Sift II

A fortnight ago I suggested how to start a dumbbell colony: by sifting the big dumb rocks out of the pebbles and regolith; so's to dig into the latter, easier. Once at the pebbles and regolith - then what? I figured - then, we'd want in on the topmost layer of the pebbles and regolith. I'm starting the spin easy, at Luna gravity 'pon the roof: 15m down for S-types, 30m for C-types.

I reckon we can "dig" more easily with a second net. This mesh will be a little finer than the rough thick-cabled net which got our big rocks onto the counterweight. What I'd do here, would be to sift out the smaller-but-still-sizable rocks - themselves no greater than 15m ideally - above the pebbles-and-regolith. That secondary net (tertiary, counting the net around the counterweight) would be 400 meters wide and less than 400 meters long (because curved). Once this roof is hoisted above the naked gravel, we lay down epoxy on that gravel, and put up some rough rock columns periodically. Ceiling maybe ... aluminium? titanium? or even plastic. We want a design as can keep gas from escaping a flattish rectangle.

As we fill this bubble with gas [UPDATE 10/14 744.1 kg/dekameter³, which I don't envy for rockies], we lay the rocks back down there. Fifteen meters of shield above, all worthless chunky rubble. Below-decks the colonists get that much more percentage of regolith from which to make glass and fibre. As for how high the ceiling of our inbetween gap: that much depends on spin-rate and the distance from the fulcrum, not to mention how much gas (in practice: nitrogen) we can spare to fill it with. The great cathedrals are 25m-50m aloft. For a S-type without the volatile-reserves of a carbonaceous, I recommend a modest start. 15m approaches 50'; a dekameter height makes the maths easier.

The upper-parts will mainly look like the gymnasium in Revenge of the Nerds. Low-g and high-nausea do suck, but it's all better than what ISS inhabitants get. Top/innerside makes a fine site for running-sports - less shock on the knees! Although, for ballgames, Coriolis encourages only one goal. That is: baseball or cricket, neither which I recommend at low-G in cramped conditions.

As time goes along, I am hoping to turn as much regolith into building-material as possible; to burrow into the lower layers. Meanwhile scatter some of the topside rocks down and aft. At the same time we're lengthening the distance from the fulcrum, to increase gravity belowdecks. I was aiming no more than 850 N/m² stress on the bottom/outward shell.

The top low-gravity layer will become stepwise, fore remaining 300 m above the bottom, aft tapering off. Also as the rock above gets heavier we'll need and want less of it, to counter the airpressure.