The idea you see in O'Neill and other science fiction that iron is rare on the moon is bunk. There is Hematite

https://www.jpl.nasa.gov/news/the-moon-is-rusting-and-resear...

and Apollo astronauts brought back perfectly good Iron ore. It's true that there is lot of aluminum and titanium on the moon and a lunar economy might use that but there is enough iron that if loonies wanted to make things out of iron they could make things out of iron.

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gsf_emergency_2 3 days ago | parent | next [-]

Iron may not be rare but the value of iron ores is subtly dependent on eg, non-iron content

"A few smelting companies formed in the late 19th and early 20th centuries, but were unable to process the ore with any economic success due to the sandy nature and high titanium content, which tended to form hard, brittle carbides in the steel." https://en.wikipedia.org/wiki/Ironsand#:~:text=%5D%20A%20few...

Even today's "economic" process wastes all that titanium (which should be even more valuable for a lunar economy - Ti burning is a major thorn on earth!)

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jacquesm 3 days ago | parent | prev [-]

Yes, absolutely, but they specifically asked about aluminum. Mining iron or aluminum on the moon would be trivial compared to earth in terms of access. Getting the gear there to bootstrap it all would be an interesting technical problem but I think it is solvable. Why you would want to do it to me is only to jump start a deep space program taking advantage of the reduced requirements to reach escape velocity while still having a long term platform to build on. If you want to do better than that then space construction will have to go to a completely different level first.

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PaulHoule 3 days ago | parent [-]

ISRU tends to make no sense at all when you have to move things from place to place, it makes more sense when you use them in place.

For instance there may be some usable ice at the moon's poles maybe even some carbon. You could get oxygen out of rocks one way or another. You could make rocket fuel and launch stuff the conventional way but there are two problems: (1) Earth is the most competitive and cheapest market for everything in the solar system, and (2) lunar colonists might see volatiles as precious and decide to circularize them rather than expend them. [1] [2] Contrast that to Earth which has plenty of volatiles.

There is the idea of O'Neill and Heinlein [1] of the lunar mass driver, the picture you get from The High Frontier and The Moon is a Harsh Mistress that it looks like a maglev train a few km long is totally wrong because your elevation angle is pretty high if you want to target the Earth-Moon L1 point or the Earth or LEO (assuming you can aerobrake reliably) If it is a few km long it is a slanted hole a few km deep. I don't know about coilguns but a railgun with 2.5 km/s that would fit on a ship has been tested [3] and you need 3.5 km/s to get to L1 -- one way or another I think a viable mass driver looks like the Paris Gun and shoots small payloads. If you could launch a 1kg payload per second you could put up a rail car worth of material in a day.

O'Neill's students thought a lot about the "catcher" for stuff from the lunar mass driver and never came up with anything convincing if anybody else has I haven't seen it.

[1] See The Moon is a Harsh Mistress

[2] Niven's Protector talks about the problem of very long-term space colonies , starships and stuff losing volatiles at steady rate no matter how well you try to keep them in.

[3] ... and burns up the barrels

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MarkusQ 3 days ago | parent | next [-]

> ... your elevation angle is pretty high if you want to target the Earth-Moon L1 point or the Earth or LEO...

You don't point at where you want to go. You point retrograde (relative to the moon's orbit) so that, after escaping the moon, the payload is just past the apogee of a transfer orbit with the desired perigee.

Further, the moon isn't a flat disk, with the Earth "up"; getting the required angle is just a matter of choosing the right place on the surface of the moon (a sphere has multiple tangents pointing in any direction you want).

So no, you wouldn't need "a slanted hole a few km deep".

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PaulHoule 3 days ago | parent [-]

You may be right but I'd want to see the trajectories numerically integrated and plotted. What I know is that trajectories that hit the L1 point with low velocity will confound your intuition that comes from conics. Here is a recent analysis that considers a range of trajectories launched from a certain point

https://www.sjsu.edu/ae/docs/project-thesis/Ethan.Miller-Su2...

which a student project that has a lot of problems and doesn't consider the possibility of relocating the driver but they are considering moderately high angles of around 30 degrees. Their mass driver is about 500m long in the range that if you want to drill a hole that deep you can drill a hole that deep.

Practically there are other concerns about a moon base, particularly these days people are interested in polar locations. You could possibly run 1000 km of maglev to get to the base of the thing but if you are talking that big you might consider a lunar beanstalk which at least doesn't require a catcher at L1.

	▲	MarkusQ 2 days ago \| parent [-]
		A lunar beanstalk? How is that supposed to work? (Answer: it won't; Lunar-stationary orbits do not exist, since they would have a radius on the order of the Earth-moon distance, and the Earth is much more massive than the moon). https://explainingscience.org/2025/08/19/lunar-stationary-or...

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jacquesm 3 days ago | parent | prev [-]

Fascinating stuff, thank you for the comment. I always wonder to what degree the various 'hard SF' authors really run the numbers, some are very good at it, good enough that there are no immediately obvious mistakes, others get stuff glaringly wrong but still spin a good yarn.