(Note: the following is one of various posts that were copied here from the Moonwards.com forum for the sake of preserving the early days of the project. It was originally posted there on Jan 7th, 2016.)
I was talking to Doug Plata of LunarCOTS the other day, and he pointed out how big a dome made of an inflatable membrane with regolith piled over it could be, for a small payload mass. Well, true. This has motivated me to get on the job of replacing the dome design i have now with another one i was going to leave until later.
Having thought over the matter of basalt melted in place or poured into voids created in a prepared surface of regolith fines, i think even for the first dome the fabric can be left out, and the whole thing be made of fused basalt and packed regolith. Saves quite a bit of payload mass, and now that i really think about it, it seems entirely doable. So, let's say you sift and tamp powder regolith, and press voids into it using shapes for two different lengths of plank and one hexagonal shape. It would be a bit like the candy-making process in the picture, but with lava, on the Moon, with robots. So much more fun.
Then let's say you start assembling those planks into triangles, connecting them to the hexagons with slight angles so they start forming a geodesic dome. One of the nice things about that is that you can start in the middle and work outwards, propping up the outer edge to add each new row of planks and hubs. the dome armature made of these planks and hubs is light and easily shifted, and surprisingly sturdy, like the 2nd picture shows.
This doesn't take more than connecting the planks in the right position with little gobs of lava, just to tack it in place, and then thickening that join with more lava once it is well aligned. The hubs and planks have to be massive enough to not warp when the lava for joining is added. When you have your full dome framed in, you cover over the triangles with triangular basalt tiles and start building up a thickness of spattered lava over all of it. You end up with the same solid basalt shell of the trough design, without using any fabric and without needing specialized machinery that does nothing but build it. Then you start a second shell, this time from the bottom. build a circle a couple of meters away from the inner shell out of planks, pack it with regolith. Connect it to the inner shell in a few spots with rods to keep it rigid. Build up layers like that, of planks that hold in packed regolith, and eventually you have a solid outer shell as well.
This process is pretty tolerant of little screw-ups, and can go up fast if you have a good steady supply of lava, which is easily done with light durable equipment that uses virtually no power.
I've been messing a lot with getting layouts well organized, and adding a lot of very preliminary material to try to give a sense of the overall direction of the project. I'm going to enjoy spending some time on models again.
And let's see. I'm going to say 50 m span instead of 40, and move the crane to one side instead of in the middle, and figure out how to better use the payload saved. I think this may well mean the dome frame is done on the first mission. It doesn't need a crane, and it sure would be an impressive site.