Ben Smith via Slack #moon
Here are a few things about lava tubes to think about:
- We have no direct experience with Lunar lava tubes. We have indirect evidence that they probably exist but that's from remote sensing. Any temperature information is strictly theoretical. At this point -20 deg C is as good a guess as anything.
- However, that's a tube in it's natural state. Any activity will start to rapidly increase the temperature inside. @Mike Delaney is right. Getting rid of the heat is a much bigger problem. Any Lunar settlement is effectively in a vacuum bottle. Heat will build up if you don't have mechanisms to take it away from the habitats.
- There's no reason to think that lava tubes will be free of regolith dust. The stuff gets everywhere. And it's awful. Any construction inside a tube will have to find ways to deal with it.
- Lava tubes, if they exist, have been in a stable environment for a very long time. Introducing heat, humidity, vibration, breathing gases, etc. into them could very well make them unstable. Even if the tube is lined with some kind of material, something always leaks through.
- @Watson asked about drilling into the walls of a tube. That's probably doable but it really depends on how unstable we make the tube due to our activity. We have no hard data for any of this (that I know of) so at best it's all SWAGs (Scientific Wild Ass Guesses).
- We have no evidence of easy entrances to lava tubes. We might have to go in vertically through a skylight. That's going to be more difficult than it sounds. The floor of lava tubes are also thought to be full of debris. We'll need serious construction equipment to clear it for habitation.
- Spray on liners and sealing off large sections of a tube will probably require a lot of supplies from Earth. The bigger, but more rewarding, challenge will be to figure out how to do it using only locally available resources. The same goes for Earth-built nuclear reactors. Settlement is highly unlikely if they are completely reliant on Earth for all their basic needs.
- It's going to be hard to grow anything in unprocessed Lunar regolith. A large percentage of it is very fine particles that will prevent water from flowing through. And the particles are all very sharp and jagged, which will be hard on root systems. However, it should be OK if you screen out the fine particles and run the rest through a tumbler to knock of the sharp edges. I haven't read anything that suggests it is chemically toxic, unlike Martian regolith. Lunar mare mega-regolith and bedrock are simply basalt. It's not that different from Earth basalt. It would be easy to run agricultural experiments from home.
I hope this helps. I'd be happy to discuss any of this in more detail. We've got a lot of other knowledgeable people here so call me out if I got anything wrong! (edited)