But of course you have to make the fuel there in the first place. The obvious choice for this is water, which can be split to produce hydrogen and oxygen. We know that there is water on the moon, but we do not yet know how much and whether it is concentrated in large deposits. Given that uncertainty, people have also looked at other materials that we know are present on the surface of the moon.
And there is probably nothing more abundant on that surface than Regolith, the dust has remained from constant small effects that moonstones have eroded over time. The regolite consists of a variety of minerals, many of which contain oxygen, usually the heavier component of rocket fuel. And several people have devised the chemistry involved in separating oxygen from these minerals on the scale required for the production of rocket fuel.
But knowing the chemistry is different from knowing what kind of infrastructure is needed to do that chemistry on a meaningful scale. To get this an idea, the researchers decided to concentrate on the isolation of oxygen from a mineral called ilmenite or fetio3. It is not the easiest way to get oxygen – iron oxides that wins there – but it is well understood. Someone patented the oxygen production of Iilmenite in the 1970s and two hardware prototypes were developed, one of which can be sent to the moon on a future NASA mission.
The researchers propose a system that would harvest regolite, partially purify the ilmenite and then combine it with hydrogen at high temperatures, which would strip the oxygen as water, leaving purified iron and titanium (both can be useful to have). The resulting water would then be split to feed the hydrogen back into the system, while the oxygen can be sent for use in rockets.
