The key advantages of a tube vs. a railway track are that it can be built above
the ground on pylons and it can be built in prefabricated sections that are
dropped in place and joined with an orbital seam welder.
Did anyone else read this and imagine laser beams fired by satellites?
Not really. It's a valid welding http://en.wikipedia.org/wiki/Orbital_welding), but I imagine it might be quite a task to scale it up to pipes as large as would be needed for this project.
For some reason Elon Musk is extremely enamored of welding technology. I remember seeing a page on an old version of the SpaceX site containing a high-level overview of the Falcon 9, where they went out of the way to mention how great circumferential friction stir welding is compared to whatever NASA used to do. And here he is bragging about it being the large stir welded thing ever created: http://www.nasaspaceflight.com/2009/01/musk-ambition-spacex-.... It's a revolutionary vehicle in many regards, but Elon seems to have a particular soft spot for welds.
Makes sense, most of the volume in a rocket is a tube structure. I imagine that SpaceX has spent a lot of time evaluating ways to precisely and cost-effectively build tubes...
Orbital welders can be used in pipes on any size (smaller sizes often need special welders). Not sure what the record is but they are commonly used on water pipes that are several meters in diameter. Should work fine for the Hyperloop tube. Seems like all the required technology is proven but I'm sure we will hear more from all the experts in the various fields.
I do not get this part. These are not advantages of tube v railway track, because a railway track can also be built above ground and can also be build from prefabbed sections. In fact I would think that building a railway track would be much cheaper than building an airtight tube.
Unless Musk has found a way to make the cars weightless, the tube must support the weight of the cars. Further, the pylons must support the weight of the tube and the cars, over a smaller footprint.
