1. Dubai and Abu Dhabi is only 100 miles. That's not nearly enough to make the Hyperloop economically attractive even if it were to work (which it won't, see point #2). Regular high-speed rail can make this trip in 30 minutes. It's just not worth paying N times as much for some value of N>>1 to shave 18 minutes off of that. 300 miles (like San Francisco to LA) is about the minimum distance for the hyperloop to compete with conventional high speed rail even under ideal circumstances.

2. Dubai has bigger thermal swings than California, so the thermal expansion problem -- which is still unsolved -- will be that much worse in Dubai.

2. It is hot down there but from what I have experienced, the thermal swings are lower than on a normal Central European or American day. This means in October 35 C during the day, 30 C at night.

Furthermore, there is definitely a large market for people that want to get between AD and Dubai in as short as possible a time. Sure, high speed rail would be great but people would be willing to pay extra to shave off 12 minutes.

That would make it the longest subway in the world by a factor of 3. Not going to happen.

However, I don't see how the difference in thermal swings between California and Dubai matters. The proposed solution probability of success or failure should be the same no matter what are the thermal swings. We are talking about (maybe?) 300 meters vs 500 meters per day of expansion for the same tube length. And Dubai - Abu Dhabi route length is much shorter than SF - LA, as you've correctly noticed.

[1]: "The tube will be supported by pillars which constrain the tube in the vertical direction but allow longitudinal slip for thermal expansion <…> Specially designed slip joints at stations will be able to take any tube length variance due to thermal expansion."(http://www.spacex.com/sites/spacex/files/hyperloop_alpha.pdf, page 28, section 4.2.3)

It doesn't really. But whatever thermal expansion problems you have in California you will have them worse in Dubai.

> Specially designed slip joints at stations will be able to take any tube length variance due to thermal expansion

See:

http://www.leancrew.com/all-this/2013/08/hyperloop/

for a detailed explanation of why this is not an adequate solution.

"But the real problem isn’t with the slip joints at the ends; it’s with the pillar supports along the way. Musk thinks the dampers, “tucked away inside each pylon,” need to accommodate only “the small length changes between pylons.” Wrong."

In other words, the original hyperloop white paper assumes that the movement at each pylon is small, and that the only large-scale movement is at the ends. But this is wrong. There is large-scale movement throughout the system. The thermal expansion motion reaches a maximum at the ends, but it doesn't magically go away as soon as you leave the station. If the tube at the station is moving 100m then the tube near the station is moving 100 meters minus epsilon.

The later parts of Hyperloop paper are more precise. I've already quoted "longitudinal slip for thermal expansion" from section 4.2.3. And, unfortunately, leancrew.com article author missed the proposed solution for the problem they spent many words talking about.

> If the tube at the station is moving 100m then the tube near the station is moving 100 meters minus epsilon.

Yes, of course. I agree that the problem of 100m thermal expansion is real and needs to be solved. And I'd like some arguments about why won't Hyperloop "longitudinal slip" solution work (where tube could freely move past the pillars).

You could argue that writing "pillars which constrain the tube in the vertical direction but allow longitudinal slip for thermal expansion" and "slip joints at stations…" is not detailed enough. I've concluded this "longitudinal slip" means some kind of linear bearing on top of each pillar, where straight tube could slowly move without constraints in the direction of the cumulative thermal expansion, while being constrained vertically.

      v    v
    -------------
     tube
    -------------
      ^    ^
      |    |
      |    |

      v    v
    -------------
            tube
    -------------
      ^    ^
      |    |
      |    |

Leancrew author missed the "longitudinal slip" part, because most of the article proves that thermal expansion accumulates. Of course it does! Thus the "longitudinal slip" solution.

Yes, Hyperloop paper could be more detailed and more clear. Indeed, it confused leancrew author.

Do you anyone knowledgable (in mechanical engineering?) who could comment on "longitudinal slip" solution? How feasible is it?

Indeed.

> How feasible is it?

Not even remotely feasible. You would need to have bearings at each column. Friction slip joints would introduce way too much stress.

Remember: the tube is not only moving hundreds of meters at the ends, it's moving >>1m along (very nearly) its entire length.

That's the kind of discussion I'd love to have! Of course, you need linear bearings [1] at each column. But what kind of bearings? Ball or roller bearings? [2] Plain/solid bearings? [3] Something else? What are the forces the tube would produce while expanding? What would be the linear expansion speed? What bearings would be able to sustain those speeds and forces? Would the tube and the pillars be able to sustain them? Do bearings with necessary parameters even exist? How expensive would they be? So on and so on.

Unfortunately, I haven't seen such discussion yet. I could try doing the calculations myself (starting at [4], for example). But I'm afraid I would make some silly newbie mistake in the process.

> Remember: the tube is not only moving hundreds of meters at the ends, it's moving >>1m along (very nearly) its entire length.

Yes, of course the tube is moving by hundreds of meters along most of its length. The questions are: how fast? with what load against the pillar?

[1]: https://en.wikipedia.org/wiki/Linear-motion_bearing

[2]: https://en.wikipedia.org/wiki/Ball_bearing

[3]: https://en.wikipedia.org/wiki/Plain_bearing

[4]: http://www.pbclinear.com/Blog/Calculating-PV-for-a-Plain-Bea...

But what the hell, I need to get my mind off politics, let's do the math.

The fatigue limit stress for steel is about 200MPa. You'd want a 50% safety margin, so let's limit it to 100MPa (which also make the math a little easier). The maximum stress is in the middle of the run, where you are pushing or pulling against N/2 pylons on both sides. Pylons are spaced every 30m. LA to SF is ~450 km. Let's call it 300 to make the math easier. So that's 30k pylons.

There are two different tube designs: passenger only, and passenger plus vehicle. Let's just do passenger only. The tube diameter is 2.23m with a wall thickness of 20-23mm, so the cross-sectional area of the steel is 0.14-0.16 m^2. Let's call it 0.15. So the maximum tensile load we can tolerate is 15 mega-newtons, or about a kilonewton of differential stress per pylon.

The mass of the tube segment borne by each pylon is 0.15 x 30m x 8000kg/m^3 (density of steel) = 36 tons. The weight of this segment is about 350 kilonewtons. So you'd need a coefficient of friction no greater than 1/350. Interestingly, that seems to be just about what you can get out of an industrial roller bearing, so there is no way that you can get anywhere close to that from a sliding bearing.

I wasn't able to find cost figures for roller bearing capable of handling a 36 ton load. I'm sure they exist. I'm equally sure that they're pretty frickin' expensive and require a lot of maintenance.

It looks like our estimation of "Hyperloop thermal expansion problem solution" feasibility now comes down to your last sentence:

> I wasn't able to find cost figures for roller bearing capable of handling a 36 ton load.

I don't know, railroad car steel wheel? Max load per axle for train cars: 26 - 40 ton. Searching on alibaba.com for "train car wheelset" and "train car bogie" never comes up with more than $2500 per piece. Maintenance seems doable, if we look at millions of train car running around the planet.

> These are the questions that would need to be answered by a hyperloop proponent, not me. The burden of proof is on the person making the claim. The only claim I'm making is that no one has proposed a solution. The two sentences that the Hyperloop white paper devotes to this issue is not a solution.

Yeah, I agree with that sentiment. Luckily, we are not the people making an actual practical decision on Hyperloop. Like you said, we are just trying to get our minds off politics.

The BBC needs to get their facts straight. Elon Musk did not conceive the Hyperloop. This concept has been around for much longer. The trademarked name Hyperloop is what's generally known as a vactrain and the idea has been around for at least 100 years. https://en.m.wikipedia.org/wiki/Vactrain

But I bet it turns out to be maglev in a vacuum tube, not aerodynamic flying.

[1] https://news.ycombinator.com/item?id=12708576

Now if someone successfully builds a maglev in a hard vacuum tube, then that would definitely not be a Hyperloop, it would just be a classic vactrain. On the other hand, I don't think Musk would be the least bit disappointed if somebody was able to actually build an operational vactrain.

https://sooeet.com/speed/speed-of-sound-in-atmosphere-graph....

https://www.hrw.org/middle-east/n-africa/united-arab-emirate...

"The government arbitrarily detains, and in some cases forcibly disappears, individuals who criticized the authorities, and its security forces face allegations of torturing detainees."

2. I don't see how boycotting the governments/nations will help resolve this issue. In fact, it'll probably make it worse.

In which way is this relevant to the argument?

After all if you are going to use a train just add cars to increase capacity.

Don't forget vacuum cleaners are hardly high vacuum systems.

But he was the first with a marketing budget for it.

Only if you count the SpaceX student competition, but that's not marketing, it's recruiting.

Not sure how it elevates him from yet another billionaire entrepreneur...

And with that, I'll stop feeding the trolls.

https://www.youtube.com/playlist?list=PLSPi1JFx4_-Gz0Fm0qq2K...

So now it's one of those "feasibility" projects?

Hyperloop suffers from the same problem as Solar Freakin' Roadways and Artificial Gills, I'm afraid: too much saying, not enough doing. I am instantly suspicious of projects that have lots of hyped up marketing but little to no prototypical substance.

To me, Hyperloop One still seems like a sci-fi pipe dream (pun intended).

If it's an HN thread about the latest social media startup, the lament is that SV doesn't innovate enough. If it's about a company tackling something hard, out come accusations of 'vapourware', and predictions of their imminent doom.

You realize that isn't actually how a capital market based economy works, right? Investors are the "command" part of the economy, responsible for allocating resources. If they decide to only invest in ridiculous, worthless ideas then we all definitely lose. So far that hasn't happened, but never forget that it is very important for us all where investors put their money.

This "somewhere, someone is losing money!" concern trolling fallacy is one "usefully idiotic" source of our repeated bailout follies, so I'd like never to see it again.

One bad decision here or there won't make much of a difference, because it doesn't dent the whole, and it likely doesn't affect anyone directly connected to us. But many bad decisions is a whole other ballgame.

Here the argument seems to be that a transportation project in Dubai is somehow the same as Goldman purchasing CDSs from AIG.

When the general welfare is invoked to justify extraordinary action, but the action itself doesn't contribute to that at all, the original argument ceases to convince. Cui bono?

I had trouble parsing this, is there an idiom in here that I'm not familiar with?

Thanks!

"somewhere, someone is losing money": Any functioning market in securities will have winners and losers, so it isn't automatically a problem that someone has lost in any particular situation.

"concern trolling": This is when e.g. I pretend that I'm worried about something bad that might happen to you, but in reality the advice I'm giving is meant to help myself instead. We see this typically when a consultant from one political party claims to be worried about consequences for the other political party.

"fallacy": Something lots of people believe, that isn't true.

"usefully idiotic": A "useful idiot" is someone who believes the bullshit peddled by class enemies to such an extent that she'll repeat that bullshit in all seriousness, to her own detriment.

"bailout follies": We've had lots of economic downturns, but somehow only those overseen by Goldman alumni as Treasury Secretaries have required the taxpayer to give Wall Street lots of money.

However, it seems a bit premature to say that it's too much saying and not enough doing. It's only been out there for about three years. There have been scale-model pods built, and test tracks are under construction. If anything, progress seems remarkably fast for such a radical machine.

The Hyperloop is technically possible. It will struggle for the same reason Maglev struggled: It won't be cost effective to build or maintain within the safety factors people are comfortable with.

You really have to look at the history of Maglev because the parallels are considerable. Maglev undeniably works, but nobody is building Maglev systems aside from a few pet vanity projects because High Speed Rail is "Good Enough" and cheap!

Hyperloop takes all of the cost issues that Maglev had and makes them worse. Even if the tube didn't have a negative pressure (just a tube with atmospheric pressure) it would be a cost nightmare, but you add in the costs of building something which can withstand negative pressures and the whole thing is just a farce.

Maglev, like Hyperloop, initially wanted to build on raised towers. But it largely wasn't because being able to escape during an emergency is kind of a big deal, same reason why the Euro-Tunnel is 2x larger than it needs to be to support escape tunnels.

A project like Hyperloop won't ever be able to win against real life problems like bombings, earthquakes, fires, extreme weather, and so on. Or at least it won't within the normal realms of cost.

Japan is building the Chuo Shinkansen, which will be a major intercity Maglev line. It's expected to connect Tokyo and Nagoya in 40mins, down from 100mins on the Tokaido Shinkansen (although a good chunk of that is due to a more direct route through the mountains), and later Osaka.

I could believe it's not necessarily a cost effective investment, but I don't know if I'd call it a vanity project. My impression is that they're trying to duplicate the success of the original Shinkansen, by building something similarly ahead of its time.

For them, this is just another innovation to put the country on the map of the world as an innovative and futuristic place, and that attracts tourism; which is said to be a large part of the economy here.

Blow up a support for a segment of tube in the right spot at the right time, and you turn the train into a kinetic kill weapon. (it's traveling 50% faster than a 747!) I'd hate to see that done when it was going through a city.

Blow up a support at any point at the right time, and you've murdered a tube of passengers, plus completely shut down an entire segment of transportation infrastructure for a significant amount of time. Do you know how much it cost the US to shut down all air traffic on 9/11?

Basically, hyperloop is a lot more feasible in a world without homicidal nutjobs - but, alas...

(what rail lacks in speed it makes up in tonnage)

Yes, the Madrid 2004 bombing happened, but events like that have been very rare. Do you think they'd be more frequent against a hyperloop?

Secondly, UAE is a pretty safe country in terms of terrorism. At least thats the perception you get if you live here. I haven't heard of one terrorism related activity here. That may be because the media is tightly controlled, but word still gets out if something that major were to happen here. This might just be because they have very tightly controlled borders, and are surrounded by friendly states that also have a relatively good security record (Saudi, Oman).

Just my take on these issues. I don't have any hard data, this is just my perception from having spent 3 years in this country.