I’ll send the question off to my son the rocket scientist (I never get tired of saying that! 
) But when we’ve discussed this in the past, I believe he has said water would be the greatest find. Or perhaps it would be more accurate to say the immediately necessary find, which would enable additional efforts.
To state the obvious, in addition to getting you and your payload back to earth, water and fuel from the moon or elsewhere would allow you to go further out.
See, I think most of the worthwhile things people are proposing are only worthwhile to further space exploration/colonization. The big question is, what’s in it for the Earth? We’re talking economically here, not exploration-wise. I’m all for space exploration, but that’s a different discussion.
He3 is the best so far, but fusion is still a pipe dream that’s 50 years away (as it has been for the past 50 years … and will still probably be 50 years from now…). I can’t see anything that would likely be worth the trouble.
We went to the moon without knowing what’s it made of. We will be going back no matter what we think is there. It’s already made of the stuff that will keep us going back. Dreams.
Space travel isn’t supposed to benefit humanity. Space travel is the *purpose *of humanity.
I agree with you but the question posed in the GQ was an economic one. The answer to the GQ appears to be nothing which is a shame because that would be a way to convince people who don’t share our view to fund or support government funding for such an endeavor.
If we knew we could get them, they’d be worth any price you could care to name. Most Grand Unified Theories (i.e., uniting the electroweak force with the strong force) predict that the proton is unstable, and eventually decays into (eventually) a positron and a bunch of photons and neutrinos. Now, under ordinary circumstances, this decay is extremely slow, taking many orders of magnitude longer than the lifetime of the Universe. But these theories also predict that the reaction would be catalyzed by the presence of magnetic monopoles. Which would mean that you could get total release of all of the energy contained in mass. Now, in practice, a big chunk of that energy release would be in neutrinos, which are effectively lost. But even a 20% efficiency or so would revolutionize pretty much everything.
What happens to the monopole after the interaction? Is it consumed - theoretically of course.
Once you’ve established a moon base, a railgun would be easy. A big one, running up the side of a mountain or a crater wall, could shoot stuff into Earth orbit very cheaply. It wouldn’t work for people or other living things, because of the 100+ g acceleration. But for rocks or refined minerals, it would be perfect.
You could power it with a large solar farm, or a nuclear reactor.
The big drawback is it needs metals. But I think the container/projectiles could be made mostly of aluminum, which shouldn’t be a problem on our Moon.
Nope, magnetic charge is just as absolutely conserved as electric charge-- The only way you can “consume” it is by balancing it out with another, opposite monopole. That’s why I used the word “catalyzed”.
Incidentally, when I say absolutely conserved, I mean it. Even black holes, which sneer contemptuously at most other conservation laws, still respect both electric and magnetic charge.
The Earth is pretty much self sufficient in everything at the moment so we don’t yet need to mine moons for materials. So why do it? The answer would be: lifting mass out of Earth’s gravity well is expensive; it is better to find the resources needed for space travel and colonisation in space itself.
Our moon has oxygen, aluminium, silicon and plenty of other materials that could be used in a space-based economy; we could build and fuel spacecraft and provide them with oxygen, ready for them to go further out to exploit the rest of the Solar System.
Once there is sufficient industrial infrastructure on the Moon, building ships from lunar materials would be cheaper than lifting them up from the Earth. By building large numbers of spacecraft using lunar materials we could gain access to the resources of the other moons and planets - not to bring them all back to Earth, but to use them to support a population in space.
How would the Earth benefit from a florishing space economy? Well, in the long run, we will start to run out of some material resources; rare earths for instance. If there is a florishing space economy then I’m sure the Earth will find something of value to trade with the spacers in exchange for ruthenium and so on. Earth would be richer and more resistant to long-term shortages if it were imbedded in a densely populated solar-system.
Sorry for misunderstanding the thread.
My son’s strong interest since he was a pre-teen was his perception that we need to get more payload into space more cheaply.
He’s currently an engineer w/ ULA, maker of the Atlas and Delta.
He hasn’t gotten back to me yet, but I suspect his opinion would be that with today’s technology no substance would merit the cost.
Interesting discussion, tho.
(Maybe he’ll respond to a text more quickly than this old fuddy-duddy’s e-mail!)
Probably off on a tangent, but I think one of the benefits of exploration is that it creates infrastructure and standardizes procedures which might be expected to create efficiencies for future commercial applications - including mining.
My kid’s response:
**The most potential profit could be wrung from mining water and building materials to be used in orbit. However, that requires a large infrastructure to be constructed before it can be used - which may eliminate that market.
At the moment, the only material that beats the cost-to-orbit mark is the platinum group metals which are used in many ways. But the more you bring in, the lower the value.
The real question is whether an orbital architecture can be constructed or not.
He3 is in the future, when US reserves run out (grumble about stupid US legislation). Right now He is artificially cheap on earth.**
Just the opinion of one person I know who spends a lot of time thinking about this.
Thanks for this, and thank your son as well. It’s always great to get a professional’s response. Very interesting, especially about the platinum, which I knew we’re very valuable in a lot of industries, but not so much that looking to space might be a cost-efficient scenario.
Exactly. I can think of plenty of reasons for us to be exploring space. (And do a lot moe exploring than the pittance we do know…) But that’s not the OP.
All right, now we got the kid thinking about this, neglecting his work undoubtedly, and sending me texts. The latest (which I’m not sure I entirely understand):
An interesting idea for asteroid mining would be to establish orbital depots for H2-LOX fuel and sell that to interplanetary missions. That would greatly increase the mass/decrease the cost of interplanetary missions, if the cost of mining/producing the fuel is less than about $10k/kg.
He’s big on exploitation of Lagrange points, and pissed that the ISS was not sited at one.
The ISS is at 250 miles. A Lagrange point is at ~800,000 miles. Siting something there in the future might be sensible, but trips of a week each way can’t be justified in today’s world.
All these ideas for colonizing space are too much like fusion power. They’ve been 25 years away for the past 50 years.
Yeah - orders of magnitude more difficult. But at least a station there would serve some purpose.
We’ve barely managed to place a chair on the front porch. Asking for a play fort in the back yard is a little more difficult.
Yeah - far better to spend our fortune achieving easy goals like bringing peace to Afghanistan and Iraq! 
Why is the question about raw materials? Are there not amazingly useful processes that can only be performed in zero G? If we can mine the asteroids and then finish them in space, they could be valuable enough to justify the expense. Something like maybe that odd FeAl alloy they found in the “UFO crash” in Texas a century ago.