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Old 02-17-2017, 03:08 PM
copperwindow copperwindow is offline
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The hyperloop

I saw a thing on TV and few years back on how the hyperloop was going to change the way people got around. It seemed very implausible to me and I haven't heard anything about it since. My questions are 1; was this a real thing and 2; what is the latest news on it.
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Old 02-17-2017, 03:12 PM
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There was a proof of concept test run done about nine months ago. Supposedly the tunnel Elon Musk is building right now to get to the airport in Los Angeles is being built with Hyperloop in mind. Whether it all pans out remains to be seen but it is not forgotten.

The theory of the thing is fine. No particular reason it can't work. It just seems to me it is waaay too susceptible to attack. A vacuum tube running across the state? Seems to me one joker with a pistol could poke a hole in it and then it will tear itself apart as air rushes in to fill the vacuum.

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Old 02-17-2017, 03:17 PM
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There was a proof of concept test run done about nine months ago. Supposedly the tunnel Elon Musk is building right now to get to the airport in Los Angeles is being built with Hyperloop in mind. Whether it all pans out remains to be seen but it is not forgotten.

The theory of the thing is fine. No particular reason it can't work. It just seems to me it is waaay too susceptible to attack. A vacuum tube running across the state? Seems to me one joker with a pistol could poke a hole in it and then it will tear itself apart as air rushes in to fill the vacuum.
Or an earthquake or some other sort of a natural disaster and everyone in it is dead. I have problems believing the government would allow such a thing.
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Old 02-17-2017, 03:18 PM
Shagnasty Shagnasty is offline
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Don't expect to ride on a hyperloop pod anytime soon but the idea is real and in development. Elon Musk has already built a test tunnel and has gotten teams of engineers to have speed competitions in it. He is also trying to invent a boring machine that is 5 - 10x faster than anything that already exists. The basic idea works in theory. There is no cutting edge physics involved but the logistical challenges to build very long tunnels at a reasonable price are immense.

http://www.geekwire.com/2017/elon-mu...tunnel-spacex/
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Old 02-17-2017, 03:41 PM
Bill Door Bill Door is offline
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Or an earthquake or some other sort of a natural disaster and everyone in it is dead. I have problems believing the government would allow such a thing.
Yeah, like in 1989 when 42 people were killed during the Loma Prieta earthquake as the upper deck of the Nimitz freeway collapsed. They ran right out and closed all the freeways. No, wait, they did that other thing. They left them open, because people have to get around.
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Old 02-17-2017, 04:02 PM
copperwindow copperwindow is offline
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Yeah, like in 1989 when 42 people were killed during the Loma Prieta earthquake as the upper deck of the Nimitz freeway collapsed. They ran right out and closed all the freeways. No, wait, they did that other thing. They left them open, because people have to get around.
A very small earthquake probably won't do anything to a freeway, but that same earthquake could kill everyone in the hyperloop.
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Old 02-17-2017, 06:03 PM
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They are working on a project in Dubai:
https://www.zawya.com/mena/en/story/...012017_190151/
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Old 02-17-2017, 06:17 PM
Evan Drake Evan Drake is offline
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Well, Elon Musk isn't in the business of vaporware. He's a member of the president's business council.
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Old 02-17-2017, 06:19 PM
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There was a huge thread back when this idea first popped up, in which many of us looked at the practical issues relating to this. The thing about the hyperloop is that the idea isn't new. It was floated at least a century ago. Elon Musk popularized it recently, but issues involved aren't about whether it's hypothetically possible (again, that's been known for a long time), but whether it's practical and cost-effective.
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Old 05-14-2017, 07:30 PM
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There was a proof of concept test run done about nine months ago. Supposedly the tunnel Elon Musk is building right now to get to the airport in Los Angeles is being built with Hyperloop in mind. Whether it all pans out remains to be seen but it is not forgotten.

The theory of the thing is fine. No particular reason it can't work. It just seems to me it is waaay too susceptible to attack. A vacuum tube running across the state? Seems to me one joker with a pistol could poke a hole in it and then it will tear itself apart as air rushes in to fill the vacuum.
Did Elon get some kind of permission to be tunneling under L.A.?
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Old 05-14-2017, 08:30 PM
suranyi suranyi is offline
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Did Elon get some kind of permission to be tunneling under L.A.?
As far as I know he only got permission to dig under his own property. Which makes what he's doing even more puzzling.
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Old 05-14-2017, 10:07 PM
Snarky_Kong Snarky_Kong is offline
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A very small earthquake probably won't do anything to a freeway, but that same earthquake could kill everyone in the hyperloop.
Why do you believe it would kill everyone?
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Old 05-14-2017, 10:23 PM
Sam Stone Sam Stone is offline
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The tunnels he's digging have nothing to do with hyperloop.

I'll start believing the hyperloop companies are something more than a scam to attract investment money when I see any of them invest even half the time solving the serious engineering problems involved than they do preparing cool videos and designing futuristic pods and terminals that look good in investment brochures but which don't address the serious engineering challenges of this thing.

The first place to start is metal expansion. Musk claims that hyperloop will be a solid welded steel tube, with expansion being taken up at the end terminals. This is a complete non-starter, because the tube isn't straight. Therefore, metal expansion will cause the entire shape of the loop to change - by many hundreds of feet. and going straight isn't even possible because the earth is curved and a straight line between two points is a great circle arc.

If you solve that problem, you can then consider buckling problems from differential heating on the top and bottom of the tube. And note we haven't even talked about the challenges of maintaining a vaccuum, how you are supposed to get people out of the thing if a car stops in the middle, how you protect it and the people from catastrophic failure if the immense forces on it are released by a puncture, and on and on.

These are challenges with no current engineering solutions. So if you see a company claiming to be building a hyperloop but all they have to show you is lots of pretty models of termnal buildings and futuristic capsule designs, grab your wallet and run.
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Old 08-27-2018, 08:21 AM
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Why do you believe it would kill everyone?
Because a hole in the tunnel lets air in, this re-pressurising would cause great turmoil in the vacuum tube.

The pressure difference between inside/outside the tunnel is greater than that between a plane and the atmosphere.

Train running at 500mph vs any turmoil is an accident waiting to happen.
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Old 08-27-2018, 12:03 PM
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Because a hole in the tunnel lets air in, this re-pressurising would cause great turmoil in the vacuum tube.

The pressure difference between inside/outside the tunnel is greater than that between a plane and the atmosphere.

Train running at 500mph vs any turmoil is an accident waiting to happen.
This explanation doesn't explain why the poster being asked the question thinks it will 'kill everyone in the hyperloop'. This implies that the poster asserting this doesn't understand that it won't be one contiguous tunnel with a uniform vacuum throughout, or that engineers working on this would create a system that would kill literally everyone traveling in it if the tunnel depressurized. Which is kind of a silly thing to assert.

It would be like asserting that a loss in cabin pressure in your plane example would always kill everyone on board...which, you know, isn't the case. Right?

ETA: Didn't notice this was a revived thread.
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Old 08-27-2018, 12:08 PM
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As far as I know he only got permission to dig under his own property.
Well, then, all he has to do is buy a strip of land 100 feet wide and the length of the proposed Hyper Loop, and he is in business!
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Old 08-29-2018, 10:50 AM
Khendrask Khendrask is offline
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This explanation doesn't explain why the poster being asked the question thinks it will 'kill everyone in the hyperloop'. This implies that the poster asserting this doesn't understand that it won't be one contiguous tunnel with a uniform vacuum throughout, or that engineers working on this would create a system that would kill literally everyone traveling in it if the tunnel depressurized. Which is kind of a silly thing to assert.

It would be like asserting that a loss in cabin pressure in your plane example would always kill everyone on board...which, you know, isn't the case. Right?

ETA: Didn't notice this was a revived thread.
A loss in cabin pressure on an aircraft is nowhere near the catastrophic event of a train full of passengers moving at nearly the speed of sound suddenly hitting a wall of air. It would be about the same as slamming into concrete at the same speed. This isn't about depressurization, it is about losing vacuum integrity.
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Old 08-29-2018, 03:03 PM
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A very small earthquake probably won't do anything to a freeway, but that same earthquake could kill everyone in the hyperloop.
Uh, no? Everyone thinks everything is a rubber balloon or soap bubble just waiting to burst. If there was a breach in the hyperloop, the trains would run less efficiently. Vacuums don't explode and the tunnel is already under the pressure/weight of the atmosphere and structurally sound so it wouldn't implode either. A breach would equalize the pressure (that is, reduce the net pressure on the walls). Why would this suddenly cause an explosion or implosion?

If the cabin, not the tunnel, were punctured odds are it would be a slow leak. Again, solid steel trains are not soap bubbles or rubber balloons, and the explosive decompression you see in movies resulting from, say, a stray bullet is... bad movie physics. Now, a high explosive bomb that blows open a huge swath of the train might do it... but derailing a normal train would have the same effect, and probably take less high explosives to achieve (blow the tracks).
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Old 08-29-2018, 03:26 PM
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The tunnels he's digging have nothing to do with hyperloop.

I'll start believing the hyperloop companies are something more than a scam to attract investment money when I see any of them invest even half the time solving the serious engineering problems involved than they do preparing cool videos and designing futuristic pods and terminals that look good in investment brochures but which don't address the serious engineering challenges of this thing.

The first place to start is metal expansion. Musk claims that hyperloop will be a solid welded steel tube, with expansion being taken up at the end terminals. This is a complete non-starter, because the tube isn't straight. Therefore, metal expansion will cause the entire shape of the loop to change - by many hundreds of feet. and going straight isn't even possible because the earth is curved and a straight line between two points is a great circle arc.

If you solve that problem, you can then consider buckling problems from differential heating on the top and bottom of the tube. And note we haven't even talked about the challenges of maintaining a vaccuum, how you are supposed to get people out of the thing if a car stops in the middle, how you protect it and the people from catastrophic failure if the immense forces on it are released by a puncture, and on and on.

These are challenges with no current engineering solutions. So if you see a company claiming to be building a hyperloop but all they have to show you is lots of pretty models of termnal buildings and futuristic capsule designs, grab your wallet and run.
Isn't the temperature static once you get a few feet underground?
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Old 08-29-2018, 03:28 PM
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Uh, no? Everyone thinks everything is a rubber balloon or soap bubble just waiting to burst. If there was a breach in the hyperloop, the trains would run less efficiently. Vacuums don't explode and the tunnel is already under the pressure/weight of the atmosphere and structurally sound so it wouldn't implode either. A breach would equalize the pressure (that is, reduce the net pressure on the walls). Why would this suddenly cause an explosion or implosion?

If the cabin, not the tunnel, were punctured odds are it would be a slow leak. Again, solid steel trains are not soap bubbles or rubber balloons, and the explosive decompression you see in movies resulting from, say, a stray bullet is... bad movie physics. Now, a high explosive bomb that blows open a huge swath of the train might do it... but derailing a normal train would have the same effect, and probably take less high explosives to achieve (blow the tracks).
You're discussing multiple small leaks from every direction. copperwindow was discussing a single, substantial rupture. In that case, you could end up with something like this:

https://www.youtube.com/watch?v=wBY3Z4F0dxk
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Old 08-29-2018, 05:34 PM
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Isn't the temperature static once you get a few feet underground?
Depends how much temperature variation you want to allow - according to this page, 6 feet deep gives you around a 20degF swing from winter to summer in Virginia, and you need to get down to 30 feet for temperature variation to be negligible. Digging down might help solve thermal expansion, but brings other challenges with maintenance, right-of-ways, and especially cost.

As Sam mentioned, there are a huge number of engineering challenges that are often minimized by the cheerleaders. Elon Musk's initial back-of-the-envelope cost estimates were absurdly optimistic - and even more absurd was his proposed ticket price of $20 per person per trip between LA and San Francisco. I think the only way this ever gets built is if some government or billionaire wants to build one as a money sink, as it seems exceptionally unlikely to ever be an economic mode of transportation.
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Old 08-30-2018, 03:09 AM
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You're discussing multiple small leaks from every direction. copperwindow was discussing a single, substantial rupture. In that case, you could end up with something like this:

https://www.youtube.com/watch?v=wBY3Z4F0dxk
Yeah... square cube law dude.

Humans weigh a hell of a lot more than a ping pong ball, especially in relation to our surface area. You'll have at maximum about 1 atmosphere of pressure, and that only for a few microseconds as the air expands into the vacuum, not the essentially infinite volume of air of the room's atmosphere relative to the "cannon" and you might recall that humans weigh substantially more than a bloody ping pong ball and have significantly greater mass per unit surface area.

Not a good example. Things that work on a tiny scale don't immediately scale up to a scale an order of magnitude higher. Especially when dealing with air related things.
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Old 08-30-2018, 07:13 AM
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Yeah... square cube law dude.

Humans weigh a hell of a lot more than a ping pong ball, especially in relation to our surface area. You'll have at maximum about 1 atmosphere of pressure, and that only for a few microseconds as the air expands into the vacuum, not the essentially infinite volume of air of the room's atmosphere relative to the "cannon" and you might recall that humans weigh substantially more than a bloody ping pong ball and have significantly greater mass per unit surface area.

Not a good example. Things that work on a tiny scale don't immediately scale up to a scale an order of magnitude higher. Especially when dealing with air related things.
The hyperloop with a rupture is basically a very big shock tube. You have a supply of pressurized air on one side and a tube with vacuum on the other. If you have a rupture, a wall of pressurized air will travel down the tube faster than the Speed of sound while the pod is travelling in the other direction with a couple of hundred mph.
The pod will basically be crushed together with everyone in it.
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Old 09-02-2018, 12:35 PM
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The hyperloop with a rupture is basically a very big shock tube. You have a supply of pressurized air on one side and a tube with vacuum on the other. If you have a rupture, a wall of pressurized air will travel down the tube faster than the Speed of sound while the pod is travelling in the other direction with a couple of hundred mph.
The pod will basically be crushed together with everyone in it.
That sounds impressive, until you realize the speed of sound is only 0.343 km / s, 300 mph is only 0.134112 km / s (for a total of 0.477 km / s), and vehicles like lunar modules travel at 10 km/s during atmospheric re-entry. That's not just one order, that's two orders of magnitude greater, and no, there is no magical, steel-crushing force that obliterates everything in its path.

Air is not a solid like concrete. Air is also not a liquid, like water, with surface tension and an inability to be compressed. Air is a gas, and colliding with a gas is not nearly as catastrophic as you seem to imagine. It doesn't have all that much mass, relatively speaking, and even the speed of sound is not an impressive figure. Heck, have a friend take a belt and snap you on the leg with it. That's something traveling at the speed of sound hitting your bare flesh.
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Old 09-02-2018, 02:22 PM
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One way is someone puts a truck bomb or gets access to an exposed part of the hyperloop pipe and wraps it with cutting charges. Cutting the heavy steel pipe all the way around or blowing it into fragments would possibly kill trainload(s) of people in that tube who are in transit.

But it's relative. Terrorists could also drive that truck bomb into a crowd somewhere, and with near future automated trucks, it need not be a suicide mission. Or park it next to a Federal building.

The threat we are talking about now is somehow shoots an elevated section of the pipe with an armor piercing rifle, or just an accident happens and a seam lets go partially somewhere. So it's a moderately slow leak into the tube.

Obviously the instant pressure gets detected at a sensor in the tube, every train in it is going to begin emergency braking. The actual hyperloop prototypes are mag lev, not air hockey style like Musk's original plan. So I guess it's just a matter of timing.

If the trains are stopped from emergency braking and this wall of air comes down and hits the trains, it would do..what? What do people think will happen? These trains won't have any windows and will be streamlined against the small amount of air in the tunnel. And unless it's a complete tunnel rupture, the air is going to be at low pressure.

Last edited by SamuelA; 09-02-2018 at 02:24 PM.
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Old 09-02-2018, 04:25 PM
Sam Stone Sam Stone is offline
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That sounds impressive, until you realize the speed of sound is only 0.343 km / s, 300 mph is only 0.134112 km / s (for a total of 0.477 km / s), and vehicles like lunar modules travel at 10 km/s during atmospheric re-entry. That's not just one order, that's two orders of magnitude greater, and no, there is no magical, steel-crushing force that obliterates everything in its path.
First of all, the lunar modules don't return to Earth. Second, the Apollo command module which did return has a special ablative heat shield designed to burn away and carry the tremendous heat built up from hitting the atmosphere at that speed. Third, re-entry starts at 400,000 ft, where air pressure is only about 5 * 10^-8 psi, and maximum G loading from atmospheric drag occurs around 200,000 ft, where air pressure is still only .003 psi. So re-entry tells us nothing about what would happen if a 700 mph wind were to hit a capsule at 14.7 PSI.

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Air is not a solid like concrete. Air is also not a liquid, like water, with surface tension and an inability to be compressed. Air is a gas, and colliding with a gas is not nearly as catastrophic as you seem to imagine. It doesn't have all that much mass, relatively speaking, and even the speed of sound is not an impressive figure. Heck, have a friend take a belt and snap you on the leg with it. That's something traveling at the speed of sound hitting your bare flesh.
You have no idea what you are talking about. Think about the destruction caused by 150 mph hurricane winds. Now consider that the energy in the wind goes up with the square of the speed.

And yes, the speed of sound is an impressive figure. Capt. Brian Udell and his navigator ejected from an F-15 at 800 mph. The navigator was killed instantly, and Udell had both his legs snapped in half, his arm dislocated, his helmet torn off and all the blood vessels in his face broken by the force of the windstream. This despite being strapped to a chair that wad supposed to protect him and wearing serious protective gear. I believe he is the only pilot to survive an ejection at that speed.

Ever see what happens to an aircraft if it loses streamlining at those kinds of speeds? It's usually converted into confetti with a few heavy pieces. The Reno Air Races have had several fatalities where a failed control surface caused the aircraft to basically disintegrate, killing the pilots instantly.
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Old 09-02-2018, 04:37 PM
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That sounds impressive, until you realize the speed of sound is only 0.343 km / s, 300 mph is only 0.134112 km / s (for a total of 0.477 km / s), and vehicles like lunar modules travel at 10 km/s during atmospheric re-entry. That's not just one order, that's two orders of magnitude greater, and no, there is no magical, steel-crushing force that obliterates everything in its path.

Air is not a solid like concrete. Air is also not a liquid, like water, with surface tension and an inability to be compressed. Air is a gas, and colliding with a gas is not nearly as catastrophic as you seem to imagine. It doesn't have all that much mass, relatively speaking, and even the speed of sound is not an impressive figure. Heck, have a friend take a belt and snap you on the leg with it. That's something traveling at the speed of sound hitting your bare flesh.
I think someone in this thread really needs to do some math, because there are two widely divergent opinions and that's unnecessary when there is actual math that can be done on the subject.

I am amenable to either view, but it needs to be supported by something beyond assertion.
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Old 09-02-2018, 04:42 PM
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One way is someone puts a truck bomb or gets access to an exposed part of the hyperloop pipe and wraps it with cutting charges. Cutting the heavy steel pipe all the way around or blowing it into fragments would possibly kill trainload(s) of people in that tube who are in transit.

But it's relative. Terrorists could also drive that truck bomb into a crowd somewhere, and with near future automated trucks, it need not be a suicide mission. Or park it next to a Federal building.

The threat we are talking about now is somehow shoots an elevated section of the pipe with an armor piercing rifle, or just an accident happens and a seam lets go partially somewhere. So it's a moderately slow leak into the tube.

Obviously the instant pressure gets detected at a sensor in the tube, every train in it is going to begin emergency braking. The actual hyperloop prototypes are mag lev, not air hockey style like Musk's original plan. So I guess it's just a matter of timing.

If the trains are stopped from emergency braking and this wall of air comes down and hits the trains, it would do..what? What do people think will happen? These trains won't have any windows and will be streamlined against the small amount of air in the tunnel. And unless it's a complete tunnel rupture, the air is going to be at low pressure.
So now what? Conceding that there are scenarios where there might be a low pressure leak that forces the trains to stop, you now have people sitting in an enclosed steel tube in the California sun, potentially hundreds of kilometers from the nearest exit. Are you going to cut them out? Remember, Musk's design calls for a one piece solid welded steel tube. There are other reasons that can't work, but assuming it did, what's the emergency procedure? are they expected to limp along at 50k for hours while baking in an enclosed tube?

Aside from metal expansion, the big thing to worry about is the vacuum itself. Have you see what happens to a tanker car when it loses just a few pounds of pressure due to cooling? It can crush flat. Tanker cars have roughly the same wall thickness as the Hyperloop spec. And they have special valves that allow pressure to equalize if the liquid or gas payload cools down and therefore lowers air pressure in the tank.

I believe the Mythbusters only had to drop a tanker car to about 4 psi (after disabling the safety valves) before it suddenly crushed like a pop can.

But here's the thing: Let's say these problems are potentially fixable. The thing that makes me highly suspicious of the various hyperloop companies is that they seem to be focusing their engineering efforts on things like making little maglev cars go faster, or hosting design competitions for futuristic terminal buildings, instead of trying to figure out how to handle 1300 ft of expansion between night and day, or buckling loads from differential heating, or expansion joints that can hold a vacuum and not require constant maintenance, or how to draw a vacuum in reasonable time from hundreds of kilometers of tubing, or...

Real engineering companies tackle the hard and potentially show-stopping problems first, so they can validate the feasiblility of the project before investing more money. Companies that focus on flashy public events and headline grabbing stunts are generally trying to attract money from governments or private investors, and the actual engineering can come later - or never. I have seen this kind of rent-seeking startup with a bogus product too many times to count. This has the smell of the same kind of thing.

Last edited by Sam Stone; 09-02-2018 at 04:43 PM.
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Old 09-02-2018, 05:05 PM
Sam Stone Sam Stone is offline
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I think someone in this thread really needs to do some math, because there are two widely divergent opinions and that's unnecessary when there is actual math that can be done on the subject.

I am amenable to either view, but it needs to be supported by something beyond assertion.
He just converted the speed to km/s, I guess because he somehow thinks that this makes it look slower or less threatening or something.

Let's put it in another perspective: A .44 magnum bullet travels about 450 m/s, (or if you like, a measly .45 km/s) and weighs 16 grams. A cubic meter of air at sea level weighs about 1.3 kg.

Air may seem insubstantial, but it has inertia like any other mass. The faster you hit it, the more energy you must expend either moving it out of the way, or compressing it to slow you down. At the speeds we are talking about, air isn't quite a brick wall, but it's enough to turn a lightweight capsule into a jumbled mess in very short order.

By the way, it's a myth that surface tension is what makes water hurt when you dive into it from a height. What makes water hurt (or kill you) if you fall into it from a height is simple inertia. The water can't move out of the way fast enough, so the energy get dissipated by your body instead. And once you jump from a certain height (250 ft or more) you might as well jump onto concrete.
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Old 09-02-2018, 06:45 PM
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So now what? Conceding that there are scenarios where there might be a low pressure leak that forces the trains to stop, you now have people sitting in an enclosed steel tube in the California sun, potentially hundreds of kilometers from the nearest exit. Are you going to cut them out? Remember, Musk's design calls for a one piece solid welded steel tube. There are other reasons that can't work, but assuming it did, what's the emergency procedure? are they expected to limp along at 50k for hours while baking in an enclosed tube?
Ok that part is addressable. Obviously the train would have onboard batteries so in the near term, it's not going to overheat because there life support would be running off the batteries.. There would have to be doors that can be closed, with safety interlocks, so you can separately pressurize-depressurize sections of this thing. So the solution would be to close the doors before and after the stopped train and then open some pressurization vents to fill the tunnel in that section.

Once that happens, pressure interlocks would allow for the doors inside the train to be opened from the inside, and there would have to be some headlamps or something in the emergency kit. Passengers could then walk to the nearest emergency airlock which you could put every few kilometers or so.

But yes, all this hardware adds cost. One thing discussed is building much smaller cargo hyperloop systems first. Since cargo systems would need far less safety mechanisms and would need not be as reliable. This has historical precedence - the first elevators were used in factories and were considered too dangerous for passengers.

Also, these heavy pressure doors? Located in unguarded stations every few kilometers? Terrorists could probably hot-wire a door to close, putting a steel door in the way of a train going several hundred mph.

Of course, eurorail has the same vulnerability. I am not even sure why this doesn't happen more often. All a terrorist would have to do would be to drive a cement truck or something onto the tracks, ramming through any protective fences, a few seconds before a train is about to come.

Last edited by SamuelA; 09-02-2018 at 06:48 PM.
  #31  
Old 09-02-2018, 07:05 PM
RTFirefly RTFirefly is offline
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Let's take a more mundane problem with a hyperloop: capacity.

The D.C. Metro's cars can hold 175 people each. It can run 8-car trains at rush hour, so that's 1400 people per train. it can run trains at 5-minute intervals, so that's 12*1400 = 16,800 people per hour.

To match that capacity, a hyperloop with 1-person pods would have to shoot them through the tunnel at intervals of roughly 1/5 of a second apart. Can the engineering handle that? I'm skeptical. And if it can't, then it's not a meaningful mass transit solution.
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Old 09-02-2018, 07:33 PM
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Let's take a more mundane problem with a hyperloop: capacity.

The D.C. Metro's cars can hold 175 people each. It can run 8-car trains at rush hour, so that's 1400 people per train. it can run trains at 5-minute intervals, so that's 12*1400 = 16,800 people per hour.

To match that capacity, a hyperloop with 1-person pods would have to shoot them through the tunnel at intervals of roughly 1/5 of a second apart. Can the engineering handle that? I'm skeptical. And if it can't, then it's not a meaningful mass transit solution.
Run longer trains, be cheaper per train as well.

I am sure you can see quite trivially that the hyperloop has more capacity per track due to the higher speed. If you did 1400 person hyper-trains, you could launch them every 2 minutes or sooner because the higher acceleration means the tracks are cleared sooner.

With that said I don't think the hyperloop is all that feasible. The problem with building ones is a local government has to agree, clearing the needed land and helping with the funding. At numerous levels, not just 1 government, all the governments along the route. Especially somewhere like California, where landowners can file a suit and block progress until the cases are decided in a court. Even if the landowners always eventually lose, adding 10 years to a project easily makes it infeasible.

Less expensive airline travel, or autonomous busses are just more practical. The simple reason is if I invent an autonomous bus or minivan tommorrow :

a. Nobody has to agree but the NTSB*. As long as they approve my vehicle for the road, it can start making revenue immediately without delay. (while a train is useless unless the entire track and 2 full stations are completed)

b. Hyperloop stations are in fixed locations. As ridership changes, autonomous busses can just go to whereever they are summoned.

c. You can easily change the size of the bus, from a minivan to an actual bus, or use multiple sizes.

d. You can make the vehicles actually drop people off where they are needed, it's an end to end solution.

e. Slower speeds and armor in the vehicle itself can make fatalities uncommon.

f. Yes, it takes longer but the busses would have wifi and charging plugs and reclining seats and automated security.

*this isn't true today but Congress is reasonably likely to pass a bill giving the Feds exclusive power to regulate autonomous vehicles and not state governments. It's obviously within their power as it's clearly interstate commerce.

Last edited by SamuelA; 09-02-2018 at 07:35 PM.
  #33  
Old 09-02-2018, 08:22 PM
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He just converted the speed to km/s, I guess because he somehow thinks that this makes it look slower or less threatening or something.
No, I converted to km/s to make a direct comparison to another figure generally given to km/s that hit's a "wall" of air at a considerably faster rate and doesn't instantly crumple as the person I was responding to seemed to think it would.

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Let's put it in another perspective: A .44 magnum bullet travels about 450 m/s, (or if you like, a measly .45 km/s) and weighs 16 grams. A cubic meter of air at sea level weighs about 1.3 kg.
So what? You literally just threw out random numbers without considering any of the implications. By your quoted figures, a small, soft piece of metal travels through air at 450 m/s (about the speed of the "wall of air" impact) and does not deform, but I'm to believe a hardened structure at several times the mass will fold like paper.

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Air may seem insubstantial, but it has inertia like any other mass. The faster you hit it, the more energy you must expend either moving it out of the way, or compressing it to slow you down. At the speeds we are talking about, air isn't quite a brick wall, but it's enough to turn a lightweight capsule into a jumbled mess in very short order.
So they wont build the hyperloop out of balsawood. What, did you think it would require some infinitely light vehicle to achieve a measly 300mph (the number the above poster gave)? Japanese bullet trains move faster than that without a vacuum and are certainly not flimsy constructions. Even if we go with the proposed speed of about twice that, it's only 4 times the kinetic energy and not enough to crumple solid steel.

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By the way, it's a myth that surface tension is what makes water hurt when you dive into it from a height.
Which is why I specifically explained that air can be compressed as the major difference between it and a liquid.

Quote:
What makes water hurt (or kill you) if you fall into it from a height is simple inertia. The water can't move out of the way fast enough, so the energy get dissipated by your body instead. And once you jump from a certain height (250 ft or more) you might as well jump onto concrete.
Air is not like water because air can be compressed. Air gives way readily, water does and cannot because water is a liquid. Surface tension adds a small amount of force but is a non factor. The physical state of water is what is more important (and its density).
  #34  
Old 09-02-2018, 08:38 PM
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First of all, the lunar modules don't return to Earth. Second, the Apollo command module which did return has a special ablative heat shield designed to burn away and carry the tremendous heat built up from hitting the atmosphere at that speed.
That's cute and all, but no one was saying that the hyperloop would hit air at that speed, so the heat you ramble about is entirely irrelevant. My point was that it's insufficient crushing force to crumple the module like a tin can. Anything else is you either trying to look smart or missing the point.

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You have no idea what you are talking about. Think about the destruction caused by 150 mph hurricane winds. Now consider that the energy in the wind goes up with the square of the speed.
Wooden framed structures filled in with drywall are not the same as a solid steel tube. There's also a significantly larger surface area involved in hurricane force winds against a building, and wind passing down a tube dude. That's not even remotely comparable.

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And yes, the speed of sound is an impressive figure. Capt. Brian Udell and his navigator ejected from an F-15 at 800 mph. The navigator was killed instantly, and Udell had both his legs snapped in half, his arm dislocated, his helmet torn off and all the blood vessels in his face broken by the force of the windstream. This despite being strapped to a chair that wad supposed to protect him and wearing serious protective gear. I believe he is the only pilot to survive an ejection at that speed.
And bare flesh is comparable to steel in your mind? Why do you keep making comparisons to really, really, soft materials as if they're relevant? Yes, I'd hate to be buck naked hitting the air at that speed. So what?

Quote:
Ever see what happens to an aircraft if it loses streamlining at those kinds of speeds? It's usually converted into confetti with a few heavy pieces. The Reno Air Races have had several fatalities where a failed control surface caused the aircraft to basically disintegrate, killing the pilots instantly.
Yeah, drag can definitely rip off the joints on a piece of metal sticking up from a plane's surface, and that can chain into a cascading failure of the structure. So, instead of having ailerons, flaps or other potentially jutting structures, the engineers would be sane enough not to add silly jutting structures that are only needed for controlling aircraft and just use a bullet or other substantially lower drag creating design.
  #35  
Old 09-02-2018, 08:46 PM
RTFirefly RTFirefly is offline
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Run longer trains, be cheaper per train as well.

I am sure you can see quite trivially that the hyperloop has more capacity per track due to the higher speed. If you did 1400 person hyper-trains, you could launch them every 2 minutes or sooner because the higher acceleration means the tracks are cleared sooner.
But Musk is selling this as one-person pods.

Mode of Transport X has more capacity than Mode of Transport Y if X is faster than Y and everything else is the same. But can you accelerate a 1400-person train in a vacuum tube? Doesn't the whole idea rely on the capsules being fairly light in order to get them up to a few hundred mph really quickly?

Maybe you can take your time to accelerate that hypertrain if it's going from LA to SF, but if it's just going to Dodger Stadium from a nearby subway stop, or to O'Hare from downtown Chicago (these are two of Musk's hyperloop proposals), how's that going to work?
  #36  
Old 09-02-2018, 09:00 PM
SamuelA SamuelA is offline
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But Musk is selling this as one-person pods.
Cite please. I read the original hyperloop plans when Musk first released them.
  #37  
Old 09-02-2018, 09:08 PM
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But Musk is selling this as one-person pods.

Mode of Transport X has more capacity than Mode of Transport Y if X is faster than Y and everything else is the same. But can you accelerate a 1400-person train in a vacuum tube? Doesn't the whole idea rely on the capsules being fairly light in order to get them up to a few hundred mph really quickly?

Maybe you can take your time to accelerate that hypertrain if it's going from LA to SF, but if it's just going to Dodger Stadium from a nearby subway stop, or to O'Hare from downtown Chicago (these are two of Musk's hyperloop proposals), how's that going to work?
You can't accelerate any faster than passenger comfort allows anyway, which limits you to a G or so. It only takes a couple minutes of this acceleration to get you to any reasonable speed you would be looking for.

For shorter jaunts, if hyperloops are used at all, lower speeds would be used.

The O'Hare to Chicago would be about 10 miles, about the shortest that such a track would have any use. You could get up to speed on that route, if you wanted to, or just top out at 200mph or so, still get there a bit faster than through traffic.

I will agree that one person pods is not a great idea, unless the pods are capable of linking together and acting as a single unit.
  #38  
Old 09-02-2018, 09:44 PM
etasyde etasyde is offline
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Cite please. I read the original hyperloop plans when Musk first released them.
This is also news to me, every design I've seen or read about has been more like a train car. Sure, each car might operate independently, but not as pods for individuals. I can't see individual pods being particularly more useful than a train car anyway. With a train-car, all of the "stopping time" at a station is essentially in parallel for each passenger, no need to gum up the tracks doing it sequentially. If this hyperloop is intended as a mass transit system and not a luxury of the ultra-rich, then having 20+ cars waiting to slowly align to the station, load/unload and then launch again seems inefficient. Way worse so if it's more like 200+ (BART) or 2000+ (Tokyo) passengers at each stop.

I also don't know why you'd need a bullet train or faster for a short run like 10 miles. Metro lines are more than sufficient for that, already in place, and probably cheaper to operate. I'd imagine a commuter would best be served by, say, boarding in one city then deboarding in another and transferring over to the local metro system. Likewise, taking the local metro to the hyperloop and then looping across country or between cities. The idea that it'd replace cars sounds like Elon being, well, Elon.
  #39  
Old 09-03-2018, 01:09 AM
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Maybe you can take your time to accelerate that hypertrain if it's going from LA to SF, but if it's just going to Dodger Stadium from a nearby subway stop, or to O'Hare from downtown Chicago (these are two of Musk's hyperloop proposals), how's that going to work?
I don't think those are proposed as hyperloops. They're dumb and unworkable and probably never going to happen, but for other reasons.

Last edited by Lord Feldon; 09-03-2018 at 01:11 AM.
  #40  
Old 09-04-2018, 01:58 PM
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I agree that all the talk of the hyperloop going on is just silly. You don't need high speed trains to go to Dodger Stadium.

If anybody wanted to build one, it should be transcontinental. Otherwise, what's the point? It's supposed to be a viable alternative (faster, cheaper, safer) to flying.

I envision it as being like the "subshuttles" of Gene Roddenberry's pilot "Genesis II". To wit:
An elaborate "Subshuttle" subterranean rapid transit system was constructed during the 1970s, due to the vulnerability of air transportation to attack. The Subshuttles utilized a magnetic levitation rail system. They operated inside vactrain tunnels and ran at hundreds of miles per hour. The tunnel network was comprehensive enough to cover the entire globe.
The two pilot movies never addressed what happens if the train breaks down three miles down and 2000 miles from the coast in the mid-Atlantic or mid-Pacific. I know I'd want to know before I'd ride it!
  #41  
Old 09-05-2018, 01:47 PM
iamthewalrus(:3= iamthewalrus(:3= is offline
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But Musk is selling this as one-person pods.
I've read a decent amount about the hyperloop and you're the first person I've seen mention 1-person pods. I think you might be mistaken here.

As you point out, 1-person pods make no sense at all.
  #42  
Old 09-13-2018, 02:21 PM
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The one Musk envisions for Chicago,https://www.inverse.com/article/4595...deal-announced uses 16 people cars, reworked model x's, I think. Everything I have read says his billion dollar price tag is ridiculous. But he told the mayor that he would cover the entire cost so Rahm said "sure".
  #43  
Old 10-04-2018, 01:24 PM
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Update:

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Hyperloop Transportation Technologies Inc. unveiled its first full-scale passenger capsule, offering the world a peek at the future of travel.
The capsule, 105 feet (32 meters) long and weighing 5 tons, was shown in Spain and will be moved to Toulouse, France, for additional assembly before it’s used on one of the first commercial tracks, the California-based startup, known as HyperloopTT, said in a statement. Named the Quintero One, the product is made almost entirely out of composite material.

SOURCE: First Hyperloop Passenger Capsule Unveiled
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  #44  
Old 10-04-2018, 02:09 PM
Sam Stone Sam Stone is offline
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Nobody questions the ability of a company to make futuristic capsules. The fact that they are focusing their efforts on the easiest problem makes me even more skeptical.

Show me a ten mile curved test track with a vacuum in it that can adjust to temperature swings, detailed plans for emergencies and a design for a pump that can evacuate hundreds of kilometers in reasonable time for reasonable cost. Then I might believe you are serious about building a hyperloop.

Until then, it's just flash for the suckers.

Last edited by Sam Stone; 10-04-2018 at 02:09 PM.
  #45  
Old 10-04-2018, 03:45 PM
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Show me a ten mile curved test track with a vacuum in it that can adjust to temperature swings, detailed plans for emergencies and a design for a pump that can evacuate hundreds of kilometers in reasonable time for reasonable cost. Then I might believe you are serious about building a hyperloop.

Until then, it's just flash for the suckers.
According to the article there are now two other competitors: Arrivo and Virgin Hyperloop One and Virgin is in talks with India to build a hyperloop.

Also, this capsule is supposedly headed for a commercial track somewhere and HyperloopTT is setting up a track in China (all in that article).

I am dubious as well that it will all pan out but it does seem like some are having a real go at it. It would be weird to have three companies working on it separately if it is all a joke.
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Last edited by Whack-a-Mole; 10-04-2018 at 03:46 PM.
  #46  
Old 10-04-2018, 04:21 PM
Sam Stone Sam Stone is offline
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Not at all. When there is a whiff of government or venture capital money in the air and an opportunity for free promotion because ir's the buzz of the day, the rent seekers come out in droves.

Go look at how much money the various 'water from air' solutions have extracted from gullible governments or NGO's. Check out the disastrous history of the PlayPump, and all the money that got invested in it despite it's having been a ridiculously flawed concept from the beginning.

Just recently, France wasted a whole lot of money on 'solar roadways', despite the obvious ridiculousness of the concept. Then there's the Moller Skycar, which has blown through hundreds of millions of dollars by being 'ready to fly in six months' for the past 30 years.

There are a lot of rich idiots in Silicon Valley, and a lot of NGO's and governments who care more about looking good than actually achieving something. These goofball ideas are aimed right at them.

I'll repeat: Any serious engineering firm wouldn''t have spent a nickel on fancy pod designs and terminal designs until they did the R&D to prove that the 'showstopper' items could actually be solved. And Hyperloop has a number of problems that there are no existing engineering solutions for, none of which involve capsule or terminal design.

Last edited by Sam Stone; 10-04-2018 at 04:22 PM.
  #47  
Old 10-04-2018, 04:40 PM
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Why is the capsule streamlined? I thought this was supposed to work in a vacuum?
  #48  
Old 10-04-2018, 04:42 PM
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Why is the capsule streamlined? I thought this was supposed to work in a vacuum?
I think it's low pressure, not a complete vacuum. Plus, it probably looks cooler that way.
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  #49  
Old 10-04-2018, 06:45 PM
Sam Stone Sam Stone is offline
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No, it's essentially a vacuum. There is residual air pressure left over because it's pretty much impossible to get a perfect vacuum, but it's on the order of 1/1000 of normal sea level pressure. The difference between that and a perfect vacuum is just about nil when it comes to the forces on the tube, the car, etc. So the argument that it's just a 'partial vacuum' is wrong. For engineering purposes, it's a vacuum.
  #50  
Old 10-04-2018, 06:52 PM
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From Hyperloop One, a competitor of the company referenced above:

Quote:
Why is Virgin Hyperloop One's test pod (XP-1) aerodynamic, given it operates in a low-pressure environment?

Our hyperloop system exists in a low-pressure environment, not a complete vacuum. When XP-1 moves in the tube, the pressure rises and drops, and air flow accelerates and decelerates around it. The shape of the pod (the aerodynamic shell or aero-shell) has been optimized to accommodate aerodynamic loads while adhering to strict constraints.
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