All About Space
Future tech sustainable space travel
How we'll be making oxygen and water in space to travel among the stars
Anew study, recently published in Nature
Communications, has proposed a new way to manufacture oxygen (to breathe) and hydrogen (for spacecraft fuel) while in space. The idea involves transporting large amounts of water (H2O) on board the spacecraft, a semiconductor material and the ever-present resource that is sunlight. The idea behind the process is to split molecules of water into their constituent atoms using an electric current.
There are two ways of separating water molecules. One way is through a process known as electrolysis, which involves passing an electric current through a water sample containing some soluble electrolyte. This will break down water into hydrogen and oxygen and they are collected at different electrodes. Although this is theoretically possible, the equipment is not readily available and appropriate for spaceflight as of yet.
The method proven more appropriate for spaceflight is a process called ‘photocatalytic water splitting’. In this scenario, a semiconductor is inserted into the water and absorbs photons, which gives enough energy to an electron on the semiconductor to jump and leave a hole. This free electron can then interact with protons to form hydrogen, whereas the hole absorbs electrons from the water to form protons and oxygen.
This process can also be reversed, and the molecules can be ‘recombined’ in order to create water in a fuel cell, which returns solar energy. The idea that three vital elements for long-term space travel – water, hydrogen and oxygen – can be used and created in a sustainable way is tantalising. The only issue with this is what to do with the bubbles.
The researchers wanted to test the viability of the photocatalysis in space by setting up an experiment down a 120-metre (394-foot) drop tower. With an object in freefall, gravity is essentially nonexistent, creating the perfect environment to test experiments without actually going to space. During the drop the researchers showed it is possible to split the water, but there is a problem with the bubbles that are created.
When bubbles are created on Earth, gravity automatically makes sure the bubbles rise to the top and dissipate. In space the bubbles do not know where to go and permeate the water. If the bubbles were to stick on the catalyst, there would be no free room for the next bubble to form. The researchers combated this problem by creating pyramid-shaped zones where the bubbles could easily be released from the catalyst. However, there was still a problem with the evacuation of bubbles from the liquid. To prove viable there needs to be artificial gravity, as it will provide the force needed to evacuate the bubbles from the water.