This is a long road for InSight’s Mole. InSight landed on Mars almost two years ago, in November 2018. While other lander instruments are working properly and returning scientific data, the Mole is struggling to hammer the surface of the planet.
After much effort and a lot of patience, Mole finally managed to bury himself until Marian regolited.
But the drama is not over yet.
The Mole is a 16-inch length heat probe that fills itself deep into the surface. Its maximum depth is 5 meters (16 ft) below the surface, and that is the ideal depth of its operation. But it can also gather useful scientific data at shallow depths of about 3 meters (10 ft). As of today, the mole does not have the deepest depth to make any science.
But two years later, it was still the deepest.
The real name of the mole is the Heat Flow and Physical Properties Package, or HP3. It is designed to measure the heat coming from the interior of Mars. The tether that connects it to the InSight lander contains heat sensors along with its length. InSight means Internal Discovery using Seismic Investigations, Geodesy and Heat Transport. Part of the mission heat transport is mole work.
Since the instrument was deployed, it has faced problems. The mole penetrated by hammering slowly into the ground. But that movement of the hammer depends on the friction between the mole and the edges of its hole. Without that friction, the instrument simply bounces back into the hole.
The problem is the so-called duricrust. It is a hardened layer of surface that forms in arid areas. And Mars is definitely arid. The duricrust around the mole prevents the ground from falling into the mole hole while it is hammering, and removes the instrument from the necessary friction for hammering towards Mars.
While InSight is primarily a NASA mission, the Mole was designed and built by the DLR (German Aerospace Center). They are working with NASA’s JPL, which has an engineering version of Mole in a test-bed. There they tried to overcome these challenges.
They tried to use the scoop on the arm end of the InSight instrument to apply sideway pressure to the Mole, expected to provide the necessary friction. They tried to push down the mole, while, carefully avoiding the sensitive tether. And they tried to scoop loose material into the scoop and put it in the Mole hole.
Today, NASA has announced that the Mole is finally completely buried in the dirt. That is a kind of success, but it will be far from over. Now that it is buried, the InSight team will continue to take more ground on top of the instrument and release it before resuming hammering operations.
But it all takes time.
“I am very happy that we are recovering from the unexpected ‘pop-out’ that we have experienced and that the mole is even deeper than before,” said Troy Hudson, a scientist and engineer at NASA’s Jet Propulsion Laboratory. . to get the mole digging. “But we are not done yet. We want to make sure there is enough soil at the top of the mole to enable it to dig without help from the arm,” Hudson said in a statement.
Scooping the ground and removing it will take several months. NASA says it is unlikely that the operation of the hammer will continue until January 2021. Part of preventing the operation is the accumulation of dust on InSight solar panels. That reduces the energy available throughout the mission.
Tilman Spohn is the Scientific Director for Mole at DLR. He writes a blog about the mole’s hard work. In this October 16, 2020 entry, Spohn discusses the next steps, and how they work towards another “Free Mole Test.” The free mole test is when they let try to hammer the mole under the surface without help from the scoop.
“After some discussion about the next steps, we decided that two parallel scoop movements should be carried out on Saturday 17 October (Sol 659),” he wrote.
“Then, a thermal conductivity measurement will be carried out, which should give us indirect indications about backfilling,” Spohn wrote. “Then, the filling will be forced to compress the sand and hit the Mole. Depending on the result of backfilling, further actions to fill the pit will be planned before further hammering and another Free Mole Test will take place later.”
On Earth, it would be simple to use a drill to penetrate below the surface. But drills are heavy, require a lot of strength, and need stability to prevent rotation rather than drilling. That is not only possible on Mars. A drill will weigh too much and will require more strength than weight. The mole is only 1 inch (2.7 centimeters) wide and about 16 inches (40 centimeters) long. It should be both light enough and small enough to fit within the mission constraints.
I hope, the mole will eventually reach the depth of its working. In the meantime, other InSight instruments work and return data. Thanks to SEIS (Seismic Experiment for Internal Structure) we know that Mars is a seismically active planet.
But without the mole and heat transport readings, the InSight lander would never live up to its mission.