• Engineers at a NASA lab managed to dust off the solar panels of the InSight mission by throwing sand on them, according to our partner The Conversation.

  • This action had become a necessity due to the significant silting up of the lander's solar panels, considerably reducing the energy available for the mission and its scientific instruments.

  • The analysis of this experience was carried out by Charles Yana, SEIS operations project manager for the InSight mission of CNES (National Center for Space Studies).

NASA has just announced a great first for a planetology space mission, in this case with the InSight mission which landed on Mars in 2018: the cleaning of a solar panel by an action other than the wind or via natural conditions on the surface of the planet.

Engineers from the Jet Propulsion Laboratory (JPL, a NASA laboratory) managed to dust off the solar panels… by throwing sand on them!

This counter-intuitive activity is made possible by the saltation effect: large grains of sand, pushed by the wind, come to tear the smallest grains of dust stuck to the solar panel, allowing to increase the energy production of this latest.

This map of Mars shows the Perseverance rover landing site compared to previous successful Mars missions.

Most recent addition t © Nasa (mars.nasa.gov)

This action had become a necessity due to the significant silting up of the lander's solar panels, considerably reducing the energy available for the mission and its scientific instruments.

It stems directly from the burial of the cable of one of the instruments of the mission, which I will present to you.

Extended at the end of 2020 by NASA for two more years, the InSight mission now focuses on the operations of the French SEIS seismometer, listening to the tremors and vibrations of the planet Mars since the landing in the plain of Elysium Planitia on the 26th. November 2018.

InSight, part of NASA's 12th Discovery program, aims to determine the major mechanisms of the formation and evolution of terrestrial planets by measuring and finely characterizing the internal structure of Mars. All this thanks to the SEIS seismometer (developed by the Center national d'études spatiales and the Institut de physique du globe de Paris, with the support of numerous French, European and American partners), as well as with the HP3 temperature probe, developed by the German Center for Aeronautics and Astronautics, whose objective was to sink into Martian soil to a depth of 5 meters in order to measure the heat fluxes below the surface. The two instruments SEIS and HP3 had been deployed on Mars soil shortly after landing, thanks to the robotic arm of the InSight lander.



SEIS to listen to the heart of Mars beating (CNES)

If SEIS was able to quickly record the first Martian earthquakes, the penetration of the HP3 probe into the ground proved to be more difficult and the latter was never able, after almost two years of attempts, to sink completely into the ground.

The unsuccessful attempts to drill the German HP3 temperature probe were abandoned in early 2020 in order to free the robotic arm of the lander and allow the SEIS cable to be buried under Martian regolith (the fine dust on the surface planet) thanks to the shovel installed at the end of the arm. Indeed, if it is installed on the ground of Mars, the SEIS seismometer remains connected to the lander by a cable called


, in charge of transmitting the commands to SEIS and of transferring its scientific data.

The installation of SEIS and its cable was particularly meticulous in order to avoid any mechanical stress of the cable on the structure of the seismometer. The strong temperature gradients on the surface of Mars indeed generate mechanical effects of retraction and expansion of this cable. At nightfall, around 6 p.m. on Mars, temperatures drop by nearly 80 ° C in 1 hour. This has the effect of generating thermoelastic cracks in the cable which generate seismic noise on the SEIS data,


that the team is still seeking to better understand and characterize.

In order to reduce the frequency and amplitude of these creaks, the IPGP teams had the idea of ​​burying the cable under a layer of sand in order to thermally insulate it.

Ultimately, the objective is to improve the performance of SEIS, which is already excellent, and the quality of the scientific data produced.

The opportunity presented itself with the extension of the mission by NASA over the years 2021 and 2022, because the nominal duration of the mission was only two years, until the end of 2020.

Extremely careful burial

This activity has been carefully prepared since the start of the year by the CNES and JPL teams.

The engineers operate the InSight arm on the basis of instructions from the CNES operational team, which bases its action plan on the tests carried out at CNES on the seismometer qualification model.

Launched on March 14 and March 28, the first two shovelfuls deposited the regolith directly on the shield covering SEIS, thus making it possible to be as close as possible to the instrument by letting the sand slide down to the


(the cable which connects the instrument to the lander), making it possible to cover the few centimeters closest to SEIS, which are believed to be the most critical with regard to seismic noise.

The operation went perfectly and covered the end of the cable closest to SEIS with a few millimeters of sand, but the spectacular images returned from Mars raised some questions.

Cross-section of the SEIS seismometer, the cable to be buried is on the right of the image © NASA / JPL-Caltech / CNES / IPGP, CC BY

First, the deposit fell a little further to the left of the


than expected

, which was still largely covered. This is due to the domed shape of the heat shield, as well as the mechanical imprecision of arm placement. The result turned out to be a little different from the tests on Earth, which were carried out with an identical model of the SEIS shield.

There was also the question of the effect of the wind on the deposit and its influence on the dispersion of the regolith which is released from a fairly high place (about 40cm) for safety. As the energy of the lander was limited, the wind sensor of the weather station (also operated at CNES) had not been turned on. The dispersion of fine particles however clearly appeared on the trace left by the regolith on the shield, the surface of which was spectacularly cleaned of its dust accumulated over the past two years.

Finally, the quantity of sand deposited on the cable necessarily depends on the quantity of sand which may have been transferred to the shovel beforehand. The photos taken before and after the operation are the only way to ensure for example that the shovel has emptied well, or to estimate the filling volume, necessarily difficult to determine from an image seen from above. . Each deposition operation allows the teams to progress in the understanding of the underlying mechanisms, and to gain in efficiency with each new test.

On the strength of this initial experience, the operational teams were able to continue the activity without wasting time.

Mars is approaching its aphelion (point in the orbit of a planet where it is at the greatest distance from the sun), which will mark the coldest temperatures of the year for InSight.

In addition, the solar panels are starting to be heavily covered with dust, which limits the energy available for operations.

The first shovels deposited the regolith on the shield that covers SEIS © Nasa (mars.nasa.gov)

A plan on 6 to 8 depots has thus been put in place by this summer before energy runs out.

The activity is complex and requires taking into account many parameters:

  • The temperature on the surface of Mars in the first place, because the arm cannot be operated at too cold temperatures.

  • The uncertainty in the placement of the arm and the height of the deposit then, although they become more refined as the operations progress.

  • The wind is also essential, because if gusts are never to be excluded, the residual wind changes the appearance of the deposit on the ground.

    It is thus taken into account to estimate the point of deposit (to the nearest cm) and finally measured in real time during the execution of the activity with the wind sensor.

  • Finally, the shadows cast are important in estimating the height of the regolith pile, and activities therefore take place late in the day, when the sun is low in Elysium Planitia.

An idea for dusting solar panels

The first two deposits were made directly on the heat shield, before sliding down to the ground. This had the effect of cleaning the dust that had accumulated on the panel. This could have indirectly given the engineers of JPL the idea for the team to carry out a similar activity to dust one of the solar panels by saltation effect (the other panel not being reachable by the robotic arm): by depositing from high enough on the landing gear deck at a place close to the solar panel and at one time of the day with sufficient wind in the right direction, the large grains pushed towards the panel by the wind come to tear off the dust glued to the panel by bouncing on the surface by saltation.

The deposits are preceded by a “scraping” phase during which the shovel scrapes the ground in order to collect enough regolith on the ground.

The shovel is then filled in this heap before the deposit.

The third and fourth deposits were aimed at the pinning mass, the small appendage added to the


to adjust the latter during the deployment phase.

If the first depot turned out to be a little nearby (the wind had not finally blown as hard as expected), the 4th depot was a great success, largely covering the cable.

The SuperCam Mars Perseverance team from CNES (Toulouse, France) © C. De Prada / CNES

The effects of this activity are already visible in the quality of the scientific data, with a slight reduction in glitches, these thermoelastic cracks that disrupt seismic signals. The more complete effect is expected from 8 deposits on Mars, an objective which can be reached before the summer if the available energy allows it, or from the start of the new school year once temperatures have risen on Mars.

Deposits 5 and 6 were made on May 10 and 17 respectively, still on the pinning mass which is now well covered. The next step for SEIS is to cover the part of the cable farther from SEIS, but this is more sensitive because a “bridge” was created below when the instrument was deployed two years ago. Indeed, during the deployment phase of SEIS just after landing, the cable was adjusted on the ground thanks to the shovel (the same which is used to unload the regolith on the cable) which pulled the latter towards the cable. 'lander. This had the effect of “bulging” the cable a little and lifting it slightly from the ground approximately in the middle.

As the cable does not rest directly on the ground, it is necessary to prevent the regolith deposited on it from creating a mechanical stress and modifying the installation of the cable.

Tests are underway at CNES to determine the best approach for this risky activity.

Our “CNES” file

The burial activity of the SEIS cable is carried out jointly by CNES and JPL (which operates the robotic arm in particular), with the scientific support of the Institut de Physique du Globe de Paris, the Laboratory of Planetology and Geodynamics of Nantes, and of the Navier Laboratory.

To date, the InSight mission has 600 earthquakes detected by the SEIS instrument, of which about ten can be qualified as major (of magnitude 3.1 to 3.6).

They all come from the Cerberus Fossae seismic zone, located 1,600 km east of InSight.


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This analysis was written by Charles Yana, SEIS operations project manager for the InSight mission of CNES (National Center for Space Studies).

The original article was published on The Conversation website.

Declaration of interests

Charles Yana does not work, advise, own shares, receive funds from any organization that could benefit from this article, and has not declared any affiliation other than his research organization.

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