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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

by hwillis 10y ago

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)

Fjolsvith 10y ago
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?
- hwillis 10y ago
  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.
  - WJW 10y ago
    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.
  - vorotato 10y ago
    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.
graycat 10y ago
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.
- hwillis 10y ago
  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?
  - graycat 10y ago
    > 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.

by hwillis 10y ago

Fjolsvith 10y ago

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?

hwillis 10y ago
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.
- WJW 10y ago
  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.
- vorotato 10y ago
  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.

graycat 10y ago

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.

hwillis 10y ago
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?
- graycat 10y ago
  > 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.