Sift

As we're looking at asteroid-colonies, Janhunen might start with pure regolith from our Moon. At some point even he must approach a free-floating asteroid. C-type (and some S-type) asteroids are rubble. Not all rubble is equal.

For our purpose, we're starting as light and as simple as possible. Janhunen finds a 90kT floating jumble for a colony. Miklavčič comes along with a bag to throw over it; then Jensen orders some robots to spin the bag (bro). Er. Where's the counterweight?

Miklavčič says, what counterweight. Big torus-section, evenly-distributed mass, it'll never get unbalanced to suddenly shift rotation at the wrong axis. LOL chaos isn't real. Although I am told that he can fix this by spinning a second big torus-section, of the same mass, in the opposite direction.

To the extent Miklavčič be justified (I'm a skeptic) I deem his design to apply only to the high-Jensen volumes. Given how little space-infrastructure we now own, we must start with Janhunen and low-Jensen volumes. Once we have that (small) colony, we don't want to share it with fifty-tonne hard silicates ("enstatite chondrites" as Earthers call 'em). You can't chip homes into them so easily; and they might not be great for mining straightway compared to the anhydrous glass which David Jensen liked. Much less, those valuable volatiles locked into the sooty bits.

I think Janhunen should like to sift the bag as it spins. The outer bag is, yes, some nanofibre as holds in the dirt and doesn't let too much regolith out. I suggest he cast additionally - internally - a net, with a good deal of tensile strength, designed to keep the biggest boulders apart from the rest.

Some of the larger rocks might be big useful chunks of hydrated coal, or platinum. If they exist - great! these can be plucked out from the rest of the larger rocks, by hand.

Once the thing is spinning good-enough that a good haul of large rocks have come up, those large rocks get dragged outside the others, and the rest of the rubble gets spun against that net of rocks.

It follows by the way that Janhunen's dumbbell is a very late stage of colonisation, if it be a stage at all. I'll have more to say on that.