MOXIE makes oxygen out of Martian air
Perseverance carried a toaster-sized box that heated Martian carbon dioxide to 800°C and made 5.4 grams of oxygen — the first time a spacecraft manufactured a consumable on another planet.
On 20 April 2021, Perseverance's sixtieth sol, a toaster-sized box warmed up for two hours and ran for one, drawing in Martian air and producing 5.4 grams of oxygen — about ten minutes of breathing for an astronaut at light work. Everything any spacecraft had consumed on another world until then had come from Earth.
Mars's atmosphere is about 95 percent carbon dioxide at roughly six-tenths of one percent of Earth's sea-level pressure, so the first job is compressing a near-vacuum. MOXIE then heated the gas to around 800°C and passed it through a solid oxide electrolysis stack, which strips an oxygen atom from each CO₂ molecule and vents the carbon monoxide overboard. Running that hot in a rover built for Martian nights took 3D-printed nickel alloy parts, aerogel insulation and a thin gold coating to keep infrared off nearby hardware. Michael Hecht of MIT's Haystack Observatory led the experiment.
The application is propellant, not breathing. Getting four astronauts off Mars and back toward Earth takes on the order of 25 tonnes of liquid oxygen for the ascent vehicle; making it on arrival with a one-tonne machine takes that mass off the launch manifest.
MOXIE ran sixteen times, finishing on 7 August 2023 with a 9.8-gram run. Spread across a full Martian year, the tests deliberately covered awkward conditions: the year's thinnest air, the dusty season, the thermal swing between day and night. Total production was 122 grams, at best 12 grams an hour — double the design target — at 98 percent purity or better.
That is roughly what a small dog breathes in ten hours. An ascent-vehicle plant would have to run for more than a year at some two hundred times MOXIE's best rate, and do what MOXIE never attempted: filter dust indefinitely, run unattended for fourteen months, and liquefy and store its product. MOXIE vented everything it made back into the atmosphere. No scaled-up version has been built, funded or scheduled.