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The idea is to melt the fine-grain portion of basalt regolith using a large Fresnel lens, and let it cool to a solid. The lens would track along a tamped bed of material leaving a molten puddle something like 2 cm thick. This would be done on top of more regolith with the same characteristics - which means some of the material would sink into the stuff below and get mixed. Then it is left to cool to a solid.

The conjecture is that Fresnel lenses, and the equipment needed to create flat beds of tamped powder regolith and track such lenses across it, is so light that it could be a good way of creating construction materials. If they aren't very good materials they could make up for that in the simplicity of making them and the possibility of making enough that the fact they have weaknesses doesn't matter - just use more.

What might the material yielded by such a process be like?

Edit: Since someone asked, this could yield thin basalt objects of any 2D shape, or objects built up of various layers into 3D shapes. Such objects can be joined with more molten basalt and parged to form continuous rock walls, floors, and arches. An approach to excavation also based largely on the use of lenses (for trenching, and boring for the placement of explosive micro-charges) is used to create voids that are then lined with rock this way.

It is explained more here, and here is the current model of the equipment:

Lunar Melt in place bed with lenses

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  • $\begingroup$ I'd imagine that melting it down would just result in the same composition lava from which it originated. Then it would cool again, in the same fashion that it cooled originally, and the result would just be more basalt. Probably with fewer volatiles in it though. This question probably belongs in a geology forum rather than in Space Exploration. $\endgroup$
    – Phiteros
    Jul 5, 2016 at 20:02
  • $\begingroup$ @Phiteros This is here because the conditions on the surface of the Moon are sufficiently different to change the results compared to Earth. If it goes unanswered i might move it to Earth Science but the best answers would come from experienced planetary scientists. Would it cool into a glass or have a crystal structure? Would it sink far into the underlying grains and be full of inclusions? Will it crack as it cools? $\endgroup$
    – kim holder
    Jul 5, 2016 at 20:31
  • $\begingroup$ @kimholder: I don't think tracking along the surface would be very useful. OTOH, I can well imagine a "solar forge", an array of mirrors (say, along a crater edge) melting regolith in one place, in a controlled manner, the lava cast into forms (possibly from regolith dust) to produce infrastructure prefabricates; more mirrors can be used to control the tempo of cooling process to prevent cracking. $\endgroup$
    – SF.
    Jul 5, 2016 at 20:59
  • $\begingroup$ @SF presently i'll edit this to be more clear. For an initial mission, i think the scanning technique is more feasible. $\endgroup$
    – kim holder
    Jul 5, 2016 at 23:11
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    $\begingroup$ I think that part of the resulting rock will depend on how large of a volume you melt. If it's just a small amount, then it will be able to lose heat via conduction to the surrounding rocks. This would cool it quickly, reforming basalt. But if you were to melt a large enough volume, it would have to lose heat radiatively, making it cool slowly. The fact that you're mixing in unmelted regolith makes it even more complicated, as the lava will lose energy heating up those unmelted bits. Ultimately, I'd imagine it would form a glass at the surface, with basalt along the bottom and edges. $\endgroup$
    – Phiteros
    Jul 6, 2016 at 15:40

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Melting lunar dust of basaltic composition will result (unsurprisingly) in basalt lava. There might be some volatile loss - if for some reason the basalt had some H2O or CO2 trapped in the solid you will most likely lose it. It's probably not going to change its chemical properties much though.

On Earth, as lava cools down fast, for example when it's erupted underwater, or when it's the top of a lava flow in contact with air, it quenches to volcanic glass. When it cools down slower, there is enough time for small crystalline material to form in it. These are usually tiny crystals in the μm size. On the Moon, I reckon the lava would cool down slightly slower than on Earth (since there is no air to conduct away heat), but since you're talking about a lava layer which is only 2 cm thick I'm pretty sure it will cool down fast enough for the formation of glass, and any crystalline portion of it will be negligible. I am not sure whether it will crack or not. From my own experience of melting rocks, when you have a similar amount cooling down in Earth's atmosphere, they crack. But then, silicate glass does not crack when cooled down in air. I guess it comes down to the composition of the rock/glass.

The lava will not percolate down to the regolith. Lavas hardly penetrate soils on Earth, so it is probably not going to happen on the Moon where the gravity is much weaker.

If I were looking for construction materials on the Moon, I would just build a quarry. Seems easier than melting down dust.

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  • $\begingroup$ The regolith on the Moon is between 10 and 30 m deep, and on the very edge of a crater such as proposed, it is deeper as the surface has been folded back on itself by the impact blast. A quarry at the very beginning seems difficult, but there are plenty of large boulders. I don't know how hard it would be to cut them into precise shapes, i'll have to look into it. $\endgroup$
    – kim holder
    Jul 26, 2016 at 14:06
  • $\begingroup$ @kimholder As hard as cutting basalt glass sheets into shapes? I guess that's one of the reasons we don't have colonies on the moon yet. $\endgroup$
    – Gimelist
    Jul 27, 2016 at 10:40
  • $\begingroup$ I had thought the cutting could be done just before the sheet froze. And the sheet can be melted into specific shapes in the first place. $\endgroup$
    – kim holder
    Jul 27, 2016 at 13:23

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