After months of setbacks, NASA says that the InSight Lander’s Mole is working again.
InSight landed on Mars on Nov. 26 2018 in Elysium Planitia. Its mission is to study the interior of the planet, to learn about how Mars and other rocky planets formed. InSight (Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport) is a NASA mission with other partners, including the DLR (German Aerospace Center.)
The Mole, or Heat Flow and Physical Properties Package (HP3,) was designed and built by the DLR. It penetrates the Martian surface and measures the heat flowing from the planet’s interior. It works like a hammer drill, pounding and rotating its way into the ground.
InSight only had one chance to deploy the Mole, and it took a good look around before doing it. Mission engineers used the lander’s cameras to examine its instrument placement area and find a place free of obvious rocks. But they couldn’t see under the surface.
After deployment, the Mole got a short way into the ground, then stopped. The InSight team thought it had hit a rock, but they weren’t certain. They kept working with it, and then the Mole got canted over at about a 15 degree angle.
After working their way through different scenarios on test-beds here on Earth, they came to a conclusion: the Mole relies on friction between itself and the surrounding material to penetrate into the ground, and the surrounding material wasn’t filling the hole the way it did when they designed and tested the Mole here on Earth.
Operator’s removed the Mole’s housing to get a better look inside the hole. They found a type of soil they call duricrust a few centimeters below the surface, and that duricrust was compacted and wouldn’t fill the cavity the Mole created as it penetrated the surface.
The InSight team used the scoop on the end of the lander’s instrument placement arm to push down on the soil surrounding the Mole’s hole. But that didn’t work. The instrument arm could barely reach that far, and it couldn’t apply much force.
NASA and the DLR came up with another solution. This time, they would use the scoop on the instrument arm to apply sideways force on the Mole. They hoped that by pushing the Mole against its hole, there would be enough force and the Mole would make progress again.
On October 15th, NASA said things were looking good, but they couldn’t be absolutely certain.
NASA calls the new technique “pinning.” By pinning the Mole against the side of the hole, there’s enough friction for the instrument to keep penetrating. Without that friction, the Mole will just bounce in place as it tries to hammer its way into the ground.
Now, NASA confirms that the pinning technique is working.
“Seeing the mole’s progress seems to indicate that there’s no rock blocking our path,” said HP3 Principal Investigator Tilman Spohn of DLR. “That’s great news! We’re rooting for our mole to keep going.”
There’s still a long way to go. The Mole is nowhere near its desired operating depth of five meters. But they’re making progress.
“The mole still has a way to go, but we’re all thrilled to see it digging again,” said Troy Hudson of JPL, an engineer and scientist who has led the mole recovery effort. “When we first encountered this problem, it was crushing. But I thought, ‘Maybe there’s a chance; let’s keep pressing on.’ And right now, I’m feeling giddy.”
The Mole is not in the clear yet. There’s no way of knowing if it’ll get stuck again. If it does get stuck again, at a greater depth, the pinning option won’t be available. The InSight team could try to scoop dirt down into the hole, or try to press down on the exposed top of the instrument. But that’s risky; the sensitive instrument tether is attached to the top.
But for now, there’s progress. The Mole’s maximum operating depth is five meters, but it can still do science at a shallower depth. It’s just not ideal, and will take more work to understand the results.
With luck, and possibly with more advanced problem-solving skills like the team has already used, the Mole will succeed. And Mars will reveal more of its secrets.
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