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Comment by pjungwir | Hacker News Reader

    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?

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But in China vast expanses of high speed track are built on pylons. Here is an example of one such track (and some unfortunately placed apartment blocks): http://msnbcmedia.msn.com/j/MSNBC/Components/Photo/_new/pb-1...

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.

Orbital welding on this scale and much larger is already done in the offshore oil industry.

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.

Railway track built above ground has to support weight of the cars, which seems significantly higher ....

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.

Railway cars weigh approximate 30 tons (unloaded) to 140 tons (loaded).

Even a Ford F150 truck only weighs 2 tons.

Well how else would you propose welding them together?

I immediately imagined drones in FTL. Some shoot lasers, others shoot beams, and a few can repair your own ship while orbiting around it.

I did. It would be so cool :)

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