NASA engineers hope to use the scoop at the end of the lander's robotic arm to get the Insight lander's heat probe burrowing once again.

UPDATE (October 17, 2019): NASA has announced that it has used the new technique described below to help the Insight lander's heat probe to dig down an additional 2 centimeters. The movement, while small, shows that the technique is working.

Mars Mole
A raw image from October 6th, showing the scoop on the end of InSight's robotic arm positioning to push on the mole, left of the scoop.

It’s been tough going so far for one of the instruments that's part of NASA’s Interior Exploration using Seismic Investigations, Geodesy and Heat Transport mission, known as Insight. While the geophysics mission landed safely on Mars and has otherwise been a great success, drilling into the planet's surface has proven problematic.

Insight placed the Heat Flow Physical Properties Package (HP3) on the Martian surface on February 4, 2019. Designed and built by the German Aerospace Center (DLR), the package includes the self-hammering heat probe, known as the "mole." Designed to dig as deep as 5 meters (16 feet) into the regolith, the mole must reach a depth of at least 3 meters in order to return useful science. The aim of the mole is to measure heat escaping from the Martian interior and determine, among other things, how active the planet is now.

Scoop push
Using the scoop to attempt to compress soil around the mole.
NASA / JPL-Caltech

Trouble struck on March 7, 2019, when the hammering mole stopped digging, and instead began to simply bounce in place. The mole is currently stuck at a depth of only 35 centimeters (14 inches) below the surface. At first, the team thought that the mole had encountered a rock it couldn't nudge out of the way, but now the team is thinking the soil is the problem. The mole needs friction in order to operate, but it appears the regolith around the probe has become compressed. As a gap widened around the probe, that left nothing for the probe to push against as it attempted to hammer downward.

This summer, the team moved the probe's support structure out of the way so that they could image the area. The mole wasn’t designed for repositioning, and moving the support structure out of the way to investigate the problem wasn’t without its risks, as it could have also pulled the mole out of the ground for good. The operation was successful, though, and images confirmed that the regolith is a rare kind of compact soil. Rather than fall into the hole that's created, this soil compresses alongside the probe instead.

Now, working with a replica probe and replica regolith located in the Mars Rock Garden at the Jet Propulsion Laboratory in Pasadena, California, NASA's engineers have hit upon a possible solution, to be implemented in the coming weeks. They plan to use the scoop on the end of the robotic arm to push the mole against the wall of the hole, giving the mole something to push against as it burrows.

This feat is more complicated than it sounds, as the HP3 package was placed as far away from the InSight Lander as possible, so that the lander’s daily shadow would not interfere with heat measurements. This prudent measure unfortunately places the mole at the very end of the robotic arm’s reach, making it a tough spot to apply pressure.

“We’re going to try pressing the side of the scoop against the mole, ‘pinning’ it to the wall of its hole,” says Sue Smrekar (NASA / JPL) in a recent press release. “This might increase friction enough to keep it moving forward when the mole hammering resumes.”

Pushing, Pinning, and Scraping

Earlier this summer, the team used the scoop on the end of the robotic arm seven times to push next to the mole, in an effort to compress the soil around the hole and collapse the hole itself. But no luck.

“We’re asking the arm to punch above its weight,” says Ashitey Trebi-Ollennu (NASA JPL). “The arm can’t push the soil the way a person can. This would be easier if we could, but that’s just not the arm we have.”

If the new pinning maneuver does not work, the next option is to use the scoop to scrape soil into the hole. While pushing down on the Martian surface was difficult for the robotic arm and scoop, as they were working from an angle due to their distance from the probe, scraping soil into the hole will be easier work.

Launched on May 5, 2018, Insight was the only mission to take advantage of the 2018 launch window to Mars. Insight also featured the first set of interplanetary CubeSats, the twin Mars Cube One relays. Since Insight landed, it has successfully detected Marsquakes, monitored the weather conditions at the Elysium Planitia landing site, and detected minute land tides, along with minute temperature changes, raised by the passage of Mars’s inner moon Phobos.

And there’s more to come. 2020 is the year that no less than four missions from four separate collaborations hope to make the trip to Mars, including NASA’s Mars 2020 rover, the joint Roscomos/European Space Agency Rosalind Franklin rover, United Arab Emirates’s Mars Hope orbiter, and China’s Global Remote Sensing orbiter and rover.

The mole issue may be problematic, but the story is far from over. It’s worth checking in on the lander’s raw image page to see what’s up, as the drilling drama unfolds on the surface of Mars.


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