1. Technology--We can send manned craft around, we can send stuff to Mars, we can probably send manned craft to Mars, but we've never tried. And if something messes up out there, there's nothing they can do but try and fix it with what they brought or make peace with their god(s).
This is the same for Luna as Mars. Even in optimal conditions, it would take weeks to get an emergency craft up.
Differences:
1. We've been to the Lunar surface.
2. An escape craft from Luna would be possible.
2. Money--We have it. We won't spend it. Luna is much closer, much safer, and actually superior for other reasons I'll discuss below.
Distance doesn't mean as much in space as it does on Earth. The energy spent going from Earth to Mars is not significantly greater than the energy spent going from Earth to Luna for this reason.
There are other considerations, too. Time is money, after all, and communication would be painful over those distances...to say nothing if when the Sun was in the way...
Supplies on the craft would have to last a lot longer, too. You could probably get a colonizing craft to the Lunar surface within a week, and therefore would only need supplies for that week, plus however long it takes you to set up the colony's farms. Trips to Mars would take months.
1. Power. Specifically, solar. Luna is closer to the sun, which increases the amount of energy available for power. Mars has a dusty atmosphere, which reduces energy and can damage the panels.
Luna has a dusty surface, which is electrostatically changed and thus sticks to everything it comes into contact with and tries its damnedest to never come off. It is also deadly toxic.
There's no wind, though. You should be able to build the actual panels a foot or so off the ground or something. Also, why would you eat moon dust? Those space suits are there for a reason.
The atmosphere isn't particularly dense, though, so there's still the risk of meteorite impacts.
This is more of an issue on Luna! The whole moon isn't covered in craters for show, it has been taking the brunt of near-Earth objects for billions of years now.
My point is that it wasn't a noticeably smaller risk on Mars.
2. Gravity. Luna has a gravity of about 1/6 of Earth's. Bad? Not for a geriatric colony!
You are never going to convince old people to give up the remainder of their lives toiling on Luna until they die of the conditions there. We probably won't have much need for that anyway. Centrifugal beds would be a good way to go about maintaining bone density.
Why would they be "toiling?" Okay, I'll admit I was a bit unclear on that point, but I was envisioning some sort of Lunar nursing colony, founded once the main one was up and running.
4. H3. I'm not sure how much Mars has, but it's harder to ship stuff to Earth from Mars. H3 is pretty valuable, and what's more it could stimulate fusion research, which would be a good thing.
He3's potential for fusion is an unknown, and there's another issue: You would have to process 150 tons of Lunar regolith in order to extract one ton of He3. It isn't a very cooperative resource.
Wikipedia suggests that the price for H
3 is around $100 per liter, but a Discovery News article suggests that this number is out of date. It says that the price is closer to $5,000 per liter (or was, when it was published), but either way that's not exactly minor. I'd have to know the density of H
3 and the cost of extracting it, but it seems to be a fairly profitable industry. If it's not, we could skip it.
Anyways, the "research" includes figuring out if it's good for fusion. That's why I didn't say "it will fuel our fusion reactors!" Even a failure on the fusion count could help us discover something.
