Making oxygen from the Martian atmosphere

Mars ice cap. © Kevin Gill (CC BY 2.0).

DOI.ORG/10.58214/MIT3497MH

The possibility of a manned mission to Mars is gaining traction. But how do you create the oxygen necessary for the astronauts to remain on the planet and, more importantly, how do you develop the rocket fuel necessary to bring them back? MOXIE is the answer.

Michael Hecht is the associate director of the Massachusetts Institute of Technology’s Haystack Observatory. He is also deputy project director on the Event Horizon Telescope Collaboration and principal investigator on the MOXIE programme, which is looking at the feasibility of producing oxygen on Mars.

The Massachusetts Institute of Technology-led MOXIE programme is currently on Mars producing the oxygen that, one day, will be crucial should man ever set foot on the red planet and, more importantly, have a means of return.

The concept behind the Mars Oxygen ISRU Experiment (MOXIE), an instrument the size of a car battery on NASA’s Perseverance rover mission that touched down in February 2021, is to take the carbon dioxide-rich atmosphere of Mars and separate it into breathable oxygen and carbon monoxide.

The scientists behind the programme recently announced that MOXIE had been able to produce oxygen on seven experimental runs, in a variety of atmospheric conditions, including during the day and night, and through different Martian seasons. In each run, the instrument reached its target of producing six grams of oxygen per hour – about the rate of a modest tree on Earth.

MOXIE is led by Michael Hecht, associate director of MIT’s Haystack Observatory, and five-time astronaut Jeffrey Hoffman, who is now professor of aeronautics and astronautics at MIT. Aether caught up with Hecht to find out more about how MOXIE came into being, and what it can do should a future surface-based Mars mission occur.

Aether: Can you tell me a little bit about the timeline of MOXIE?

MH: It was probably the early 1990s when I first got involved in this area. Daniel Goldin was the head of NASA and he suggested we could have people on the surface of Mars by 2011. He was talking about 15 years in the future. It is still 15 years away now and the question is, has anything changed, or will it always be 15 years away? Personally, I believe a lot has changed and we are nearer than we were in 1996. But what it underscores is the fact that this is more than just about technology; it is about the political will.

I was a material scientist, a surface scientist, and I was just starting to play around with planetary science, getting into techniques like micro fabrication, micro machining and the development of instruments. I had a group that was developing small instruments at the Jet Propulsion Laboratory at the California Institute of Technology, and I had a particular insight into how you could do measurements on Mars that maybe most of the planetary scientists didn’t have.

I was asked to take the minutes at a meeting that was discussing the 2001 Mars lander mission that never actually happened, but they were laying out their priorities. There were four of them: they wanted to know about the safety of Mars with respect to dust and soil hazards; they wanted to know more about radiation; they wanted to know about landing large vehicles on Mars and how lift to drag ratios, for example, would be impacted given Mars’ atmosphere; and they wanted to know about what they called ‘in-situ propellant production’.

In-situ propellant production (ISPP) is now subsumed into the in-situ resource utilisation (ISRU) field, but essentially, there was a need to work out how to develop a fuel supply whilst on Mars and part of the research there created the prototype to MOXIE, not that it ever flew.

The first two areas of interest, soil and dust, and radiation, were eventually flown on the 2007 Phoenix mission. I was the principal investigator on the soil and dust payload, called MECA (Microscopy, Electrochemistry, and Conductivity Analyzer), that was on that mission. We have since also learned a lot about the landing of larger vehicles, so three out of the four questions have been studied.

But the fourth; the ISPP/ ISRU got left behind.

Many years later, I had relocated back to the east coast, to MIT and the Haystack Observatory, where I was immersed in the Event Horizon telescope project, measuring and taking images of supermassive black holes, when I got a call out of the blue about ISPP and it potentially being resurrected for the Perseverance mission.

Old colleagues got in touch, and we thought perhaps we could finally fly this ISPP technology. We put a team together, I was principal investigator, and we won a tendering process. It was the culmination of a process that began in the 1990s.

And this is where Jeffrey comes in. I knew him when I was a student back in the 1970s and he was a young professor of astrophysics. I moved to the west coast, and he went on to become an astronaut flying five missions. It so happens that he came back to MIT just before me and was in the same building I had studied in in 1975.

We’d talked a few times when a sudden thought came to me; I had sent instruments to Mars, he had flown in space five times and NASA was asking for somebody to develop a payload to Mars to prepare for human exploration.

The two of us proposed together and it worked. It’s not how payloads for Mars are supposed to happen, but that is the backstory. We skipped all the technology readiness levels and MOXIE, eventually, landed on Mars in February 2021.

Aether: Since then, you have been running tests with MOXIE. Have you had the results you expected?

MH: That’s always a difficult question to answer. We are scientists and we are trained to think that things will go wrong and when nothing goes wrong, you get a little suspicious. But yes, it has worked, and we got what we expected. Everything we have asked it to do, it has done.

Off the back of it we have also learned a great deal about how to build the next generation system. We’ve learned how to improve on it, we’ve learned those things that are difficult and not sustainable with respect to the eventual use. By that I mean something we send to Mars and we’ll run night and day for 15 or 20 months – right now we’re in a mode where we run every month or two, and so we have a long time to plan out each run, to test and to validate.

We’re well aware that when we turn this on in the future, perhaps 25 years from now, it will be to actually make oxygen for astronauts. We’ll turn it on once and leave it on, but it needs to be a lot smarter, a lot more robust and resilient to changes in the environment. It has to have efficient power, efficient mass, and be volume efficient. None of that is true today.

I feel we have learned enough to take that leap without having to go back to Mars again. And that’s really the objective. We have learned what we need to learn on Mars, and I believe we can do the rest in the laboratory.

Aether: To be feasible MOXIE needs to be upscaled from something that is the size of a car battery currently, to the size of a washing machine. Is that achievable?

MH: It needs to be, absolutely. We need tens of kilowatts for the scale-up. If we had had the power, if we had the mass and if we had the volume, it would have been substantially easier to have built a full-size version of this and flown it on Perseverance rather than what we actually did, which was fly a system that fits in a very small space and runs on very little power.

One of the most difficult challenges is a system that can turn itself on and off at will without damaging itself. If you look at comparable things on Earth, the people who build them say never shut them off.

That’s the last thing you want to do because they run at very high temperatures, and every time you cool it down to room temperature then heat it up again, you damage it. It’s well known. But we have turned MOXIE on and off a total of 19 times now, the majority on Mars, and we’ve learned from this.

Aether: Is it the case that if we ever have a space base on Mars, MOXIE, or its descendants, will be producing oxygen for both the astronauts in the base and as a fuel to help them get back to Earth?

MH: That basic outline is correct. Both a rocket and a human being burn fuel. That’s the commonality. When we say burn fuel, that means you’re chemically reacting fuel with, generally, an oxidant, which is almost always oxygen on Earth. And if you consider we eat perhaps two or three times a day, but we are constantly breathing, then you get an idea of the ratio.

So, then the question is, how do we compare astronauts living for a year to a rocket? If you think about the size of the rocket fuel tank and compare it to the amount the astronauts eat, even in a year, the amount they eat is ten times less than the amount of fuel they’re going to burn just to get into space.

And accordingly, they’ll need ten times as much oxygen to get into space as they will need to breathe for the year and a half on the ground. If you put those into numbers, a crew of four to six can get by with a couple of tonnes of oxygen for breathing. That compares to the 25 to 30 tonnes needed to get back to space.

Once you consider that, you then look at how the system might work. We are looking to bring a large MOXIE unit that can fill up a tank of oxygen and make sure there is a little bit extra so the crew can survive long enough to get back into space. That’s critical. You can conceivably rescue astronauts, but you can’t help them if they don’t have what they need to breathe.

What will it look like? That is another story. Everything we are doing now is envisioning a single oxygen production plant filling up a large tank and the contents of that tank would probably be transferred to a rocket. Conceivably. It might be the rocket tank itself, but most likely we would fill up a storage tank, which would then be transferred to a rocket. Some of the contents of that storage tank could also be transferred to an oxygen tank outside the human habitat.

If we look ahead to a sustainable base, without doubt we will start to tap the water resources on the planet. Mars has a lot of water, in the form of ice, and we will find it. Then we will have not only carbon dioxide to work with, but water as well. H₂O and CO₂ is a very potent combination. You can make not only oxygen, but you can also make rocket fuel. You can make many, many things.

So, looking ahead, and this is just my imagination, but I envisage many little MOXIE units. One for each rover, or building or astronaut, wearing something a little bit like a scuba diving canister. I think like that because if you have a single centralised oxygen plant and that goes down, then you are in a world of hurt. If you have lots of MOXIE units, then you have resilience.

Aether: Do you think a space station orbiting Mars, which could happen within a decade, would be the stepping stone to actually putting astronauts on the surface?

MH: If you had asked me that four or five years ago, I would have bought into it. But the decision was made to go back to the moon. I think that delayed the trip to Mars substantially. I’m not saying it’s a bad idea; it has a lot of merit, but it certainly delayed the ultimate destination in my mind. There are certainly some interim gains, and it makes it more of a step-incremental programme rather than an Apollo-style push.

A few years ago, I was talking to some astronauts, and I suggested that from a scientific point of view, there’s an awful lot of merit to going to Mars and going into orbit rather than landing. You can do things there that you cannot do from Earth due to the time lag. I envisaged the collecting of samples and bringing them back to Earth and so forth.

The gist of their response was: “No way are we going to Mars and not putting boots on the ground.” And I think they might be right. If you had asked me to choose, I would say, I don’t think they’ll do a space station. I think they’ll go the whole way.

And today it’s not just about NASA anymore. There are other space agencies and there are private organisations like Blue Origin and SpaceX. It’s not just about Elon Musk; there are others. It gives us resiliency and that also encourages international ventures, which make this whole idea more likely.

I do think we’ll get there.

Michael Hecht

Principal Investigator MOXIE

Associate Director MIT Haystack Observatory

www.haystack.mit.edu