Elon Musk's 'Hyperloop' idea for San Francisco-LA link

[muriel_volestrangler]

US-based entrepreneur Elon Musk has unveiled his proposed supersonic "Hyperloop" transport concept to link Los Angeles and San Francisco.

The SpaceX, Tesla and Paypal founder envisions using magnets and fans to shoot capsules floating on a cushion of air through a long tube.
...
Capsules could depart as often as every 30 seconds and could also carry personal automobiles, travelling faster than 700mph, Mr Musk said.
...
The San Francisco to Los Angeles route would be elevated alongside a current California motorway, which would enable it to be constructed with minimal disputes over land rights, Mr Musk said. The tube and supporting columns would be designed to withstand earthquakes.

http://www.bbc.co.uk/news/world-us-canada-23677205

The paper: http://www.spacex.com/sites/spacex/files/hyperloop_alpha-20130812.pdf

An earlier discussion, before the plans were released: http://www.democraticunderground.com/10023442609

I think I was right that (a) it's not faster than sound (Mach 0.91 is the suggested figure) and (b) it's not 'pneumatic', in that it's not air pressure from behind pushing it. It is, in a way, a hovercraft/lifting body cross, inside a tube. It's interesting he thinks batteries can power the fan to direct the air out of the way of the body, and underneath it to support it. That is, of course, his speciality area.

[muriel_volestrangler]

1. My first thought, after a glance through - how do small movements affect the air support?

Hyperloop capsules will float above the tube’s surface on an array of 28 air bearing skis that are geometrically conformed to the tube walls. The skis, each 4.9 ft (1.5 meters) in length and 3.0 ft (0.9 meters) in width, support the weight of the capsule by floating on a pressurized cushion of air 0.020 to 0.050 in. (0.5 to 1.3 mm) off the ground. Peak pressures beneath the skis need only reach 1.4 psi (9.4 kPa) to support the passenger capsule (9% of sea level atmospheric pressure). The skis depend on two mechanisms to pressurize the thin air film: external pressurization and aerodynamics.

The aerodynamic method of generating pressure under the air bearings becomes appreciable at moderate to high capsule speeds. As the capsule accelerates up to cruising speed, the front tip of each ski is elevated relative to the back tip such that the ski rests at a slight angle of 0.05º. Viscous forces trap a thin film of air in the converging gap between the ski and the tube wall. The air beneath the ski becomes pressurized which alters the flow field to satisfy fundamental laws of mass, momentum, and energy conservation. The resultant elevated pressure beneath the ski relative to the ambient atmosphere provides a net lifting force that is sufficient to support a portion of the capsule’s weight.

However, the pressure field generated by aerodynamics is not sufficient to support the entire weight of the vehicle. At lower speeds, very little lift can be generated by aerodynamic mechanisms. Temperature and density in the fluid film begin to rise more rapidly than pressure at high speeds, thus lift ceases to increase as the capsule accelerates into the transonic regime.

Lift is supplemented by injecting highly pressurized air into the gap. By applying an externally supplied pressure, a favorable pressure distribution is established beneath the bearing and sufficient lift is generated to support the capsule. This system is known as an external pressure (EP) bearing and it is effective when the capsule is stationary or moving at very high speeds. At nominal weight and g-loading, a capsule on the Hyperloop will require air injection beneath the ski at a rate of 0.44 lb/s (0.2 kg/s) at 1.4 psi (9.4 kPa) for the passenger capsule. The air is introduced via a network of grooves in the bearing’s bottom surface and is sourced directly from the high pressure air reservoir onboard the capsule.

0.5mm to 1.3mm is not much clearance. This means the inside of the tube must be pretty smooth and clean (welds must not intrude, for instance). And while they can engineer the structure to stay in one piece during tremors (inevitable in California), how much would it still move, in comparison to a several ton capsule with significant inertia? Do they expect the occasional contact between pad and tube wall, and engineer with that in mind?

[MineralMan]

2. Completely impractical and unaffordable.

I wnt even mention seisnic risks, and shouldn't have to. Pipe dream stuff.

[NV Whino]

3. Well, lots of things began as pipe dream stuff

Wright Brothers. Jules Verne. Just think of all those science fiction rocket ships. And lasers. And tasers... Well, you get the idea.

[AZ Progressive]

5. Yeah but the probability that something like this would be built is very very small

Anyone can come up with an idea and even experts as well but implementing it in the real world is a whole other thing. And it's even another thing of whether or not there would be any legal issues, the faster you go the worse any accident could be fore one.

[MineralMan]

7. That's true. However, this particular plan is

completely unrealistic. One earthquake shaking that tube with capsules going 700 MPH and you'd understand why. California shakes regularly, especially along the route this thing would take. The cost, too, is prohibitive, and the design is untested.

[killbotfactory]

4. This sounds awesome

Hyperloop Update: Elon Musk Will Start Developing It Himself
http://www.forbes.com/sites/hannahelliott/2013/08/12/latest-update-elon-musk-will-start-the-hyperloop-himself/

I'm not an engineer, but other than the politics involved with large scale projects of this nature, nothing raises red flags as to why this would be impractical given the motivation and money to do it.

[Kablooie]

6. Disney did this years ago.

And they even shrunk you down and shot you into an atom as well.
Try to beat THAT Musk man!

[malaise]

8. One question

How does this work in an earthquake zone?

[muriel_volestrangler]

9. There's some stuff about earthquake design in the paper

It should be fairly easy to design the tubes and pylons to withstand quakes and stay in one piece. My question, in reply #1, was how the millimetre distances between capsule and tube would be affected - is the cushion of air under the pads strong enough to prevent contact of metal on metal at 760 mph?

[malaise]

10. We'll find out I guess

Good question

[KarKar]

11. Sounds like some Ayn Rand bullshit.

[ksoze]

12. "Everything that can be invented has been invented." -- U.S. Office of Patents, 1899.

"Computers in the future may weigh no more than 1.5 tons."

-- Popular Mechanics, forecasting the relentless march of
science, 1949
-----------------------

"I think there is a world market for maybe five computers."

-- Thomas Watson, chairman of IBM, 1943
-----------------------

"I have traveled the length and breadth of this country and talked with the
best people, and I can assure you that data processing is a fad that won't
last out the year."

-- The editor in charge of business books for Prentice Hall,
1957
-----------------------

"But what ... is it good for?"

-- Engineer at the Advanced Computing Systems Division of IBM,
1968, commenting on the microchip.
-----------------------

"There is no reason anyone would want a computer in their home."

-- Ken Olson, president, chairman and founder of Digital
Equipment Corp., 1977
-----------------------

"This 'telephone' has too many shortcomings to be seriously considered
as a means of communication. The device is inherently of no value to
us."

-- Western Union internal memo, 1876.
-----------------------

"The wireless music box has no imaginable commercial value. Who
would pay for a message sent to nobody in particular?"

-- David Sarnoff's associates in response to his urgings for
investment in the radio in the 1920s.