One of the hardest things about sending astronauts to Mars will be getting them home. Launching a rocket from the surface of the Red Planet would require huge amounts of oxygen, which, along with rocket fuel, makes up the propellant: a rocket with a crew of four would need about 25 tons of oxygen to produce thrust, using 7 tons of rocket fuel.
The Mars Oxygen In-Situ Resource Utilization Experiment, or MOXIE, is an experimental tool that differs from the primary purposes of the Perseverance rover, whose main goal is to capture rock samples that might bear signs of ancient microbial life. MOXIE, on the other hand, focuses exclusively on the engineering needed for future human exploration efforts. In situ resource utilization, or ISRU, involves using what is available in the local environment. This includes finding frozen water that could be melted for use, but also generating oxygen for rocket propellant and, of course, breathing.
Breathing is just a side benefit of MOXIE's real goal, said Michael Hecht of the Massachusetts Institute of Technology, the instrument's principal investigator. Rocket propellant is the heaviest consumable resource the astronauts will need, so being able to produce oxygen at the destination would make the first manned trip to Mars easier, safer and cheaper. Mars' atmosphere is extremely thin, and is composed of 95 percent carbon dioxide; oxygen makes up about 0.13 percent, compared to 21 percent in Earth's atmosphere. MOXIE draws in air through a pump, then uses an electrochemical process to separate one oxygen atom from each carbon dioxide (CO2) molecule, releasing carbon monoxide (CO) as a byproduct. As the gases flow through the system, they are analyzed to verify the amount of oxygen produced, its purity and the efficiency from the system.
This reaction, however, requires high temperatures to operate, around 800°C. In order to handle these high temperatures, MOXIE, which is slightly larger than a toaster, is made of especially heat-resistant materials. Special 3D-printed nickel alloy parts heat and cool the gases flowing through the instrument, while super-lightweight insulation called aerogel traps heat to minimize the power needed to keep it at operating temperatures. MOXIE's exterior is coated with a thin layer of gold, which prevents high temperatures from radiating to other parts of the Perseverance rover.
MOXIE is designed to produce 6 to 10 grams of oxygen per hour, enough to keep a small dog breathing for an hour. In April 2021, during the first two tests, the MOXIE system was able to produce between 4 and 5 grams in total. A problem associated with this technology, however, lies in the high power required by MOXIE, Perseverance in fact is not able to perform other experiments or collect other data during the course of the tests. Eight more experiments should be scheduled in the coming months, making slight modifications to optimize oxygen production.
Michael Hecht estimates that a full-sized MOXIE system on Mars could be a little larger than a household stove and weigh about a ton, almost as much as the Perseverance rover itself. A full system, designed to produce propellant to enable a flight to Earth, would have to increase oxygen production by about 200 times what the current version of MOXIE allows.
It could be a long time before astronauts land on Mars - NASA is talking about the early 2030s, while Elon Musk's SpaceX promises that this will happen even sooner. Any crew arriving on Mars will likely have their own device aboard their spacecraft that produces oxygen to breathe, so the biggest problem to solve remains the production of the propellant they'll use to make the journey home.
"The commitment to MOXIE's development shows that NASA is serious about this project," Hecht says. "MOXIE is not the complete answer, but it is a key part of it. If successful, it will demonstrate that future astronauts can rely on this technology to bring them home safely from Mars."
Written by Marco Sanna of the VGen Engineering Hub
