Space Elevators and Other Alternatives

[mistergrinch]

If you doubt the scientific plausibility of space colonies, please google Gerard O'Neill, a physicist I'm sure many of you know about. He and his students at MIT created detailed plans for orbiting colonies back in the 1970's that, as far as I know, are still sound. What exactly about space colonization do people find so fantastical?

I understand that it's very unlikely a natural catastrophe will wipe out humanity, but there are many other threats which are potentially worse -- Astronomer Royal Martin Rees only gives us a 50% chance of surviving this century! But my main point was that there can be much less chaos and danger and a higher quality of life in habitats designed from the ground up for humans (at least after a period of dangerous pioneering work, which is the risk I was talking about), but it takes some imagination to see that. If you want to call such things fantasy then we might as well not be discussing space elevators either.

I'm very surprised at the can't-doism and negativity I'm hearing on a forum of physicists. I'm trying to imagine what people of Feynman's generation would have said on these topics compared to you folks. Of course they were busy building rockets to the moon instead of chatting on internet forums, which might be a big part of our problem today. When I hear people talking like this I’m reminded of the scientists who confidently claimed in the late 19th century that heavier than air flight was impossible/impractical/contrary to God’s plan etc. and in the 1930's said similar things about space flight. This lack of hubris makes me very sad!

"There shall be wings! If the accomplishment be not for me, 'tis for some other." –Leonardo da Vinci

 

[JaredJames]

I understand that it's very unlikely a natural catastrophe will wipe out humanity, but there are many other threats which are potentially worse -- Astronomer Royal Martin Rees only gives us a 50% chance of surviving this century!

So? I give us a 100% chance of surviving this century. It doesn't mean anything. They are non-sense comments.

But my main point was that there can be much less chaos and danger and a higher quality of life in habitats designed from the ground up for humans (at least after a period of dangerous pioneering work, which is the risk I was talking about), but it takes some imagination to see that. If you want to call such things fantasy then we might as well not be discussing space elevators either.

Humans on habitat = humans on Earth. We would over consume and over populate just the same. The threat of disaster and disease is ever present. Again, why do you believe the humans up there would be different to those down here?

I'm very surprised at the can't-doism and negativity I'm hearing on a forum of physicists.

This stems from the fact it's a forum of physics, not a forum of fantasy. The physics don't allow us to do this - this is the key point you are failing to grasp. Our current technology means we either need the raw materials in situ or we need to carry them with us - even when in situ we'd still need enough with us until a processing system is up and running.

I'm trying to imagine what people of Feynman's generation would have said on these topics compared to you folks. Of course they were busy building rockets to the moon instead of chatting on internet forums, which might be a big part of our problem today.

Or, shall we stick with reality and realize that they had funding and were supported by the public? They were in the space race. First man in space, first man on the moon, big things. After those events, interest died and now people are more concerned with things that actually affect them.

When I hear people talking like this I’m reminded of the scientists who confidently claimed in the late 19th century that heavier than air flight was impossible/impractical/contrary to God’s plan etc. and in the 1930's said similar things about space flight. This lack of hubris makes me very sad!

Out of curiosity, I take it you are a Nuclear Engineer, Aerospace Engineer, Mechanical Engineer, Astrologist, Cosmologist, Physicist, Biologist, Chemist, or any space related field? As such, I take it you are speaking from vast experience and/or knowledge in said fields? And by extension not speaking from a purely fantastical point of view - which is all you have demonstrated so far.

 

[sophiecentaur]

The thing that gets me with the space elevator is the basic physics. How is angular momentum conserved? The glib response is usually that the Earth is slowed as the payload rises to conserve angular momentum. But this does not address the possibility of the orbiting station being slowed and essentially dragged back to earth, also conserving angular momentum. You'll need to keep sending fuel to keep the station moving to counter this, yes?

Which bit of Physics tells you this would happen? Of course the tether would be tilted back a fraction but what would make it fall down?

 

[bonker]

Which bit of Physics tells you this would happen? Of course the tether would be tilted back a fraction but what would make it fall down?

Conservation of momentum and Newtons third law require both the Earth to slow and the satellite to get pulled down out of orbit.

"Tilted back" as you put it actually means pulled back to earth. This is basic mechanics, angular momentum must be conserved.

 

[Nano-Passion]

I sense some sort of fallacy in the argument. It appears the argument just keeps going in circle. mistergrinch I know you feel very strongly but that feeling won't win you the argument. Put a little more scientific support, its really side-tracking. I don't want my topic closed.

With that said, I hope cheaper ways of getting into space comes into reality. I mean the 10,000-11,000 dollars per pound is just too much.

Space elevator seems flawed.. What are other future alternatives?

 

[sophiecentaur]

Conservation of momentum and Newtons third law require both the Earth to slow and the satellite to get pulled down out of orbit.

"Tilted back" as you put it actually means pulled back to earth. This is basic mechanics, angular momentum must be conserved.

Your "Basic Mechanics" needs to be applied correctly. The total angular momentum will, of course, be conserved and so the Day would be shorter by an amount you couldn't measure. Irellevant.
The tilting I refer to is just a smallish angle which will bring the tethered mass to a position at which the forces will be balanced.
I think you need to re-consider your position on this and bear in mind that the theory of the proposal has been gone over and verified by far smarter people than you (Niether of us can doubt this and no offense should be taken). If you start off by assuming that you have got something wrong in your reasoning and that you won't overturn the whole of Physics then you can get to understand why it Will work, rather than Won't work.

 

[Zentrails]

Which bit of Physics tells you this would happen? Of course the tether would be tilted back a fraction but what would make it fall down?

The fundamental problem of Space Elevator physics that I keep seeing is mixing up the physics of "really high towers" and the physics of geosynchronous orbiting objects. There's no question you can run a tether down from an object in geosynchronous orbit as long as you simultaneously move a counterweight in the other direction.

The real question is how close to the Earth can you get with that tether before the equilibrium becomes impossible to maintain.

 

[D H]

There's no question you can run a tether down from an object in geosynchronous orbit as long as you simultaneously move a counterweight in the other direction.

No question? The longest tether experiment to date was TSS-1R, which deployed a satellite at the end of tether. The tether was eventually reeled out to a length of 19.7 km. This was one of those NASA "successes" never to be repeated again because it was a success on paper only.

We haven't the foggiest idea how to safely reel out a 20 km-long cable, let alone scale up by 3+ orders of magnitude. There are huge questions as to whether "you can run a tether down from an object in geosynchronous orbit as long as you simultaneously move a counterweight in the other direction".

 

[sophiecentaur]

I don't think anyone is considering doing this in the next few weeks.

But, as a project, it has a lot more feasibility than many of the whacky schemes I have read about in some other places on the web! It certainly has some elegance.

 

[Zentrails]

No question? The longest tether experiment to date was TSS-1R, which deployed a satellite at the end of tether. The tether was eventually reeled out to a length of 19.7 km. This was one of those NASA "successes" never to be repeated again because it was a success on paper only.

We haven't the foggiest idea how to safely reel out a 20 km-long cable, let alone scale up by 3+ orders of magnitude. There are huge questions as to whether "you can run a tether down from an object in geosynchronous orbit as long as you simultaneously move a counterweight in the other direction".

I agree with you. I should have said that there is no question that the physics is sound as long as you can figure out a way to keep all sections of the tether at the correct tangential velocity, no easy feat.

Can you tell me if that tether was stationary with respect to it's center of mass or was it rotating? Rotation would be the result I would expect if you simply shot a tether towards the Earth and another one directly away from the Earth at the same time using something similar to the TOW antitank missile. I would expect the thing to start rotating, then eventually becoming a tangled mess unless you could keep it "taut" somehow.

I was in the US Navy and we used to routinely launch hundreds of expendable bathythermographs:

http://oceanworld.tamu.edu/resources/ocng_textbook/chapter06/chapter06_09.htm

with no failures that I can remember, so perhaps because of that, I probably incorrectly think a tether wouldn't be too hard to send out in space as long as you could "send" it out at a reasonably constant velocity and keep tension between the end going out and the reel somehow.

Maybe you could put a small ion engine on the projectile to give it a little boost to correct the tangential velocity as it is reeling out? I would think it would be a considerable engineering challenge, but the physics is pretty simple. Obviously as the tether gets longer, the difficulties increase, probably exponentially.

They were able to measure an induced current as well in that tether experiment didn't they? suggesting a possible future source of power for orbiting devices?

I, too, wonder why the tether experiments have not continued, it is fascinating to speculate about. Maybe that experiment was not very successful at all, like you said.

 

[Fun Value]

I do not understand how the conservation of momentum would allow the space elevator to work. But I would like to see the elevator happen. To me it seems the safest and least expensive of the alternatives - even if each elevator would need rockets to accelerate to sixteen or seventeen thousand miles per hour until it reaches the station.

 

[Fun Value]

To actually return to the topic at hand, I believe there are a few problems that need to be resolved before a space elevator can come to be. The space elevator is dependent on a very long cable, one side connected to Earth and one side connected to a station in orbit. This tether would have to be 24,000 miles long. Should it ever snap, a cable that long could do some serious damage on Earth. Radiation exposure for travelers passing through the Van Allen radiation belt is another concern. Also, space debris and micrometeors could damage the tether. Orbital objects that are not in sync and below the maximum altitude of the cable would eventually collide with it. And finally, the materials desired for the tether have not been discovered yet.

I think the tether would have to be attached to a heafty space station 62000 miles out well beyond geosynchronous orbit. I think it should be strong enough so that each elevator could carry fuel to accelerate it (if necessary to compensate for the angular momentum problem) from about 1000 miles per hour at the surface to about 16000 miles/hour by the time it gets to the space station - about a four day journey.

I also think there are a lot of smart people in the world to make this possible.
I think the world community (this time) needs as many ways to access space as we can think of. There are a lot of threats out there as well as opportunities.

It seems like there has been a lot of babeling over the love of money for this and that. Yet ever since the space race it seems like there has been a big decline in the great inventions, replaced by a lot of the cheap inventions for the quick, easy money.

(I was just trying to think of an example when just now my son's friend called and asked him to come skate-boarding. It seemed like an act of God, so I'll use it in place of examples I thought would be better. Skate-boarding seems insane. These kids think they are doing tricks that are impossible. They get broken arms, legs and one of my son's friends got hit and killed by a car. I think they spend more hours than it takes to get a phd in physics.)

I would not be surprised if our pursuit of space would again bring together the great minds resulting not only in success with the elevator, but in solutions in everything from the kitchen to healthcare. I would not be surprised if the space elevator could be the motivation to bring us out of this recession.