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Continued Success for Space Elevator Tests
Jacki O writes "According to their Web site the Space Elevator company Lifport recently managed to get their platform and climbing robot to the mile-high mark over the Arizona desert." From the announcement: "A revolutionary way to send cargo into space, the LiftPort Space Elevator will consist of a carbon nanotube composite ribbon eventually stretching some 62,000 miles from earth to space. The LiftPort Space Elevator will be anchored to an offshore sea platform near the equator in the Pacific Ocean, and to a small man-made counterweight in space. Mechanical lifters are expected to move up and down the ribbon, carrying such items as people, satellites and solar power systems into space."
A little progress is better than no progress.
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Far from it. All of the components of a space elevator will be revolutionary, not just the ribbon. The climber's mechanical parts have to work flawlessly for about 100,000 km. The actual problem of gripping a cable isn't trivial, either. And it needs to be very low weight. Oh, and very low power. And just to make things even more fun, it'll need to work in vacuum as well.
If you read some of the papers on concerns for the climber at the space elevator conference, you realize that there's nothing easy about this. It's unsurprising that the climber is seeing the most progress first, but that first concern (perfect reliability over 100,000 km) will take a long time, so better to start now.
Really? Are you sure? Can you build a bearing for a 20-cm wheel that will be able to turn 500 million times with zero chance of failure? And can you do it lightly? And in vacuum?
While we don't have the ribbon yet, we don't have the climber, and we don't have the power delivery system either. That's why it's called inventing. They're doing something that hasn't been done before.
And when you've got multiple independent difficult problems, you might as well work on all of them at once. Which they are doing.
Go and read the talks on building the climber at the last space elevator conference before you call it "trivial".
Personally I'm surprised no one has tried just shooting things into space.
Oh, and I didn't see this. Fundamentally, this is a bad idea. First off, the idea of a modified Howitzer? That's just explosive propulsion. This is fundamentally the same idea as a rocket - it's just that a rocket is far, far more effective in terms of thrust per unit mass.
You could imagine electromotive propulsion - a rail gun - but the problem with that is that you're imparting all of your momentum in the thickest part of the atmosphere, at which point it would just be bled away as air resistance. You'd need to supply a ridiculous amount of energy to do it, and the craft would have to have a ridiculous amount of stress support and heat resistant material. It gets to the point where there is no way that it would ever be economically feasible.
On an atmosphere-free planet, though, it does become pretty feasible, though a space elevator is likely to be more generically useful for large cargo.
The challenges of a space elevator aren't in the climber; they're in the cable.
... well, large, but not unreasonably large. It would just cost a lot more.
C'mon. That's not true. The main reason it seems like this is because you think you know how to build the climber, but you have no idea how to build the cable. Ask a materials scientist who's working on carbon nanotubes, and they might disagree with you.
Plus, you do not need a 100 GPa cable. You need a 100 GPa cable for a small taper. At 50 GPa the taper becomes
There are a lot of issues with the climber design. A lot. Speed, reliability, weight, and power. Reliability in particular will take a lot of time to nail down. It makes sense to tackle that one first, because it can be done in parallel with the cable design, and in addition, the third major challenge (power delivery) can't really be done until the climber design is finalized.
So you've got three difficult tasks - the cable, the climber, and the power delivery system. The last two are coupled. What makes sense is having two separate tasks, one of which handles the cable, the other the climber, and then the power delivery system. Oh look! That's exactly what they're doing.
Given our lack of experience in building cheap vehicles that can travel 100,000 km with zero failures (with low power, in vacuum) I think it's safe to say that all parts of the elevator are difficult.
I word things very carefully. Read it again. I said "planes can pretty much do that." I was actually thinking about commercial airlines, which fly above 72% of the atmosphere.
But, of course, there's this nugget from Wikipedia:
Balloons typically reach altitudes of 100K feet, which is above all but a fraction of a percent (it's a few Torr).
simply by building our velocity high enough to escape velocity while in the atmosphere and letting inertia take us out.
Ignoring that whole "air resistance" and "speed of sound" thing.
And curiously, if it wasn't for those two things, we could do that right now.
We use rockets for velocity, not altitude. If you doubt me, consider that the Space Shuttle's two solid rocket boosters shut off at lower altitudes than the X-15. Why don't we use a jet to boost the Shuttle to that altitude? Because the SRBs get the Shuttle to a much, much higher speed.
There's nothing "special" about Geosynchronous orbit which means you can "get the velocity from the Earth".
I get velocity from the Earth all the time. It's called standing on the ground. (Curiously enough, if I didn't, I would start flowing in these little circly patterns, called Hadley cells, which are what happens when you have a viscous medium gravitationally sitting on top of a rotating sphere. If the atmosphere extended enough, it essentially wouldn't be rotating.)
That's what special about geosynchronous orbit. Orbital velocity is slow enough that I can use the Earth's rotation to supply it.
You DO have velocity.
Which I got... from the Earth. Like, when a plane lands, after heading west, how the Earth speeds it up in a matter of seconds?
The idea is at that height, escape velocity is negligable.
It's not "negligible" - it's two thousand miles an hour (curiously, roughly 1 km/s). It's just neglible in the rotating frame of the Earth.
Nanotube ropes are *far* weaker than individual tubes, usually at somewhere between 5 and 15 GPa. They're weakly bound together by VdW and pi bonding. I could go into more detail on the other ways your analogy is flawed (we're talking about tensile stress, not shear; we're talking about gram per gram; we're talking about linearly staggered over a long distance, instead of continuous elements; and we're talking about nanoscale, not macroscopic for starters).
Liftport doesn't have a "get out of physics free" pass.
You can't change that... by gettin' all... bendy.
Your post makes me incredibly glad I learned physics using only metric units.
Megainches??? Do real scientists seriously use such a measurment?
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