I recently re-read, for the who-knows-how-many-times, the Mars series by Kim Stanley Robinson. In it, he describes a space elevator in order to make it extremely cheap to get stuff into space. It is a large astroid which is positioned geosynchronously(?) over the planet (Mars first, Earth later) with a looonnnngggg cable of incredible tensile strength. The cable is…balanced(?) between the pull of gravity and the centrifugal (yes, I know there is no such thing) force of the spinning of the planet. Regular elevators run up and down the cable counterweighted by each other.
Soooo… here’s my question. Is something like this possible in the future, say the next 150 years?
Actually, there would be centrifical force if the outer “station” were placed just outside normal geosyncrounous orbit (As it would have to be, if the cable were not self-supporting). Since it would try to fly away naturally, the cable anchors it in place. Actually, the even more optimal sollution would be to put the mass of the cable into account so that the station is as close to the geosyncronous point as possible without being too close (Falls out of orbit) or too far (Too much tension on the cable). If it were at that point, then it should work.
Eventually, if the technology continues to increase, it should be possible. Within 150 years? Not a clue Possible. If a material with a high enough tensile strength with a light enough weight were able to be manufactured, were not insanely cost intensive, and was able to be manufactured in enough length, then it could be done.
The only thing that seems incorrect is the elevator cars counterweighting eachother. Works well in buildings (Actually, the elevator cars don’t counterweight eachother, they each have their own counterweight) but the car at the top would be at effectively 0 gees, while the car at the bottom would be at a full gee. The car at the top would offer no energy to lift the other. And when the “up” car gets near the top, it has to decellerate against twice the mass, as the other car now is exerting much more upward force on it than it is exerting downward force. Would probably be better to just discard the idea of counterweighting all together
I recall reading that nanotubes, one of the forms of carbon, are strong and light enough to be able do it. The current problem is making nanotubes in quantity and in long lengths.
Somone will probably pop in and do all the math (and follow the teachers orders, showing all of their work), but if I read it, it must be true, right?
Either way, the X-Prize will be won within the next ten years, and space tourism will be possible within thirty.
Hopefully I can live on the moon for my retirement in forty years, unless the conspiracy theorists were right and it actually isn’t possible to travel through the Van Allen radiation belts and live
Well, you got the part about incredible strength right. But the cable would have to be incredibly rigid. That is because even though the top of the apparatus, on Earth say, is geosynchronous and appears not to be moving relative to a point below it, it is traveling along at about 7000 mph. So the elevator car and cargo has to be pushed forward faster and faster along its entire trip up the cable, or tower if that’s a better description.
Just imagine the torque from, say, a two ton payload on lever arm that is thousands of miles long. It is feasible, but Oh Brother that baby better be strong!
By the way, geostationary orbit would put the mass approximately 42,164 km from the center of the Earth, which is approximately 35,787 km above mean sea level.
While googling for that tidbit, I also found out that geostationary and gesynchronous orbits aren’t the same.
Ground-fixed space elevators are considered a big joke among knowledgable physicists/engineers. Assuming you have a magic wand to erect it and pixie dust to make the material, it would be astonishingly unstable. I.e., crashing down/apart in less than day.
It’s purely a pipe dream talked about people who don’t know squat about the Real World.
Important Real World problem glossed over by these guys: There would be an amazing amount of angular momentum to overcome at the anchor end. The whole thing is trying to rotate about its own center of mass. (And non-uniformly too.)
It is completely unlike swinging a rock on a string in the yard.
Just in case my previous post was misinterpreted: when I said incredibly strong I meant just that. Unbelievably strong. As in, we have no materials whatsoever strong enough to make this thing.
And I meant feasible from the theoretical side. You can figure out all of the stresses that would be present in some design and specify the needed material strength. You’re just not going to find those materials lying around the job site.
The biggest problem with a space elevator is tht you’d have to get rid of everything else in non-geosynchronous orbit first.
A space tether would have to be built at the equator - it’s the only stable position for it. All orbits intersect the plane of the equator, and for a non-geosynchronous orbit, the spot where they intersect the equator will change from orbit to orbit. Wait long enough, and everything that’s not in a geosynchronous orbit will strike your tether. Orbittal velocity meeting a stationary object is going to bad no matter what magic materials your tether is made from.
Couple interesting threads to peruse on this very topic:
chain to the moon?, which includes some discussion of superstrong material to construct tethers out of, as well as a link to an ABCnews article about an elevator to geosynchronous satellite and other miscellaneous space elevator discussion.
Space Elevator, with an OP eerily similar to the present one, but perhaps a little less hard info than the “chain to the moon” thread.
The incredibly strong part, as has been noted, is correct. I have a feeling even defect-free carbon nanotubes ain’t gonna do it.
At the same time Arthur C. Clarke wrote The Fountains of Paradise, Charles Sheffield wrote The Web Between the Worlds, an eerily similar book about a Space Elevator. Arthur C. Clarke even wrote the intro, to show there was no plagiarism. He didn’t agree with Sheffield’s dramatic way of building and “grounding” the space elevator, though. I’m not sure how Clarke had hist constructed. In his 3001: The Final Odyssey, the single Space Elevator has grown into an entire orbital ring around the earth, with a lot of spokes.
By the time Heinlein wrote Friday the concept was so familiar that he could get away with a toss-away line about the Space Elevator that’s typically Heinleinian. It’s something like “I caught the Beanstalk down.”
If you want more speculations and alternatives for the Space Elevator, see Robert L. Forward’s book Indistinguishable from Magic.
If I recall my Clarke correctly (just what was mentioned in the epilogue to 2061, I didn’t bother with 3001), his space elevator was constructed out of bits of the Jupiter core diamond that was thrown into the general Jupiter-star neighborhood by its ignition. As I recall, he also depicted the monuments of the 20th century still being in pristine condition thanks to a diamond film coating. I’m not if he covered what the space elevator’s counterweight would was constructed out of.
Yes, several of Robert L. Forward’s books deal with the “Skyhook” concept in detail, that’s where I first heard about it, and the idea was very influential with other SF writers. Forward is the hardest of hard-science SF and if he presents the physics, you can be assured of its accuracy. Here’s a quickie outline of the concept:
This 1981 article asserts that carbon-graphite composite materials would be sufficiently strong for a skyhook, certainly carbon nanotube materials were a long ways off at that time.
Maybe Big Donald would like to take a whack at building the thing. Can’t you imagine chips (magnetic) that would have to “stick” to the betting tables? How about the VIP suites in the 1 Billion Star Hotel? Drinks at the bar are like little astronaut food tubes (Oh, bartender, I’ll have another bag of dry martinis!).
I’m concerned about the stability problem. Assuming you have a cable of sufficient strength/weight ratio, the next problem is, is the tower stable? What about lunar and solar gravity? What about the effect of moving loads up and down it? What about the earth not being a perfect oblate spheroid? I remember that a plot point of Fountains of Paradise was that they had to ground the tether at that particular longitude because anywhere else it would have drifted off station. Is this true?
If you did make an orbital ring, you wouldn’t have to put it in geosynchronous orbit. Then you could drop tethers into the upper atmosphere, to which you fly and attach jets of some sort.
It’d be quite expensive and unlikely, but it’d probably be easier than the tether. Of course, you’d probably have to be mining other plantets/asteroids for the material, which would completely negate the main point of having the elevator in the first place.
The angular momentum problem is significant. Remember the old high school physics trick where you hold some 5-lb weights at arm’s length in a spinning chair, then you pull them closer? The weights want to maintain their angular momentum, so they start spinning you faster.
Now imagine that weight is the payload of a descending elevator car which is supposed to maintain the same rotational velocity (that of the earth).
You can’t move a rotating mass closer to the center of rotation while simultaneously maintaining its angular momentum and rotational velocity.
I’ll take the naysayers at their word and assume that on Earth, with the size of its gravity well, with its many artificial satellites and with its atmosphere, a space elevator would not work.
But how about on our Moon? Disregarding whether it would serve any purpose, could a working space elevator be built for Luna?
How about Mars (Kim Stanley Robinson does some great things, from a fiction standpoint, with Martian elevators in his Mars trilogy)?
Could a working elevator be built from the sub-Charon point on Pluto to the sub-Pluto point on Charon?
In Blue Mars, Kim Stanley Robinson had an Earth space elevator that forked close to the Earth, so that it had twin anchor points straddling the Equator. I think he put one in Trinidad and the other in Brazil. Assuming a space elevator would work at all, would this dual-anchor system work as well?
Possible. If a material with a high enough tensile strength with a light enough weight were able to be manufactured, were not insanely cost intensive, and was able to be manufactured in enough length, then it could be done.