The engineers are still solving the problem Why the mole of Mars InSight is blocked and will not go further

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Mars InSight Lander from NASA has always been a tricky business. The fixed lander has a chance to do things well because he can not move. Although the mission went well in the beginning and the landing site looks good, the mole is struggling to penetrate deep enough to fulfill his mission.

InSight landed on Mars on November 26, 2018. Its landing point is in the Elysium Planitia, a vast plain of the Martian equator. The goal is to study the inside of Mars and understand how this planned was formed.

Elysium Planitia is a vast plain on the equator of Mars. Image credit: Onboard visual camera onboard the ESA Mars Express / ESA - http://www.esa.int/spaceinimages/Images/2018/11/Elysium_Planitia_labelled_view, CC BY-SA 3.0, https: // commons .wikimedia.org / w / index.php? curid = 74676354
Elysium Planitia is a vast plain located on the equator of Mars. Image credit: Onboard visual camera onboard the ESA Mars Express / ESA – http://www.esa.int/spaceinimages/Images/2018/11/Elysium_Planitia_labelled_view, CC BY-SA 3.0, https: // commons .wikimedia.org / w / index.php? curid = 74676354

It has several instruments, including the "Mole" probe or the heat flow and physical properties probe, HP3 to shorten it. The mole is designed to penetrate the surface of Mars, where it can take accurate measurements of the heat flowing from the inside of the planet.

The InSight team had to choose a suitable place to penetrate the surface, but they could not see anything under the drill site. At first, the mole was doing well and was making its way to Mars. But then it stopped.

In this image, the heat flux and physical properties probe is inserted into Mars. Image: NASA
In this image, the heat flux and physical properties probe is inserted into Mars. Image: NASA

The Mole, or HP3, is the contribution of the German Aerospace Center (DLR) to the InSight lander. They managed to penetrate the probe 30 cm (11.8 inches) from the surface, but on February 28, she stopped. And so far, they have not been able to progress beyond the first 30 centimeters.

DLR and NASA both have replicas of the heat flux probe in test areas in the United States and Germany. They have done tests to see how they can proceed, but until now they have been stuck.

"We are now rather certain that the lack of soil adhesion around the mole is a problem."

Tilman Spohn, Principal Investigator, HP3 experience at the DLR Planetary Research Institute.

In a new press release, the DLR says that it may be that friction is not enough to allow proper operation of the probe, because of the lower gravity on Mars. They also believe that small cavities have formed between the probe and the ground, thus preventing the hammering of the probe.

Illustration of the probe partly in the Martian surface. The probe is tilted and is only 11.8 inches deep and is not completely submerged. It's not deep enough to do science. Image Credit: Credit: NASA / JPL-Caltech
Illustration of the probe partly in the Martian surface. The probe is tilted and is only 11.8 inches deep and is not completely submerged. It's not deep enough to do science. Image Credit: Credit: NASA / JPL-Caltech

Now, engineers and scientists using the probe have announced that they will use the robotic arm of the undercarriage to detach the support structure from the probe. This will allow them to examine the problem more closely. They think that they might be able to use the arm to assist the probe that is trying to infiltrate the ground.

The process of lifting the structure will begin at the end of June and will take place in several stages. The arm will first grab the structure and then move it in three stages, capturing the images as it works. This will prevent engineers from accidentally removing the probe from the ground.

"If that happens we will not be able to reinsert it in its hole or move it elsewhere, because the arm has no way to pick up the mole directly. "

NASA engineer Troy Hudson.

"We want to lift the support structure because we can not visualize the mole under the basement and therefore we do not know in what situation it is," says Tilman Spohn, principal investigator of HP.3 experience at the DLR Planetary Research Institute. "We are now rather certain that the lack of soil adhesion around the mole is a problem because the friction caused by the surrounding regolith under the lower gravitational pull on Mars is much lower provided that."

This image was taken by the InSight Lander instrument deployment camera mounted on the robotic arm of the LG. The bent grapple at the end of the arm is folded, but it unfolds and serves to deploy the scientific instrument of the undercarriage. The black cylinder on the left is the thermal probe, which will pierce up to 5 meters from the Martian surface. Image: NASA / JPL-Caltech
This image was taken by the InSight Lander instrument deployment camera mounted on the robotic arm of the LG. The folded grab at the end of the arm is folded, but it unfolds and serves to deploy the scientific instrument of the undercarriage. The black cylinder on the left is the thermal probe, which will pierce up to 5 meters from the Martian surface. Image: NASA / JPL-Caltech

It is also possible that the mole hit a rock. It is designed to make its way out of the rocks, but it may have hit an obstacle that it can not move. Another possibility is that it is caught between a rock and its supporting structure. If this is the case, moving the support structure could release it. According to Spohn, however, the probability of the mole being blocked by a rock is low.

"We plan to use the robotic arm to squeeze the ground close to the mole. This extra load will increase the pressure on the indenter and thus the friction on its outer surface, "says Spohn. "Our calculations at DLR suggest that we need to get closer to the device. Immediately above the mole, which is placed at a small angle to the vertical with respect to the surface and near it, the effect is maximal. Without removing the support structure, we would be too far and the effect would be too weak. "

The support structure of the heat flux probe and physical properties. The structure is slightly displaced during hammering, as shown by the rounded imprints in the surface. Image credit: NASA / JPL-CalTech.

It is a delicate affair, and a meticulous drama is played out at 227 million km from the Sun. The structure must be gradually lifted because it contains springs that can be in contact with the back of the mole. If they accidentally remove the mole from the hole, they are in trouble.

"If that's the case, we want to be careful lifting the structure so that we do not accidentally pull the mole off the ground," says Troy Hudson, NASA engineer. "If this happens, we will not be able to insert it into its hole or move it anywhere else, because the arm has no way of picking up the mole directly. So we will lift the support structure little by little, making sure that the mole will not come with it. "

On the JPL InSight Lander test bench, engineers carved a gravel-like material on a replica of the InSight landing site on Mars. The wood marks the limits of the placement zone of the LG instruments. Unfortunately, the test bed can not reproduce the Martian gravity and the regolith. Image Credit: NASA / JPL-Caltech / IPGP
On the JPL InSight LG test rig, engineers carved a gravel-like material on a replica of Mars' InSight landing site. The wood marks the limits of the landing gear of the landing gear. Unfortunately, the test bed can not reproduce the Martian gravity and the regolith. Image Credit: NASA / JPL-Caltech / IPGP

However, moving the mole is not really a solution because they are almost certain that the problem is the lack of friction. "We are convinced that the probability of hitting a big stone is only a few percent," Spohn said in a press release.

"We think the problem is a lack of friction in the Martian regolith. So, even if we could lift the mole, it would not matter where we put it – there would always be the same friction problem, "said Hudson.

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