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Aquilla
I came across this article, and since I spent quite a few years studying orbital physics, I have to think on this a bit. There are some basic physics here that bother me about the feasibility of doing something like this, but still, it is fun to think about I think.

Basically, this guy is talking about building a "space elevator" using some sort of nano-technology carbon fibers as a "cable". I don't know about that technology, I'm not a materials person, but like I said the physics do bother me a bit. From the article.....

QUOTE
WASHINGTON - President Bush (news - web sites) wants to return to the moon and put a man on Mars. But scientist Bradley C. Edwards has an idea that's really out of this world: an elevator that climbs 62,000 miles into space.


Edwards thinks an initial version could be operating in 15 years, a year earlier than Bush's 2020 timetable for a return to the moon. He pegs the cost at $10 billion, a pittance compared with other space endeavors.


"It's not new physics — nothing new has to be discovered, nothing new has to be invented from scratch," he says. "If there are delays in budget or delays in whatever, it could stretch, but 15 years is a realistic estimate for when we could have one up."


Edwards is not just some guy with an idea. He's head of the space elevator project at the Institute for Scientific Research in Fairmont, W.Va. NASA (news - web sites) already has given it more than $500,000 to study the idea, and Congress has earmarked $2.5 million more.




Ok, question for debate....

Is this a possibility or just another crackpot idea?
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Cube Jockey
Is this a possibility or just another crackpot idea?

I think the physics would be complicated, but not impossible. Based on my (very) limited understanding of physics (and I'm fully willing to admit I'm no where close to an expert), the biggest challenge here would be keeping some kind of object with decent mass in a steady orbit around earth (such as an asteroid) to anchor the elevator cable. The orbit would not only have to be steady, but at exactly the same speed as the rotation of the earth.

We would also probably have to develop computer software which could automatically make small adjustments on the fly if the orbit or velocity started to change.

It seems like a possibility that is much more real now than it ever was when science-fiction writers first considered the idea.

I would wager that 2019 is a bit ambitious for completing the project though.
Azure-Citizen
Is this a possibility or just another crackpot idea?

I haven't spent any time studying physics beyond your usual generic college courses and certainly have no real expertise to shed on the subject. However, I can't help but to interpret the question in the aspect of time. It seems to me that the technology and ability to do this is probably inevitable. Has any practical testing been done with the "nanotube" bundles of carbon atoms that Edwards is talking about? They claim that a cable three feet wide would support a payload of 13 tons.
Cube Jockey
QUOTE(Azure-Citizen @ Jun 25 2004, 03:13 PM)
Has any practical testing been done with the "nanotube" bundles of carbon atoms that Edwards is talking about?  They claim that a cable three feet wide would support a payload of 13 tons.

I'm not sure about the specific materials they are talking about here, the article is pretty general and I haven't been able to turn up anything via google yet.

However, in theory this is possible. Your standard garden variety elevator can hold between 1 and 2 tons and is generally running along a steel cable only a few inches thick.

If the cable were strong enough and steady enough, 13 tons could be lifted fairly easily.
Aquilla
hmmm.gif I am running a real risk here of sounding like some sort of a snotty academic on this I'm afraid, but I don't think it would be useful to get into the post-graduate level of astro-physics and orbital mechanics in this forum, so I'll attempt to reduce the problem to reasonable levels. Please don't hold that against me.

WE are all familar with spining an object at the end of a string and feeling the force it has against us. We are told in basic physics that this force is called "certrifugal force" and that it is outward, and that seems reasonable because that's what we feel. So, when we hear about an object in orbit, we understand that it stays there because it's "centrifugal force" equals gravity, that makes sense, right? That's fine for most concepts, but the reality is that it's really called "centripedal force" and in the world of orbital mechanics it's an entirely different thing. The force you feel on the string when you spin the object is not the object trying to fly straight out from you, but rather the object trying to fly in a straight line and you keep making it turn in a circle. Think of throwing a baseball and neglecting the drag or air friction, it goes up and eventually comes down because of gravity. The faster you throw it, the further it goes before it hits the ground. Now, imagine if you could throw it fast enough that the curvature of the earth made the ground "drop away" as fast as gravity made the ball fall towards it. That in a nutshell is what we call an orbit. A continuous falling towards the earth with the earth continuously falling away. The forces exactly match and if you happen to be in that object, you have no forces acting on you so you are weightless. Now, if you introduce any other external force into the mix, like an elevator car coming up the cable, there is suddenly an inbalance in the forces and something's got to give. You need to either provide additional energy to balance the force, or you fall down. That's the problem I have on the surface with this idea.

I wonder if I could get $2.5 mill to see if it will work...... hmmm.gif
Christopher
I cannot speak as to the physics involved with the elevator but the idea seems to be pretty sound from what I have read. The biggest drawback has been the materials needed.
That's why nanotubes are so very important. Imagine something much stronger than steel but flexible and as light as aluminum to steel. Something that can actually be "grown" into the desired shape.
As for the three feet wide cable, with nanotubes it would be very realistic.
But we aint there yet.
The Japanese as usual are way ahead on this--much like with artificial diamond instead of silicone for chips--and the progrees IS nearing a point for some commercial opportunities in the next 15 years--say goodbye to the steel industry folks, nanotubes will be much cheaper to produce and able to be custom formed on top of it.
The problem with the elevator idea is in my opinion best summed up by the scene in Armageddon where the NASA geek tries to offer Solar Sails as an option to get to the Comet.
Thanks to folks Like Rutan we can begin to see some realistic options for getting into space. Using technolgy that is almost off the shelf really.
We need to get it away from the NASA geeks and into private business.
Damn someone lend me 50 Million. I'll have people on the moon, the Hubble in perfect working order and a ROI that'll cause involuntary ejaculation.
logophage
QUOTE(Aquilla @ Jun 25 2004, 03:35 PM)
That in a nutshell is what we call an orbit.  A continuous falling towards the earth with the earth continuously falling away.  The forces exactly match and if you happen to be in that object, you have no forces acting on you so you are weightless.  Now, if you introduce any other external force into the mix, like an elevator car coming up the cable, there is suddenly an inbalance in the forces and something's got to give.  You need to either provide additional energy to balance the force, or you fall down.  That's the problem I have on the surface with this idea.

Aquilla, you're correct in your skepticism but I do believe this is solved in one of three ways:

1. have mass at the end of the tether which can be moved up or down as a counter balance;
2. have a descending elevator of corresponding mass match the ascending elevator;
3. place the tether at significant enough tension with mass at the end to have the rising mass of the elevator be insignificant.
Aquilla
QUOTE(logophage @ Jun 25 2004, 03:59 PM)
QUOTE(Aquilla @ Jun 25 2004, 03:35 PM)
That in a nutshell is what we call an orbit.  A continuous falling towards the earth with the earth continuously falling away.  The forces exactly match and if you happen to be in that object, you have no forces acting on you so you are weightless.  Now, if you introduce any other external force into the mix, like an elevator car coming up the cable, there is suddenly an inbalance in the forces and something's got to give.  You need to either provide additional energy to balance the force, or you fall down.  That's the problem I have on the surface with this idea.

Aquilla, you're correct in your skepticism but I do believe this is solved in one of three ways:

1. have mass at the end of the tether which can be moved up or down as a counter balance;
2. have a descending elevator of corresponding mass match the ascending elevator;
3. place the tether at significant enough tension with mass at the end to have the rising mass of the elevator be insignificant.

hmmm.gif Dang..... hmmm.gif Good point, Logophage, that might take care of the potential energy portion of the problem, but I'm somewhat concerned about the kinetic energy side of the equation. I'd have to sit down and calculate how fast something would have to move in geostationary orbit at 62,000 miles, the normal spot for that is around 23,000 miles. Quick calculation here for an orbital period of 24 hours at a height of 62,000 miles is around 17,000 miles/hour (and I'm not sure that's even possible to do). Ok, so discounting some other things I need to consider at a later time this evening over a single malt scotch, somehow we must find a way to accelerate this "elevator" from stop to 17,000 miles per hour without disrupting the orbit of the counter-weight holding the entire thing up.

I dunno...... unsure.gif
logophage
QUOTE(Aquilla @ Jun 25 2004, 04:48 PM)
QUOTE(logophage @ Jun 25 2004, 03:59 PM)
QUOTE(Aquilla @ Jun 25 2004, 03:35 PM)
That in a nutshell is what we call an orbit.  A continuous falling towards the earth with the earth continuously falling away.  The forces exactly match and if you happen to be in that object, you have no forces acting on you so you are weightless.  Now, if you introduce any other external force into the mix, like an elevator car coming up the cable, there is suddenly an inbalance in the forces and something's got to give.  You need to either provide additional energy to balance the force, or you fall down.  That's the problem I have on the surface with this idea.

Aquilla, you're correct in your skepticism but I do believe this is solved in one of three ways:

1. have mass at the end of the tether which can be moved up or down as a counter balance;
2. have a descending elevator of corresponding mass match the ascending elevator;
3. place the tether at significant enough tension with mass at the end to have the rising mass of the elevator be insignificant.

hmmm.gif Dang..... hmmm.gif Good point, Logophage, that might take care of the potential energy portion of the problem, but I'm somewhat concerned about the kinetic energy side of the equation. I'd have to sit down and calculate how fast something would have to move in geostationary orbit at 62,000 miles, the normal spot for that is around 23,000 miles. Quick calculation here for an orbital period of 24 hours at a height of 62,000 miles is around 17,000 miles/hour (and I'm not sure that's even possible to do). Ok, so discounting some other things I need to consider at a later time this evening over a single malt scotch, somehow we must find a way to accelerate this "elevator" from stop to 17,000 miles per hour without disrupting the orbit of the counter-weight holding the entire thing up.

I've read about different variants to the synchronous orbit problem. The Arthur C. Clark style space elevator has a 52,000 mile tether so that the mass of the tether itself is exactly counter-balanced. However, most newer space elevator designs I've run across have the tether being just over 26,000 miles with large masses at the end to counter-balance.

Your point about the kinetic energy issue is well-taken, however I believe this is also solved by the fact the kinetic energy of the entire tether/elevator system increases as the elevator rises. Let's say you had a rope with a ball threaded through it. Now you could use the rotational velocity of the rope to give kinetic energy to the ball thereby slowing the whole rotation down. However, the other solution is to add energy to the ball externally. Let's say you use an air hose to blow it towards the end of the rope. In this case, the rope would retain a continuous rotational rate but the ball would move up the rope.

This is in effect what would happen with the space elevator. From what I've read, a maser would be used to beam energy to the elevator as it rises along the tether. The energy would power a magnetic linear drive (basically an unrolled motor) mounted on the tether itself.
overlandsailor
OK, I am no scientist and I have no idea how to figure out how this could be made to work through the various physics problems.

My problem with it is security.

The moment you create something like this that is always there, is the same moment you create a new icon to Western ingenuity and thus a new target for all the radicals and fundamentalists that hate the west.

How long before something was flown into the cable?

Also, what about all of the objects that in would risk intersecting with. Planes, satellites, meteors, space junk, etc. Being stationary, without much maneuverability would make it difficult to avoid all of these things would it not?

What is the benefit of this project over a space station that would warrant these risks? At least a space station would be alot harder for an extremist to attack, they would first have to find a way into orbit.

I'm not saying it couldn't work, just wondering how to avoid these problems.
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logophage
QUOTE(overlandsailor @ Jun 25 2004, 06:09 PM)
OK, I am no scientist and I have no idea how to figure out how this could be made to work through the various physics problems.

My problem with it is security.

The moment you create something like this that is always there, is the same moment you create a new icon to Western ingenuity and thus a new target for all the radicals and fundamentalists that hate the west.

How long before something was flown into the cable?

Also, what about all of the objects that in would risk intersecting with.  Planes, satellites, meteors, space junk, etc.  Being stationary, without much maneuverability would make it difficult to avoid all of these things would it not?

What is the benefit of this project over a space station that would warrant these risks?  At least a space station would be alot harder for an extremist to attack, they would first have to find a way into orbit.

I'm not saying it couldn't work, just wondering how to avoid these problems.

Couple of things about security:

1. The plan is to place it in the south pacific where there is very little weather or air traffic. The location is very remote. The likelihood of accidental severing is much lower. How low is a good question.

2. The tether itself will be relatively thin: 1-2 meters wide and millimeters thick. Thus, it is very hard to actually fly something into it. This is not say that someone couldn't do it. Also, even if someone did fly something into it, it is not clear that the tether would actual sever. Neverthess, this is a real security issue which would have to be worked out.

3. As for space junk & satellites, the plan is have the end of the tether in orbit to be somewhat mobile. You can induce a vibration on the tether somewhat like a jump-rope to avoid large obstacles. Small obstacles may still impact. However, since it is a ribbon-style cable, the actual structure would not be irreversibly damaged. It is possible to "patch the hole" as it were.

Now for cost:

Ballistic launches into orbit are very expensive and somewhat risky. Afterall, you're trying to overcome the effect of gravity all in one go. The space elevator would move slowly, that is, it would take days to get into geosynchronous orbit. This is a much less expensive as the specific impulse requirements are much, much lower.

Morever, the bulk of the cost of the space elevator is in the construction of it. Yes, there will be maintenance costs but not in the same ballpark as construction. So, it is reasonable to assume that there is a viable future-value proposition.

Finally, the space station is not a platform for getting to orbit. It is merely a structure that's already in orbit. You still need someway of getting to orbit. Also, because of the Russian lauch requirements, the space station is not in a very good orbit (that is, it isn't equatorial). Because of the shuttle launch requirements, the space station has a pretty low altitude as well. Both of these factors make the space station a poor platform for extra-orbital lauches.
Cube Jockey
Looks like the idea is gaining some support, apparently there have been conferences of scientists held to study this for the past three years. space.com has a decent article covering that.

QUOTE
At the third annual international conference on the space elevator being held in Washington, D.C., scientists and engineers are tackling hurdles that must be overcome for the concept to, quite literally, get off the ground.

<snip>

Edwards is quick to run down what’s up on the space elevator challenges, from carbon nanotube technology, power beaming, climber hardware to space debris impacts on the ribbon, health and safety issues, as well as cost, politics and regulations.


They also have some cool conceptual images linked from the article.

Unfortunately this article doesn't provide much in the way of technical details (even put in a layperson manner), but it does show people are serious about the idea. I for one would be more interested in what aquilla and logophage have to say about it smile.gif
Aquilla
QUOTE(Cube Jockey @ Jul 1 2004, 12:43 PM)

Unfortunately this article doesn't provide much in the way of technical details (even put in a layperson manner), but it does show people are serious about the idea.  I for one would be more interested in what aquilla and logophage have to say about it smile.gif

I'm still thinking about the orbit mechanics problem on this one and it's going on 30 years since I did any really serious work with stuff like that. Apparently the concept is to put an object into a high orbit with an excess energy (or speed if you will) and then constraint it to that orbit with a tether which in a sense adds additional "gravitational" force. Not sure if that will really work or not.... hmmm.gif

Another thing that dawns on me though is that even if it were to work, I don't think the object or things in it would be at "zero g" anymore (ie. weightless) because their would be a net force opposing the tether force. I think... unsure.gif

Seems to me that apart from the terrific view the mainly cool thing about being in orbit is being weightless. Have to think on this one a bit more.
Government Mule
QUOTE(Azure-Citizen @ Jun 25 2004, 03:13 PM)
They claim that a cable three feet wide would support a payload of 13 tons.

There is a company in Seattle that HAS developed a cable for NASA that will act likle a sling shot in space. The cord is less than an inch thick and strong enough to "capture" a launched satelite, and "hurl" it into deep space. The idea is pretty simple.

The CORD rotates in orbit above the earth similar to a 2 winged windmill. The Satelite is sent into space, headed towards the spinning cord. The cord "catches" the satelite with one end of the cord, and "slings" the satelite into deep space at speeds closer to the speed of light then we have ever sent anything.

Another one of their projects involves a electro-magnetic "sail". The satelite would be sent into space, where it would extend a 10km wide electro-magnetic field out in front of it, and the solar wind would constantly increase it's speed as it travels into deep space. Anyone that knows about physics will know that in the abscence of friction, constant acceleration, however small, would result in speeds that approach light speed.

It is a pretty neat little company, and if they were not a client of mine, I would give you their name.

What was the question? NanoTubes? I do work with some nanotube companies, and I'll be honest, I have trouble comprhending the whole idea, but there are many comapanies involved with them, and they promise to be the next "Industrial" movement.
logophage
QUOTE(Aquilla @ Jul 1 2004, 01:21 PM)
QUOTE(Cube Jockey @ Jul 1 2004, 12:43 PM)
Unfortunately this article doesn't provide much in the way of technical details (even put in a layperson manner), but it does show people are serious about the idea.  I for one would be more interested in what aquilla and logophage have to say about it smile.gif

I'm still thinking about the orbit mechanics problem on this one and it's going on 30 years since I did any really serious work with stuff like that. Apparently the concept is to put an object into a high orbit with an excess energy (or speed if you will) and then constraint it to that orbit with a tether which in a sense adds additional "gravitational" force. Not sure if that will really work or not.... hmmm.gif

It doesn't really create additional "gravitational" force. The only part of the space elevator which will be at the "correct" orbital velocity is the part at geosynchronous velocity. Anything which is lower in altitude will be moving too slow and anything which is higher in altitude will be moving too fast with regard to a stable orbit. This is okay because the entire length of the cable is a counter-balance. That is, all things equalize: the "too fast" part of the cable will compensate for the "too slow" part.

There will be atmospheric drag. However this is easily compensated for by adding more energy to the system. The elevators themselves require energy to be introduced to raise themselves. Additionally, energy can be regained when the elevators are lowered.

QUOTE
Another thing that dawns on me though is that even if it were to work, I don't think the object or things in it would be at "zero g" anymore (ie. weightless) because their would be a net force opposing the tether force.   I think... unsure.gif 

Seems to me that apart from the terrific view the mainly cool thing about being in orbit is being weightless.  Have to think on this one a bit more.

As the elevator rises you will feel more and more weightless. This is not because you are further away from the Earth (well, it's negligible); it is because you are increasing your tangential velocity. At the point you reach the geosynchronous point of the cable is when you will be completely weightless. If you were to pass the the geosynchronous point, you would gain "negative" Gs. In other words, you'd be spinning so that you're standing on the "ceiling" of the elevator.

As for the issues involved with the space elevator itself. I see a number of obstacles to overcome:

1. mass fabrication of sufficiently long nanotubes
2. process of weaving/gluing nanotubes together
3. controlling "dynamo" effects of having a long string moving through the Earth's magnetic field.

And for human transport....shielding against radiation while moving through the Van Allen belt (particularly lower belt).

I have a lot more hope with the dirigible scheme being worked on by JP Aerospace. There seem to be no technological hurdles for this one.
crashfourit
QUOTE(logophage)
3. controlling "dynamo" effects of having a long string moving through the Earth's magnetic field.

We could syphon the energy left by the earth's magnetic field on the carbon cord to suppliment the power to the elevator when it is going up and use that energy to help supply the 'base' that the carbon cable is conected to.
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