I have encountered the term in another context.

> A "skyhook" is an imaginary device for hanging an object from the sky. The word originated in a sarcastic remark by a frustrated pilot of a reconnaissance plane in the First World War, when told to stay in the same place for an hour: "This machine is not fitted with skyhooks," he replied.

From, "The Evolution of Everything: How New Ideas Emerge" by Matt Ridley

I doubt this would be anywhere near strong enough for a space elevator. And i think a sky hook is something else

There are a lot of science fiction uses of "skyhook" this is one is them.

A skyhook is generally a space elevator that doesn't go all the way to the ground, and so doesn't have to be quite as precise about orbital velocity and the like.

I thought a skyhook was one of those things you send the apprentice kid to the stores for, like tartan pain, spirit level bubbles, long stands and a weight with no point? Maybe even a left handed screwdriver...

At scout camp we'd send the new kids down to the waterfront for 50 feet of shoreline.

Pretty sure it's the thing in batman that allows troops to reverse skydive.

You mean that thing by the CIA which was successfully tested in 1958, and later was a plot device in a Batman movie: https://en.wikipedia.org/wiki/Fulton_surface-to-air_recovery...

Also on display much earlier in Thunderball and The Green Berets.

Wifi cable

Main problem is more that there is no advantage to a skyhook if you're just putting things into orbit. Every kilo you lift with a skyhook pulls it down and it has to be used to de-orbit that mass, or lifted up by rockets or thrusters etc. Unlike an actual space elevator, or orbital ring, or launch loop, it doesn't hold itself at altitude.

Also, there's really no need for the tether to be conducting. For one, you could just use carbon fiber, or have a single conductor mixed in with tensile fibers, or just use a solar panel, or just spin the whole thing (which gives you the real advantage of bringing you up to orbital velocity)

I was being very simple. I used skyhook as informal and humorous and did not know that it had a technical meaning in this context. I was thinking more of what is commonly called a space elevator but did not look up the details, e.g., synchronous orbit or some such.

Really I was just commenting on the spider silk with carbon fibers that might add some of the needed strength and also permit sending power to whatever was crawling up the string of the elevator.

Again, I was just commenting on the OP and the fiber and not trying to get into space elevators in detail.

Oh, I figured you meant it. In that case carbon fiber is stronger, more conductive, and cheaper. Why bring up space elevators if you have no interest in saying or learning something about them?

> Why bring up space elevators if you have no interest in saying or learning something about them?

Because when I looked into space elevators, the main problem was getting the cable strong enough for its weight. So, with spider silk, already amazingly strong, with carbon, a first guess, or hope, for an application would be for a space elevator.

So, in response to the OP, I mentioned the cable, string, whatever, for skyhooks, space elevators, or whatever.

Again, my understanding is that space elevators are well enough understood and the main issue is just the cable. So, given the OP, I mentioned the cable, mostly just the cable, without digging into the well understood details of space elevators. I wasn't trying to discuss space elevators in general, just the cable and just in response to the OP.

If there was a big counterweight out at the far end of the cable, and it was sufficiently long enough, wouldn't the centrifugal force acting on the weight counteract the kilos lifted?

No, that doesn't work for anything less than a space elevator or the other devices I mentioned. A space elevator is tied down to the earth, and constantly trying to fly off into space. A skyhook is basically nothing more than a LEO satellite with a very, very long rope hanging off it. If you pull on the rope, you pull the satellite down since there is no centrifugal force besides the inertia keeping it in orbit.

If you make a very heavy counterweight, it just delays the inevitable pulling down, and its that much harder to get into orbit. There's no point.

While the energy imparted to the object being leunched is the same, you would be able to use high-ISP thrusters like ion engines to boost the counterweight back up. They can't be used lower down though, due to not having enough thrust for use in the atmosphere. This would have the advantage of raising the average ISP during the launch, thus having to use less propellant overall.

It might even be possible to use tether-based propulsion for the counterweight, which wouldn't need any propellant at all but push against the Earths' magnetic field.

Landing on the moon also pulls it down, also landing on existing satellites. There is no special nature of ropes that "pulls down". Secondly there's no reason why we couldn't take a space object and use it as the very heavy counterweight.

What if a plane gets tangled up in it?

Proposals were made around 1000 km altitude at the lower tip. Boeing proposed a 600km tether with a transfer altitude of 100km (at mach 10), and later increased that to 150 km. The Lockheed U-2 is one of the highest flying airplanes ever, our main cold war spy plane. It flew twice as high as a passenger jet, and cruised at 70,000 feet, just over 21 km.

Planes would not get tangled in it.

Thanks. The GP's comment "attach the string at, maybe, the equator of earth" is what confused me, thinking the string is attached to the earth, with the weight in orbit.