Please turn on javascript in your browser to play chess.
Science Forum

Science Forum

  1. Standard member sonhouse
    Fast and Curious
    08 Mar '17 11:30
    http://www.sciencealert.com/these-are-the-first-images-of-what-will-soon-be-the-world-s-first-hyperloop-tube

    I did think of one problem, the 'train' inside going 760 km/hr.

    Terrorists thinkiing, nice thing to attack.

    It would not take much, one charge against the side, instant atmosphere in tube, train going that fast, now slams into wall of atmosphere....
  2. 08 Mar '17 12:31
    Originally posted by sonhouse
    I did think of one problem, the 'train' inside going 760 km/hr.

    Terrorists thinkiing, nice thing to attack.

    It would not take much, one charge against the side, instant atmosphere in tube, train going that fast, now slams into wall of atmosphere....
    All aircraft and any high speed rail is subject to the same risks. Admittedly attacking an aircraft's track is not easy, but I would say that derailing a train would be easier than damaging the hyperloop.
  3. Standard member sonhouse
    Fast and Curious
    08 Mar '17 12:34
    Originally posted by twhitehead
    All aircraft and any high speed rail is subject to the same risks. Admittedly attacking an aircraft's track is not easy, but I would say that derailing a train would be easier than damaging the hyperloop.
    I think the terrorists would say, we've DONE trains, lets try something new.
  4. 08 Mar '17 12:38
    Originally posted by sonhouse
    http://www.sciencealert.com/these-are-the-first-images-of-what-will-soon-be-the-world-s-first-hyperloop-tube
    It is actually not the first test track:
    http://www.popularmechanics.com/technology/infrastructure/a24967/watch-some-test-pods-zoom-down-spacexs-hyperloop-test-track/

    My own opinion of the hyperloop is it is yet to be demonstrated as fully viable, and I am glad to see a genuine test track. Until now there has been far more hype than loop and the marketing budget has far exceeded the engineering budget. When I see that I always think 'scam'.

    There are a few major engineering concerns that need to be double checked and I am not knowledgeable enough to know whether they can be overcome. The fact that there seems to have been no genuine effort to check them even on a small scale is of major concern and suggests the promoters did do so and failed, or believe they are not trivial to test or are afraid of a negative outcome and are deliberately holding off.
  5. Standard member sonhouse
    Fast and Curious
    08 Mar '17 16:10 / 2 edits
    Originally posted by twhitehead
    It is actually not the first test track:
    http://www.popularmechanics.com/technology/infrastructure/a24967/watch-some-test-pods-zoom-down-spacexs-hyperloop-test-track/

    My own opinion of the hyperloop is it is yet to be demonstrated as fully viable, and I am glad to see a genuine test track. Until now there has been far more hype than loop and the marke ...[text shortened]... ey are not trivial to test or are afraid of a negative outcome and are deliberately holding off.
    Musk usually does what he says he does. His space exploits are well known, doing something NASA, ROSCOSMOS, ESA, the French, and the rest never did, a rocket that lands itself safely.

    What I wonder is just how much of a vacuum they will be aiming for. I work with vacuum tech all the time, roughing pumps, cryo pumps, diffusion pumps, titanium sublimation pumps, LOX moisture traps and such. I work from atmosphere to 8 range vacuum. The question is, what level of vacuum do you need to be able to get up to the claimed 760 Klicks? I would presume there would need to be magnetic bearings and linear motors where the inside passenger tube would never actually touch the walls, don't think bearings would hold up at that kind of velocity.

    Say you have bearings 500 cm circumferance, 160 cm diameter, would represent about 400 revs per second or about 24,000 RPM. Certainly possible in the short term but I doubt they could be built to last so they would have to have magnetic bearings for main support and thrust from linear motors and maybe 160 cm wheels for emergencies, that seems to be the long and short of that aspect.

    In stupid units, that wheel bearing would be over 5 feet in diameter. 24,000 RPM? It would probably fly apart. What would be the centripital force for that size and RPM?

    MV^2/r. So lets say it masses 100kg, and 760,000 meters/second/80 cm. Do those units work together ok? That comes out to 7 E14 something units newtons? Sounds like it would fly apart for sure.

    Probably too much for any kind of real use.
  6. 08 Mar '17 16:31
    Originally posted by sonhouse
    Musk usually does what he says he does.
    And it is notable that he has not started a Hyperloop company. He has encouraged research into it. No more. So far, there are a few companies that look like scammers, and a lot of students having fun (but not all that serious). I have not seen any serious engineering research into the basic feasibility of the idea.

    What I wonder is just how much of a vacuum they will be aiming for.
    That is one key question.

    I would presume there would need to be magnetic bearings and linear motors where the inside passenger tube would never actually touch the walls, don't think bearings would hold up at that kind of velocity.
    Actually it is entirely possible that air bearings would be feasible. You need just enough air in the tube and the correct shaped car, that it lifts the car off the surface.

    But forget all that. Forget the insane speeds. Focus on the important thing which is the vacuum.
    1: How do you get people in and out while maintaining the vacuum?
    2. How much energy does it require to maintain the vacuum?
    3. Is the tube safe on failure, ie does the vacuum cause catastrophic damage on failure?
    4. What are the basic economics of building such a tube?
  7. 08 Mar '17 16:35
    One would think that it would be a fairly trivial exercise to build a test track mere centimeters in diameter and meters long demonstrating a tiny vehicle running in a vacuum and dealing with the problem of putting passengers on and off at the ends. Why has no such track been built? Meanwhile, millions have been built on fancy looking models that have all to do with marketing and nothing to do with engineering.
  8. Standard member sonhouse
    Fast and Curious
    08 Mar '17 19:31 / 3 edits
    Originally posted by twhitehead
    One would think that it would be a fairly trivial exercise to build a test track mere centimeters in diameter and meters long demonstrating a tiny vehicle running in a vacuum and dealing with the problem of putting passengers on and off at the ends. Why has no such track been built? Meanwhile, millions have been built on fancy looking models that have all to do with marketing and nothing to do with engineering.
    There is that. I think the key is the mean free path, the difference between laminar flow and molecular flow. I think you would have to have a vacuum of molecular flow area, I think something like 1 millitorr. Here is a piece by Pfeiffer Vacuum:

    https://www.pfeiffer-vacuum.com/en/know-how/introduction-to-vacuum-technology/fundamentals/types-of-flow/

    The chart there shows molecular flow depends not only on the absolute vacuum level but also on the pipe size and of course a real hyperloop would need at least 3 meters and the chart there stops at 1/10th meter and it says the vacuum has to be better and better for molecular flow so it looks like they want a vacuum level there at least industrial vacuum level, like my sputtering machines and ion implanters and ion etchers, of around at least 1E-6 torr and if that is correct that requires more than just roughing pumps which poop out at about 5 millitorr, after that you need something much better like at least a diffusion pump but for multiple kilometers of run which of course means pumping stations every few hundred meters at best.

    I think maybe this is going to prove to be too expensive to operate.

    Cryopumps give very clean vacuum, dif pumps always puts some oil vapor in the chamber, which may not be a problem for a hyperloop, does screw stuff up at the sub micron level of electronics today, where one microdrop of oil can spoil a circuit.

    At least they wouldn't have that problem on a hyperloop but still, even if there was no terrorist threat, think of the cost of the accelerator in Cern, which of course has to have a vacuum level a thousand times better than the run of the mill sputtering tool or ion implanter.

    Still going to be an extremely expensive proposition no matter how you slice it.

    Units in the chart are in pascals, 1 pascal =~ 7.5 millitorr, 1000 pascal = 7.5 Torr.

    760 Torr = 1 atmosphere so 101325 pascals ~= 1 atmosphere.
  9. 08 Mar '17 20:07
    I don't think it needs to be too serious a vacuum. There is talk of using the air in the pipe to support the carriages (air bearings) as well as having powerful fans in the carriage to move air from the front to the back - and there have even been suggestions of using that for propulsion.
    The main thing stopping trains from going faster is air resistance. An vacuum in a pipe allows you to reduce that resistance, but it doesn't have to be near zero, just noticeably lower than the atmosphere.
    One aspect of the pipe is that it is planned to be much smaller than a traditional railway, which can potentially lower construction costs and enables cheaper tunneling. But this comes with two major downsides:
    1. The risks of being in a tunnel and difficulties inherent in maintaining it.
    2. Whether people will want to travel on it. Trains are large and spacious because people like that. Ordinary trains could equally be made much smaller with everyone packed in like sardines which would save on infrastructure costs. But nobody would use them.
  10. Standard member sonhouse
    Fast and Curious
    08 Mar '17 22:47 / 1 edit
    Originally posted by twhitehead
    I don't think it needs to be too serious a vacuum. There is talk of using the air in the pipe to support the carriages (air bearings) as well as having powerful fans in the carriage to move air from the front to the back - and there have even been suggestions of using that for propulsion.
    The main thing stopping trains from going faster is air resistance ...[text shortened]... one packed in like sardines which would save on infrastructure costs. But nobody would use them.
    Have you seen anything from Musk about propulsion? It seems to me linear motors would be more efficient than fans. And the better the vacuum the less the drag and the less air has to go around the vehicle.

    One thing, it seems to me the thing would have to be powered by electricity powered by fuel cells or batteries since there would be no air to use in reactive devices. I assume therefore it would have to be some kind of battery which would mean it would have a pretty short range no matter what propulsion is used. Air bearings require a constant flow of air and at a pretty high pressure too.

    We use an air bearing assembly in one of our computer test sets, it has an X Y linear motor for X and Y movement held off the linear iron drivers by air pressure so it slides around under electromagnetic control, and it has a Z axis for the probes, up and down a few mm for contacts of dozens of almost microscopically tiny probes. Very delicate probes I might add, the probe assembly costs 3000 dollars and they go out quite a bit. I know, I destroyed on accidentally once

    Anyway I don't think air bearings would work very well in that system. Think about how much drag there is even in a plane at 100,000 feet up. My guess is they would need a vacuum better than that if they wanted the speed advertised.

    The main drawback, assuming a real vacuum in the minus 6 range would be the range since it would have to be driven by electricity and you can only keep so much in the way of batteries onboard. But with a high enough vacuum it could have a pretty significant range, much better than anything running at full atmosphere.

    If we ever get cities on the moon, they will have linear motor trains that will go a lot faster than 800 klicks since there is almost zero atmosphere and a good source of sunlight most days.

    I envisioned a trans-lunar railway going only 16 or so klicks powered by a huge array of solar cells atop the train, say a couple klicks long and able to send power into the tracks besides moving from station to station, 24/7, it goes around the moon every 28 odd days and stays always with the sun overhead so it has always got the full 1400 watts per square meter, and of course by then they will have 70% cells so it supplies power to a large number of urban centers, a hundred megawatts sent by the room temperature superconductors which will have been developed then, which will have a junior version of the martian magnetic shield, a few turns around the lunar equator making a nice mag field which will protect the citizens. When they prove it works on Luna they start doing the same for Mars and then crash a few small comets onto Mars to generate an atmosphere.

    Hey, it could happen
  11. 09 Mar '17 07:47
    Originally posted by sonhouse
    Have you seen anything from Musk about propulsion?
    Musk is not designing it.
    Various methods of propulsion have been proposed. The largest company actively developing it is Hyperloop One and they are currently working one a linear motor which they showed off a few years ago. Again, a marketing stunt not a technology test.

    It seems to me linear motors would be more efficient than fans. And the better the vacuum the less the drag and the less air has to go around the vehicle.
    A fan helps to deal with the pressure problem. A vacuum becomes more and more difficult to deal with the stronger it is.

    One thing, it seems to me the thing would have to be powered by electricity powered by fuel cells or batteries since there would be no air to use in reactive devices.
    It would be electric.

    I assume therefore it would have to be some kind of battery which would mean it would have a pretty short range no matter what propulsion is used.
    You assume wrong. It would be trivial to include an electric rail in the tunnel to provide power to the cars.

    Air bearings require a constant flow of air and at a pretty high pressure too.
    Those requirements would be met.

    We use an air bearing assembly in one of our computer test sets,
    Not the same thing at all.

    Think about how much drag there is even in a plane at 100,000 feet up. My guess is they would need a vacuum better than that if they wanted the speed advertised.
    And my guess is you haven't thought it through. What are the exhaust velocities on a typical jet engine? This is not a airplane, this is a cylindrical object in a pipe. There are very significant differences.

    The main drawback, assuming a real vacuum in the minus 6 range would be the range since it would have to be driven by electricity and you can only keep so much in the way of batteries onboard. But with a high enough vacuum it could have a pretty significant range, much better than anything running at full atmosphere.
    With a linear motor, you don't need any power whatsoever on the car other than for lighting. For a fan, you would, but you would still get the the power from the track.

    I envisioned a trans-lunar railway .
    I see absolutely no requirement for a trans-lunar railway. That's like putting a railway in the Sahara because the land is cheaper there. Cheap, but useless.

    so it supplies power to a large number of urban centers,
    So you are imagining all this fancy future technology, and you want to move the panels round the moon because simply doubling the number of panels and a few batteries would be too expensive? You haven't thought this through. You are trying to solve a problem that simply doesn't exist and will never exist.
  12. 09 Mar '17 11:03 / 5 edits
    Unfortunately I have lost the relevant web link for this so I cannot show you but I am absolutely certain I remember reading on a link that explained in scientific depth why the hyperloop is one huge scam (not necessarily a deliberate scam as there may be much innocent ignorance and delusion involved) based on wildly over optimistic unrealistic estimations of the cost-effectiveness and the company's ability to solve the formidable engineering challenges and deal with the formidable safety issues. They haven't done their homework on the basic physics and engineering especially when dealing with the thermal expansion of the tubes over many kms were they appear to be planning to simply rigidly weld the tubes end to end without allowing for any sideways movement from thermal expansion. If they did that over many Kms, the whole structure will collapse. There are some proposed solutions to that problem but all massively expensive and economically unrealistic.

    I make a prediction; 50 years from now, a practical and used hyperloop would still not be a reality; and probably will never be so.
  13. Standard member sonhouse
    Fast and Curious
    09 Mar '17 12:11
    Originally posted by humy
    Unfortunately I have lost the relevant web link for this so I cannot show you but I am absolutely certain I remember reading on a link that explained in scientific depth why the hyperloop is one huge scam (not necessarily a deliberate scam as there may be much innocent ignorance and delusion involved) based on wildly over optimistic unrealistic estimations of ...[text shortened]... ealistic.

    I make a prediction; 50 years from now, the hyperloop would still not be a reality.
    And that is only ONE of the potential problems of such a system. Suppose the loop sections are 3 meters by 100 meters, just picking numbers out of a hat. Suppose you have to have a fairly good vacuum, say 99% evacuated. That would be equivalent to the atmosphere on Mars. Don't know if even that would be good enough for a real loop but anyway, that would be a stress on the frame of 11,000 tons or so. That would require a lot of thick metal loops internally to manage that much stress, and of course that means dollars.

    Deepthought pointed out you wouldn't at least need internal power sources, like if it was done by linear motors the tracks would provide power so at least that is taken care of.

    I guess it's wait and see what Musk comes up with, if anything.

    It might not even GET to the full scale model he is planning.
  14. 09 Mar '17 14:06
    Originally posted by humy
    Unfortunately I have lost the relevant web link....
    This perhaps?
    YouTube
  15. 09 Mar '17 14:07
    Originally posted by sonhouse
    I guess it's wait and see what Musk comes up with, if anything.

    It might not even GET to the full scale model he is planning.
    Once again. Musk is not designing it!