Of all tasks essential to future missions to Mars or beyond, keeping up the oxygen supply may be the hardest – after all, if most aspects of a mission fail you may have days to fix them, but not breathing is an immediate threat. Therefore, oxygen production on the International Space Station (ISS) is one of the more expensive and complex parts of an operation that is not known for being cheap or simple. If we want to go to Mars at an affordable price, we probably need something better. A team of researchers thinks the answer may lie in magnets, describing in the journal npj Microgravity how this could work.
Electrolysis of water is advancing rapidly as a more environmentally friendly way to produce hydrogen. You might think we could just do the same thing in space, but with oxygen as the desirable product. However, study author Dr Katharina Brinkert of the University of Warwick noted in a statement; "Efficient phase separation in reduced gravitational environments is an obstacle for human space exploration and known since the first flights to space in the 1960s.”
Without gravity to separate gasses from liquids, bubbles of gas stay suspended in the water. The ISS operates using centrifuges that produce what is sometimes called “artificial gravity”, but they take up a lot of space and energy to operate, not to mention maintenance.
A staggering range of alternative methods have been tried, from springs to ultrasonic standing waves. Some, such as firing rockets, came with fairly obvious problems, but have been trialed nevertheless. Other approaches work temporarily but have not proven reliable.
These researchers want to use magnets to perform the same role with lower energy requirements – and hopefully greater reliability. They used the Bremen Drop Tower, which simulates microgravity for 9.2 seconds each time it is used, to demonstrate the viability of their technique.
They showed that when neodymium magnets are immersed in certain water-based solutions in microgravity gas bubbles will be attracted to or repelled from the magnets.
"These effects have tremendous consequences for the further development of phase separation systems, such as for long-term space missions, suggesting that efficient oxygen and, for example, hydrogen production in water (photo-)electrolyzer systems can be achieved even in the near-absence of the buoyant-force," Brinkert said.
Not surprisingly, the authors didn’t simply decide to drop magnets from the tower out of pure speculation. The team had spent years investigating the idea in theory until they were confident enough to give it a try. Brinkert had even demonstrated the potential of related ideas four years ago, but in that case, was only able to get them to work with a specific combination of solution and nanostructured cells.
The most important application of the paper by far is likely to be producing oxygen for breathing – and perhaps hydrogen for fuel – on long space missions. However, that may not be the only use to which the work can be put, since it could make possible the separation of all sorts of gasses and liquids, which could help with recycling wastewater and removing carbon dioxide from the air.
To demonstrate the flexibility of the approach, the authors tested air bubbles in ultra-purified water, a MnSO4 solution, a broth used to grow bacteria, and olive oil. Greater viscosity induced a drag effect that made the separation less noticeable, but it was observed in every case.
Magnetic fields have also been shown to increase the speed and efficiency of electrolysis, even under Earth conditions.