Membranes on Mars

Thin membranes could help people go to Mars and clean the air here on Earth.

The ideal technology for space travel would be simple, robust, reliable, lightweight, and volumetrically efficient. It would have no moving parts, which would make it less likely to break. It would be a passive technology, not requiring any energy from the outside. It would be small. It would be light. An ideal technology for space, says chemical engineer Doug Way, is the membrane.

Well, OK, membranes can't do everything. Membranes won't boost us into space. And they won't carry us to Mars. But membranes could solve some of the problems of travelling there. And once we arrive, they could help us get back.

Basically, membranes are a semi-permeable barrier. They're like a wall, except that gases, and even liquids, can seep through them. But - here's the key point - different molecules move through membranes at different rates. Membranes can therefore be used to sort things out, separating one type of molecule from another.

Doug Way of the Colorado School of Mines and Lockheed engineer Larry Mason are working on a project that uses membranes to help produce rocket fuel from the Martian atmosphere. The principle is simple: The Martian atmosphere is 95% carbon dioxide (CO₂). Using membranes, explorers could extract some of that CO₂, which when mixed with hydrogen and then heated yields methane - a useful propellant for rockets or rovers.

Water is a byproduct of this type of methane production, called the Sabatier process (discovered by the French chemist Paul Sabatier in the nineteenth century). What's more, water can be electrolyzed into oxygen, for breathing, and hydrogen, which can be used to produce another round of methane.

Image credit: Doug Way (Colorado School of Mines) and Larry Mason (Lockheed Martin). A membrane inside a test cell

Although the Martian atmosphere is almost pure CO₂, it's not pure enough for the Sabatier process. Carbon dioxide must be separated from the other atmospheric gases before it's processed. Otherwise unused gases - mostly nitrogen and argon - build up, and will eventually keep the procedure from working. Way and Mason are developing a membrane that will separate out CO₂.