The Sunken Hall (Extensive Edit)

(Originally posted on site forum April 2nd, 2016.)

New and improved! All the external main stuff looked at. Here are a bunch of images of this key ingredient to the colony concept, an excavated space reinforced with fused basalt material and turned into a nice, bright, quite large habitation space. Man building this took a lot longer than i thought it would. But i think i’m getting faster with these things. I was going to talk about each image but that effort would probably be better applied to the main page of the website, with the whole marker and tooltip setup. Though this model is really getting into the territory where it would be much better to have a 3d model people can rotate and move around in, or you don’t see how it all works together or the details. In fact i’m not sure it would be helpful to put up all these images, as there are so many.

At any rate, a couple of highlights. The berms of material around the sides of the area with the arched roof ensure there is no direct view of the sky from the sides, cutting the radiation dose down to something safe, even over decades and even if you spend half your time in that area. The bottom image shows how a view of the sky is visible between the beams of that area, which i call the dugout. You get a significant dose of radiation from that direction due to that, but because you are so well protected from other directions it doesn’t endanger you. All the beams have the same gap, so you can walk from end to end of that area, always have a view of the sky above you, and always have natural sunlight falling on you (minus the UV and gamma ray spectrum). The area is very well adapted for growing plants. The idea is gone over more in this post. Also through the windows at the end of both the tunneled sunken hall and the end of the dugout, a mirror has been set up that reflects in a view of the Earth. The Earth moves only a little in the Moon’s sky, and does so quite slowly, because of the way the Moon is tidally locked to the Earth. Those mirrors will always keep the Earth in view.

None of the interior has been modeled yet, of course. I just put in the two airlocks and the structure. Doing the interior will be fun. The space is 40 m long, 30 m wide at the top and 15 m wide at the bottom, by 20 m high, in the dugout area. The hall area (the tunneled part) is 78 m long, 27 m wide, and 13 m high. There is all kinds of space to play with, and all kinds of things that are possible in that space that have never been possible before in, uh, space. I have been playing with ideas for exercises that take advantage of the room. On the Moon if you have enough distance, you can jump high enough to load your muscles and bones the way they are loaded on Earth. That might be very helpful to reducing health issues due to low gravity. You can leave large enough areas open to give something of a feel of the outdoors, or at least large enough not to feel positively claustrophobic after a few weeks.

That outside door you see on the airlock is actually 6 m tall by 5.3 m wide. The other airlock, in the dugout, also has a door that is much larger than an ordinary door. Don’t let them fool you as to scale, they were just made very large so they can accommodate anything that might need to be brought inside. Use the little green men in the image below for scale.

A couple of notes:

The transparent areas will indeed all be windows. I don’t care what they cost, the views are critical to maintaining mental health. And i don’t think they will be that expensive, actually. They can be made of laminated sheets of sapphire, which isn’t terribly expensive these days. The images show pretty large spans without reinforcement - actually the biggest open spans would be the squares shown with a reinforcing brace halfway vertically and horizontally, making the unsupported area about a meter square. That’s about 1.1 tons each would have to bear if a full atmosphere was inside (and to start it would likely be more like two thirds of an atmosphere). Most would have 3 braces, vertically and horizontally, for spans of 50 cm. For the area of windows shown, for each centimeter thick the glazing is, it will mass 3.2 t. I really don’t know how to assess how thick it needs to be to bear the pressure of an atmosphere across a span of a meter or 50 cm. If all of it was 2 cm thick, that is 6.4 t. That really seems worth it for how gorgeous it will be. One of the main undertakings in the early days will be broadcasting and film, a gorgeous place really helps with the success of that. Aside from how mentally refreshing that view would be. The windows looking out over Lalande crater would show you a big section of the crater interior. The dugout windows would only show you the Earth in the mirror, but you’d be able to see it throughout the whole dugout space. And besides, it occurred to me later probably most of that outer wall should be mirrored, for a wider view of the sky.

The arched beams over the dugout are held down at each end by those great big long solid beams with the series of holes along them. The holes show where anchors would been bored deep into the regolith, 3 from each hole at different angles. There is a technique for that that comes from putting together two promising techniques. Both are of course untested, but seem promising. Microwave Sintering of Lunar Soil and In-Situ Rock Melting Applied To Lunar Base. You melt through the regolith with a microwave emitter on the end of a long tube, down as deep as you can go, hopefully at least 20 m. The lava produced is forced out by displacement, and a hollow tube through the regolith is the end result. The microwave emitter sits at the bottom of the tube for a while melting a puddle of regolith around it. Any voids left are back-filled with lava. Deep strong anchors under the long beam on either side of the dugout is the end result. The thick basalt fiber cables running along the top of each beam are attached to these anchors. Similar anchors under the floor of the hall are also made and used to anchor the arches above.