabees: “You rock, rock.”