The Perseverance Robotic Arm Tightrope of Abrasion Proximity Science

Mars Perseverance Sol 482 - Front Left Hazard Avoidance Camera (Hazcam): Sol 482 Front Left Hazcam image showing the WATSON imager positioned by the robotic arm at a 7cm standoff for a reconnaissance image after abrading the Thorton Gap target. Credits: NASA/JPL-Caltech. Download image ›

The SHERLOC and PIXL proximity science instruments on Perseverance have enabled more detailed observations of Martian chemistry and minerology than ever before. PIXL can isolate features as small as a grain of sand.  To achieve this, these instruments on the end of the robotic arm must be placed at a precise distance from the feature of interest - very close, but not too close. PIXL even has a “hexapod” adjustment mechanism that compensates for drift in its position from the arm expanding and contracting over the many hours of observations.

The ideal surface for proximity science is dust-free and flat. But Mars is a rather dusty place, with rocks that have a variety of surface textures and geometries. Perseverance was designed to create this ideal, abrading with its drill and removing the dust from the resulting flat patch.

To ensure that we’ll succeed in abrasion and actually be able to use the patch as intended, many things need to be considered:

  • The location of the drill prongs for abrasion should be stable and keep the drill in place.
  • The surface should support a complete abrasion patch being created without fracturing the patch or remaining rock.
  • After the abrasion it must be possible to position the dust removal tool with the robotic arm at the necessary angles to blow away the dust.
  • It must be possible to then place PIXL above the abrasion patch at a height of 2.55 cm, about an inch, and SHERLOC at a height of 4.8 cm.
  • PIXL hexapod motion should not be able to collide with the surface surrounding the patch, since it cannot detect this.

There are two main factors that create challenges in meeting these. First, Perseverance’s robotic arm is tightly packed with instruments and tools, including PIXL, SHERLOC, the drill, a facility contact sensor, and a dust removal tool – which could be damaged from incidental impact with the ground. Second, the robotic arm cannot be placed with perfect precision. Its position is impacted by sources of uncertainty such as thermal expansion of all of its components, and our knowledge of where a given spot on the surface will be with respect to the arm when it aims for it.

We use automated tools that factor in the constraints and accuracy to determine whether we’ll be able to place the instrument. When the answer is no, we iterate on the position.  We improve the arm positioning accuracy before abrasion with additional steps such as taking reconnaissance images with the WATSON imager on the robotic arm and adjusting the arm position to reflect where it actually ended up when we tried to command it to the target.

As of sol 554 Perseverance has successfully performed proximity science in nine abrasion patches. We’ve arrived at Enchanted Lake and may soon be performing proximity science at a location that could contain evidence that Mars once was home to microscopic life.

About This Blog

These blog updates are provided by self-selected Mars 2020 mission team members who love to share what Perseverance is doing with the public.

Dates of planned rover activities described in these blogs are subject to change due to a variety of factors related to the Martian environment, communication relays and rover status.

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  • Mariah Baker
    Planetary Scientist, Smithsonian National Air & Space Museum
    Washington, DC
  • Matthew Brand
    SuperCam/ChemCam Engineer, Los Alamos National LaboratoryLos Alamos National Laboratory
  • Sawyer Brooks
    Docking Systems Engineer, NASA/JPL
    Pasadena, CA
  • Adrian Brown
    Deputy Program Scientist, NASA HQ
    Washington, DC
  • Denise Buckner
    Student Collaborator, University of Florida
    Gainesville, FL
  • Fred Calef III
    Mapping Specialist, NASA/JPL
    Pasadena, CA
  • Alyssa Deardorff
    Systems Engineer, NASA/JPL
    Pasadena, CA
  • Kenneth Farley
    Project Scientist, Caltech
    Pasadena, CA
  • Phylindia Gant
    Mars 2020 Student Collaborator, University of Florida
    Gainesville, FL
  • Brad Garczynski
    Student Collaborator, Purdue University
    West Lafayette, IN
  • Erin Gibbons
    Student Collaborator, McGill University
    Montreal, Canada
  • Michael Hecht
    Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) Principal Investigator, Massachusetts Institute of Technology
    Westford, MA
  • Louise Jandura
    Chief Engineer for Sampling & Caching, NASA/JPL
    Pasadena, CA
  • Lydia Kivrak
    Student Collaborator, University of Florida
    Gainesville, FL
  • Rachel Kronyak
    Systems Engineer, NASA/JPL
    Pasadena, CA
  • Steven Lee
    Perseverance Deputy Project Manager, NASA/JPL
    Pasadena, CA
  • Justin Maki
    Imaging Scientist and Mastcam-Z Deputy Principal Investigator, NASA/JPL
  • Sarah Milkovich
    Assistant Science Manager, NASA/JPL
    Pasadena, CA
  • Eleanor Moreland
    Ph.D. Student, Rice University
    Houston, Texas
  • Matt Muszynski
    Vehicle Systems Engineer, NASA/JPL
    Pasadena, CA
  • Claire Newman
    Atmospheric Scientist, Aeolis Research
    Altadena, CA
  • Avi Okon
    Sampling Operations Deputy Lead, NASA/JPL
    Pasadena, CA
  • Pegah Pashai
    Vehicle Systems Engineer Lead, NASA/JPL
    Pasadena, CA
  • David Pedersen
    Co-Investigator, PIXL Instrument, Technical University of Denmark (DTU)
    Copenhagen, Denmark
  • Eleni Ravanis
    Student Collaborator, University of Hawaiʻi at Mānoa
    Honolulu, HI
  • Kathryn Stack
    Deputy Project Scientist, NASA/JPL
    Pasadena, CA
  • Vivian Sun
    Science Operations Systems Engineer, Staff Scientist, NASA/JPL
    Pasadena, CA
  • Iona (Brockie) Tirona
    Sampling Engineer, NASA/JPL
    Pasadena, CA
  • Jennifer Trosper
    Project Manager, NASA/JPL
    Pasadena, CA
  • Vandi Verma
    Chief Engineer for Robotic Operations, NASA/JPL
    Pasadena, CA
  • Rick Welch
    Deputy Project Manager, NASA/JPL
    Pasadena, CA
  • Roger Wiens
    Principal Investigator, SuperCam / Co-Investigator, SHERLOC instrument, Purdue University
    West Lafayette, IN

Tools on the Perseverance Rover+

The Perseverance rover has tools to study the history of its landing site, seek signs of ancient life, collect rock and soil samples, and help prepare for human exploration of Mars. The rover carries:


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Image of a rover pin-point at Perseverance's location on Mars, Jezero Crater

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