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Comment Re:only Americans would get excited about a hyperl (Score 1) 385

Only if the said motor is acting in the direction of deflection of the important modes. It so happens, it won't. I'd like not to have to remind everyone that there are, like, um, engineers working on that thing. Presumably with some, like, structural experience with things that are notoriously difficult. Especially aerospace is kinda notoriously difficult, with good, quiet cars not far behind.

Comment Re:only Americans would get excited about a hyperl (Score 1) 385

There are no linear motors. Well, um, yes, there are linear motors, if you look for them with a very good flashlight, that is. They cover about 1-2% of the length of the track. The words used in the fine description of the system are used for a reason. It's a mostly passive capsule, an almost ballistic system, with a compressor in the front of the capsule to provide compressed air to the air bearings and to bypass the plunger-in-a-syringe effect in a cheaper way than merely throwing a bigger tube at the problem. The linear motors reboost the capsule periodically. It will be coasting for about 29 out of 30 minutes. They also apply a force that doesn't give big reactions in the direction of easy to excite modes of the tube walls. After all, the motors push the capsule forward (or pull it backward); they should be symmetrically arranged so that there is no net pitching moment. Thus there is, to a first order at least, no excitation of the serious modes of the tube.

Comment Re:Funny (Score 1) 146

With one button, there isn't much to figure out, I'd hope. I mean, how simple can it get? A macbook, in addition to its keyboard and the screen latch, has exactly one extra button as well. Never had any problems with how to turn it on and off. Can you elaborate what exactly is your beef? (seriously, I'm all ears, no sarcasm intended)

Comment Re:Sure it's a loopy idea (Score 1) 385

You are aware that the design literally calls the "cars" capsules, right? And that you'd be strapped down for the entire time into a shaped, reclined seat? 2g would be nothing much, you wouldn't even notice it most of the time. There's no walking and no peeing in the hyperloop, and I agree with this approach. With the capsules spaced 30s apart in rush traffic, you go pee, then you leisurely catch the next capsule.

Comment Re:Well-Known Principle: PTT (Score 1) 385

Not even close. The friction losses on having a 500 mile long column of air going at 700 mph would be crazy. Scaling matters. Just because you can have it work in a bank or a big box store, or even in a downtown financial district, doesn't mean that you can willy-nilly both speed things up and increase the distance, by a factor of 100 no less.

Comment Re:only Americans would get excited about a hyperl (Score 1) 385

Given that this system rides on 1mm thick air bearings inside of a smooth tube, I don't think that noise pollution is much of a concern on the outside of the tube. The air inside the tube is at roughly 1/1000 of atmospheric pressure, so the sound doesn't propagate all that efficiently inside of the tube. The only sources of acoustic noise is the vibration of the intake compressor at the front of the pod, transmitted through the thin air bearing cushion. This is relatively easy to mitigate, since rotating machinery running at a constant speed is about the easiest thing to deal with in terms of NVH (noise, vibration, harshness). An internal combustion engine is way harder to tame, and even that has been pulled off successfully :)

The tube/pylon system will of course be subject to excitation from the radial forces by the passing capsules. So far, the significant modes are around 2-4Hz, so that's not a big problem. There will be dampers between the pylon and the tube, those will keep the number of cycles of oscillation "low" (ideally: it'll be critically damped).

Comment Re:Wacky! (Score 1) 385

The point being that early aviation needed very little in the way of a supporting infrastructure.

That's IMHO very short-sighted. Yes, it needed very little except that it was in the times when the landscape was littered with machine shops, material depots and people capable of actually making things out of said material. A lot of this is mostly gone nowadays, replaced by dedicated logistical chains that are not in the spotlight, but are huge, critical operations. Airlines need lots, lots of support, it's just not the very visible tracks, roads and runways kind of infrastructure.

Comment Re:There's a big difference between (Score 4, Informative) 385

What do you crash into? There is a big difference between a head-on collision, and merely a slide along the tube without air cushioning. When you're in a tube, the only other thing you can crash into is another train that goes the same way (or has stopped). Since there's no on-board propulsion, there's no scenario in which a train can propulsively overtake and hit a train in the front. It can only happen if the train in the front brakes, and somehow this doesn't get the trains behind it to stop. Very, very unlikely. The braking systems would be entirely passive, so basically if you blow the fuses on all the on-board batteries, the thing mechanically brakes an in entirely passive fashion. Also, for the trains to stay unbraked, they must be in constant communications with the control center. Presumably if the communications are lost for more than a 100ms, the brakes come out.

Oh, and they are not stupid, they did plan the route in detail, with bend radii and speed profiles all included.

Comment Re:Sure it's a loopy idea (Score 2) 385

It's quite interesting to analyze what would happen should a bomb be brought into a capsule, and a capsule would explode. It's not clear if a charge small enough to destroy a capsule would be enough to repressurize the tube. Let's not forget that the tube sees a roughly 1 bar overpressure from the outside, the inside is pretty much vacuum when you look at the explosion-scale overpressures. Whatever overpressure is caused by an explosion in the capsule, can really only propagate through the air in the capsule, and uses whatever gas was generated in the explosion proper. Once you're in the tube, the pressure wave has really no medium to travel in (air at 0.75 Torr, ha ha), so as the explosive gasses expand, the pressure drops very quickly. It's very different from an explosion in normal atmosphere.

There's a rather large gap between the capsule proper and the tube, but only a tiny gap between the air bearings and the tube. Presumably if a capsule blows up, it'll scratch up the inside of the tube, perhaps even dent it here and there, but it would be rather quick to fix. I'd imagine they could be up and running again in a week or so. As soon as communications are lost with a capsule, everything else would stop, same as if an explosion-type local overpressure event was sensed (there are pressure sensors in the tube anyway!). It's all engineering, and very doable engineering. It'd be wicked cool to be on the team that works on all that.

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