[Physics] most infeasible about a sky hook (as in space travel not Batman)

gravityorbital-motionspace-travel

We need to get things into space but it costs too much. Lots of people talk about space elevators but no one talks about the skyhook idea. I'm referring to this:
Skyhook (Wikipedia), not the thing in Batman. It is also illustrated in this low-budget video. Is this idea really (even) less feasible than a space elevator? What is the most difficult aspect of implementing it?

Best Answer

The Wikipedia article suggests feasibility:

  • Hypersonic speeds needed to capture goods
  • High tensile strength of the cables
  • Recharge of energy to maintain tether

And notes that a space elevator is essentially a class of skyhook with an orbital period of one day.

Currently we don't have working (let alone cost effective) hypersonic craft; cables of sufficent strength for length; ways to grab asteroids to recharge the tether (assuming it's a skyhook and not a space elevator).

I'd bet hypersonic craft will come sooner than cables of the required tensile strength but we probably need a working space programme before the energy recharge is practical and in that case the requirement for the skyhook itself may be redundant.

So it's a neat idea for scifi novels (and I enjoyed the skyhook in Jack McDevitt's novel Deepsix though Hutch needs to stop getting herself into such trouble) but I think that conventional chemical rockets will win out, at least over the next five decades.

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