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Hyper...what?

This morning, after kicking the cats down the table and sitting down for breakfast, I was having a look at the newspaper, after the first 68 pages, all dedicated to the glorious victory of Ajax, I found this "article" that states that the Noord Holland region (where I am), will work at the constructions of an "Hyperloop"

between the airports of Schipol and Frankfurt. You can see the whole article in its glory here and a translations is the following:

Schipol (largest airport in NL) - The NoordHolland region is going to work with the Hardt Hyperloop company to build the first Vacuum Hi-speed tube-train for travellers between the airports of Schipol and Frankfurt. The trip could  be covered in half an hour, "making flight no longe necessary".
Hardt Hyperloop is a joung company, composed by students of the Technical University of Delft with the blessing of pioneer Elon Musk (Tesla), that will work to the development of the new mean of transportation that will be able to transport people and good at over 1000 km/h.

"This Vacumm Tube is a transport system with which is possible to drastically reduce the time required to move between large city, making it a perfect alternative to airplanes. Since the whole climate and noise problems is necessary to think to alternative". Said the spokepersone Elisabeth Post. The hyperloop is, according to her, an important part of the region effort to innovation. To begin with, 50k euro will be invested. "In the beginning of 2020 we will decide about further financing".

In the coming years there will be investigation on the possibility for connections and where and how this new system could fit with the existing infrastructure. "the most important part is to ease the traffic on Schipol, decreasing the noise and improving the environment".

Now, because it's printed, otherwise I'd talk about "click-bait titles". So... Hyperloop. Ok, let's start by putting down a few points before the "Musketeers" starts to piss all over the place.

1. Elon Musk IS NOT an engineer. He has a degree in Economy and one in Physics, this last one from the College of Arts and Science.
2. Elon Musk DID NOT created PayPal. He co-founded (with his brothers) a software house that was bought by PayPal that was then bought by eBay. And musk was booted from the CEO position mostly because he wanted to move the whole IT infrastructure to Windows (!).

Maybe he has nose for business, but he is definitively not a scientist. And now let's talk science.

The term 'Hyperloop' define nothing more than a "train" that travels into a vacuum tube. In fact, the idea isn't new at all, a first proposal is from 1870.

Everybody should know that, beyond a certain speed, the biggest problem to movement is areodynamic resistance and not the wheels (assuming they are doing their job properly). So if we get rid of the air we remove the largest problem.

But... There is But. Remove the air from every container costs energy. A lot of it. And air, being all over the place, tend to try to get back in. A lot. The result is that making really vacuum container costs a lot and is difficult. And the large the container the more difficult and the more expensive it is.

An example: the Glenn Research Center is (until now) the largest vacuum "building", is part of Nasa labs to test space craft and capsules (that have to be in space). It's made of concrete to resist the pressure and cost a lot of money to operate.

A few years go, after Musk came out with this idea, a 'test tube' was built in California. Total length: about 1 Km. Diameter: less than 2 meters. Well, to pump out the air from that thing the time required was about 3 hours.

Now, somebody could say, "you don't need to pump the air out of the tube every time. Once it's empty, the train goes into a "decompression chamber" and then move to the tube". Now that is logical, but introduce another problem: a decompression chamber that has to be train-sized and connected to the tube with zero leaks. And air that must be pumped out every time, introducing stress to the structure. If the 'test' tube is anything to go by, the time spent waiting for the decompression could be more than the time for the whole trip, making the whole thing mooth.

And somebody could also argue that the tube doesn't need to be "vacuum" but just "low pressure". Well, based on the specs, this thing should operate at "about 1/6 of the pressure of Mars" or "equivalent to flying above 150.000 feet" (data from the hyperloop white paper), if this doesn't sound like a lot, consider this: the normal airline flying height is between 29.000 and 45.000 feet, that is between 8000 and 14000 meters, at that quota the air pressure is about 0.18 atm, very little, but nothing if you consider that at 150.000 feet, that is 45.000 meters (45km) the air pressure is 0.0001 atm, so basically a vacuum.

Pipes, or better, every structure, tends to expand and contracts with heath. Railways knows that, and in fact rails have gaps between each section that allow the metal rails to expand without deform. But rails aren't vacuum tubes. A steel pipe 1 km in lenght expand about 0.7 cm for degree. If we assume a temperature differential of 10 degrees between night and day, the pipe expands 7 cm. Not much, until you consider it attached to a decompression chamber that has to be in totally air tight. And we're not talking a 1 Km tube.

The distance between Schipol and Frankfurt is 364 Km, so such a tube, in the condition definde above, should expands about 250 meters (!). And build a decompression chamber that is able to move 250 meters between day and night is definitively an harder engineering problem.

One of the advantages of the hyperloop versus the more conventional "high speed train" is that train sometimes crashes. That is true. It is kinda rare, but it happens. Now, let's ignore for a moment the wounded, death and the human drama. The train has to be removed from the rails, that require probably a crane and maybe some demolishion works to take the parts away. Then you have to fix the rails and then you can put the line back into service.

Now, let's imagine an incident in the hyperloop. First of all, we have a 'train' that travels at sound speed. Inside a pipe. Any "incident" ought to be catastrophic. The Mythbusters have tested what happens when a vacuum container fails.

How do you pull the train out of that thing? You need to take apart. And then you have to rebuild it. And do you trust it to pump it vacuum again? Sure, railways accidents do happens, but they don't put the whole line out of commission forever.

In short, it doesn't violate any physical law (like a lot of the "perpetual motion system" that I see around), but the whole thing has a lot of engineering problems to tackle.

Davide Bianchi
17/04/2019 10:18

Comments are added when and more important if I have the time to review them and after removing Spam, Crap, Phishing and the like. So don't hold your breath. And if your comment doesn't appear, is probably becuase it wasn't worth it.

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