Weighing dumbbells

Jensen's minimum mass was Bennu, a C type of 73.3e+9 kg. Janhunen had figured 89000 tonnes which is slightly over a thousandth that, 89e+6 kg. Janhunen would have 78e+6 kg of that as asteroidal. Were Jensen and Janhunen competing as North Baltic weightlifters, Jensen is in the heavyweight class (aiming for Atira!) and Janhunen is decidedly welter'. Since Jensen didn't look at Janhunen's scheme, I'll volunteer this blog for it.

The welterweight advantage is, obviously, the choice of material. There are simply that many more small rubblepile asteroids than large ones. So Janhunen is spoilt for choice as to starting-distance. Once there his dumbbell is easier to budge from one orbit to the next. And Earthlings don't worry so much about impacts. They'll let him work with his 89e+6 kg and move his station, like, maybe into the Lunar Gateway. Or into some Terran Trojan trajectory (or Greek - see below). As for spinning the dumbbell, that's easy. It might start with sails with some aid from an Earth-based laser. Heat-radiation could also focus in one direction although here the thrust might be negligible.

Now for the bad news, which Janhunen already suspects. Janhunen made a point to plan his habitat for shielding. He was thinking 2% for water, and boron-10 to soak up what neutrons the water can't. Janhunen can't drink this water. Also Janhunen wasn't planning massive physical exports; he's fine with a robogreenhouse, between the two weights of the dumbbell. And Janhunen must skim his shield for deuterium, tritium, and - over the years - helium-3 (admittedly all valuables as can pay for the investment). So Janhunen's choice of rock will have to be restricted, after all; or else someone gotta ship him the water.

By contrast Jensen's rocks are so yuuge that his colonists can simply burrow in at, what, 50 15-30 meters over the outer shell. And Jensen can probably find, in his hundreds-meters of rock, about as much water as Janhunen got - which Jensen can subsequently drink. Jensen also has ores to transport, and if not ores then anhydrous glass of which Janhunen was unaware. This can open room for more people, even a community of people as won't be inbred.

Jensen's issue is that his big lumbering rocks cannot be moved as well. And they cannot be spun up as quickly. And-and the wires between the big rocky bits will need more tensile strength.

Which is not to say that these schemes are incompatible. Once Janhunen is at the "Greek" L4 halo, he can take over 2010 TK₇ or even the Jensenesque (614689) 2020 XL₅.

Two years ago I'd already said that Janhunen's dumbbell is unsuited for permanent settlement so is, instead, a shuttle; so, here I guess I'm just proving that.