InSight mission seeking new ways to fix heat flow probe

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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.