NASA’s Perseverance rover, which is scheduled to land on Mars on February 18, 2021, as part of the Mars 2020 mission, will reportedly carry eleven metal additively manufactured parts.
The Mars 2020 mission is part of a larger programme that includes missions to the Moon as a way to prepare for human exploration of Mars. Charged with returning astronauts to the Moon by 2024, NASA will establish a sustained human presence on and around the Moon by 2028 through NASA’s Artemis lunar exploration plans.
A key objective of Perseverance’s mission on Mars is astrobiology, including the search for signs of ancient microbial life. The rover will characterise the planet’s geology and past climate, paving the way for human exploration of Mars, and will be the first mission to collect and cache Martian rock and regolith (broken rock and dust).
Andre Pate, the group lead for Additive Manufacturing at NASA’s Jet Propulsion Laboratory in Southern California, commented, “Flying these parts to Mars is a huge milestone that opens the door a little more for Additive Manufacturing in the space industry.”
NASA explains that Curiosity, Perseverance’s predecessor, was the first mission to take Additive Manufacturing to Mars when it landed in 2012 with an additively manufactured ceramic part inside the rover’s oven-like Sample Analysis at Mars (SAM) instrument. NASA has since continued to test AM for use in spacecraft to ensure the reliability of the parts is well understood.
NASA’s Jet Propulsion Laboratory (JPL) is managed by Caltech in Pasadena, Southern California, which built and manages operations of the Perseverance and Curiosity rovers.
Of the eleven metal additively manufactured parts travelling to Mars, five are contained within Perseverance’s Planetary Instrument for X-ray Lithochemistry (PIXL). This lunchbox-size device is said to help the rover seek out signs of fossilised microbial life by aiming X-ray beams at rock surfaces to analyse them.
PIXL shares space with other tools in the 40 kg rotating turret at the end of the rover’s 2 m long robotic arm. To make the instrument as light as possible, the JPL team designed PIXL’s two-piece titanium shell, a mounting frame, and two support struts that secure the shell to the end of the arm to be hollow and extremely thin. The parts, which were additively manufactured by Carpenter Additive, are reported to have three or four times less mass than if they’d been produced conventionally.
“In a very real sense, 3D printing made this instrument possible,” stated Michael Schein, PIXL’s lead mechanical engineer at JPL. “These techniques allowed us to achieve a low-mass and high-precision pointing that could not be made with conventional fabrication.”
Perseverance’s six other metal additively manufactured parts can be found in an instrument called the Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE). This device will test technology that, in the future, could produce industrial quantities of oxygen to create rocket propellant on Mars, helping astronauts launch back to Earth.
To create oxygen, MOXIE heats Martian air up to nearly 800℃. Within the device are six heat exchangers – palm-size nickel-alloy plates that protect key parts of the instrument from the effects of high temperatures. NASA explains that while a conventionally machined heat exchanger would need to be made out of two parts and welded together, MOXIE’s were each additively manufactured as a single piece.
Samad Firdosy, a material engineer at JPL, who helped develop the heat exchangers, reported, “These kinds of nickel parts are called superalloys because they maintain their strength even at very high temperatures. Superalloys are typically found in jet engines or power-generating turbines. They’re really good at resisting corrosion, even while really hot.”
In order to avoid potential pores or cracks during the Additive Manufacturing process, the plates were treated in a hot isostatic press – a gas crusher – that heats the material to over 1,000℃ and applies intense pressure evenly around the part. Engineers then used microscopes and mechanical testing to check the microstructure of the exchangers to ensure they were suitable for spaceflight.
Firdosy added, “I really love microstructures. For me to see that kind of detail as material is printed, and how it evolves to make this functional part that’s flying to Mars – that’s very cool.”