Posted on 09/28/2005 1:16:19 PM PDT by saganite
Capture an asteroid for the counterweight? As to RightWhale's comment about the tensile strength needed for the cable/ribbon, if everthing is balanced does it matter?
Oh brother - what next?
"NASA proposes a Space Shuttle: It will take off and land like a plane, it will be cheap, it will be reusable, ...."
It will end up...
Taking the groceries up
and
Bring the trash back
Yawn
The only way to travel in deep space is to 'place' yourself at your destination... there won't be any rocket... or propulsion-type vehicle involved. In essence... you will project a 'traveling-labratory' to pre-calculated coordinates.
IMO... that's exactly what UFO's do.
Here's a related story about testing of some of the required technology.
The tensile strength of the cable has been one of the big show stoppers to the concept. Carbon nanotubes might be strong enough but until very recently they couldn't be mass produced.
The other one is a significant electrostatic discharge that would follow a path from the ionosphere to ground.
Probably. There have been a lot of elevator threads in the past few years. When it comes to nanotech I can't tell the difference between that and nanotubes, but I suppose they are completely different. Nanotubes could give us outer space; nanotech could give us grey goo.
No, not to the moon. Think Geostationary orbit. Although it's not quite that simple. Like communications satellite the upper anchor of the elevator would remain fixed over a given point on the equator.
As the article indicates, this notion has been around a long time, and is well studied. The only real problem is getting a material strong enough.
Think of the cable as the spine of the system. It stays stationary. The cars crawl up and down structures fixed to it, or are raised and lowered on their own much lighter cables, much like a regular elevator. A counterweight is probably mandatory, for dynamic as well as energy consideration, but it can be a returning car rather than a dead weight.
An asteroid, or material from the moon have both been proposed. But not for a counterweight in the sense of something that goes up and down. It would be the space side anchor for what amounts to a vertical suspension bridge. It's not the cable pulling the cars that is a problem, you'd probably not have one of those, anymore than a suspension bridge pulls the cars across the bridge on a cable. It's the suspension cable that holds up the structure that supports the cars that needs to be really strong.
Hanging inverted from the roofs of caves, I presume -- and voting DemocRAT.
Centrifugal force doesn't exist, it's only an apparent force. What you have in orbit, geosynchronous or not, is an acceleration due the gravitational force, which only serves to change the direction, but not the magnitude of the velocity vector of the orbiting body. When you twirl an object on a string around, the force of the string pulling on the object provides the same sort of acceleration, perpendicular to the velocity, which accelerates the object toward the direction of the string. But because the acceleration is normal to the velocity, it only changes the direction and not the size or magnitude of the velocity vector. Thus the object continuously changes direction, but not speed. The same happens with a body in a circular orbit. Elliptical orbits are more complicated, in that the force doesn't always act perpendicular to the velocity vector, so the object speeds up and slows down, although the sum of it's potential (due to it's altitude) and kinetic (due to it's speed) energy remains constant.
When 20,000 pounds goes up, 20,000 pounds must come down. If frictional losses are considered, even more must come down than goes up. Good idea? I am having trouble managing a clear idea of how the counterweights will work. It's very complicated, especially making adjustment for the change of weight as the distance from ground changes. Stages? One stage a mile?
If that hotel in on the space end of such a elevator, then you go flying off to a higher orbit, because the thing isnt' really in a geostationary orbit at 22,000 miles, because the stress in the cable is providing an additional force on the "hotel", and so it will orbit be orbiting faster than a regular circular orbit would at that altitude.
One way to envision the situation would be to imagine an object connected by two cords to fishing reels, each with a different drag setting. If one cord broke (the other representing the gravity force, which doesn't "break") the other cord would be pulled out until the force on it was the amount of the drag setting. Even though centrifugal force doesn't really exist, the situation can be most easily explained by invoking it. A longer string, that is a higher orbit, means a lower centrifugal force for the same speed. F = m (V^2/R). where V = speed, m = mass, R = lenth of the string or orbital height.
No, Helotes, your knowledge of physics is about 500 years out of date. Inertia is the tendency of a body to maintain its state of uniform motion unless acted on by an external force. You even misquote the grade school maxim, which, in fact states, "An object at rest stays at rest, an object in motion stays in motion." In fact, Newton's first law was a direct refutation to the commonly held belief of his day that all objects inherently tended towards motionlessness.
Centrifugal force is a fictional force, from Aristotelian physics, which has been shown not to exist. (Some have actually used the term centrifugal force to describe the force the smaller, circling body places upon the larger, encircled body. That is to say, the force which keeps the earth from ever-so-slightly falling towards the sattelite!)
Well no, it doesn't have to come down. There's quite a bit of junk left laying on the moon, the lander "first stages" for example, not mention several spacecraft headed out beyond the solar system (remember Vyger?)
You make up the frictional losses with solar power, or just a power cable from the ground. You store the energy going down, and reuse it going up, plus adding a little for those losses. You don't absolutely need a counterweight, although it makes the dynamics of the weight moving up and down the cable much simpler to control. The counter weight need not weigh exactly the same as the "up" car. It wouldn't really be a counterweight, in the sense that it would not be physically connected to the "up" car. It would just be the down car. Just as an elevator could operate without a counter weight, although it would mean the motors on the cars would have to be more powerful. They'd probably be linear induction motors, with the car going down putting energy into the system, while the car going up takes it out, and a control system making up the difference with an external power source.
BTW, there are even more radical proposals that don't involve exotic materials, or a support cable at all. They are called space fountains. There's also a possibility of a sort of skyhook, which would be rotating version of the "beanstalk" type system. When one end of the rotating cable came down (it would appear to come pretty much straight down, it would hook on to a car and pull it up into space, releasing it at the other end. All sorts of ways to get to space one you've been there. You still need rockets to build at least the first one, and then to travel around once you are in space. But that takes allot less energy than getting out of earth's gravity well in the first place. If you are in a hurry, those could be nuclear rockets, either Nerva or Orion type (aka "old bang bang".. look it up). If you're not in such a hurry, you can use ion propulsion, low thrust but you can run it all the way to wherever and back.
It's a lot of energy to store. Getting to geosynch will cost the same energy this way as lifting with a rocket. How much can be stored and returned to the system? It would be amazing if they can get even half of it back. Whether it is mechanical, electrical, or chemical, the energy storage system is going to be even harder to build than the main cable.
The basic effect would be that of a dumb waiter. But you do throw some water on the enthusiasm of the article: Whatever total space-borne mass will exist in orbit must still be placed into orbit. A space elevator wont so much get a human into space cheap, but will instead permit allow one person to replace another in space cheap.. or exchange the weight of useless bulk with his own weight. I guess that's where the big cost savings are: It is much cheaper to send simple bulk into space than a human being.
My understanding is there would be many stages, and that there would be a minor amount of propulsion needed to account for the minor loss of weight across the distance of one stage... That's probably why it takes six days!
Anyway, the stopper up to now was the main cable. If the solution to that is as good as in hand, then it is time to figure out the next hard problems.
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