The International Space Station's air supply systems have undergone significant development over the past 25 years, driven by the need for regular maintenance, repairs, and upgrades to ensure the reliability of future spacecraft.
Creating breathable air in space is a complex task that requires two fundamental components: supplying oxygen and removing exhaled carbon dioxide before it builds up. Every astronaut in space needs approximately 0.8 kilograms of oxygen per day, which is typically met by storing oxygen on board in pressurized tanks.
However, the launch of the first space station marked a turning point, as crews would remain in orbit for months, not days, necessitating a more efficient oxygen supply system. A typical 6 to 8 month expedition with seven crew members might require over a thousand kilograms of oxygen, demanding about 30 large tanks.
Consequently, engineers developed a solution using water and a process called electrolysis, which makes oxygen directly onboard. Water is relatively easy to come by on the ISS thanks to its robust recovery system, which captures nearly all moisture onboard— from sweat, exhalation, wash water, and even urine— and purifies it into fresh, potable water.
This clean water is routed to an electrolyzer, a device equipped with two electrodes, one positive and one negative. When an electric current is applied, the electrolyzer breaks down water molecules into oxygen and hydrogen gases. Oxygen collects near the positive electrode, and hydrogen gas bubbles form near the negative electrode.
However, there's a problem— getting these gases out of the water. On Earth, bubbles naturally float to the top of denser liquids due to gravity. But in orbit, where everything is in freefall, bubbles tend to cling to the electrodes. One solution is to pump water through the electrolyzer, carrying the bubbles away to a separator.
Here, the gas-filled water is spun much like a washing machine in its final spin cycle, forcing the liquid outward while the gas collects in the center. But this system isn't perfect. The process for separating bubbles from water relies on many complex moving parts that are prone to breaking or malfunctioning.
As space agencies set their sights on expeditions deeper into space, like year-long crewed trips to Mars, this approach becomes increasingly impractical. So, researchers are exploring new ways to separate out this gas.
One promising solution is to spin the gas-filled water inside the electrolyzer using magnets. This system takes advantage of a fundamental property of how electrons and magnets interact.
When negatively charged molecules move perpendicularly through a magnetic field, the field applies a force on the molecules called a Lorentz force. It pushes them sideways, at a right angle to both the electric and magnetic fields.
So, by positioning the magnets and current path in just the right way, this Lorentz force can swirl the liquid, separating out the oxygen and hydrogen gases— no pump or separator needed.
