The last man to have stood on the Moon, Gene Cernan, died today at 82. Our goals as a nation, as a species, seem to have changed since he climbed back onto the lunar lander in 1972.
When I was a kid, the plan was to launch ever increasing explorations into space--first low earth orbit, then the moon, then perhaps permanent manned space stations, ultimately to include Mars and other planets, along with the asteroid belt. It was presumed that we'd have hundreds or even thousands of people permanently in space by the start of the 21st century. Just look at the vision of the great movie 2001: A Space Odyssey.
That didn't happen. It turns out that the space program was largely a byproduct of the military's quest for ever more powerful weapons. The boosters used to put men into orbit in the Mercury and Gemini program were re-purposed ICBMs and the vast majority of things actually put into for the first 30 years or so of space flight were spy-in-the-sky stuff, like the KeyHole orbiting cameras. Even the first planned space station, the Manned Orbiting Laboratory, was really a spy satellite and when robots fulfilled the things capabilities, it was cancelled.
But there are commercial purposes to space. Weather and communications satellites are extremely valuable. There is science that can be done better in space than on the ground--the space telescope and robot missions to other planets are illustrations. There is enormous mineral wealth up there too. It's much easier to get stuff from space, even from the asteroid belt, onto the earth than it is to get stuff up there. It's easier yet to use it up there. The time will come, I believe that a large fraction of our satellites will actually be built in space. Nearly everything we need is there--but not the people to do the work.
Robots do a lot of things well, but they need a guiding hand. And that hand cannot be more than a tiny fraction of a light-second away, lest the latency overwhelm the control. The only way to build a satellite in space is for at least some of the workers to be up there. This means permanent occupation. I think the way to do it either to do a rotating ring style space station, or even an O'Neill cylinder. They are impractical much smaller than about 1000 foot diameter (where 1.2 RPM would give 1/4rd G). A cylinder 1000 feet in diameter and 100 feet long would have 31,400 square feet of bottom floor space, and would probably be built 10 floors deep or so which probably means a population of a hundred or so. That's a big thing.
The moon is almost as good and has some advantages. The moon's gravity well is 1/6th what the earth's is, which means it takes a lot less energy and fuel than getting off of earth. Unfortunately, there's no atmosphere to slow landings, so landing takes just as much energy as taking off. But as SpaceX has been demonstrating, computers are getting pretty good at this. Most of the people will need to live underground, to protect them from radiation, but there's no shortage of material. The biggest problem is water. But there's lots of oxygen, lots of silicon with which to make solar panels, lots of metals, etc. The weakest link is hydrogen, which may be available in the minerals, but may be difficult to extract. And there are so many advantages to building satellites on the moon that it's hard to imagine we won't eventually do that.
We can also build gigantic space telescopes and radio telescopes, completely free from atmospheric and radio interference, by simply building them on the far side of the moon. Who knows what else?
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