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posted by cmn32480 on Wednesday June 17 2015, @10:48AM   Printer-friendly
from the zoom-zoom dept.

On Monday, SpaceX announced that it would be holding a Hyperloop pod competition, inviting universities and private companies to build passenger pods based on SpaceX CEO Elon Musk's open sourced Hyperloop design. The company said it would build a one-mile test track for the pods on a lot adjacent to its Hawthorne, California headquarters.

The Hyperloop has been described as high speed rail combined with an air hockey table: in the system, human-sized pods are propelled by linear induction, with magnets on the outside of the pod repelling the magnets lining the track, which is enclosed in a low-pressure tube (to reduce drag on the pods). The system is supposed to move humans and cargo at a rate of 760 miles per hour.

The impetus for the idea was Musk's disapproval of California's attempts to build a high-speed rail system between Los Angeles and San Francisco. Musk detailed this in a 58-page document in 2013 (PDF), claiming that his Hyperloop idea could be built over the same stretch of land as California High Speed rail but for just $6 billion. (California's train system was estimated to cost around $68 billion as of this January.) But Musk decided to step back from the Hyperloop idea as soon as he put it forward. He made his designs open source and publicly said that neither SpaceX nor Tesla Motors, his electric vehicle company, would be building a Hyperloop.

Is a 1 mile long track long enough to test a train that goes 760 miles per hour?


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  • (Score: 4, Informative) by kaszz on Wednesday June 17 2015, @01:15PM

    by kaszz (4211) on Wednesday June 17 2015, @01:15PM (#197232) Journal

    Is a 1 mile long track long enough to test a train that goes 760 miles per hour?

    Translating..

    Is a 1.6 km long track long enough to test a train that goes 1216 km per hour?

    The quick answer is that provided the train has instant acceleration. It can go on for 1600 / (1216000/3600) = 4.7 seconds. Kind of really fast. So the test track is probably too short for really accurate testing but using engineering maths and knowhow one can probably deduce real world performance.

    The distance New York to San Francisco 4125.91 km would then take 12 215 seconds (3.4 hours) at 1216 km/h.

    So the key question is perhaps what kind of acceleration and retardation is this system (track + vehicle) supposed to have? this analysis [gizmag.com] claims that no more than 0.5 g is a good idea due to passenger comfort. So if one accelerates at 0.5 g (ie 4.91 m/s²) then it should take 18.1 seconds to reach the midpoint at 800 meters. And the speed should then be 88.6 m/s at it's maximum (319 km/h or 199 mph). So at that acceleration pods will not reach maximum speed.

    The gizmag article mentions acceleration to 338 m/s (1216 km/h) using a 4000 meter long accelerator. That translates into 14.3 m/s² (1.45 g) so the test setup without humans might perhaps reach a much higher speed like 257 m/s?

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  • (Score: 3, Funny) by WizardFusion on Wednesday June 17 2015, @01:20PM

    by WizardFusion (498) Subscriber Badge on Wednesday June 17 2015, @01:20PM (#197234) Journal

    What if they build a second circular track that they could use to test top speed stresses.?
    Maybe use the new Apple HQ :)

    • (Score: 3, Funny) by kaszz on Wednesday June 17 2015, @01:34PM

      by kaszz (4211) on Wednesday June 17 2015, @01:34PM (#197246) Journal

      Perhaps they could use it to "Swift"-ly wipe out that walled garden? ;-)

      • (Score: 2) by DeathMonkey on Wednesday June 17 2015, @07:15PM

        by DeathMonkey (1380) on Wednesday June 17 2015, @07:15PM (#197459) Journal

        And in true Soylent fashion the first application for this technology we come up with is to turn it into a railgun.
         
        I approve this message.

  • (Score: 2) by jcross on Wednesday June 17 2015, @01:22PM

    by jcross (4009) on Wednesday June 17 2015, @01:22PM (#197236)

    If the one mile track were a loop (just a regular one, not even the hyper kind), the pod could be accelerated to an arbitrary speed. Though I'm not sure how much curvature the design allows for; that would be an important consideration.

    • (Score: 2) by kaszz on Wednesday June 17 2015, @01:32PM

      by kaszz (4211) on Wednesday June 17 2015, @01:32PM (#197245) Journal

      The Gizmag mentions that changes in location of the tube when traveling at high speed could make it uncomfortable for passengers..

      The curvature is likely limited by the air cushion?

      • (Score: 2) by jcross on Wednesday June 17 2015, @04:13PM

        by jcross (4009) on Wednesday June 17 2015, @04:13PM (#197357)

        Curvature could be limited by a bunch of stuff. The length and geometry of the pod would be a major factor, the wall clearance, the maximum load on the air bearings, but especially the maximum amount of sideways force that riders can comfortably experience when making the turns. This is the main thing that makes retrofitting high speed trains so expensive: buying up the extra right-of-way to make the turns wide enough to be gentle on the passengers. It's quite easy to make tracks and trains that handle existing turns at high speed, but passengers are another matter. I would hope the hyperloop design considers this as well, since turning forces would be a major factor at those speeds, but as I understand it the main advantage is that it can be built on pylons over existing highways, which reduces the amount of real-estate needed considerably. You know that's got to be a major part of the cost in California. Still, I think being stuck in a me-sized capsule with no windows and unpredictable g-forces sounds fairly hellish no matter how you slice it.

  • (Score: 2) by Immerman on Wednesday June 17 2015, @01:27PM

    by Immerman (3985) on Wednesday June 17 2015, @01:27PM (#197241)

    It's been a day or three since I read the announcement, but I believe the it specifically mentioned that the test train would not be getting anywhere close to 760mph. I also think it was planned as a closed loop (oval?) track, though that might be mental interference from the "loop" in the name.

    It would make sense though - a loop would give the pods time to get up to speed and cruise for extended periods to test systems in steady-state, even if the lateral accelerations would put a definite upper limit on speed. There's a reason they don't test race cars on a straightaway after all.

  • (Score: 3, Interesting) by tibman on Wednesday June 17 2015, @02:08PM

    by tibman (134) Subscriber Badge on Wednesday June 17 2015, @02:08PM (#197262)

    338 m/s is making love with the sound barrier : ) I haven't looked into the hyperloop but this would be a fantastic engineering challenge for a university team.

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    • (Score: 2) by kaszz on Wednesday June 17 2015, @02:44PM

      by kaszz (4211) on Wednesday June 17 2015, @02:44PM (#197279) Journal

      I think there's some errors in my calculations. But the ballpark figure that they won't reach maximum design speed for a full scale track is probably right. One might also wonder how braking will be done. I wouldn't rely solely on linear motors to do that job. A power switch failure at a critical time might turn the pod(s) into a bullet that will reshape any end station [theoldmotor.com].

      (1895 Paris [wikipedia.org])

      • (Score: 2) by Immerman on Wednesday June 17 2015, @03:10PM

        by Immerman (3985) on Wednesday June 17 2015, @03:10PM (#197297)

        Wouldn't a loop track make far more sense for testing purposes? So no end station, just a loading/unloading segment, and if they overshoot they keep going in circles until they coast to a stop or the power comes back on.

        • (Score: 2) by tibman on Wednesday June 17 2015, @03:26PM

          by tibman (134) Subscriber Badge on Wednesday June 17 2015, @03:26PM (#197315)

          I do like the idea of a failure mode that is basically a decelerating loop.

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          SN won't survive on lurkers alone. Write comments.
  • (Score: 0) by Anonymous Coward on Wednesday June 17 2015, @03:27PM

    by Anonymous Coward on Wednesday June 17 2015, @03:27PM (#197317)

    I am quite surprised that you don't understand how to use different units given that you seem to be capable of doing simple calculations. I guess it is sort of if all you have is a hammer, then every problem looks like a nail.

    It is really amazing how something as basic as scaling factors really seem to perplex people around here.

  • (Score: 2) by hubie on Wednesday June 17 2015, @03:37PM

    by hubie (1068) Subscriber Badge on Wednesday June 17 2015, @03:37PM (#197326) Journal

    Assuming constant acceleration, to get to speed on that track I calculate you'd need to accelerate at 3.7 g's. If you need to get to speed and then stop on that track, you'd need to accelerate/decelerate at 7 g's (assuming you decelerate at the same magnitude as you accelerated).

    • (Score: 2) by kaszz on Wednesday June 17 2015, @05:00PM

      by kaszz (4211) on Wednesday June 17 2015, @05:00PM (#197372) Journal

      The Gizmag article writes about a 4000 meter long linear accelerator to reach 338 m/s using 65 MW at peak load. I think that's the maximum acceleration that will be used. And then given that the test track is 1600 meters long the rest is math. For passenger comfort the g-force has to be artificially limited to no more than 4.91 m/s².

      I think the questions to ask is:
        * Maximum possible speed at 800 meters?
        * Time it takes to travel the test track at maximum acceleration and retardation?
        * Limitations by side forces?
        * How will linear motor failure be handled when the pods need to stop?

      Designing it as a loop would solve some problems but introduce others too, like side forces.

      (and who will put up 6 billion US$ to make this happen?)

      • (Score: 2) by hubie on Wednesday June 17 2015, @08:50PM

        by hubie (1068) Subscriber Badge on Wednesday June 17 2015, @08:50PM (#197525) Journal

        On a 4000 m track, getting to 338 m/s would take (ideally - no wind drag, constant acceleration) about 1.5 g's. At that acceleration, the fastest you can get in 800 meters is about 151 m/s. The time it would take to go the 800 meters is about 10.6 seconds (assume an equal amount to stop).

        For what it's worth, if don't care about stopping, it would take you about 15 seconds to run the 1600 meters and you'd be going about 218 m/s.