5 ms·

I do not know a lot about the technology, but I remember reading that the hyperloop is not a full vacuum, just a lower pressure environment. That alone means a

I do not know a lot about the technology, but I remember reading that the hyperloop is not a full vacuum, just a lower pressure environment. That alone means all these videos are bunk themselves.

Qantourisc 10y ago
Low pressure, vacuum, I doubt physics care (not a physicist), it's just a pressure differential, just a bigger or smaller one. So the effects would just be smaller.
- wtvanhest 10y ago
  Right, but using a true vacuum as your comparable for the construction of a partial vacuum is nonsensical. This structure has a differential closer to an airline, not a space shuttle. Airplanes can handle that pressure differential with a thin layer of aluminum. They can even have windows! Thinking through this a little more. In basic terms, you just need a tunnel big enough combined with low enough pressure that at speed, the train has significantly less air to push out of the way. I'm sure it is some complex math, but someone who understands the math could figure it out.
  - deleted 10y ago
    [deleted]
  - danbruc 10y ago
    The air pressure 10 km above sea level is about 25 % of the air pressure at sea level, the Hyperloop paper says the air pressure in the tube will be 0.1 % of the air pressure at sea level. So the pressure is way closer to a perfect vacuum than to the air pressure outside of airplanes.
    - stouset 10y ago
      It's still a linear change. The tube needs to withstand 1 ATM of pressure, which isn't all that much in the grand scheme of things.
      - danbruc 10y ago
        Withstanding one atmosphere is certainly not an unsurmountable challenge but given the dimensions and given that this thing is supposed to be cheap it is also certainly not a negligible issue. You also have to maintain the quality of the vacuum, possibly in presence of expansion joints, and you have to deal with the consequences of a loss of vacuum for whatever reasons.
      - jessriedel 10y ago
        Yes, the mechanical forces involved with a 0.75 ATM differential are very similar to a 1 ATM differential. But the same isn't true for leaks and residual gas because the difficulty isn't linear. Pushing a vacuum 0.1 ATM to 0.01 ATM is much harder than from 0.51 ATM to 0.501 ATM.
- GarrisonPrime 10y ago
  Even a small pressure differential might be a huge boost. At least from what I've seen in my basic physics lab, you don't have to get anywhere near a vacuum or even what most people would call "low pressure" for it to make a significant difference. Just running a tube between two cities of different elevation might allow for zero energy transport of small pods.
rukittenme 10y ago
That concern is accounted for repeatedly in the debunking videos. It is not valid. Too much air pressure and the hyperloop is pointless. Too little air pressure and the hyperloop is impossible. If your goal is low pressure, low cost, and high speed then build an airplane. No tracks required, no vacuum pumps required, no permitting required.
- adanto6840 10y ago
  Pretty sure that building an aircraft requires a LOT of 'permitting' -- for instance, airworthiness certifications. And that's not just on the aircraft as a whole, but each individual aspect as well as the aircraft design itself.
  - deelowe 10y ago
    No new permitting. The existing permitting process is well defined and understood.
- icebraining 10y ago
  Low pressure is only reached for a portion of the flight. In a relatively short trip like LA-SF, as Hyperloop was proposed to do, the plane spends quite a bit of its flight time climbing and descending: https://www.youtube.com/watch?v=J01iDyHq2p0 https://www.youtube.com/watch?v=J01iDyHq2p0
rrrazdan 10y ago
^^I read this a lot on hyperloop forums and articles, but it doesn't really matter. What pressure constitutes a vacuum ? What pressure do you mean by low pressure? Zero pressure(perfect vacuum) is impossible to do in life. So what these articles/videos mean by vacuum is sufficiently low pressure that can reduce drag and that is essentially impossible to do across a tube of any meaningful size.
- pitaj 10y ago
  Incorrect. It's not "essentially impossible" as it's very far from a vacuum, or even a near-vacuum. The Hyperloop paper explains why it doesn't require high cost to build the tube or maintain the vacuum within with only pumps at the two ends of the tube.
PhearTheCeal 10y ago
Thunderf00t's video got that same response quite a few times. He made an additional video that directly responds to common complaints about the first video: https://youtu.be/DDwe2M-LDZQ?t=238 https://youtu.be/DDwe2M-LDZQ?t=238
- stcredzero 10y ago
  I watched that video as well. He doesn't respond to more than a small fraction of the objections in the reddit thread.

I do not know a lot about the technology, but I remember reading that the hyperloop is not a full vacuum, just a lower pressure environment. That alone means all these videos are bunk themselves.

Qantourisc 10y ago

Low pressure, vacuum, I doubt physics care (not a physicist), it's just a pressure differential, just a bigger or smaller one. So the effects would just be smaller.

wtvanhest 10y ago
Right, but using a true vacuum as your comparable for the construction of a partial vacuum is nonsensical. This structure has a differential closer to an airline, not a space shuttle. Airplanes can handle that pressure differential with a thin layer of aluminum. They can even have windows! Thinking through this a little more. In basic terms, you just need a tunnel big enough combined with low enough pressure that at speed, the train has significantly less air to push out of the way. I'm sure it is some complex math, but someone who understands the math could figure it out.
- deleted 10y ago
  [deleted]
- danbruc 10y ago
  The air pressure 10 km above sea level is about 25 % of the air pressure at sea level, the Hyperloop paper says the air pressure in the tube will be 0.1 % of the air pressure at sea level. So the pressure is way closer to a perfect vacuum than to the air pressure outside of airplanes.
  - stouset 10y ago
    It's still a linear change. The tube needs to withstand 1 ATM of pressure, which isn't all that much in the grand scheme of things.
    - danbruc 10y ago
      Withstanding one atmosphere is certainly not an unsurmountable challenge but given the dimensions and given that this thing is supposed to be cheap it is also certainly not a negligible issue. You also have to maintain the quality of the vacuum, possibly in presence of expansion joints, and you have to deal with the consequences of a loss of vacuum for whatever reasons.
    - jessriedel 10y ago
      Yes, the mechanical forces involved with a 0.75 ATM differential are very similar to a 1 ATM differential. But the same isn't true for leaks and residual gas because the difficulty isn't linear. Pushing a vacuum 0.1 ATM to 0.01 ATM is much harder than from 0.51 ATM to 0.501 ATM.
GarrisonPrime 10y ago
Even a small pressure differential might be a huge boost. At least from what I've seen in my basic physics lab, you don't have to get anywhere near a vacuum or even what most people would call "low pressure" for it to make a significant difference. Just running a tube between two cities of different elevation might allow for zero energy transport of small pods.

rukittenme 10y ago

That concern is accounted for repeatedly in the debunking videos. It is not valid. Too much air pressure and the hyperloop is pointless. Too little air pressure and the hyperloop is impossible. If your goal is low pressure, low cost, and high speed then build an airplane. No tracks required, no vacuum pumps required, no permitting required.

adanto6840 10y ago
Pretty sure that building an aircraft requires a LOT of 'permitting' -- for instance, airworthiness certifications. And that's not just on the aircraft as a whole, but each individual aspect as well as the aircraft design itself.
- deelowe 10y ago
  No new permitting. The existing permitting process is well defined and understood.
icebraining 10y ago
Low pressure is only reached for a portion of the flight. In a relatively short trip like LA-SF, as Hyperloop was proposed to do, the plane spends quite a bit of its flight time climbing and descending: https://www.youtube.com/watch?v=J01iDyHq2p0 https://www.youtube.com/watch?v=J01iDyHq2p0

rrrazdan 10y ago

^^I read this a lot on hyperloop forums and articles, but it doesn't really matter. What pressure constitutes a vacuum ? What pressure do you mean by low pressure? Zero pressure(perfect vacuum) is impossible to do in life. So what these articles/videos mean by vacuum is sufficiently low pressure that can reduce drag and that is essentially impossible to do across a tube of any meaningful size.

pitaj 10y ago
Incorrect. It's not "essentially impossible" as it's very far from a vacuum, or even a near-vacuum. The Hyperloop paper explains why it doesn't require high cost to build the tube or maintain the vacuum within with only pumps at the two ends of the tube.

PhearTheCeal 10y ago

Thunderf00t's video got that same response quite a few times. He made an additional video that directly responds to common complaints about the first video: https://youtu.be/DDwe2M-LDZQ?t=238 https://youtu.be/DDwe2M-LDZQ?t=238

stcredzero 10y ago
I watched that video as well. He doesn't respond to more than a small fraction of the objections in the reddit thread.