Friday, July 22, 2016

Why this isn't being placed at the poles

(Note: the following is one of various posts that were copied here from the forum for the sake of preserving the early days of the project. It was originally posted there on Nov 7thth, 2015.)

The Lunar poles are all the rage, especially the South Pole and Aitken Basin. There is now good evidence that there is a lot of water ice trapped in permanent darkness there. That ice also contains carbon monoxide and nitrogen. Those volatiles can be put to excellent use on a lunar base.

There are also the Peaks of Eternal Light, which don't quite live up to their utopian names, but still have daylight about 80 to 90% of the time. That makes the power supply much less of an issue and evens out temperatures. Those are pretty big advantages, so why have i placed the VMC at the equator, where the nights are long and harsh and water can only be had from Earth?

The main point is the poles should be home to the second base, not the first. Getting that water and other stuff is not going to be easy at all. They are in extremely cold places, kilometers below the sunny spots where a base would be. What form they come in is far from clear, but they are probably not more than 5% of the ground material in those shadowed hollows. To collect them in significant quantities will require a lot of infrastructure. They couldn't be used to supply an inhabited base for years, while all that is built and gotten rolling. Once it is rolling, the idea is it supplies the income that justifies that - you split the water into oxygen and hydrogen and sell it as rocket fuel. I have serious doubts there.

That much infrastructure could also be used to create industrial scale production of oxygen at the equator - or anywhere else for that matter, the Moon is almost half oxygen. Oxygen is most of the mass of propellant, so it is still a major advantage to future missions if they can get supplies of it in space. Also it is very far from certain that the market for propellant will spring up nicely just when you need it. Basing the economic model of a settlement on a market that doesn't exist strikes me as a bad idea. I understand the temptation, but i think it is misguided.

If you aren't mining it for profit there is no reason to mine it at all. It is much easier and more reliable to ship the water and nitrogen you need for the early phase of human settlement from Earth. Enough for 10 or 20 people can come up on one or two rockets. As life in space gets going, you can start mining those resources when the right moment arrives, and in the meantime, you can scout and study those areas thoroughly. And you can keep scaling up your oxygen production, there at the equator, using infrastructure already created for production of building materials and pure metals and metal oxides. Then you can sell LOX, with much less up front investment, and scale production smoothly as the market develops. When you finally decide to mine the poles, it could well be mostly to get water and nitrogen for a quickly expanding colony, not to sell as propellant. Also remember that once we go poking around under the lunar surface, via lava tubes or simple mining of the bedrock, there will be surprises. One of them could be volatiles trapped in bubbles and tubes that have been sealed for millions or billions of years. If so, those deposits could be much simpler to tap.

How about the handy near-constant sunlight? I'm not that impressed. Temperature fluctuations are not a big deal with this construction method, it gives you lots of thermal mass quickly, in the domes and galleries themselves and much more so in the thermal connections they form with mega-regolith through the foundation. We are talking about building at scale, in that situation including energy storage systems for the nights isn't that hard. I've already gone on about storage of potential energy in the form of boulders lifted and lowered, and Joe has mentioned the other options of flywheels or batteries, or just sticking to nuclear for power available all the time. The amount of extra infrastructure that involves is a good deal for what you get in exchange: basalt, KREEP, and easy access.

There is no basalt within 1000 km of the poles. The dome construction technique being proposed right now would still work with highland regolith, but you won't be making rope or cloth out of it. Anything that needs to be flexible has to come from Earth, which includes composites that contain fiber layers. Over the long term that really sucks.

Phosphorus, potassium - absolutely essential, great to have nearby, and only found in KREEP deposits, which are only in Oceanus Procellarum. Those deposits also come with concentrations of thorium, and uranium too. Long term, that means nuclear reactors for energy would be an option, and more importantly, nuclear rockets. You want to open up space? Nuclear thermal rockets without the politics sound pretty awesome.

Also evacuation from the equator is easier than from the poles. If you have people there, you really want to have the option of launching at any time. At the equator you can do that with a smaller, less expensive rocket because you can keep an upper stage in orbit and rendezvous with it within an hour or two at any time. That trick only works at the poles every two weeks. The fuel to the equator is also less, which means bigger payloads.

So, that's why. If you say that means there is no business case for settling the Moon, well, let me come back to that.

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