Perseverance is a well equipped geologist
Rover exploration sets the stage for human missions to Mars Metal Tech News – April 14, 2021
Last updated 8/2/2021 at 10:13am
The long-term exploration and colonization of Mars will not be able to rely on the expense of rocketing goods beyond the gravitational pull of Earth and then another 171 million miles to the Red Planet. Instead, the mining of ice and other minerals for fuel, water and building materials from local resources will need to be carried out by Martian robots and humans.
So, it is no wonder that NASA's first three Mars rovers are basically robotic geologists exploring the Martian surface for the resources essential for Earth's first human emissaries to the Red Planet.
Perseverance, Earth's newest robotic ambassador to the Red Planet, is an especially well-equipped geologist – boasting a toolkit that allows the rover to determine mineralogy and elemental composition on the Martian surface, gain centimeter-scale resolution of subsurface geology, and a drill to collect the first Martian rock and soil samples destined for future transport to Earth-based labs for more detailed analysis.
In addition to better understanding the geology and resources available, this equipment will seek signs of ancient life in a river delta at the edge of the 28-mile-wide Jezero Crater, which was a large lake when Mars was still a water planet.
The cache of geological tools aboard Perseverance, however, would not be very useful without the seven-foot-long robotic arm that has the brawn to heft them and the dexterity to ensure they are deployed with precision and without damaging the scientific payload.
"That's the main tool the science team will use to do close-up examination of the geologic features of Jezero Crater, and then we'll drill and sample the ones they find the most interesting," Robert Hogg, Mars 2020 Perseverance rover deputy mission manager said after the rover flexed the five joints of its arm. "When we got confirmation of the robotic arm flexing its muscles, including images of it working beautifully after its long trip to Mars – well, it made my day."
It was also a big Sol (Martian day) for Tom McCarthy, vice president of business development and co-founder of Motiv Space Systems, a California-based company that designed and built Perseverance's robotic arm.
"Between the arm and the cameras, we are very fortunate that these very few days of the mission, a lot of return there," McCarthy told Metal Tech News on Sol 47 (April 8) of Perseverance's mission.
The robotics and geological tools being exercised by Perseverance are likely precursors of technologies that will shape the future of mining Martian resources and transforming them into elements essential to human settlement of the Red Planet.
Aside from boasting the most state-of-the-art technologies in the Solar System, Perseverance's geological tools are not that much different than the equipment utilized by human geologists to identify the resources we need here on Earth.
On our homeworld, geologists use a magnifying lens called a loupe to see fine details of terrestrial minerals in rock samples, X-ray fluorescence (XRF) analyzers to determine the elemental composition of rocks, geophysics to "see" structures beneath the surface, and drills to get an accurate sample of the regolith being studied.
To emulate these same functions on Mars, Perseverance's geological toolkit contains:
• Planetary Instrument for X-ray Lithochemistry (PIXL) – The combination of a geologist loupe and XRF analyzer, PIXL has a camera that takes super close-up pictures of rock and soil textures that allow scientist to gain a better understanding of the mineralogy and potential signs of ancient life forms. This two-in-one instrument also has an X-ray spectrometer that uses particles of light to analyze the elemental make-up of the regolith being studied.
• Radar Imager for Mars' Subsurface Experiment (RIMFAX) – A geophysical tool that uses ground-penetrating radar capable of providing high-resolution stratigraphic information for more than 30 feet below the surface, a first for Mars. In addition to providing scientists with a first look below the Martian surface, RIMFAX will be used to characterize the stratigraphy of drill samples collected by Perseverance.
• Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals (SHERLOC) – Mounted on the rover's robotic arm, SHERLOC uses cameras, spectrometers, and an ultraviolet laser to search for organics and minerals that have been altered by watery environments and may be signs of past microbial life. SHERLOC is assisted by WATSON, a color camera for taking close-up images of rock grains and surface textures.
• SuperCam – An imaging system that uses a very powerful camera (hence the name), laser and spectrometers to determine the chemical and mineral makeup of targets as small as a pencil point more than 20 feet away from the rover. This allows Perseverance to analyze targets out of the reach of the robotic arm.
• Sample handling – While not christened with a flashy name or acronym, Perseverance's ability to drill and store rock and soil samples for future transport to Earth is one of the most exciting abilities of the newest rover. While the rover's big arm reaches out and drills rock, the rover belly is home to a small robotic arm that works as a "lab assistant." The small arm picks up and moves new sample tubes to the drill, and transfers filled sample containers into a space where they are sealed and stored. These samples will be cached in well-identified locations on the Martian surface for future retrieval.
Perseverance's seven-foot-long arm is doing most of the heavy lifting when it comes to the rover's Martian geological exploration. While Curiosity has a similar arm, the Perseverance appendage is longer, stronger, and has a better sense of touch than its predecessor.
With a shoulder, elbow, and wrist joints for maximum flexibility, this arm lets the rover work as a human geologist would – holding and using PIXL, SHERLOC, WATSON, and the drill with its "hand" or turret.
Hefting and deftly using this comprehensive set of geological tools presented new challenges for the arm's creators at Motiv Space Systems.
"The scientific instrumentation and the coring, or drilling, implementation on the turret got significantly heavier. So, that is very different from the Curiosity rover, and required a lot of work," McCarthy told Metal Tech News.
To allow Perseverance to carry around this heavier tool kit for exploring the Martian landscape, the robot engineers at Motiv added joints that made the arm more dexterous and strengthened the motors and gearing in those joints to make the arm beefier.
One of the most important upgrades to the Perseverance arm, and a facet McCarthy and the team at Motiv are particularly proud of, is a revolutionary six-degree of freedom force-torque sensor that provides the rover "a sense of touch."
This allows Perseverance to avoid damaging its arm and the tools it is carrying and increases its functionality, both vital to a robot geologist working 171.5 million miles from its closest human counterpart.
"When it goes to sample a rock or selection of soil ... the moment the arm makes contact with any of those features, that information is transmitted through that sensor and fed back to the rover," McCarthy explained.
This provides the rover inputs on how much load is being felt by the robotic arm and drilling feedback, such as how much weight is being applied to the bit while coring a particular rock sample.
Much like the mineral exploration geologists here on Earth, the Mars rover has very strict protocols for storing, analyzing and preparing rock and soil samples for later analysis. Getting this regolith to the assay prep facility, in this case the body of the rover, exercises the dexterous abilities of the arm.
"Once it has actually picked up the sample, then it has to return that sample back to the rover," McCarthy said. "The way it does that is it docks with an interface on the rover that allows the sample just received through the coring bit and passes that through to the rover where it ultimately gets sealed, cached, and prepared for further use."
The force-torque system ensures that the arm does not get bound up and the sample being delivered to the prep facility goes smoothly.
Retrieving the samples
While most of the geological and biological data collected by Perseverance is digital and can be transmitted via radio waves, there is a lot more to be learned about the soil and rock samples at labs here on Earth.
Perseverance has strict protocols to ensure the integrity of the sample and the exact location it was collected. This includes measures to ensure that materials from Earth do not inadvertently get into the sealed sample tubes.
With the idea of eventually sending these Martian rock and soil samples back to Earth for further study, Perseverance will drop them at a designated cache depot that will be well-documented by local landmarks and precise coordinates.
Scientists are excited about the prospect of being able to study samples collected directly from the Mars surface for the first time ever. The sample retrieval system, however, has not yet been fully designed.
McCarthy believes the samples cached by Perseverance could be delivered to terrestrial labs for unprecedented study of Martian soil and rocks within a decade.
"Now that we have a rover that is on the surface of Mars that has the ability to encapsulate these materials and harvest them for work or study, we would definitely like to be part of the whole ecosystem of sending something, go get these samples, and then bring them back," he said. "It would be very exciting for us to be a part of that journey."
As currently envisioned, a Mars lander carrying a sample collection rover would launch in 2026 and touch down near Jezero Crater in 2028. The fetch rover would pick up the stashed samples and transfer them to a rocket that would be launched to a separate orbiting spacecraft that would shuttle them back to Earth.
This will push the envelope of our interplanetary technologies, but scientists believe they are ready for the task.
"When you have to launch a rocket from the surface of Mars just to get something back, that is a next-level challenge that has taken a lot of thought but now it looks like things are lining up pretty well to say, 'we are ready to go do this,'" McCarthy said.
Preparing for a Martian future
The Mars 2020 Perseverance mission is part of NASA's Moon to Mars exploration approach, which includes Artemis missions to the Moon that will help prepare for human exploration of the Red Planet.
The geological information collected by Perseverance and other Mars missions will help identify the best places to mine water, oxygen, and building materials needed to achieve the ultimate goal of the Artemis program.
Once material scientists and engineers have a better understanding of the available resources and where they are located, they can formulate a means of harvesting and transforming them into the structures and other necessities for human settlers on Mars.
Much like the early exploration, it is expected that robots will carry out much of the mining of the elements essential to human survival and building of the structures for Martian immigrants to live, work, and play.
"You are reducing the risk to the humans and you are also improving their efficiency – if you really want them spending more time in the discovery model as opposed to the construction model then that seems to make sense," McCarthy said, when talking about the role of robotics on Mars.
Engineers have already designed automated systems for 3D printing buildings here on Earth, technologies that would likely be ideal precursors for Martian colonies.
"There is definitely an evolution of those systems, obviously leveraged a lot from what we have learned from construction and mining techniques here on Earth," said McCarthy.
Maybe we will see a future industrial-scale Motiv robot with attachments that allow it to 3D print structures for the first permanent Mars settlements.
"We hope to keep developing our technologies and capabilities because we feel that robotics are a critical part of that long-term vision," the co-founder of Motiv Space Systems told Metal Tech News.