Ewellix (Gothenburg, Sweden) has developed and manufactured a planetary roller screw that landed on Mars as part of NASA’s Mars 2020 Perseverance Rover Mission. Ewellix worked in collaboration with NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, CA to develop a roller screw component that would be robust enough to withstand the extreme conditions of outer space and Mars, which can reach -80 °C.
After a 203-day journey, Perseverance touched down on Mars to search for signs of ancient microbial life. The rover’s mission is to extract and seal Martian rock and soil samples for testing and onboard storage. NASA will then decide when and where the rover will leave the samples for pickup by a future mission in approximately 2031 to bring them back to Earth for detailed analysis.
Perseverance carries 43 sample tubes, 38 of which have been tasked to carry different samples from a variety of geologic units and surface materials. The other five are “witness tubes” that (prior to launch) were loaded with materials geared to capture molecular and particulate contaminants. They’ll be opened one at a time on Mars to witness the ambient environment primarily near sample collection sites, so the science team can catalog any impurities that may have traveled with the tube from Earth or contaminants from the spacecraft that may be present during sample collection.
Made chiefly of titanium, each sample tube for Perseverance weighs less than 2 ounces (57 grams) and is less than 6" long. A white exterior coating guards against the possibility of heating by the Sun potentially changing the chemical composition of the samples after Perseverance deposits the tubes on the surface of Mars.
The belly of the rover houses all the equipment and supplies needed to collect samples. It contains a rotating drill carousel — a wheel that contains different drill bits. Next to that are the 43 sample tubes waiting to be filled.
While the rover’s main arm reaches out and drills rock, the rover belly is home to a small robotic arm that works as a “lab assistant” to the larger arm. 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.
Sealing the Samples
Ewellix’s planetary roller screw is housed inside the sealing station on the base of the rover and will generate the high force required to hermetically seal the 43 sample tubes on board. The rover has a small servo motor that drives the roller screw nut. This rotational movement is converted into linear displacement that pushes on a ram, which in turn presses the seal inside the open end of the sample tube with extremely precise force, speed, and position.
It was critical to save mass on the rover and Ewellix’s roller screw provided a tremendous amount of force load in a small mechanism, making it an ideal component for load rating and weight. Other benefits are long service life by design, high reliability, and the ability to withstand frequent changes of loading direction, high linear speed, and some amount of contamination.
The planetary roller screw is a fully customized version of a standard SR/HR planetary roller screw product. All parts and materials were adapted for the unique conditions through extensive analysis and testing. Adaptations include aerospace-grade materials and heat-treatment operations provided by US-based suppliers with aerospace certifications.
The customized planetary roller screw took several years to develop, prototype, manufacture, and test, from concept to system validation, where one of the final product samples was selected for the mission. Extensive system testing, including the roller screw, was performed at JPL.
Jean-Pierre Collognat, Project Lead and Business Development Manager at Ewellix explained some of the challenges of the project. “There were certainly some firsts for us along the way due to challenging application conditions and environment and the need to downsize our components as much as possible to reduce space and weight, yet still optimize the load rating and reliability. All materials have to work at all times at extremely low temperatures; hence all of the component’s materials were subjected to specific heat treatments.”
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