Friday, July 22, 2016

Components of Phase 1 VMC - Dome under construction

(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 Oct 5th, 2015)

These posts are rough drafts of what will go on the main page this week. It is crunch time now for the Lunar Exploration Analysis Group annual meeting, that i leave to attend in 2 weeks. I've been making models for the last few weeks, i'm not very good at it yet because i'm mostly learning as i go, but they are good enough to explain the main concepts.

This one comes first, a dome 40 meters across under construction

I have to figure out how to get the models to render better for these images. Anyhow...

This illustration shows a continuous tube construction system for the dome. It doesn't show the tube filling and placement system - but there is a model for that, it will go in the next post. So really the tubes that have been laid should be in a spiral, and the Tube Filler (i'm so tempted to give it some much funkier name*) should be visible trundling along, continuing to spiral upwards and inwards until the inward curve of the half-sphere being made reaches about 30 degrees. Then it is done and a different system is used to close off the remaining span, which would be about half the width and a fifth of the height.

That different system is illustrated in the roof structure of the - what, the foyer of the dome? That has 2 levels. The main level will eventually get airlocks in that doorway - which is about 3.5 m tall and 2 m wide, so equipment can be moved through it. The upper level is only connected to the dome interior and is pressurized when the whole thing is finished. The roof is sustained by the basalt beams at its corners. So the lava mold and melt-in-place operations need to produce those beams - (though narrower profiles could be placed at first and then built up with more lava troweled on when it is thick or spattered on when it is more viscous). Basalt cloth is stretched between those beams, a layer on the outside and a layer on the inside, and filled with regolith, tamped tight.

A heliostat is shown connected to the window. (It lacks some details, but the configuration is accurate. There are bits missing from the supports and the gear box and motor to turn it to track the sun aren't there. Also the smaller mirrors that transfer the light to the interior probably should have some thickness and mass to ensure they don't melt or deform - magnesia or graphite mass, chromium mirror surface, sapphire outer surface protecting the mirror surface?) It is large enough to fill the interior of the foyer with sunlight more intense than the full noon-day sun on Earth, all through the 2 weeks of lunar daylight. (Actually maybe i should scale it down a bit.)

Heliostats just like it, but bigger, would be attached to the main dome at the height where the tube filler finishes its job. One on the north side, and one on the south side. As Cernan's Promise is almost right on the equator, both would get full sun all day long. Pass the light from them into the dome and onto surfaces designed to scatter it throughout the dome. If those heliostats are sized to fill the dome with light as intense as full noon sun on earth, those scattering surfaces are going to heat up a great deal. So put channels in the basalt mass behind those surfaces, created when layers of lava are built up, put some water in them, and create a micro steam turbine system. Get electricity out of that heat, and spread it out too, making use of the dome's thermal mass to create an even warmth comfortable for people.

But that comes later and i really hope i have time to mock up a quick model of that stage before i leave, most of the elements are already done. Really i said that to get to the next point. The level where the tube filler stops is a convenient point to switch to building up lava facades on the inside and outside of the dome, and creating a strong ring of solid basalt at that height, and installing the heliostats there. The span that is open to the sky will help the lava to cool and properly solidify by the time the robots are ready to complete the cap of the dome. During that time lava has to be spread over the whole floor and built up to a good thickness.

The image shows the beginning of that process. First, tiles of lava are attached to the rods distributed between tube levels during placement. (Maybe they come from the melt-in-place lava facility, loose regolith that has been raked to remove chunks and smoothed level should melt evenly enough as a beam of concentrated sunlight is passed over it that tiles can be produced.) Inside and outside, the whole dome gets those tiles. Next, those tiles allow solid basalt to be built up. Lava can't be applied directly to the tubes, or the fabric will melt away and the regolith will fall out. But if the tiles deform a bit when lava is troweled over them it doesn't matter, they just have to allow the solid basalt portion to be unified so that a solid basalt dome builds up.

So as i've written this out i've thought of weaknesses and possible improvements, which is why i do it this way. I wanted to mock up this method first, but there are several ways this could be approached. Now that i've done this i'm not sure this is actually the fastest and most efficient way. Well, this is a process, after all. Onwards...

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