It is always a sad day when a mission ends. And it’s even sadder when the mission didn’t get off the ground at all.
There we are with NASA’s InSight lander. The entire mission is not over yet, but the so-called mole, the instrument designed and built by the German DLR, has been declared dead.
The mole is of course the package for heat flow and physical properties (HP3). It is an instrument for measuring the heat that flows from the interior of Mars to the surface. The entire InSight mission (interior exploration with seismic surveys, geodesy and heat transport) focused on learning more about the interior of Mars.
HP3 is probably the most important and complicated instrument on the land. So, losing it is a major blow to science. But implementation has always been difficult, and the mission designers knew it.
“That’s why we take risks at NASA – we have to push the boundaries of technology to learn what works and what doesn’t.”
Thomas Zurbuchen, Associate Administrator for Science, NASA.
The mole’s job was to burrow into the surface of Mars to a depth of 5 meters. A tether would connect the mole to the lander, and there are evenly spaced heat sensors along that tether. By studying the thermal properties of the planet’s interior, scientists could have learned a great deal about its geological history.
But getting the instrument into the ground was always difficult. The mole is a self-hammering instrument that is designed to slowly work its way into the surface. Due to the mission’s weight and energy limitations, a more powerful and powerful way of driving the instrument into the ground was not possible.
The mole was designed to slowly drift under the surface of Mars. According to DLR, CC-BY 3.0, CC BY 3.0 de, https://commons.wikimedia.org/w/index.php?curid=87348555
The mole has had problems since its deployment in March 2019. At first it made some progress, but after a few inches it stopped. At first, the mission workers thought it was blocked by a stone.
Universe Today has covered the saga of the mole in a number of articles. There were signs of progress and despair along the way. However, over time it became clear what was preventing the mole from realizing its potential.
The surface of Mars on which the InSight lander is located is covered in a type of soil called duracrust. It is a compacted layer of earth that does not fall back into the mole’s hole as it moves down. That’s a problem.
The mole relies on friction between itself and its surroundings. However, because Duracrust is too tight and won’t flow into the hole, it doesn’t provide the friction required.
The mission staff tried everything to provide the missing friction. They used the instrument arm shovel to push the mole. They used it to put sideways pressure on the mole. And they tried to use it to shovel the soil they needed into the hole. Either method gave hope, but in the end the mole couldn’t get deep enough to do science.
This May 2020 picture shows the shovel at the end of InSight’s robotic arm, gently pushing the mole as it works its way into the ground. Photo credit: NASA / JPL / DLR
Now the mole has been declared dead after 500 final and ultimately unsuccessful hammer blows in January.
“We gave everything we have, but Mars and our heroic mole remain incompatible,” said the lead investigator at HP3, Tilman Spohn from DLR.
But all is not lost.
The last resting place of the mole after 500 hammer blows in early January. Photo credit: NASA / JPL-Caltech
The lander’s other instruments, including its seismometer, are still working. So the mission still has scientific value. And although the mole failed, despite the best efforts of the people at NASA and DLR, failure may lay the foundation for future success.
“Fortunately, we’ve learned a lot that will benefit future missions that try to dig underground,” said Spohn.
In the InSight Lander test environment at JPL, engineers shape a gravel-like material into a replica of InSight’s landing site on Mars. The wood marks the boundaries of the lander’s instrument placement zone. The engineers chose the best looking place to deploy the mole, but there were no second chances. After the mission, the mole could not be removed and used in another location. Photo credit: NASA / JPL-Caltech / IPGP
This is the first time a mission has attempted to dig into the Martian surface in this way. So the whole company was in unknown territory. There was no way of knowing what was going to happen for sure to the mole. But it was a fascinating episode as members of the Mole team tried to figure out a way forward.
“We are so proud of our team that worked hard to bring InSight’s mole deeper into the planet. It was amazing to see them fix bugs from millions of miles away, ”said Thomas Zurbuchen, associate administrator for science at the agency’s Washington headquarters. “That’s why we take risks at NASA – we have to push the boundaries of technology to learn what works and what doesn’t. In this sense we have been successful: We have learned a lot that will benefit future missions to Mars and elsewhere, and we thank our German partners from DLR for providing this instrument and for their cooperation. “
This artist’s concept from August 2015 shows NASA’s InSight Mars lander, which was used entirely for the investigation of the deep interior of Mars. Photo credit: NASA / JPL-Caltech
Other missions have given us a clear view of the Martian surface. Mission designers felt that the mole’s hammer design would give it the best chance of completing its mission. Apparently it was the right call. But the Duricrust came as a surprise and proved too great an obstacle to overcome. While that failed, the entire company was unprecedented from the start.
“The mole is a device with no inheritance. What we’ve tried to dig so deep with such a small device is unprecedented, ”said Troy Hudson, a scientist and engineer at NASA’s Jet Propulsion Laboratory in Southern California who made efforts to get the mole deeper into the Martian crust. “Having the opportunity to see this through to the end is the greatest reward.”
The other parts of InSight’s mission continue. The SEIS (Seismic Experiment for Internal Structure) is still busy measuring Marsquakes and other events, and the RISE (Rotation and Interior Structure Experiment) instrument is still working to find out the size of the iron-rich core of Mars. The lander’s weather station is also still working.
InSight was launched in May 2018 and landed on Mars on November 26, 2018. The mole was used on February 12, 2019. The mission was extended to December 2022.
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