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Comment by sandworm101 | Hacker News Reader

Not mentioned in video: there can be only one. We couldnt have multiple 1000km long objects on different orbital planes. Collissions would be inevitable. These things change speed with every 'hook' event. Predicting collisions would be extreemly difficult, and impossible to do in time to setup an avoidance. And just give up on those 30,000+ unit sat constellations. Flies to the flyswatter.

We would have to keep them all in one plane, probably to line up with the moon. This would seriously limit thier use beyond orbits in that one plane.

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I am picturing it being similar to a ferris-wheel. You could add more carts (more hooks), allowing for more capacity.

But I'm also imagining a more sophisticated ferris-wheel, where you stick two together (side-by-side), allowing for even more capacity.

Picturing it like spokes on a bicycle wheel might also help.

I wonder if there would be much need for more than one.

Except you cant. The rotation of one tether changes witg each hook event. No two would ever be turning at the same rate. So you cannot bolt multiple into a wheel system. You could certainly improve one, make it heavier/longer/bigger, but it cannot have multiple strands.

https://youtu.be/dqwpQarrDwk?t=360

Fair point, that would indeed be a problem.

This part of the video alludes to what I'm getting at. Granted, they are using a moon as the weighted object, so rotation wouldn't be affected by hook events.

I wonder how massive the weighted object would have to be to make rotation changes negligible, or at least manageable.

Even with a moon, there would be considerable wobble. A strand lifing a ship would slow down relative to the moon. The moons rotation would eventually accellerate the strand back up to the moon's rotation rate, but there would be considerable back-and-forth motion. Pick up too heavy a load and the strand may start to wrap around the moon.

I think thats too pesimistic - indeed, with current sats limited by current high launch costs to no or low available delta-V, it would be difficult. With more advanced hight delta-V sats & tugs to move dead sats it should be perfectly possible to avoid collisions via active guidance.

> And just give up on those 30,000+ unit sat constellations. Flies to the flyswatter.

The satellites in these constellations are constantly maneuvering. There's no reason they couldn't easily avoid a sky hook with active correction.

> We would have to keep them all in one plane, probably to line up with the moon.

What keeps them from being synchronized? By moving counter-weights up and down the tether, you can adjust the rotation speed with no net expenditure of energy. So as long as there is a schedule such that skyhooks in different orbital planes are "horizontal" when crossing each other, you can actively maintain that schedule even as ships are extracting and depositing energy from the skyhook.

Sounds like a massive first-mover advantage to whoever builds one first and controls access - USA or China.

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