(Originally posted on site forum Oct 6th, 2015)
I made a new lava maker after being concerned about the weaknesses of the parabolic bowl mirror i posted yesterday. This one is a bit less complete, i keep trying to tell myself i need to hurry now and leave details for later.
Here we get around the issue of melting secondary mirrors and wasting energy by simply putting the lava tank at the focal point of the heat. I’d thought of this before but wasn’t sure how to handle access to the tank. Splitting the mirror into two halves that are slightly separated helps a lot. All the support infrastructure is out of the mirror’s light, and it doesn’t need to rotate, it is at the axis of rotation and the mirrors rotate around it. It just means several components have twin halves.
That makes for a somewhat awkward tank shape. The orange half-egg dome shape that can only be seen in the reflection here is hit by the focused sunlight, as is one on the other end. The focal points would be at the centers of those dome areas, so the beams on them there would be small half-circles of very intense light, and as the mirrors rotated over the course of a day the half-circles would travel around the domes’ bottom halves. The light blue parts are reflective insulation hoods (and the main body of the tank has such insulation as well*). The hoods over the domes are connected to the spokes that go to the strut systems backing the mirrors - they rotate as the mirrors rotate. Thus in this version, the heat is received on the ends of the tank, and has to diffuse through its contents from there. Again my guess is the materials that make sense are graphite and tungsten.
The flared hopper at the top is where the crane drops in regolith. It would have a lid within it that can be opened for that, and then shuts air-tight, and maybe it should also have insulation that can be closed over it. The green parts are my tremendously ignorant guess at what a gas collection system on the tank might look like. It is basically there to represent the idea. Oxygen collection systems can be integrated into this design.
The purple part is the area where motors would go that slowly rotate the ring at the center of the spoke system 180 degrees over 14 days. A few rollers would need to be spaced around the twin cradles the twin rings sit in. I wonder what the best design is for a motor that moves so slowly. I suppose it would be possible to not have motors, and just swing the crane around every two hours and turn the ring one notch, shifting the mirrors by 1 degree. Maybe there could be a crank system somewhere, so a rover could also come do the job if the crane is busy.
And this design could also be a half-bowl instead of a full-bowl, like this:
Here you can see the spout for emptying the contents of the tank, sticking out rather obscenely. It isn’t really visible in the top image, in that version it sticks out of the part at the back of the tank. Who knows how many times a tank could be filled and emptied over one lunar day. As many times as possible would be the goal. Aside from where the limitations of the materials and resources fix that number, it might be good to leave the lava boiling for some time at an extra-hot temperature. Like yesterday’s design, the goal here is to raise the temperature of the whole internal volume to at least 2500 Celsius, and sustain that temperature so the mix releases oxygen which can be collected.
Here is a small version from further away so you can see the whole thing. No fancy struts on the backs of the mirrors this time. Just imagine it has the same setup as the heliostats from yesterday.