NASA’s InSight Mars lander acquired this image using its robotic arm-mounted, Instrument Deployment Camera (IDC). This image was acquired on September 29, 2019, Sol 298.
Credit: NASA/JPL-Caltech

That trouble-plagued, Mars-situated, Heat Flow and Physical Properties Package, HP3, continues to receive long-distance motherly attention.

InSight’s scoop has touched the Mole as shown in this image from the robotic arm-mounted, Instrument Deployment Camera (IDC). This image was acquired on October 3, 2019, Sol 302.
Credit: NASA/JPL-Caltech

The Germany-provided HP3 was deployed by NASA’s InSight lander that touched down on the Red Planet in November 2018.

A self impelling nail nicknamed “the mole” was designed to hammer itself down into the surface of Mars. But the device hasn’t been able to dig deeper than about 12 inches (30 centimeters) below the Martian surface since Feb. 28, 2019.

HP3 is designed to take Mars’ temperature, revealing just how much heat is still flowing out of the interior of the planet.

The self-hammering mole, part of the Heat Flow and Physical Properties Package (HP3) on NASA’s InSight lander, was only partially buried in the soil of Mars as of early June 2019, as shown in this illustration.
Credit: NASA/JPL-Caltech/DLR

Pinning tactic

Tilman Spohn, of the German Aerospace Center’s (DLR) Institute of Planetary Research in Berlin, is the principal investigator of the HP3.

In a new report, Spohn outlines the path forward in getting the Mole moving again.

Components of the HP3 heat flow probe. Top left: the radiometer (RAD), which is used to measure the radiation temperature (roughly equivalent to the ground temperature) of the surface. Right: the casing with the mole penetrometer, the temperature measuring cable (TEM-P) and the data cable (ET) connected to the lander. In addition, the casing contains an optical length meter for determining the length of the temperature measuring cable that has been pulled from the casing. The mole contains the TEM-A active thermal conductivity sensor and the STATIL tiltmeter. Bottom left: the electronic control unit, known as the back end electronics (BEE), which remains on the lander and is connected to the probe via the ET.
Credit: DLR

The InSight team has adopted a strategy of “pinning” the Mole with the spacecraft’s scoop mounted on a robotic arm. That tactic supersedes spending more time to collapse the pit. Everything seems to be ready for pinning and hammering on Martian Sol 308 which will be Tuesday October 8 with data coming down Wednesday afternoon (CET), Spohn explains.

Electronics box anomaly

“But before we could work on implementing the pinning,” Spohn adds, “HP3 had to solve an anomaly” that cropped up in an electronics box (the BEE) and that had motivated JPL to switch the experiment off until only recently.

Strange readings in downlinked data already suggested that some of the data stored in the mass memory of the BEE had been overwritten.

InSight Mars lander.
Credit: NASA/JPL-Caltech

“It was soon recognized that the most likely cause was what experts call a ‘bit-flip.’ This flipping can occur when cosmic particles hit the mass memory. This is not unusual at Mars where cosmic particles get through the thin atmosphere better then what we are used to on the Earth,” Spohn points out.

Bit-flip

Typically, electronics box designers have critical paths implemented in a three-fold configuration and logic compares the values and decides democratically on the majority of the voting. “Thus most of the bit-flip problems can be avoided,” Spohn says.

“Unfortunately, our BEE has that protection mechanism not fully implemented as we were short in mass memory,” Spohn observes. “JPL needed to be convinced then that a bit flip could not cause any further harm, for instance, by erroneously commanding the mole to hammer.”

InSight specialists at Jet Propulsion Laboratory have developed and implemented strategies to get the Mole moving again. Credit: NASA/JPL-Caltech.

Next hammering

Fine positioning of InSight’s robotic arm will be done over the coming weekend, Spohn continues, prior to the next hammering, “the first one since the diagnostic hammering on March 26th. And this time it will not be just for diagnostics!”

The number of commanded hammer strokes has been limited to 20.

The concern is that the pinned Mole could proceed quite rapidly and make the five centimeters sticking out of the ground in only a few hammer strokes. “That might cause the scoop to hit and damage the tether coming out of the Mole’s backcap,” Spohn adds.

Credit: NASA/JPL-Caltech

20 strokes

“We here at DLR have used performance data for the Mole from laboratory measurements to determine that in the best (or worst) case it would take the Mole 8 strokes to make 4 centimeters. As this was thought to be overly conservative and it was feared that the Mole might make so little progress that the latter was unnoticeable, the team settled on 20 strokes,” Spohn observes.

Spohn’s report concludes by saying “stay tuned” until the InSight/HP3 team sees what happens next week and help them keep fingers crossed!

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