Any good?
Basically it would be counterweighted - an asteroid or extending the cable itself furthur out. It would essentially behave as a tetherball being swung around in a circle.
The problem, as mentioned, is not only do you have stresses from the tension between the earth and the counterweight, you also have tidal forces on the cable as gravitational forces will change along the entire length.
I don’t believe that weather or terrorism would be as much of a problem as people think. The required strength of a space elevator cable would be such that it would take extraordinary actions to sever the cable. It’s not like a couple of Arab dudes could sneak up to it and go snip with a pair of wire cutters. Multiple cables and a high factor of safety would also go along way to ensure safety.
More troubling would be oscillations set up along the cable - due to weather or the crawlers themselves.
As for falling out of the sky, some suggest that atmospheric friction would cause this particular Big Dumb Object to settle relatively softly. Not come screaming out of the sky like a meteor. Even still, you would have 10s of thousand a miles of nearly indestructible cable to clean up.
Just realized something…there has to be some “give” due to movements of tectonic plates.
Whatever inspection costs are required may seem high compared to sending a package around the world via post service or container ship, but compare to the current process of putting payloads in orbit. Anything sent up via the space shuttle or even commercial booster is extremely secure and there are very few people vetted and qualified to handle those packages. Certainly if you maintain even the same degree of high security on space elevator payloads, you still have a huge benefit from reduced transport cost.
The main characters (whiny young brothers, as I recall) didn’t appeal to me much. I finished it but didn’t feel the need to continue the trilogy. (Bouncing off the Moon & Leaping to the Stars)
I mentioned it because he does go into some (made-up!) detail of his Skyhook and how it operates.
But currently, we send a miniscule amount of stuff into space so we can justify the costs. And the price of losing a shuttle is miniscule compared to the cost of losing an elevator.
(Excuse me because I haven’t read the entire thread, but…) As I recall, one of the early concepts for a space elevator was that a cargo container descending to earth would be “counterbalanced” by a mass ascending to a higher orbit.
I have no idea how that would work with cargo weight differences up/down.
My point was that even if the inspection costs are a “nightmare”, equaling or exceeding the procedures in place for current payloads, you still have enormous benefits in other aspects of the system. Yes, perhaps inspection issues would get worse than they are with the current system, but cost per payload weight would go down, volume would go up, and many other issues would improve compared to the current system.
I don’t think anyone is proposing that a space elevator would replace our current space shuttle and other boosters with exactly the same mission specs. That is, we’re not going to build something as massively expensive as a space elevator would be just to conduct the missions we’re conducting now (a relatively small number of commercial launches per year). We’d build an elevator in order to enable a massive increase in the number of “launches” and payload weight, on a scale that may not even be practical with chemical boosters. If security and inspection requirements are a “nightmare”, that’s one small downside for enabling the many benefits.
Raising and lowering payload in the manner of a traditional counterweight seems unlikely to me. To do that, you would need a cable running from the top of one payload cab, over a pulley and down to another cab; and that’s in addition to the main tether that anchors everything in place and guides the cab up and down. That’s an awful lot of extra complexity.
I think most of the designs for this have it operating more like climbing a ladder than a traditional elevator. And you could still recover the energy from anything descending the tether by using the electric lift motors as generators.
(What Oslo describes is actually similar to the original elevators on the Eiffel Tower. From the second level to the top used to take two seperate elevators, which largely balanced each other. You’d ride one elevator halfway up as the other was coming down, change from one to the other at the midpoint, and continue up as the first elevator descended.)
I don’t think you’d end up with huge expanses of indestructible cable if the thing somehow (through accident or sabotage) fell. Aren’t fullerenes still flammable? I would expect the cable to burn on re-entry.
As for counterweights, one nifty feature of a space elevator is that you wouldn’t need pulleys. You can (partially, at least) counterbalance one payload going up with another payload going up. Anything below the geostationary point will fall downwards, but anything above it would “fall” up. So one could have a second cable shorter than the main cable, with cars permanently attached at intervals along it, which would move up and down parallel to the main cable. Move up one step, transfer over to a waystation attached to the main cable, move the moving cable down one step, then get on the next car up. If you have equal masses going both directions (which could just be rocks from the Moon or Mars, if you have nothing else worthwhile to send back) and you’re willing to accept a large number of layovers, you can make the energy cost of the system arbitrarily low.
Another possible use for space elevators is as a spacecraft launcher/receiver. Since it extends well past geosynchronous orbit, the endpoint will be moving faster than orbital velocity. If you release a ship or cargo container from there, it will be able to leave Earth’s orbit for little or no energy. You regain the energy expended the same way you do for the elevator cars; incoming vessels grab onto the end and let it decelerate them ( presumably with some sort of hook and cable arrangement ).
One problem with space elevators that often seems to get neglected is that a load ascending or descending the elevator will exert significant lateral forces on the structure; you’re changing the orbit of the load, you have to change the velocity i.e. add/remove energy - like a ballet dancer’s spin slowing when the arms are outstretched - a load ascending the elevator is going to tend to lag behind the rotation of the Earth; a load descending is going to try to push forwards.
It isn’t solved by sending a load up at the same time as one coming down, becuase you just have big forwards forces at the top and big reverse forces at the bottom - they don’t cancel out.
Wouldn’t those lateral forces be proportional to the vertical speed of the load? Presumably, if you slowed down, you would give more time for the tower/cable/structure to push the load into its succession of new ‘orbits’…
Wouldn’t it be more like an ant moving along a ballet dancers arm given the relative masses? I can’t imagine it would be too significant.
No – if it were, then the portions of Jupiter beyond that point would be rotating at faster than orbital velocity, and get flung off into space.
In that case, wouldn’t such a force have an effect (albeit a really really tiny one) on the Earth’s orbit?
-Joe
Any method of getting things off the planet will have an effect on the Earth’s orbit, and a space elevator in particular would also have an effect on the Earth’s rotation. But first of all, the effect would be so miniscule as to not worry about, and second, it’d be cancelled out by any payloads you receive from points beyond.
There is a lot of information on this subject available here.