John Fredrick Parker
Donor
Pretty straightforward -- how soon could a space elevator be built, and what in the past century could have gone differently to make it happen sooner?
An earlier discovery of carbon nanotubes (CNT's) is entirely plausible as the ability to produce and image them was available as far back as the '60s. Have them become popular 10 or 20 years earlier than OTL and you advance their development and composites by about a decade but you still need to wait for computers to catch up.
Still, it's a very, very tricky and expensive business. I'm a materials engineer so I'm pretty well acquainted with the issues of materials design that would need to be solved. Making a CNT based space elevator will take at least 30 years of development and design, assuming that the incentive even exists and it's cheap enough to be cost effective. For example, I believe that the composites used in the 787 took over a decade of research before they were commercialized. CNT's are like that x100. Personally, I'd be shocked to see a space elevator by 2050.
Honestly, I can't venture a guess about a classic space elevator anchored to a counterweight beyond geosync altitude, because that requires carbon nanotubes.
But an orbital ring is theoretically possible even with our current materials, since the "elevators" to connect to the orbiting ring only have to just breach the atmosphere. Then you use the same maglev system that allows the tower to be suspended from the ring to accelerate your cargo to orbital speed.
Easier than building something that requires building materials that do not exist.Ayayay.
hanging stationary towers off an orbiting ring? And you think this is easier? Ouch. The energy loss at each tower will be huge, and failsafes for a magnet failing, for instance, would be ... interesting.
Youd also need multiple towers, probably four plus, pretty much equally spaced around the world. Plus, balancing loads when something was going up or down the elevator would berl really, really tricky.
The ,,cheap,, solution, might be spaceprts like in donald kingsburys ,,the moongoddess and the son,, basically orbitting mass drivers that catch a suborbital rocket, and accelerate it to orbital speed. Thats still tricky, but easier by one or two orders of magnitude than your orbital ring.
Youd also need multiple towers, probably four plus, pretty much equally spaced around the world. Plus, balancing loads when something was going up or down the elevator would berl really, really tricky.
But an orbital ring is theoretically possible even with our current materials, since the "elevators" to connect to the orbiting ring only have to just breach the atmosphere. Then you use the same maglev system that allows the tower to be suspended from the ring to accelerate your cargo to orbital speed.
The problem is that the simple elevator has to be much, much taller. A simple space elevator has to go well past geostationary altitude of 35,786 kilometers, and be anchored to a counterweight of some kind. The classic space elevator is held aloft by centripetal force, with the counterweight being swung by the earth's rotation like a ball at the end of string.If the mass and velocity magnitude of the elevator going up is approximately equal and opposite to that of the elevator going down and the mass of the elevator is small with respect to that of the cables and the mass of the cables are small with respect to the ring one would not expect this to be a particularly difficult system to load ballance.
At first glance this seems wrong the tensional loads in this would be the same as in a simple elevator design. Perhaps I have misunderstood the concept you suggest? Please could you explain a little more?
But if the mass of the elevator going up is near the mass going down, you have little to no net lift to orbit. Which rather reduces the viability of your elevator.If the mass and velocity magnitude of the elevator going up is approximately equal and opposite to that of the elevator going down and the mass of the elevator is small with respect to that of the cables and the mass of the cables are small with respect to the ring one would not expect this to be a particularly difficult system to load ballance.
But if the mass of the elevator going up is near the mass going down, you have little to no net lift to orbit. Which rather reduces the viability of your elevator.
As for the mass of the ring, youd probably need the mass LOCALLY to be much greater than the mass of the payload coming up, which, given that means that mass, linear density, has to extend the entire circumference of the earth, means a LOT of mass in orbit ... which you first have to get ther without a ring.
With an orbital ring, the tower only has to to be around 130 kilometers tall, and can be supported at least partially by the centripetal force of the orbital ring by hanging it from the ring via a magnetic levitation mechanism.