Autodesk's Idea to Knit the Hyperloop Out of Carbon Fiber
businessweek.com
businessweek.com
"[...] in less than two years, and, says Brandt, require fewer support pylons. “Elon’s estimate calls for about $2.6 billion for concrete, but we’d get that down to more like $1.5 billion,” he says."
The pylons aren't purely for lifting the steel, they're also for distributing the weight of the Hyperloop cars. If anything, an equal length of carbon fiber tube would be more flexible (not less) than the same length as steel and would potentially require the same number or more of pylons.
The air that these cars float over does not negate gravity or the effect of their weight on the tunnel that they travel through.
All that being said, it looks like our current carbon fiber pre-preg (http://en.wikipedia.org/wiki/Pre-preg) production is currently able to handle a construction project like this. According to Wolfram Alpha, a cylinder 9 feet in diameter from Los Angeles to San Francisco would have a surface area of approximately 52 million square feet.
According to the book "Boeing 787 Dreamliner" by Mark Wagner and Guy Norris, in 2007 Boeing actually expanded the capacity of carbon fiber plants they had access to in France, Japan, and the US from 125 million square feet per year to 363 million square feet per year. I would hope that 6 years later we would be able to produce 52 million square feet.
I was under the impression that carbon fiber was "stronger" than steel. I understand that stronger doesn't always mean more rigid, but I was also under the impression that carbon fiber could be woven in different ways to offer greater rigidity on a desired axis. Is it possible to construct carbon fiber in a way that is more rigid than steel?
Couldn't they also increase the amount of material used, or does that not increase rigidity? I'm thinking something like 8-ply vs 6-ply, or something like that. I'm speaking entirely from a layman's view, so I'm curious why increasing the number of plies wouldn't work.
I'm guessing that's a typo and they meant limited _quantities_, but I'm honestly not sure (not snark).
Think about those coffee stirrer straws that look like a figure 8 (it's a single straw pinched in the middle): if you hold one between your fingers the range of movement left/right is easy but an up/down movement is quite difficult (and if you push hard enough the straw buckles).
There's usually significant vertical and horizontal displacement during an earthquake. My thinking is that Elon's original design would fare better.
How about supporting near-vacuum on such a large scale?
How about dealing with earthquakes, erosion, landshifts, where even a small shift in a section of a tunnel would mean instant death for the travelers.
How about obtaining the land rights to build it between SF and LA?
The original paper attempts to deal with all of these problems, pressure, safety, land rights, it's a very interesting read.
In all, the hyperloop as it's currently being presented is much more dangerous than high-speed rail during an earthquake, and this is a legitimate concern.
http://www.spacex.com/sites/spacex/files/hyperloop_alpha.pdf
Could the (near) vacuum be compromised by any idiot with a hunting rifle and bullets optimized for piercing body armour? (At a minimum repairs and off time for a day or more.)
Can a kg of explosives put shrapnel through it and create a big crash? What is the safety distance for one of those Iranian self-fusing penetrators used in Iraq?
I think you can create a big train crash with a kg of explosives, so that scenario is already possible.
You don't even need explosives, a simple wedge welded on a rail would be enough. In the end, I don't think it is economically feasible to secure a railway against that (as well as any other kind of track). You have to make sure that nobody does stupid things like these.