Leonard David's INSIDE OUTER SPACE

Credit: NASA/JPL-Caltech

“We have made important progress in our attempts to get the mole digging again…in fact, we got it digging again!”

That’s the word from Tilman Spohn of the German Aerospace Center’s (DLR) Institute of Planetary Research in Berlin. He’s the experiment leader on the Heat Flow and Physical Properties Package (HP3), the self-hammering “mole” designed to dig down as much as 16 feet (5 meters) and take Mars’ temperature.

The HP3 has been trouble-plagued, deployed from the NASA InSight Mars lander.

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

Digging slowly but steadily

“You may recall that we have pinned the mole with the [lander’s robotic] scoop which resulted in the mole digging slowly but steadily. Four carefully planned sessions have been executed on sols 308, 311, 315 and 318, with 20, 100, 100, and 150 strokes, respectively,” Spohn reports.

At the end of sol 318, mole scientists had exhausted their capability of pinning because the mole had dug so deep that it would risk the tether if the arm under tension would move uncontrolled to the left as the mole dug below it.

“We therefore moved the arm slightly to the right – about 1 centimeter –  away from the mole thereby releasing the pin,” Spohn adds. The arm was commanded to press onto the surface.

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

Breakthrough

“With its force of 50 Newtons, we estimated that the load at the mole at shallow depth would still be more than twice the load provided by the overburden. Still, as the friction on the mole sleeve would be significantly less than from pinning, it was not obvious that the mole would continue digging,” Spohn explains.

Mole scientists and technicians commanded 50 strokes to be executed on sol 322 because they would not have proof that the scoop would indeed press on the surface as we started hammering. The mole was clearly seen to dig.

InSight Mars lander.
Credit: NASA/JPL-Caltech

“To me this is a breakthrough! It tells me that indeed insufficient friction was the root cause of the problem,” Spohn points out. “I am now confident that with the next round of hammer strokes – 500 are planned for sol 325 – we get the mole fully buried,” he notes.

The news from the site about this prospect will be available on Saturday evening Central European Time.