Based on what is known about the chemistry of the lunar surface through remote sensing and surface exploration, what raw ingredients are likely to be available that can be used to make rocket fuel?
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1$\begingroup$ If there is water ice in deep craters close to the Moon poles, liquid hydrogen and oxygen may be generated from water needing a lot of energy. But to get a storable hypergolic fuel like hydrazin and nitrogentetroxid you need nitrogen too. $\endgroup$– UweCommented Jul 20, 2019 at 22:14
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3 Answers
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There are a number of rocket fuels that can be made from moon rock, discussed in some depth in this answer and the linked papers. Aluminium and liquid oxygen seems to be perhaps the leading contender. None is as good in various respects as "normal" fuels like kerosene and liquid oxygen, and there are some engineering problems, but they are possible.
There is recent evidence of water (probably in the form of slightly less dessicated, but still thoroughly frozen rocks) at the South pole of the moon, where there are craters in permanent shadow. If that can be extracted, then liquid hydrogen and liquid oxygen can be prepared.
answered Jul 20, 2019 at 22:13
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Aluminum manufactured into nano-sized particles can be mixed with water ice to make a fuel called ALICE. NASA has already flown a small rocket using ALICE.
Another option is to use pure water with a nuclear engine heating it to extremely high temperature. This would work for point-to-point hops or trips from lunar surface to orbit and back. This has a lower ISP than a liquid oxygen/hydrogen fuel, but avoids the need for cryogenic processing, storage and transport on the moon.
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2$\begingroup$ At that point, it's less "rocket fuel" and more "reaction mass"... pedantic, I know $\endgroup$ Commented Oct 14, 2021 at 19:57
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The lunar regolith contains over 40 weight % of oxygen, but the rest of metals and silicon are not well suited to make a fuel. There is very, very little carbon or hydrogen, less than 1 %. Without finding water it is not possible to prepare a good fuel.
The ubiquity and abundance of oxygen in rocks and soils in space (42–45% by weight in lunar samples) incite scientists and engineers to devise the most efficient techniques to extract it.
Table source.
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$\begingroup$ Liberating the moon's oxygen: fly some quantity of hydrogen to the moon, reduce the iron-oxides of the regolith, put the resulting water vapour through a condenser and an electrolysis cell. This way, you run the hydrogen in a circle, and produce oxygen from lunar soil. However, you need plenty of energy, and some equippment. $\endgroup$– Dohn JoeCommented Sep 6, 2019 at 8:02
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$\begingroup$ @DohnJoe Hot iron reduces water vapor to hydrogen, that is how hydrogen was discovered by Lavoisier. But does hydrogen reduce hot iron-oxides to iron without splitting the resulting water again? $\endgroup$– UweCommented Sep 6, 2019 at 10:51
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$\begingroup$ If stream hot hydrogen through a bed of hot iron oxides, a stream of water vapour will leave your reaction vessel. Of course you need to strip the vapour from the hydrogen gas before the gas enters the reactor again. Iron oxides can be reduced by hydrogen, or carbon monoxide, when it is still solid, that's why this process is called direct reduction of iron. Thermolysis of water happens at very high temperatures. $\endgroup$– Dohn JoeCommented Sep 6, 2019 at 12:30