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One issue with sky hooks is that to keep them spinning, they need to accelerate and decelerate the same amount of mass; otherwise, they would change their velocity and might even slow down so much that they re-enter the atmosphere

Currently, with satellite constellations such as Starlink which have over 6000 satellites, the amount of mass being de-orbited and burnt in the atmosphere may actually have some serious impact on the ozone layer.

To help avoid substances such as aluminium oxide nanoparticle remaining in the atmosphere and causing ozone depletion, satellites need to stop burning up during reentry. The only way to achieve this is to lower the reentry speed enough so that satellites don’t burn up. Of course, this means that satellites would survive reentry, so there would have to be dedicated landing zones.

Using a skyhook, the second stage of a partially reusable rocket, such as the Falcon 9, wouldn’t be needed. Additionally, more satellites could be launched and de-orbited while requiring less energy since skyhooks are essentially orbital energy batteries. Given our current technological state, does it make sense to utilize a skyhook to de-orbit and launch satellites?

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  • $\begingroup$ Am I understanding your concept right that you want to capture satellites at the end of their life cycle and transfer them to some lower point in the atmosphere from where they would fall ballistically (plus drag) without burning up towards whatever "pet cemetery"? And that you want to (possibly simultaneously) capture ascending payloads, shortly after launch, after the booster stage has been spent, and transfer them to orbit with the skyhook? $\endgroup$ Commented Jul 6 at 12:52
  • $\begingroup$ @Peter-ReinstateMonica it doesn’t have to be simultaneously, but I think you have a decent understanding of the concept. Kurzgesagt made a video explaining it in a simple way: m.youtube.com/… $\endgroup$ Commented Jul 6 at 16:02
  • $\begingroup$ If SpaceEx are not doing it and not planning to do it in the near future then it does not make sense. $\endgroup$ Commented Jul 7 at 6:07

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Answer: No, it doesn’t make sense.

A Skyhook's center of mass orbits at (roughly) half the altitude of the point for pick-up of descending cargo. The altitude of satellite constellations in LEO orbit is low enough that atmospheric drag de-orbits them within a decade of decommissioning. This means the skyhook (at a much lower altitude) would experience higher levels of drag and de-orbit itself even sooner.

There is a large mis-match in velocity between the cargo and the pick-up mechanism due to both the difference in orbital altitude and the rotational velocity of the pick-up on the end of the rotating tether.

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Also, skyhooks are limited to capturing download cargo with the same orbital inclination as the skyhook's center of mass. This is tricky when dealing with a dispersed constellation. The decommissioned satellite will need to match orbital inclination and right ascension of the ascending node, match orbital phase angle and accelerate to match the pick-up (which has higher velocity than circular orbital velocity at that altitude).

And the location of this rendezvous must occur so the satellite drops into the designated landing zone.

All very challenging for a "dead" satellite.

Even without the materials and deployment issues. “Given our current technological state”, this plan is not feasible.

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