Oxygen is such an abundant resource on Earth that we rarely think about it unless we get locked in a cupboard. However, for space engineers, the question of how to get enough of the vital gas is constant, frustrating problem. To help future explorers of the Red Planet get enough oxygen for life support and powering spacecraft, NASA has included MIT’s MOXIE experiment on the Mars 2020 mission to study how to make oxygen out of the Martian atmosphere.
Sending a manned mission to Mars not only involves technical problems far beyond anything previously attempted, but also logistical problems equivalent to that of a small war stretched across a hundred million miles of space. Many tons of spares, food, water, fuel, and oxygen would need to be transported to keep the astronauts alive and many times more fuel would be needed to transport it all.
Previously, this wasn't as great a problem. When the Apollo astronauts landed on the Moon, they carried everything they needed for their journey. On Mars, that may not be practical unless you want a spacecraft the size of a small aircraft carrier. Instead, scientists and engineers are exploring ways that future missions could live off the land when they arrive on the Red Planet.
"When we send humans to Mars, we will want them to return safely, and to do that they need a rocket to lift off the planet’” says Michael Hecht of MIT's Haystack Observatory. “That’s one of the largest pieces of the mass budget that we would need to send astronauts there and back. So if we can eliminate that piece by making the oxygen on Mars, we’re way ahead of the game."
MIT’s Mars OXygen In situ resource utilization Experiment (MOXIE) is one possible answer. Developed in partnership with NASA’s Jet Propulsion Laboratory, it’s based on the fact that the Martian atmosphere, though extremely thin, is composed of 96 percent carbon dioxide, which means its a vast potential source of oxygen for future explorers and settlers. Essentially, MOXIE is a fuel cell in reverse. Instead of generating electricity by using oxygen to burn a fuel, it uses a process called solid oxide electrolysis , where electricity is employed to split carbon dioxide into oxygen and carbon monoxide.
This process would see Martian air pumped into the unit through a dust filter and pressurized before being passed into a fuel cell. At high temperatures, some ceramic oxides act as oxygen ion conductors. In the fuel cell, a thin, non-porous disc of this ceramic separates two porous electrodes. One electrode acts as the cathode and the other as the anode. Carbon dioxide passes through the cathode and when it comes into contact with the ceramic, the interaction of electricity and the ceramic causes the carbon dioxide to split into oxygen and carbon monoxide. The oxygen and the carbon monoxide are then separated and the oxygen stored.
MOXIE is one of seven major experiments be flown on the US$1.9 billion Mars 2020 mission, which is scheduled to fly in July 2020. Based on the nuclear-powered Curiosity rover currently exploring the Gale Crater region of the planet. The other instruments are intended to study Mars, but MOXIE stands out because it’s more of a practical experiment.
"If you were one of those astronauts depending on an oxygen tank for your ride home, I think you’d like to see it tested on Mars before you go," says Hecht. "We want to invest in a simple prototype before we are convinced. We've never run a factory on Mars. But this is what we’re doing; we’re running a prototype factory to see what problems we might come up against."
According to MIT, if MOXIE is successful, a scaled up version could be of great help to future explorers in providing oxygen for breathing and fuel. One scenario could see a nuclear-powered robotic plant sent ahead to produce and stockpile oxygen ready to be used when astronauts arrive.