One problem, however, has been difficult to contend with over the past several months – the lander’s self-hammering heat probe, called the Heat and Physical Properties Package (HP3) or “the mole,” has been stuck and unable to penetrate deeper into the ground as intended.
The mole was designed to dig down as much as 16 feet (five meters) into the ground, in order to measure the amount of heat escaping from the planet’s interior, but so far has only reached 14 inches (35 centimeters). The exact cause has been a bit of a puzzle, with efforts to fix the issue so far proving unsuccessful.
But recently, mission engineers have been trying a new tactic, called “pinning.”
“We’re going to try pressing the side of the scoop against the mole, pinning it to the wall of its hole,” said InSight Deputy Principal Investigator Sue Smrekar of NASA’s Jet Propulsion Laboratory in Pasadena, California. “This might increase friction enough to keep it moving forward when mole hammering resumes.”
It was thought that the probe had simply hit a buried rock, but now the consensus seems to be that the soil itself is causing more friction that anticipated. The mole requires friction from surrounding soil in order to dig. Without it, recoil from the self-hammering action causes it to simply bounce in place, and that is what the mission team thinks has been happening.
But now for the good news: it seems that this attempt to “free the mole” is working so far! The initial results were posted on the mission’s Twitter feed:
As space journalist Leonard David also recently posted:
In order to try this new technique, the mission team first needed to get a better look at the hole in the ground that the mole had created so far. The mole can’t just be picked up and relocated after it begins digging, so the only option was to remove the support structure the mole uses to keep it steady. Subsequent testing showed that the soil tended to clump together instead of falling around the mole.
The lander’s camera also showed that there is a 2 to 4 inch (5 to 10 centimeter) layer of duricrust below the surface, a kind of cemented soil thicker than anything encountered on other Mars missions and different from the soil the mole had been designed to work in.
“All we know about the soil is what we can see in images InSight sends us,” said Tilman Spohn, HP3’s principal investigator at DLR. “Since we can’t bring the soil to the mole, maybe we can bring the mole to the soil by pinning it in the hole.”
Over this past summer, the team tried using the scoop on the robotic arm seven times to break through and collapse the hole, but to no avail.
“We’re asking the arm to punch above its weight,” said Ashitey Trebi-Ollennu, the lead arm engineer at JPL. “The arm can’t push the soil the way a person can. This would be easier if it could, but that’s just not the arm we have.”
As with other Mars surface missions, NASA has a backup working replica of InSight back on Earth, including the heat probe, to help solve problems as they come up on the real lander.
The mission team is also currently trying another technique, using the scoop to scrape soil into the hole instead of compressing it.
It seems like progress is now finally being made in finding a solution to the mole’s woes, so hopefully it will now soon be able to continue digging deeper into the Martian dirt to learn more about what the planet is like far below the surface.
InSight was launched on May 5, 2018, on a United Launch Alliance Atlas V “401” rocket from Vandenberg AFB, California. It landed in the Elysium Planitia region on Mars on Nov. 26, 2018.
More information about InSight is available on the mission website.