I think one thing they missed here is pointed out by this statement in the article:<p><i>"[...] 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."</i><p>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 <i>or more</i> of pylons.<p>The air that these cars float over does not negate gravity or the effect of their weight on the tunnel that they travel through.<p>All that being said, it looks like our current carbon fiber pre-preg (<a href="http://en.wikipedia.org/wiki/Pre-preg" rel="nofollow">http://en.wikipedia.org/wiki/Pre-preg</a>) 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.<p>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.
This is interesting because they could potentially avoid the thermal expansion problem that would otherwise sink the hyperloop. Carbon fiber has a negative coefficient of thermal expansion in its axial direction, and you can pair it with a metal to get a net zero expansion structure.
That is a really good idea. But I wonder if carbon fiber wouldn't be very expensive for a static structure like that.
Why not use much less expensive glass fiber? Compared to steel it would still be much stronger, lighter and be manufactured in one piece, without welds.
>> There are machines that can churn out limited qualities of the braided carbon fiber.<p>I'm guessing that's a typo and they meant limited _quantities_, but I'm honestly not sure (not snark).
Reminds me of the carbon fiber loom Toyota came up with for making the Lexus LFA.<p><a href="http://youtu.be/AScfESzQzIQ" rel="nofollow">http://youtu.be/AScfESzQzIQ</a>
<a href="http://www.buzzfeed.com/autodesk/a-new-look-at-the-high-speed-hyperloop-b3y4" rel="nofollow">http://www.buzzfeed.com/autodesk/a-new-look-at-the-high-spee...</a> From Aug 30th with some cool images and a like to the YouTube CGI: <a href="http://www.youtube.com/watch?v=mV7lbDcaCo4" rel="nofollow">http://www.youtube.com/watch?v=mV7lbDcaCo4</a>
I'm not sure there is that much production capability for Carbon Fiber. Back in 2011 Audi attributed the delay in the Debut of the Audi R18 LMP as being due to the global shortage of Carbon Fiber caused by the 787 Dreamliner program(Not to be confused with the Mazda 787B).
This makes the Hyperloop concept feel vastly more feasible. And manufacturing carbon fiber at those scales will open up all kinds of new infrastructure/architecture possibilities. The biggest question on my mind is: how does one continuously infuse/cure epoxy?
Hmmm. I'd have to see this run through an earthquake model. It seems to me that having them stacked/connected vertically would cause problems during an earthquake.<p>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).<p>There's usually significant vertical and horizontal displacement during an earthquake. My thinking is that Elon's original design would fare better.
Building the structure is the least of the Hyperloop's problem.<p>How about supporting near-vacuum on such a large scale?<p>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.<p>How about obtaining the land rights to build it between SF and LA?
How are the safety aspects with steel or carbon fibers, considering that it will be close to roads and lots of people will have close access?<p>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.)<p>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?