Yeah, that’s what I meant.* The problem with geosyncronous orbits is that once perturbed, they are no longer geosynchronous. Not a big deal if you’re a free floating satellite because if you get a bit off from where you’re supposed to be, you fire up the main thrusters and you cruise on back to where you oughta be. (more or less) If you anchor the elevator to the ground and then it starts drifting, you’re going to have serious problems, because the ground isn’t drifting, too. Even the people who think the space elevator is possible recognize that you have to be very careful about maintaining the orbit, they just handwave away the difficulty of moving a ginormous diamond ribbon back where you want it to be.
I’m actually teaching Differential Equations this semester. I know that internet appeals to authority are not worth the paper they’re printed on, but I feel like it’s worth pointing out. I started reading about this stuff because I thought it might be a fun project for my students to work out the details of how a space elevator would work. Unfortunately, most of the equations don’t have elementary solutions, so I think it’s a project better suited to a numerical methods class. I’m still planning to use this as an “interesting real world example” though.
Also, because the Earth is flattened in the polar direction, if the inclination of an orbit is not exactly 0, it will drift. Then there’s also the issue of the ellipticity of the equator and… yeah. Not going to get into it. But the upshot is, you can’t just hang a ribbon off the actual Earth and expect it to stay put without giving it little pushes.
To add some economic talk to this discussion, I’ll just note that a space elevator or space fountain would likely be a poor means of stimulus.
It could spend a decade just in planning. Economic stimuli are things that effect the economy now, not ten years from now.
A “good” economy is one in which there is growth. The way you create growth is by figuring out some project that, if completed, will earn more money than it cost to make within a short enough period of time to be worthwhile (i.e. before you go bankrupt.) Some infrastructure programs can help to improve trade and so, even though there is no toll to use the infrastructure, the money spent on the infrastructure is made back via the increase in trade. A space elevator, though, is essentially the world’s biggest Bridge to Nowhere. Getting into space is entirely about coolness until such a time as we have the speed capabilities to take advantage of the resources and land available in space. So essentially it would just be a big money sink on the economy, not a boon. The only way it would help the economy would be via the creation of the materials used. But you could build a bridge connecting Europe and North America instead of a space elevator and get those same materials, plus something useful.
So is it safe to assume the Kim Stanley Robinson scenarios in his Mars books have no basis in reality? How much of the space elevator would survive re-entry?
I have no idea if his idea is realistic or not, but in his favor is the fact that Mars has significantly less atmosphere for the cable to burn up in. I also seem to remember the cable in his story being quite a bit larger than anything proposed in this thread.
What, exactly, do you envision when you say “anchored”? What kind of tension are we talking about at the bottom of the cable? Will this be on land or at sea? How do you imagine the “little pulls” might be accomplished?
A “space fountain” is a railgun you can never turn off, firing constantly at a station in the sky, which shoots them back down at you. It has all of the practicality of a space elevator with the extra added bonus of being a superweapon. Oh, and if you ever do need to turn it off, it falls down.
Just checked wikipedia to refresh my memory on the idea and… you need to build an airtight tower 100km tall? For reference, the tallest structure ever built, when they finish it, will be the Burj Dubai tower which has a TV antenna that’s 818m high. Make that airtight and you’re 0.8% of the way there!
Why would it burn up? It’s not moving at orbital speed, so the cable has very little kinetic energy when it hits the atmosphere. Only what it acquires during the fall.
you fall 50 miles and see how much kinetic energy YOU have
Burt Rutan’s Space Ship One “only” went up and down about 50 miles and reentry heat wasnt something they could just shrugg off. It certainly did not have anywhere near orbital velocity.
Agree. the whole idea is unsound. We don’t have the money, the materials, the technology. If we did, we still have to buck up against laws of physics dealing with orbital speeds vs earth rotational speed, altitude, tension, gravity, voltage build up on the cable (the voltages will be gigantic), etc etc etc. Let’s go with better “conventional” launch systems instead.
The technology we don’t have is the materials, and the lack of money is just because we don’t have the materials yet. So that’s really only one objection, which I’ve already explained why I think it will be resolved in the not-too-distant future. And there is nothing in the laws of physics which presents an obstacle: The physics all works out just fine, provided you have the material available.
Tenebras, one of the nice things about the fountain is that the things being shot up it help keep it up.
… it’s still easier to build than the elevator.
Another variant I like that I forget the name of is the pinwheel. Central body in space, rotating arms, no attachment to the earth. You board as it passes.
The things being shot up are the only thing keeping the station up. The space fountain is a continuously running railgun launcher. So the first thing you have to do is build a railgun launcher that works one time, and then just hold down the trigger. Again, the people who think it will work admit that one part of the process is to build a tower 100 times taller than any structure on Earth, and then pump all the air out.
Even if you discovered a scrith mine, it still wouldn’t happen. Even if you get an army of wizards to cast Wish spells until the thing is in place, and then a second army of clerics all cast Miracle to hold it there, it gets hit with a piece of garbage and goes kaplooie.
And the physics don’t work out fine. Try this: ignore the moon, sun and every other body in the universe. Assume that the Earth is an ellipsoid, flattened through the poles. What orbit are you going to put this in, and how are you going to keep it there?
