Behold the "mole": The heat-sensing spike that NASA's InSight lander deployed on the Martian surface is now visible. Last week, the spacecraft's robotic arm successfully removed the support structure of the mole, which has been unable to dig, and placed it to the side. Getting the structure out of the way gives the mission team a view of the mole - and maybe a way to help it dig.
"We've completed the first step in our plan to save the mole," said Troy Hudson of a scientist and engineer with the InSight mission at NASA's Jet Propulsion Laboratory in Pasadena, California. "We're not done yet. But for the moment, the entire team is elated because we're that much closer to getting the mole moving again."
Part of an instrument called the Heat Flow and Physical Properties Package (HP3), the self-hammering mole is designed to dig down as much as 16 feet (5 meters) and take Mars' temperature. But the mole hasn't been able to dig deeper than about 12 inches (30 centimeters), so on Feb. 28, 2019 the team commanded the instrument to stop hammering so that they could determine a path forward.
Scientists and engineers have been conducting tests to save the mole at JPL, which leads the InSight mission, as well as at the German Aerospace Center (DLR), which provided HP3. Based on DLR testing, the soil may not provide the kind of friction the mole was designed for. Without friction to balance the recoil from the self-hammering motion, the mole would simply bounce in place rather than dig.
One sign of this unexpected soil type is apparent in images taken by a camera on the robotic arm: A small pit has formed around the mole as it's been hammering in place.
"The images coming back from Mars confirm what we've seen in our testing here on Earth," said HP3 Project Scientist Mattias Grott of DLR. "Our calculations were correct: This cohesive soil is compacting into walls as the mole hammers."
The team wants to press on the soil near this pit using a small scoop on the end of the robotic arm. The hope is that this might collapse the pit and provide the necessary friction for the mole to dig.
It's also still possible that the mole has hit a rock. While the mole is designed to push small rocks out of the way or deflect around them, larger ones will prevent the spike's forward progress. That's why the mission carefully selected a landing site that would likely have both fewer rocks in general and smaller ones near the surface.
The robotic arm's grapple isn't designed to lift the mole once it's out of its support structure, so it won't be able to relocate the mole if a rock is blocking it.
The team will be discussing what next steps to take based on careful analysis. Later this month, after releasing the arm's grapple from the support structure, they'll bring a camera in for some detailed images of the mole.
InSight mission seeking new ways to fix heat flow probe
WASHINGTON — Members of the InSight mission team are using a break in spacecraft operations to study new ways to get one of the spacecraft’s key instruments to resume burrowing into the Martian surface.
Scientists and engineers involved with InSight’s Heat Flow and Physical Properties Package instrument have been working for the last several months to get the instrument’s probe, or “mole,” to start moving into the surface again. The mole, intended to hammer to a depth of five meters below the surface, stopped in early March only about 30 centimeters below the surface.
In June, the mission decided to use the lander’s robotic arm to remove the support structure for the instrument. That would allow the instrument team to get a better view of the condition of the mole and also take new steps to get the mole moving again. Scientists believed that a lack of friction with the surrounding regolith was preventing the mole from gaining traction as it attempted to hammer deeper into the surface.
Removal of the support structure confirmed that hypothesis. Images showed the top of the mole peeking out above the surface in a hole about twice the diameter of the mole. A twist in the tether linking the mole to the rest of the instrument suggested it had started to spin around, widening the hole, as it tried to hammer deeper into the surface.
The instrument team then used InSight’s robotic arm again, pressing the scoop at the end of arm against the surface around the hole to try and collapse it. In an Aug. 27 blog post, Tilman Spohn, principal investigator for the instrument at the German space agency DLR, said that images taken after those attempts showed that the pit was only, at best, partially collapsed on one side.
Spohn said it appears there is a layer of “duricrust,” or regolith that is mechanically strong, on the surface, covered by about a centimeter of loose dust. Below that duricrust, which he estimated to be five to ten centimeters thick, could be “cohesionless sand” that prevents the mole from penetrating.
InSight is currently on hiatus while it and other spacecraft at Mars are in solar conjunction, with the sun between Mars and the Earth blocking communications. Spohn said that while the break is a time for some to take a vacation, he and others are thinking about new ways to get the mole moving again.
One possibility would be to use the scoop on the robotic arm in a different way. “I am thinking towards pinning the mole with the scoop such that the pinning and the pressing of the mole against the wall of the pit would increase friction,” he wrote. “This will be more risky than the previous strategy, but with the unexpectedly stiff duricrust, it may be worth a try.”
Spohn didn’t state when the mission would try a new approach to get the mole moving again. Andrew Good, a spokesman at the Jet Propulsion Laboratory, said Aug. 29 that there will be no action immediately after the solar conjunction period ends Sept. 7. It will take about a week after that to get all the data back from InSight and other spacecraft at Mars.
“Even after that, the team is continuing to conduct testing and discuss the next move,” he said, and thus there is no firm date for deciding what to do next with the mole.