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Space Elevators Are Possible

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Re: Space Elevators Are Possible

#31

Post by grecy »

avmich wrote: post #19

The main problem with the elevator, in my opinion, for many years already is not in the strength of the material. After all, nanotubes are known for many years, and their properties are sufficient for the tether, so in principle it can be done. No, the main problem is with satellites. In fact, asking many times - what to do with existing or future satellites - I never heard a workable answer, even in principle. Just…

Would a satellite/tether collision damage the tether, or just destroy the satellite?

If it just destroys the satellite, I'm kind of tempted to say "who cares", because by then we will have other solutions, or satellites out past the counterweight, or we can easily launch more now that we have the fancy elevator, or whatever... but then we'd have the problem of an unimaginable amount of space junk orbiting the earth.

Re: Space Elevators Are Possible

#32

Post by bduerst »

bsamuels wrote: post #26
bduerst wrote: post #21

Earlier quoted context omitted.

The benefit with space elevators is that you can use mechanical energy to move payloads up the gravity well, as opposed to the chemical energy we use now. What do you think of rail guns, which use electrical energy?

You would never make it through the atmosphere. At the speeds required to achieve orbit from a surface launch, the projectile leaving the apparatus and hitting the atmosphere would be like smashing it into an ocean of water. Even on a very tall mountain the air density is still enough to stop any projectile-based solution in its tracks.

If launching from vacuum directly into atmosphere, sure.

I think that it poses an interesting engineering problem, not unlike the space elevator. If given enough velocity, a projectile with retractable wings could be launched into an atmospheric gradient and generate lift after leaving the accelerator.

Whether or not we have materials used on the craft could survive the acceleration to escape velocity is the big question. It would take some serious testing.

Re: Space Elevators Are Possible

#33

Post by eru »

briandw wrote: post #17
lutorm wrote: post #14

Earlier quoted context omitted.

That just means you get to the high-radiation regions faster...

No, you will spend more time in the http://en.wikipedia.org/wiki/Van_Allen_radiation_belt with a space elevator.

There's an interesting proposal for reming that radiation belt (https://en.wikipedia.org/wiki/Van_Allen_radiation_belt#Propo...).

But shielding seems to be doable with pretty thin layers of metal.

Re: Space Elevators Are Possible

#34

Post by andrewflnr »

lutorm wrote: post #12
mehwoot wrote: post #8

What happens if something hits the cable and it breaks? Does the whole thing drift off into space?

I didn't see it mentioned in this article, but the cable is actually very small. I read this older NASA study that said that for a carbon nanotube tether, an optimal cable would be a thin tape something like an inch across. That has pretty small cross section for being hit by a meteoroid.

On the other hand, a satellite a couple meters across has plenty of cross section with which to find the cable. Even if we take all those down (not in our lifetime), there is a lot of little stuff in orbit, and it would only take one.

Re: Space Elevators Are Possible

#35

Post by User8712 »

avmich wrote: post #19

The main problem with the elevator, in my opinion, for many years already is not in the strength of the material. After all, nanotubes are known for many years, and their properties are sufficient for the tether, so in principle it can be done. No, the main problem is with satellites. In fact, asking many times - what to do with existing or future satellites - I never heard a workable answer, even in principle. Just…

1. How fast can a satellite travel up the tether? Let's say 50km/h, and it's going to an altitude of 35,000km. That's a month just in travel time. Using the tether for that period of time would be extremely costly. Currently, around 125 satellites launch a year, so they would need to be going up the tether at 500km/h, one after the other, day and night. And if we need to wait for a platform to descend, they need to be moving at 1,000km/h. Otherwise, we need multiple space elevators, or multiple shipments climbing at once and passing one another to meet current demand.

2. What's the cost of building and maintaining a space elevator?

3. What's the cost of having a satellite climb the tether to an altitude of 35,000km? That's a lot of energy.

Taking this into consideration, is it tantalizingly cheap compared to strapping on a rocket? SpaceX has run tests with a reusable Falcon 9 rocket. Cost of fuel for a launch is $200,000. I'm skeptical the space elevator would be much cheaper.

The magic of SpaceX...

http://www.youtube.com/watch?v=9ZDkItO-0a4

Downside of a rocket, it's heavy, and most of the energy is wasted lifting the rocket, and not the payload. Advantage, you don't have to pay to maintain cables that are long enough to wrap around the entire Earth.

Re: Space Elevators Are Possible

#36

Post by shaneofalltrad »

ChuckMcM wrote: post #20
avmich wrote: post #19

The main problem with the elevator, in my opinion, for many years already is not in the strength of the material. After all, nanotubes are known for many years, and their properties are sufficient for the tether, so in principle it can be done. No, the main problem is with satellites. In fact, asking many times - what to do with existing or future satellites - I never heard a workable answer, even in principle. Just…

I was going to bring this concern as well. I expect that in theory we could build a space elevator but I doubt we could keep it in space. Between space junk, meteorites, and regular gear flying around like GPS nodes, items in a non-orbit (which they would be in this configuration) will be hit with more than enough energy to destroy even the strongest materials we have out there.

I would also want to know the impact of a counter weight attached to the earth and it's effect on our ability to orbit naturally while it's drag is attached to even water. Could an impact on this force it into a spin around Earth creating Centrifugal force or something not studied before?

Re: Space Elevators Are Possible

#38

Post by percentcer »

User8712 wrote: post #35
avmich wrote: post #19

The main problem with the elevator, in my opinion, for many years already is not in the strength of the material. After all, nanotubes are known for many years, and their properties are sufficient for the tether, so in principle it can be done. No, the main problem is with satellites. In fact, asking many times - what to do with existing or future satellites - I never heard a workable answer, even in principle. Just…

1. How fast can a satellite travel up the tether? Let's say 50km/h, and it's going to an altitude of 35,000km. That's a month just in travel time. Using the tether for that period of time would be extremely costly. Currently, around 125 satellites launch a year, so they would need to be going up the tether at 500km/h, one after the other, day and night. And if we need to wait for a platform to descend, they need to b…

Couldn't you launch multiple satellites at a time?

Re: Space Elevators Are Possible

#39

Post by spiritplumber »

beloch wrote: post #30
bsamuels wrote: post #26

Earlier quoted context omitted.

You would never make it through the atmosphere. At the speeds required to achieve orbit from a surface launch, the projectile leaving the apparatus and hitting the atmosphere would be like smashing it into an ocean of water. Even on a very tall mountain the air density is still enough to stop any projectile-based solution in its tracks.

http://en.wikipedia.org/wiki/Project_Babylon Iraq (with a Canadian scientist) almost made an artillery piece capable of putting material into orbit. Obviously, international sanctions gummed up the project a tad and it was basically over when the scientist was assassinated. Still, it was within the realm of possibility. Only recently have rail-guns started to usurp chemically propelled artillery in some roles, so it'…

Into space, or into orbit? The two are vastly different in terms of energy required.

Re: Space Elevators Are Possible

#40

Post by jccooper »

shaneofalltrad wrote: post #36
ChuckMcM wrote: post #20

Earlier quoted context omitted.

I was going to bring this concern as well. I expect that in theory we could build a space elevator but I doubt we could keep it in space. Between space junk, meteorites, and regular gear flying around like GPS nodes, items in a non-orbit (which they would be in this configuration) will be hit with more than enough energy to destroy even the strongest materials we have out there.

I would also want to know the impact of a counter weight attached to the earth and it's effect on our ability to orbit naturally while it's drag is attached to even water. Could an impact on this force it into a spin around Earth creating Centrifugal force or something not studied before?

If I understand you correctly: the Earth is way way way way way way way way to big for something like an orbital tether too have any real effect on its movement. Besides the fact that due to the counterweight there's minimal tension on the ground.

I almost wrote "nothing man made", which is true for anything we can do now. But if you think scifi enough there's little that can't be done. Turning the Earth inside out is quite possible for certain levels of civilization.

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