Calculating the energy requirements for using moon dust to create rocket fuel

An international team of engineers and space scientists has used a variety of assumptions, techniques, and math principles to calculate the energy requirements for using moon dust to create rocket fuel. In their paper published in Proceedings of the National Academy of Sciences, the group outlines all the factors and processes that would be involved in converting regolith to fuel and moving it to a space-based location for filling up a starship.

As governments and private entities around the world contemplate the possibility of humans traveling great distances in space sometime in the future, scientists continue to look into the practicalities of such ventures. One such practicality is figuring out what sort of propulsion system would be needed.

While many scientists are looking into theoretical space engines, others are focusing on the tried and true—such as plain old-fashioned engines that burn rocket fuel. In this new study, the research team wondered how much energy would be needed to convert the moon's regolith into rocket fuel, and then to transport it to a space-based gas station.

Prior research has suggested that rocket fuel could be made from regolith—in addition to minerals, it has oxygen in it. Thus, to produce rocket fuel, the oxygen would have to be separated from the other materials. The researchers used a known method to begin their energy calculations, one that involves purifying ilmenite and then combining it with hydrogen (which could be obtained from water on the moon) at a high temperature.

Using such a system would require energy use at three stages; the first would be during the hydrogen reaction that would produce an amount of water. Because it would require heating to high temperature, it would be very energy intensive. The second stage would involve splitting out the oxygen and the third converting the oxygen to a liquid form. Taken together, they found the approach would require approximately 24 kW-hr per kilogram of liquid oxygen produced.

Next, the researchers estimated that a starship fuel tank would probably hold on the order of 500 metric tons of liquid oxygen. That would mean that their system would take approximately two years to produce enough fuel for one starship, for one voyage (if it ran full time). They note that multiple systems could be used to reduce the production time.

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