5. June 2019
New strategy for the Mars ‘Mole’

Robot­ic arm will raise the sup­port struc­ture and help the Mole ham­mer

Mars ‘Mole’ - Signs of the Heat Probe Shifting on Mars
Signs of the Heat Probe Shift­ing on Mars
Image 1/6, Credit: NASA/JPL-Caltech

Signs of the Heat Probe Shifting on Mars

The sup­port struc­ture of the Heat Flow and Phys­i­cal Prop­er­ties Pack­age (HP3 ) in­stru­ment moved slight­ly dur­ing ham­mer­ing, as in­di­cat­ed by the cir­cu­lar 'foot­prints' around the in­stru­ment foot­pads.      
Mars ‘Mole’ - Testing How InSight's Arm Will Push on Mars
Test­ing How In­Sight's Arm Will Push on Mars
Image 2/6, Credit: NASA/JPL-Caltech

Testing How InSight's Arm Will Push on Mars

In a JPL lab, a repli­ca of NASA In­Sight's robot­ic arm press­es with its scoop on crushed gar­net near a repli­ca of the space­craft's self-ham­mer­ing 'Mole'. En­gi­neers be­lieve press­ing like this on Mar­tian soil may help the mole dig by in­creas­ing fric­tion of the sur­round­ing soil.      
Mars ‘Mole’ - DLR engineer Torben Wippermann with the HP3 experimental set-up
DLR en­gi­neer Tor­ben Wip­per­mann with the HP3 ex­per­i­men­tal set-up
Image 3/6, Credit: NASA/JPL-Caltech

DLR engineer Torben Wippermann with the HP3 experimental set-up

The low­er part of a bal­loon is vis­i­ble above the HP3 ex­per­i­ment. This light­ens the ex­per­i­ment to sim­u­late the re­duced grav­i­ty con­di­tions found on Mars.      
Mars ‘Mole’ - JPL engineers test heat probe strategies
JPL en­gi­neers test heat probe strate­gies
Image 4/6, Credit: NASA/JPL-Caltech

JPL engineers test heat probe strategies

En­gi­neers in a Mars-like test area at NASA's Jet Propul­sion Lab­o­ra­to­ry try pos­si­ble strate­gies to aid the Heat Flow and Phys­i­cal Prop­er­ties Pack­age (HP3) on NASA's In­Sight lan­der, us­ing en­gi­neer­ing mod­els of the lan­der, robot­ic arm and in­stru­ment.      
Mars ‘Mole’ - HP3 model in the DLR test laboratory in Bremen
HP3 mod­el in the DLR test lab­o­ra­to­ry in Bre­men
Image 5/6, Credit: DLR (CC-BY 3.0)

HP3 model in the DLR test laboratory in Bremen

A ful­ly-func­tion­al mod­el of the Mars ‘Mole’ is be­ing test­ed on sand in a box at the DLR In­sti­tute of Space Sys­tems in Bre­men. Dur­ing the ex­per­i­ments, a seis­mome­ter, which can be seen on the sand in front of the HP3 ex­per­i­ment, ‘lis­tens’ to the ac­tiv­i­ty of the Mole.      
Mars ‘Mole’ - HP3 model in the DLR test laboratory in Bremen
HP3 mod­el in the DLR test lab­o­ra­to­ry in Bre­men
Image 6/6, Credit: DLR (CC-BY 3.0)

HP3 model in the DLR test laboratory in Bremen

A ful­ly-func­tion­al mod­el of the Mars ‘Mole’ is be­ing test­ed on sand in a box at the DLR In­sti­tute of Space Sys­tems in Bre­men. Dur­ing the ex­per­i­ments, a seis­mome­ter, which can be seen on the sand in front of the HP3 ex­per­i­ment, ‘lis­tens’ to the ac­tiv­i­ty of the Mole.      

Focus: Space, exploration

There is a new plan to support the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) Mars ‘Mole’ that is part of NASA’s InSight mission. The Heat Flow and Physical Properties Package (HP3) Mole is a self-driving penetrator that has hammered itself into the Martian subsurface to a depth of approximately 30 centimetres. Since 28 February 2019, it has no longer been able to move deeper beneath the surface. Tests with the Mole on Mars and replicas of the instrument located at DLR in Germany and at NASA's Jet Propulsion Laboratory in Pasadena, California, have provided insights about the possible causes of this situation. It is likely that the Mole is experiencing insufficient friction from the surrounding soil under the lower gravity on Mars, and that small, slot-shaped cavities may have formed between the penetrator and the soil. The scientists and engineers working on the InSight mission are now planning to use the lander’s robotic arm to lift away the support structure situated above the Mole. With the support structure removed, the situation can be examined more closely, and it will become possible to assist the penetrator directly with the robotic arm as it hammers further into the subsurface.

Self-hammering mole on InSight lander
Self-hammering mole on InSight lander
The self-hammering mole, part of the Heat Flow and Physical Properties Package (HP3) on NASA's InSight lander, was only partially buried in the soil of Mars as of early June 2019, as shown in this illustration.
Credit: NASA/JPL-Caltech

The lifting process is expected to be commanded in several stages, starting at the end of June. First, the support structure will be gripped. In the course of a week, the arm will then lift the structure in three steps and acquire images. With this careful procedure, the engineers will ensure that the Mole, which is about three quarters into the surface, is not pulled out.

"We want to lift the support structure because we cannot visualise the Mole beneath the subsurface, and we therefore do not know what situation it is in," explains Tilman Spohn, Principal Investigator for the HP3 experiment at the DLR Institute of Planetary Research. "We are now rather sure that the insufficient grip from the soil around the Mole is a problem, because the friction caused by the surrounding regolith under the lower gravitational attraction on Mars is much weaker than we expected." Tests carried out at the DLR Institute of Space Systems in Bremen have confirmed that this can happen under certain circumstances. Lateral support and friction are important for the Mole, because the recoil from each hammer blow must be absorbed using resistance provided by contact with the surrounding soil.

There is also a possibility that the Mole has encountered a rock. The Mole was certainly designed in such a way that it is able to push small rocks out of its way. However, it could currently be trapped between a rock and the surrounding supporting structure. If this is the case, moving the support structure could allow it to bypass the obstacle and dig deeper. The team carefully chose a landing site that is flat and has as few rocks as possible on the surface. This usually means that there are fewer rocks in the subsurface as well. "We are confident that the probability of hitting a stone that is too large is only a few percent," continues Spohn.

Illustration Hp3 Mars ‘Mole’
Mars ‘Mole’
The self-hammering mole, part of the Heat Flow and Physical Properties Package (HP3) on NASA's InSight lander, was only partially buried in the soil of Mars as of early June 2019, as shown in this illustration.
Credit: NASA/JPL-Caltech

Once the support structure has been lifted, the researchers will decide on the best strategy to assist the Mole. "We plan to use the robotic arm to press on the soil close to the Mole. This additional load will increase the pressure on the penetrator and thus the friction on its outer surface," explains Spohn. "Our calculations at DLR suggest that we have to get close to the device. Immediately above the Mole, which is positioned at a small angle to the vertical with respect to the surface, and close to it, the effect is greatest. Without removing the support structure, we would be too far away, and the effect would be too small."

Gentle lifting of the support structure

The support structure of the HP3 experiment will be lifted step by step, as there are springs inside the support structure that may still be in contact with the rear of the Mole. "If that is the case, we want to be careful lifting the structure so that we do not accidentally pull the Mole out of the ground," says NASA engineer Troy Hudson. "If that happens, we will not be able to insert it back into its hole or move it elsewhere, since the arm has no way of picking up the Mole directly. So we will lift the support structure a little bit at a time, checking to make sure the Mole is not coming with it."
Moving the Mole would not help, even if the arm could grasp it. "We think that the issue is a lack of friction in the Martian regolith. So even if we could lift up the Mole, it would not matter where we put it – there would still be the same friction problem," adds Hudson.

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You Tube - NASA InSight: A Plan to Get the Mole Moving Again
You Tube - NASA InSight scientist/engineer Troy Hudson gives us the game plan for getting the mission's heat probe, also known as the "mole," digging again on Mars.
Credit: NASA

The HP³ Instrument on NASA’s InSight mission

The InSight mission is being carried out by NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, on behalf of the agency’s Science Mission Directorate. InSight is part of NASA’s Discovery Program. DLR is contributing the Heat Flow and Physical Properties Package (HP3) experiment to the mission. The scientific leadership lies with the DLR Institute of Planetary Research, which was also in charge of developing and implementing the experiment in collaboration with the DLR Institutes of Space Systems, Optical Sensor Systems, Space Operations and Astronaut Training, Composite Structures and Adaptive Systems, and System Dynamics and Control, as well as the Institute of Robotics and Mechatronics. Participating industrial partners are Astronika and the CBK Space Research Centre, Magson GmbH and Sonaca SA, the Leibniz Institute of Photonic Technology (IPHT) as well as Astro- und Feinwerktechnik Adlershof GmbH. Scientific partners are the ÖAW Space Research Institute at the Austrian Academy of Sciences and the University of Kaiserslautern. The DLR Microgravity User Support Center (MUSC) in Cologne is responsible for HP³ operations. In addition, the DLR Space Administration, with funding from the German Federal Ministry for Economic Affairs and Energy, supported a contribution by the Max Planck Institute for Solar System Research to the French main instrument SEIS (Seismic Experiment for Interior Structure).

Detailed information on the InSight mission and the HP3 experiment is available on DLR’s dedicated mission site with extensive background articles. You can also find information in the animation and brochure about the mission or via the hashtag #MarsMaulwurf on the DLR Twitter channel. Tilman Spohn, the Principal Investigator for the HP3 experiment, is also providing updates in the DLR Blog portal about the activities of the Mars Mole.

Contact
  • Falk Dambowsky
    Ed­i­tor
    Ger­man Aerospace Cen­ter (DLR)
    Me­dia Re­la­tions
    Telephone: +49 2203 601-3959
    Fax: +49 2203 601-3249
    Linder Höhe
    51147 Cologne
    Contact
  • Prof.Dr. Tilman Spohn
    HP³ Prin­ci­pal In­ves­ti­ga­tor
    Ger­man Aerospace Cen­ter (DLR)

    DLR In­sti­tute of Plan­e­tary Re­search
    Telephone: +49 30 67055-300
    Fax: +49 30 67055-303
    Linder Höhe
    51147 Köln
    Contact
  • Christian Krause
    Ger­man Aerospace Cen­ter (DLR)
    Mi­cro­grav­i­ty Us­er Sup­port Cen­ter (MUSC)
    Op­er­a­tion: HP³, STATIL
  • Matthias Grott
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search
    HP³ project sci­en­tist and In­Sight sci­ence team mem­ber; Fo­cus on heat flow and ther­mal con­duc­tiv­i­ty mea­sure­ments; In­stru­ment de­vel­op­ment
    Rutherfordstraße 2
    12489 Berlin
    Contact
  • Torben Wippermann
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Space Sys­tems
    Telephone: +49 421 24420-1120
    Robert-Hooke-Straße 7
    28359 Bremen
  • Dr Anko Börner
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Op­ti­cal Sen­sor Sys­tems
    In­sti­tute of Op­ti­cal Sen­sor Sys­tems
    Telephone: +49 30 67055-509
    Rutherfordstraße 2
    12489 Berlin-Adlershof
  • Dr Roy Lichtenheldt
    Ger­man Aerospace Cen­ter (DLR)
    Sys­tem Dy­nam­ics and Con­trol
    Telephone: +49 8153 28-3095
    Fax: Institute of System Dynamics and Control
    Münchener Straße 20
    82234 Weßling
  • Martin Knapmeyer
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search
    Telephone: +49 30 67055-394
    Rutherfordstraße 2
    12489 Berlin
    Contact
  • Jörg Melcher

    DLR In­sti­tute of Com­pos­ite Struc­tures and Adap­tice Sys­tems
    Telephone: +49531295-2850
    Fax: +49531295-2875
    Contact

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