So today I wake up to a post over at Phil Plait's Bad Astronomy blog about some of the mysteries of that place we can currently access right now only by looking through instruments, and it got me thinking more about one of my favorite notions. Basically, the Lunar Reconnaissance Orbiter team has spotted more pits that look a lot like what we'd expect skylights into a lava tube to look like, and one of the new ones is seriously big. Phil has a good explanation on his site for how such features form, fur what interests me is the nature of the feature they leave behind: long empty tubes. The one in the Sea of Tranquility that this pit opens into is big, the skylight alone is 100 m in diameter and the floor is about 100 m down. I read once about a concept to put habitats in there, either inflatables or actually sealing and filling the entire cavern to shirtsleeve pressures. Because they're below the regolith and some bedrock, the radiation shielding requirements of the surface are taken care of, and I've recently seen a source that suggest that the natural cave walls may be sufficiently airtight to not require any major lining operations (beyond pluging large holes like the skylight that let you find it in the first place, I guess). Oxygen could be produced from regolith, or I suppose imported from a polar base cracking ice sheets for rocket fuel. If you do this, you end up with a possibly huge pressurized volume, and for pennies on the cubic meter. The Sea of Tranquility has some nice things--history, I think the orbit is a little easier to get to, and you can communicate directly with Earth via surface dishes without requiring relays (yes, more is coming on commsats, I just haven't gotten my thoughts in order enough to write them up). What do you do with all that volume? Colony? Manufacturing? I don't know. Too much volume is never an issue space exploration has had before to my knowledge.
Oh, also on the subject of awesome space stuff last night and today, Falcon 9 flight 2 went vertical at LC40 last night and they've been doing tanking tests all day. I'm not sure I'll get the rocket flight for my birthday I was hoping for, but I think they may actually make their current "Oct. 23rd or earlier" goal. There's some occasional visibility on cameras here, I've seen it on 11 and 12 off and on depending on where they decide to point the cameras. Good luck, SpaceX. We're all eager to see what you can do, or at least I know I am.