Technicians at NASA's Jet Propulsion Laboratory lowering the MOXIE instrument into the the Perseverance rover last year. Photo: NASA/JPL-Caltech

The growing list of “firsts” for Perseverance, NASA’s six-wheeled robot, which arrived on the Martian surface on 18 February, includes converting some of the Red Planet’s thin, CO₂-rich atmosphere into oxygen.

A toaster-size, experimental instrument aboard Perseverance called the Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) accomplished the task. The test took place on 20 April.

While the technology demonstration is just getting started, it could pave the way for science fiction to become science fact – isolating and storing oxygen on Mars to help power rockets that could lift astronauts off the planet’s surface.

Such devices also might one day provide breathable air for astronauts themselves. MOXIE is an exploration technology investigation – as is the Mars Environmental Dynamics Analyzer (MEDA) weather station – and is sponsored by NASA’s Space Technology Mission Directorate (STMD) and Human Exploration and Operations Mission Directorate.

Full of promise
Jim Reuter, associate administrator for STMD, said: “This is a critical first step at converting CO₂ to oxygen on Mars. MOXIE has more work to do, but the results from this technology demonstration are full of promise as we move toward our goal of one day seeing humans on Mars.

“Oxygen isn’t just the stuff we breathe. Rocket propellant depends on oxygen, and future explorers will depend on producing propellant on Mars to make the trip home.”

For rockets or astronauts, oxygen is key, said MOXIE’s principal investigator, Michael Hecht of the Massachusetts Institute of Technology’s Haystack Observatory.

After a 2hr warm-up period MOXIE began producing oxygen at a rate of 6 grams per hr. The rate was reduced two times during the run in order to assess the status of the instrument. After an hour of operation, the total oxygen produced was about 5.4g, enough to keep an astronaut healthy for about 10min of normal activity.

To burn its fuel, a rocket must have more oxygen by weight. Getting four astronauts off the Martian surface on a future mission would require approximately 7 tonnes of rocket fuel and 25 tonnes of oxygen. In contrast, astronauts living and working on Mars would require far less oxygen to breathe.

Mr Hecht said: “The astronauts who spend a year on the surface will maybe use 1 tonne between them.”

Hauling 25 tonnes of oxygen from Earth to Mars would be an arduous task — transporting a 1-tonne oxygen converter – a larger, more powerful descendant of MOXIE that could produce those 25 tons – would be far more economical and practical.

Mars’ atmosphere is 96% CO₂ and MOXIE works by separating oxygen atoms from CO₂ molecules, which are made up of one carbon atom and two oxygen atoms. A waste product, carbon monoxide, is emitted into the Martian atmosphere.

The conversion process requires high levels of heat to reach a temperature of approximately 800°C. To accommodate this, the MOXIE unit is made with heat-tolerant materials. These include 3-D printed nickel alloy parts, which heat and cool the gases flowing through it, and a lightweight aerogel that helps hold in the heat.

A thin gold coating on the outside of MOXIE reflects infra-red heat, keeping it from radiating outward and potentially damaging other parts of Perseverance.

In this first operation, MOXIE’s oxygen production was quite modest – about 5g, equivalent to about 10 minutes worth of breathable oxygen for an astronaut. MOXIE is designed to generate up to 10g of oxygen per hr.

Technology demonstration
This technology demonstration was designed to ensure the instrument survived the launch from Earth, a nearly seven-month journey through deep space, and touchdown with Perseverance on 18 February. MOXIE is expected to extract oxygen at least nine more times over the course of a Martian year (nearly two years on Earth).

These oxygen-production runs will come in three phases. The first phase will check out and characterise the instrument’s function, while the second phase will run the instrument in varying atmospheric conditions, such as different times of day and seasons.

In the third phase, Hecht said: “We will push the envelope – trying new operating modes, or introducing ‘new wrinkles‘, such as a run where we compare operations at three or more different temperatures.”

Trudy Kortes, director of technology demonstrations within STMD, said: “MOXIE isn’t just the first instrument to produce oxygen on another world, it is the first technology of its kind that will help future missions ‘live off the land’, using elements of another world’s environment, also known as ‘in-situ resource utilisation’.

“It is taking regolith, the substance you find on the ground, and putting it through a processing plant, making it into a large structure, or taking CO₂ – the bulk of the atmosphere – and converting it into oxygen.”

“This process allows us to convert these abundant materials into useable things: propellant, breathable air, or, combined with hydrogen — water.”