Moving Janhunen

On looking into Janhunen's dumbbell I pondered if its 89000 tonnes allowed too little for permanent residence. The red flag was the proposal to shield with hydrogen and boron-10; that is, by the least-possible, which must run out. So the dumbbell might work better as a shuttle. Just move a 89000 tonne spinning 230m-radius hourglass bro.

Let's ponder how we do that. It happens that spin - where a cable can be released - is a momentum capacitor.

As ever it starts with prior-planning, at construction. We're installing equipment on these dumbbells, and testing that such would work at our 9.8 m/s². These stations-in-making are not uninhabited. Human mechanics will want on-site, wasting minimal time on commutes. Their base will be in-site, with imported shield; we'll get further into that later. Point: it's already spinning from the moments of construction.

From 9.8 m/s², the outer edge runs 47.48 m/s. That's a vector we add to the vector at any given point in the orbit. That is: bomb the nexus of the spin. One side adds the vector to the orbit; the other adds the opposite to the orbit.

In technical terms 47.48 m/s is the delta-V. So: the usual maps apply, depending where we start. For reference Earth-Venus demands 280 m/s; assuming no actual Earth or Venus gravity is interfering. The delta-V gets more helpful for a station assembled at the edge of the Moon's Hill distance as wants off the Earth's Hill, here to Venus. To do that, on the (incorrect!) assumption that the Moon's motion doesn't matter, is only 92 m/s. I will set 90 m/s as (arbitrary) budget to hop from Cruithne, to STL4 or '5. The finetuning will involve various manifold maths, which we'll skip for this poast.

Any adjustment in a cabled dumbbell's tangential velocity can be had by adjusting the cable radius, as delta-velocity is applied to the outside. From to 47.48 to 90 m/s means, from 230m to 900m. This rocketry can be gradual; think, VASIMR by way of Ebrahimi-Alfvén. If the station has inhabitants, they won't even feel it, except for experiencing less Coriolis. A 1.8 km wide disc does risk intersecting any other stations there, but our whole point is to get rid of the thing, so - we don't care, at this point. Incidentally I accept Janhunen we commence the radius at 230m.

This method wastes least for pushing one end of the dumbbell to L4 as the other goes L5. At least, if we're starting from L1-3. Note: not TLLx to STLy; this is TL-to-TL or ST-to-ST. With Cruithne, much will depend on the day the year. From a planetary orbit: ~50-m/s-increments present a (drastic) means to clamber up the gravity-well until reaching the desired orbit, like GSO. I doubt we're doing any of that over Earth; rather, Phobos can use this scheme to export mass to Deimos' dangley tether.

To return to our mechanics, under what shield they got: as they build all this, they will want as little annoying spacesuiting as possible. If a dumbbell did have permanent air, that might be a problem as the ends go zero-gee in a sudden. Last year I did some maths on balancing the ceiling against light air-pressure. Without gravity the ceiling might, er, explode. Before the dumbbells go freefall, that air needs to be sequestered or, if impossible, vented. Could be that the mechanics are camping in inflatables.

Next problem: how the future permanent-populace put gravity back to the dumbbell-ends, now sailing off to their opposite Lagranges. Answer: at our start, we build two dumbbells, spinning in opposite directions. (Which also aids in their stability; they don't crash into each other, and don't wobble unpredictably off the planned axis.) If these are cut at the same time, more or less, we'll have two 45kT masses going in the same direction, and two in the other (but a different two!). It remains to reattach the (new) pair going to L4, as the counterparty going to L5 will do.

Thus far: the above might seem to shuttle from one empty part of space to another empty part of space. To that, as Cruithne already owns plenty of rock, and as TLL2 has access to imported regolith; STL4 and STL5 have access to Trojan Asteroids. At least L4 has some nice ones, 2010 TK₇ and (614689) 2020 XL₅. As long as L5's rocks be uncharted, recommend that the shuttle to L5 be half-manned at most, with one half of the dumbbell being simple rock and junk that the Earth system doesn't want in orbit.

UPDATE 11:30 AM - I'm reassembling this stuff at Cruithne, sharing the Earth orbit. The Earth/Moon Lagranges present their own problems as must be handled later. Like: tomorrow. Not now.