Hyperloop

[RDoc]

I've been concerned about what would happen if the tube suffered a major breach that caused essentially instantaneous re-pressurization starting at one point, for example, a terrorist breaking the tube with a bomb. This would send a wave of very nearly full pressure air at close to Mach 1 down the tube which would cause on-coming cars to go from just subsonic to close to Mach 2 in a very short time, causing very rapid deceleration. To get a feel for how bad this would be, I assumed the maximum pressure would be at about Mach 1.5 and a transonic drag coefficient of 3. With a 15000 kg car and 1.5 sqm frontal area, that would result in a deceleration of about 5 g and an average pressure on the front of about 4.5 atm, so likely around 10 atm at the center. Note: I don't think these estimates are too high, but they might well be too low, maybe by a significant amount.

This would be pretty severe, although not catastrophic. Although the seat belts might be enough, if I'm off by a factor of 2 or more, air bags would definitely be a good idea. If nothing else happened it would take about 15 sec for the car to stop, but a better way to deal with this might be to have pressure sensors all along the tube that in such an event, would trigger an emergency re-pressurization of the entire tube and emergency stop of all the cars. That would avoid the wall of air effect and if the brake pads went out radially, they could help prevent the cars from being tossed around inside the tube.

This brings up an interesting mechanism for aiding an emergency stop of all the cars. Re-pressurize the tube all along it's length at a controlled rate such that aerodynamic drag would slow the cars down at a fast but safe rate to aid the mechanical brakes. If the system were really clever, it could time the re-pressurization such that parts of the tube containing cars moving away from the problem would be re-pressurized only behind the cars. Since they are moving at close to Mach 1, the air wouldn't catch up with them.

Obviously, if the terrorists blew the bomb up when a car was passing, the passengers in that car would be in serious trouble, but it would be good if it didn't wipe out all the cars in the tube.

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Definitely agree, LA-SF path seems like there are too many politics surrounding the project for it to easily get off the ground. I would love to see something like the Google Fiber project where cities pairs would bid for it. I think there could be a better option than LA-SF where land rights don't matter as much and where it could be mostly ground based. Maybe for example Dallas - Houston? Its also a much shorter route so it would require less length in track and fewer pods. I haven't done the math, but seems like it could cost half of SF-LA. It would also provide an excellent proof of concept for future city pairs to go off of.

And speaking of Google and the Fiber model... they have loads of cash and seem to go after exciting projects, this seems like a perfect match for them. They could even tie it in to their advertising business model. Imagine rolling onto the hyperloop and having 5 minutes of ads streamed to your 17in touchscreen display? or pay a little extra for an ad-free ride. And this would cost Google less than the Motorola acquisition!

Those sound like very good ideas!

 

[Palpatine]

What about rust? That is a lot of steel tube exposed to the elements.

If this was already mentioned earlier in the topic, my apologies.

 

[keys]

What about rust? That is a lot of steel tube exposed to the elements.

If this was already mentioned earlier in the topic, my apologies.

Oil pipelines are often made of steel as well. No problem there, you just have to paint it .

 

[IceWendigo]

"Anyone who wants to attack this problem is free to do so without any bidding: the whole idea is open-source."
Yes, it was a figure of speech for multiple interested parties rather than actual bid, indeed all that want to develop the hyperloop should be collaborating (governments, tech universities, corporations, public/future users).

"Dallas - Houston"
The more such pairings are imagined and potentially interested the better.

I read a comment somewhere, that we should have a hyperloop station in a new city, start a city in a uninhabited region from the ground up, with the transport/logistics/infrastructure (local monorail, hyperloop, internet, aqueducs, pneumatic distribution system, ect) designed and thought of from the beginning. It sounds like a joke, but its not that crazy.


Urban section: Could you have a modular design that would have shorter pods(maybe without compressor but maybe with an air conduit for connection) travel at lower speeds (ex: 100-300 mph) in tubes with sharper turns and closer to normal air pressure, so that you could hop in a pod in local station that would zoom above traffic at speeds varying from 50-300 mph, then arrive in the Main Hyperloop Station, connect to a Transit Hyperpod pod there, and then enter the fast low-pressure tube for the ride to the other big citie's Hyperloop terminal?
That or using something like SkyTran would be sweet.

 

[DonPedro]

Interesting blog post over at Scientific American: http://blogs.scientificamerican.com/observations/2013/08/14/we-could-make-elon-musks-hyperloop-real/

 

[AnOutsider]

Interesting blog post over at Scientific American: http://blogs.scientificamerican.com/observations/2013/08/14/we-could-make-elon-musks-hyperloop-real/

Guess this covers the heat criticism?

Oh, did I not mention the Inconel skis? These struts, made from a superalloy more commonly found on spaceships and nuclear power plant steam generators—which should give you some idea of the kinds of temperatures and pressures the supermetal can withstand—help the pod glide along the tube at 1,220 kilometers-per-hour

 

[RDoc]

Guess this covers the heat criticism?

I still don't get the "heat criticism". There can't be any significant heating of the skids under normal operation because that would be from friction which is the whole point of the air skids, the friction is so low there is almost no energy loss. If there were significant heating, it would mean there was significant frictional losses that would preclude the whole idea of the car coasting almost all the time.

 

[Palpatine]

I think Elon should form a tax deductible foundation called.... wait for it..... The Hyperloop Foundation.
Accept tax deductible donations to build a prototype of the Hyperloop.
Elon could make a tax deductible contribution to fund 10% of the prototype budget, then see if there is enough interest from the rest of the world to make this happen.

They could either find a pair of cities that volunteer to grease the skids for permits and land or they could just build it in the boonies where there are 10-20 miles of straight land for a prototype.
I am sure Ted Turner or someone else owns enough scrub land in Texas or Montana or somewhere like that.

This idea needs a physical prototype of some distance so that it can get up to a test speed to prove the concept and then decelerate again.
I think enough tube length to accelerate to 300 mph would be sufficient for the prototype. They don't need to prove the maximum 700 mph during the demo phase.

At 300 mph you are doing about 5 miles per minute. So I think this prototype needs to be at least 10-20 miles in length to get any sort of real world testing done.

Which would be better? A pair of two cities that are that length apart and they volunteer to fast track the permits?
Or should it be built way out in the middle of nowhere on really cheap land?

 

[AnOutsider]

I still don't get the "heat criticism". There can't be any significant heating of the skids under normal operation because that would be from friction which is the whole point of the air skids, the friction is so low there is almost no energy loss. If there were significant heating, it would mean there was significant frictional losses that would preclude the whole idea of the car coasting almost all the time.

This is not at all an area I'm proficient in. Given that, from some of what I've read (on the web and here), one of the issues was with the air being heated (as someone said, like when a bullet goes through the barrel of a gun). I think the solution was a huge amount of water to cool things, but looks like the material is also highly resistant to heat. Does this mean though, that the pods will be super hot when they enter the stations? Or will the water be used primarily at the end to cool them down?

 

[DonPedro]

This is not at all an area I'm proficient in. Given that, from some of what I've read (on the web and here), one of the issues was with the air being heated (as someone said, like when a bullet goes through the barrel of a gun). I think the solution was a huge amount of water to cool things, but looks like the material is also highly resistant to heat. Does this mean though, that the pods will be super hot when they enter the stations? Or will the water be used primarily at the end to cool them down?

I think this is one of the concept's weaknesses/areas of potential improvement. Bringing hundreds of gallons of water on the capsules for cooling, converting that into steam on the way and then somehow swapping one or several water & steam cartridges is not an elegant solution. Hopefully this can be improved upon.

 

[Ardie]

I had been doing a little thinking about a workable prototype.
First of all, it doesn't really have to be full-sized, and it doesn't have to run a great distance.
If a prototype runs at "only" half speed of 300-ish mph, and small 4-6 person pods, it ought to be good enough to prove the idea and to shake out any bugs.

If it were to be built in America, I can think of two possible locales off the top of my head:

A) Between Albuquerque International Sunport and Virgin Galactic's Spaceport America - about 175 miles.
Seems (to me) to be the ideal way to travel just before you blast off into space. But a 175 mile long set of pylons would be very expensive, indeed for only a few passengers a day.

B) Between Orlando Airport and Walt Disney World - about 25 miles.
A shorter (and less expensive) test. The route is not a very straight shot, though. 25 miles is almost too short for a real test. At speeds of 150 mph, you'd on and off in about 5 minutes.
Walt Disney World attracts over 15 million visitors each year, so a hyperloop transport from the airport to, say, the Contemporary Resort, where it would connect to Disney's Monorail system, seems like a perfect match. And Disney may even help fund the idea.

-- Ardie
Sign me up.

 

[Rodolfo Paiz]

Given that, from some of what I've read (on the web and here), one of the issues was with the air being heated (as someone said, like when a bullet goes through the barrel of a gun). I think the solution was a huge amount of water to cool things, but looks like the material is also highly resistant to heat. Does this mean though, that the pods will be super hot when they enter the stations? Or will the water be used primarily at the end to cool them down?

None of the above. Keep in mind that a gun barrel does not get hot primarily because of the bullet, the friction, or the air. It gets hot because of the controlled explosion of firing the gun and the cloud of fiery-hot gases that are propelling the bullet. Those heat the barrel quite a bit, the bullet itself much less so.

The water in the intercoolers on the pod is there to cool the compressed air drawn into the front of the pod, which heats up when compressed, before releasing it out the back of the pod. This water and that airflow has nothing to do with air friction on the outside of the pod itself, which is what (I think) most people are worried about when they talk about heat and friction. My understanding is that the pods should not have any real friction problem per se, because first, they ride on air bearings for very low "rolling" friction and second, the surrounding air pressure in the tube is so low.

 

[IceWendigo]

"A shorter (and less expensive) test. The route is not a very straight shot, though. 25 miles is almost too short for a real test. At speeds of 150 mph, you'd on and off in about 5 minutes."
Make it a 300mph 2 minute roller coaster ride! With twists and turns!

Orlando airport to Disney would be nice (if the NIMBY issues do not manifest themselve, no clue about Florida politics)

 

[DonPedro]

By the way, those who can't wait can have a Hyperloop straight away at a discount price of only GBP14.99: http://www.gooutdoors.co.uk/shimano-hyperloop-4000-fb-front-drag-reel-p188472

 

[Palpatine]

Here is the Hyperloop video.

 

[Rodolfo Paiz]

Not to criticize Palpatine, but the still image of that video shows one of the errors of perception out there: people think that the pod fills up the tube like the bullet in a rifle barrel (thus causing all sorts of friction concerns), and that's just not true. Avoiding friction is precisely the reason that the pod is much smaller than the tube. In terms of frontal area, the pod is barely (IIRC) 36% of the cross-section of the tube. There's a lot of space left over above and to the sides of the pod, and that's also what allows the pod to "bank" during a turn.

 

[ElSupreme]

What about rust? That is a lot of steel tube exposed to the elements.

If this was already mentioned earlier in the topic, my apologies.

You can paint it, and implement something called impressed current system. It is a form of http://en.wikipedia.org/wiki/Cathodic_protection

It works quite well.

And I keep working 12 hour days. I will hopefully get to finally read the hyperloop document tonight. It might be in there, but this is fairly common pipeline protection.

 

[BriansTesla]

As for the heat generated, why not cool the air in the tube to an appropriate temperature? This could be done with stationary chillers without adding to the internals of the pods.

And for the number of travelers per hour/day etc, is there any reason that pods could not be longer, or multiple pads linked to increase capacity?

 

[DonPedro]

As for the heat generated, why not cool the air in the tube to an appropriate temperature? This could be done with stationary chillers without adding to the internals of the pods.

I suppose that with the energy going into compression it will not make a big difference if the intake air temperature is 50 or -50. But I am not an expert.

 

[RDoc]

People ..... Please!!!!! There is no heating problem!!!


To echo Radolfo Paiz and others (including myself). The water in the car is to cool the air being compressed for use in levitating the car and pressurizing the passenger compartment. It has NOTHING to do with air resistance, friction of the car with the tubes, the air skids sliding on the walls, etc. When you compress air it gets hot, the water cools it by being turned to high pressure steam which is held in the car until it gets to the station so it doesn't have to be pumped out of the tube, condense in the tube, and so on. Turning water into steam absorbs a lot of heat energy.

Again, it has nothing to do with the motion of the car in the tube and there is not heat issue in any way related to that motion.