10 ms·

When are we going to address the elephants in the room? Just the tube alone: - largest pressure vessel in the world. How do you keep it at near vacuum? -

When are we going to address the elephants in the room? Just the tube alone: - largest pressure vessel in the world. How do you keep it at near vacuum? - Thermal expansion over such a large distance, especially if the top of the tube is warmer than the bottom. - Safety, how does an evacuation look like if the tubes are sealed?. There are many more. Some how I feel like this is a "pipe" dream. Lots of marketing, very little engineering.

Filligree 9y ago
The pressure tube doesn't need to be at near-vacuum. By the drag equation, air resistance is proportional to pressure; merely cutting pressure by 90% would reduce air resistance by the same amount, and that's trivial with perfectly ordinary pumps. Serious vacuum pumps are not required. This is not to say that keeping it airtight won't still be a major engineering problem, it just isn't as near-impossible as near-vacuum would be. To cope with expansion, you'd need to use sliding plates--which, yes, will make it harder to keep the air out. That's going to be an interesting challenge.
- wlesieutre 9y ago
  Doesn't the Hyperloop concept rely on not having a perfect vacuum? It's supposed to suck in air on the front and blow it out the bottom as an air cushion. Without the air cushion you just have "maglev in a vacuum" instead. I'm sure that's also a fast mode of travel, but like you said, the vacuum part of it takes a lot of money.
  - Robotbeat 9y ago
    Does the vacuum part take a lot of money? I would think that if anyone knows, it'd be someone like Elon Musk who has built a spacecraft company from the ground up. For many of Elon Musk's projects, I get the idea that Elon is mostly just bringing broad, multi-domain knowledge to bear on industries that have been siloed for a very long time. So everyone scoffs at a long vacuum tube and using turbomachinery, etc, but for someone with a physics background with extensive knowledge of the spacecraft environment, turbopump rocket engines, and all the subsystems and ground testing systems that enable all this, it really isn't far-fetched at all. Most physicists (of the experimental kind, i.e. those who have to have hands-on knowledge fabricating things in addition to theoretical background) that I've talked to understand his ideas and think they're fairly reasonable. People seem to base most of their criticisms on the fact that it's different than what we already do without a fundamental, first-principles understanding of the system.
    - wlesieutre 9y ago
      A real vacuum (or very close to it) would be expensive, yes. That's what Musk designed the hyperloop to avoid; it works with a "low pressure" tube instead. His original hyperloop proposal paper outlines this in the intro: http://www.spacex.com/sites/spacex/files/hyperloop_alpha.pdf http://www.spacex.com/sites/spacex/files/hyperloop_alpha.pdf Another extreme is the approach, advocated by Rand and ET3, of drawing a hard or near hard vacuum in the tube and then using an electromagnetic suspension. The problem with this approach is that it is incredibly hard to maintain a near vacuum in a room, let alone 700 miles (round trip) of large tube with dozens of station gateways and thousands of pods entering and exiting every day. All it takes is one leaky seal or a small crack somewhere in the hundreds of miles of tube and the whole system stops working. However, a low pressure (vs. almost no pressure) system set to a level where standard commercial pumps could easily overcome an air leak and the transport pods could handle variable air density would be inherently robust. Unfortunately, this means that there is a non-trivial amount of air in the tube and leads us straight into another problem. The "another problem" being that if you just do low pressure, it means your pod has air in front if it and has to pushing that air around (or if that air has nowhere else to go in the forward tubing, trying to compress it, because not enough of the air can squeeze around the pods at the edge of the tube). That's what the hyperloop is getting around by sucking air in the front and blowing it out the bottom. Working as an air cushion is something of a bonus, and if everything works out right it also lets you avoid the expense of maglev.
Faaak 9y ago
The CERN LHC tube is a 27km circle of vacuum and near-zero temperature, and they don't seem to have a problem with that (granted, they had some but it's solved now). Frankly, yes, there may be issues, but I'm confident that the Human race will be able to overcome those.
- ginko 9y ago
  The LHC's vacuum pipes are 6.3 cm in diameter..
  - iamgopal 9y ago
    What, really? What's with all those mega photos we see everywhere ?
    - Analemma_ 9y ago
      Most of that is the magnets around the beam tube, with the associated power and refrigeration equipment. The beam tube itself is quite small.
    - konschubert 9y ago
      Those are the detectors. And the magnets around the tubes.
    - delecti 9y ago
      This picture shows a cross section of part of the LHC. Those two yellow lines sticking out are the actual tubes. Everything else is equipment to manage the particles (detectors, containment, magnetic propulsion). And for a sense of scale, a human can comfortably stand in that tunnel next to it. Image: http://www.tut.fi/cs/groups/public_news/@l102/@news/@p/documents/kuva/x194225.jpg http://www.tut.fi/cs/groups/public_news/@l102/@news/@p/docum... From here: http://www.tut.fi/en/about-tut/news-and-events/tut-and-cern-collaborate-in-development-of-particle-accelerators-of-the-future-x194226c2 http://www.tut.fi/en/about-tut/news-and-events/tut-and-cern-...
  - eutropia 9y ago
The_Double 9y ago
I haven't done any work on hyperloops. But expansion seems to be a problem already solved by industry a long time ago: https://en.wikipedia.org/wiki/Metal_expansion_joint https://en.wikipedia.org/wiki/Metal_expansion_joint
- bjl 9y ago
  Metal expansion joints can't hold a vacuum.
  - MrBuddyCasino 9y ago
    Quick googling says otherwise: http://www.spiroflex.hr/expansion-joints-vacuum-technology http://www.spiroflex.hr/expansion-joints-vacuum-technology
- MrBuddyCasino 9y ago
  Sounds promising: - Resistance to high and very high pressures - Large movement absorption - Early leak indication (in case of damage) via standard check hole - Complete burst resistance - Possibility of permanent leak monitoring in critical media
dmix 9y ago
> Lots of marketing, very little engineering. It started as a technical whitepaper, not a marketing campaign, and multiple companies are building experimental models. I don't think this critique is accurate or fair. There have been far worse vapourware and hype-only concepts that haven't gotten close to hyperloop's tangible progress. No tech can be perfected from the planning stage either, it takes talent, money, and time - and you can't get those things without a bit of hype, the key is keeping it balanced. Regardless the concept seemed feasible enough to some very smart people and people with money to spend, where they see it's worth the R&D. I don't really see what the big risk or downside here of exploring this? Considering the rewards could be very high if it does work and otherwise there has been little innovation in transportation in 50yrs, it's not like there are some obvious alternatives are being neglected.
- TremendousJudge 9y ago
  >it's not like there are some obvious alternatives are being neglected A high speed train like the ones they've had in Europe for a long time? You know, the ones that regularly reach 300 km/h? If that's not fast or flashy enough for you, what about Maglev? It actually exists, and the tracks are extremely expensive even though they don't even have to maintain low air pressure
  - Robotbeat 9y ago
    We have natural gas pipelines that have to maintain a far higher pressure difference, and they are in the same order of magnitude in diameter. They're not expensive. Way less than high speed rail lines per mile.
  - dmix 9y ago
    > A high speed train like the ones they've had in Europe for a long time? I don't see what the US political inability to build infrastructure has to do with my comment. Plenty of countries are still building highspeed trains and iterating on that model... and plenty of non-US countries are looking into hyperloop, the first ones to adopt it will likely be outside of the US, as that's where most innovation is these days. And regardless there's always plenty of room for new ideas. Unless you think these billionaires should be backing American transportation mega-projects instead? There's plenty of roadblocks there outside of access to capital, where a highspeed train will likely cost 2-3x the initial projections, even if a private company does it. Not to mention the US is a car-heavy market. It seems like a risky project for any non-government entity to take on as it will be packed full of political risk and direct involvement either way... The US rarely builds major projects anymore except in the defense industry. And almost every major defense project of comparable size ends up being billions over budget or cancelled.
deleted 9y ago
[deleted]
logicallee 9y ago
Out of curiosity, have you ever built anything big? I say this because the tone of your comment is dismissive, however it seems quite low-effort. I can translate your criticisms into criticisms of building subways in 1863: - if you build a subway it will be the biggest underground railway ever built. - Rocks. They could fall in front of a subway car and cause a huge accident. - safety. what if all the lights and power go out? Also how would anyone breathe down there. And my criticisms seem stronger, not weaker, than yours. Today all cities with robust subway systems benefit hugely from them and all of these issues have been resolved. The criticism you've offered seems equally low-effort, so this is why I'm curious if you've ever helped design and build any large-scale project. I don't like gratuitous negativity on HN and it's against the rules here.
- M4v3R 9y ago
  Also, planes are a terrible idea. I mean how do you evacuate people from them if something goes wrong? I think this whole airplane thing is just vaporware.
  - KekDemaga 9y ago
    The question isn't "will this ever work?", the question is (while keeping with your airplane analogy) is Elon Musk's design closer to the Wright brothers airplane or Da Vinci's ornithopter. I'd guess the latter personally.
    - logicallee 9y ago
      The Wright brothers had a bicycle shop, whereas Da Vinci was more of a painter. The main thing Musk has in common with the Wrights is running an electric car transportation company and sending private rockets into space via SpaceX. I think you should revisit whether that makes it more Wright brothers or Da Vinci.
      - eradicatethots 9y ago
        What are you arguing? You wouldn’t take the position that it’s guarenteed to succeed, that seems absurd to me. The person you replied to only made the point that it could fail. And in your reply you actually took the opportunity to degrade artists and thinkers, which seems cruel and unnecessary. You’ve found a flaw, I think a pedantic one, in the example they gave. Here’s an example that is less flawed, and I think if you had considered their point rather than sought minute flaws you could see this yourself: the palm note vs the iPhone. Hopefully, even if my analogy is not literally flawless, you can take my point. Also, sorry for spamming you, something you wrote struck me and I wanted to see what else you wrote. Hope you don’t mind this.
jfindley 9y ago
It's easy to come up with reasons why something won't work. But, usually, it's more productive to start with the understanding that other people are smart too, and that they may have thought of these problems. In this particular case, I believe that the original white paper addresses these points. I'm not a structural engineer, so I've no idea if their solutions are valid and I'm not saying that it's never okay to criticize, but this reads to me as if you may have fallen into the trap of forgetting that the people who designed this are very smart people, and thus likely thought of the obvious problems.

Filligree 9y ago

The pressure tube doesn't need to be at near-vacuum. By the drag equation, air resistance is proportional to pressure; merely cutting pressure by 90% would reduce air resistance by the same amount, and that's trivial with perfectly ordinary pumps. Serious vacuum pumps are not required. This is not to say that keeping it airtight won't still be a major engineering problem, it just isn't as near-impossible as near-vacuum would be. To cope with expansion, you'd need to use sliding plates--which, yes, will make it harder to keep the air out. That's going to be an interesting challenge.

wlesieutre 9y ago
Doesn't the Hyperloop concept rely on not having a perfect vacuum? It's supposed to suck in air on the front and blow it out the bottom as an air cushion. Without the air cushion you just have "maglev in a vacuum" instead. I'm sure that's also a fast mode of travel, but like you said, the vacuum part of it takes a lot of money.
- Robotbeat 9y ago
  Does the vacuum part take a lot of money? I would think that if anyone knows, it'd be someone like Elon Musk who has built a spacecraft company from the ground up. For many of Elon Musk's projects, I get the idea that Elon is mostly just bringing broad, multi-domain knowledge to bear on industries that have been siloed for a very long time. So everyone scoffs at a long vacuum tube and using turbomachinery, etc, but for someone with a physics background with extensive knowledge of the spacecraft environment, turbopump rocket engines, and all the subsystems and ground testing systems that enable all this, it really isn't far-fetched at all. Most physicists (of the experimental kind, i.e. those who have to have hands-on knowledge fabricating things in addition to theoretical background) that I've talked to understand his ideas and think they're fairly reasonable. People seem to base most of their criticisms on the fact that it's different than what we already do without a fundamental, first-principles understanding of the system.
  - wlesieutre 9y ago
    A real vacuum (or very close to it) would be expensive, yes. That's what Musk designed the hyperloop to avoid; it works with a "low pressure" tube instead. His original hyperloop proposal paper outlines this in the intro: http://www.spacex.com/sites/spacex/files/hyperloop_alpha.pdf http://www.spacex.com/sites/spacex/files/hyperloop_alpha.pdf Another extreme is the approach, advocated by Rand and ET3, of drawing a hard or near hard vacuum in the tube and then using an electromagnetic suspension. The problem with this approach is that it is incredibly hard to maintain a near vacuum in a room, let alone 700 miles (round trip) of large tube with dozens of station gateways and thousands of pods entering and exiting every day. All it takes is one leaky seal or a small crack somewhere in the hundreds of miles of tube and the whole system stops working. However, a low pressure (vs. almost no pressure) system set to a level where standard commercial pumps could easily overcome an air leak and the transport pods could handle variable air density would be inherently robust. Unfortunately, this means that there is a non-trivial amount of air in the tube and leads us straight into another problem. The "another problem" being that if you just do low pressure, it means your pod has air in front if it and has to pushing that air around (or if that air has nowhere else to go in the forward tubing, trying to compress it, because not enough of the air can squeeze around the pods at the edge of the tube). That's what the hyperloop is getting around by sucking air in the front and blowing it out the bottom. Working as an air cushion is something of a bonus, and if everything works out right it also lets you avoid the expense of maglev.

Faaak 9y ago

The CERN LHC tube is a 27km circle of vacuum and near-zero temperature, and they don't seem to have a problem with that (granted, they had some but it's solved now). Frankly, yes, there may be issues, but I'm confident that the Human race will be able to overcome those.

ginko 9y ago
The LHC's vacuum pipes are 6.3 cm in diameter..
- iamgopal 9y ago
  What, really? What's with all those mega photos we see everywhere ?
  - Analemma_ 9y ago
    Most of that is the magnets around the beam tube, with the associated power and refrigeration equipment. The beam tube itself is quite small.
  - konschubert 9y ago
    Those are the detectors. And the magnets around the tubes.
  - delecti 9y ago
    This picture shows a cross section of part of the LHC. Those two yellow lines sticking out are the actual tubes. Everything else is equipment to manage the particles (detectors, containment, magnetic propulsion). And for a sense of scale, a human can comfortably stand in that tunnel next to it. Image: http://www.tut.fi/cs/groups/public_news/@l102/@news/@p/documents/kuva/x194225.jpg http://www.tut.fi/cs/groups/public_news/@l102/@news/@p/docum... From here: http://www.tut.fi/en/about-tut/news-and-events/tut-and-cern-collaborate-in-development-of-particle-accelerators-of-the-future-x194226c2 http://www.tut.fi/en/about-tut/news-and-events/tut-and-cern-...
- eutropia 9y ago

The_Double 9y ago

I haven't done any work on hyperloops. But expansion seems to be a problem already solved by industry a long time ago: https://en.wikipedia.org/wiki/Metal_expansion_joint https://en.wikipedia.org/wiki/Metal_expansion_joint

bjl 9y ago
Metal expansion joints can't hold a vacuum.
- MrBuddyCasino 9y ago
  Quick googling says otherwise: http://www.spiroflex.hr/expansion-joints-vacuum-technology http://www.spiroflex.hr/expansion-joints-vacuum-technology
MrBuddyCasino 9y ago
Sounds promising: - Resistance to high and very high pressures - Large movement absorption - Early leak indication (in case of damage) via standard check hole - Complete burst resistance - Possibility of permanent leak monitoring in critical media

dmix 9y ago

> Lots of marketing, very little engineering. It started as a technical whitepaper, not a marketing campaign, and multiple companies are building experimental models. I don't think this critique is accurate or fair. There have been far worse vapourware and hype-only concepts that haven't gotten close to hyperloop's tangible progress. No tech can be perfected from the planning stage either, it takes talent, money, and time - and you can't get those things without a bit of hype, the key is keeping it balanced. Regardless the concept seemed feasible enough to some very smart people and people with money to spend, where they see it's worth the R&D. I don't really see what the big risk or downside here of exploring this? Considering the rewards could be very high if it does work and otherwise there has been little innovation in transportation in 50yrs, it's not like there are some obvious alternatives are being neglected.

TremendousJudge 9y ago
>it's not like there are some obvious alternatives are being neglected A high speed train like the ones they've had in Europe for a long time? You know, the ones that regularly reach 300 km/h? If that's not fast or flashy enough for you, what about Maglev? It actually exists, and the tracks are extremely expensive even though they don't even have to maintain low air pressure
- Robotbeat 9y ago
  We have natural gas pipelines that have to maintain a far higher pressure difference, and they are in the same order of magnitude in diameter. They're not expensive. Way less than high speed rail lines per mile.
- dmix 9y ago
  > A high speed train like the ones they've had in Europe for a long time? I don't see what the US political inability to build infrastructure has to do with my comment. Plenty of countries are still building highspeed trains and iterating on that model... and plenty of non-US countries are looking into hyperloop, the first ones to adopt it will likely be outside of the US, as that's where most innovation is these days. And regardless there's always plenty of room for new ideas. Unless you think these billionaires should be backing American transportation mega-projects instead? There's plenty of roadblocks there outside of access to capital, where a highspeed train will likely cost 2-3x the initial projections, even if a private company does it. Not to mention the US is a car-heavy market. It seems like a risky project for any non-government entity to take on as it will be packed full of political risk and direct involvement either way... The US rarely builds major projects anymore except in the defense industry. And almost every major defense project of comparable size ends up being billions over budget or cancelled.

deleted 9y ago

[deleted]

logicallee 9y ago

Out of curiosity, have you ever built anything big? I say this because the tone of your comment is dismissive, however it seems quite low-effort. I can translate your criticisms into criticisms of building subways in 1863: - if you build a subway it will be the biggest underground railway ever built. - Rocks. They could fall in front of a subway car and cause a huge accident. - safety. what if all the lights and power go out? Also how would anyone breathe down there. And my criticisms seem stronger, not weaker, than yours. Today all cities with robust subway systems benefit hugely from them and all of these issues have been resolved. The criticism you've offered seems equally low-effort, so this is why I'm curious if you've ever helped design and build any large-scale project. I don't like gratuitous negativity on HN and it's against the rules here.

M4v3R 9y ago
Also, planes are a terrible idea. I mean how do you evacuate people from them if something goes wrong? I think this whole airplane thing is just vaporware.
- KekDemaga 9y ago
  The question isn't "will this ever work?", the question is (while keeping with your airplane analogy) is Elon Musk's design closer to the Wright brothers airplane or Da Vinci's ornithopter. I'd guess the latter personally.
  - logicallee 9y ago
    The Wright brothers had a bicycle shop, whereas Da Vinci was more of a painter. The main thing Musk has in common with the Wrights is running an electric car transportation company and sending private rockets into space via SpaceX. I think you should revisit whether that makes it more Wright brothers or Da Vinci.
    - eradicatethots 9y ago
      What are you arguing? You wouldn’t take the position that it’s guarenteed to succeed, that seems absurd to me. The person you replied to only made the point that it could fail. And in your reply you actually took the opportunity to degrade artists and thinkers, which seems cruel and unnecessary. You’ve found a flaw, I think a pedantic one, in the example they gave. Here’s an example that is less flawed, and I think if you had considered their point rather than sought minute flaws you could see this yourself: the palm note vs the iPhone. Hopefully, even if my analogy is not literally flawless, you can take my point. Also, sorry for spamming you, something you wrote struck me and I wanted to see what else you wrote. Hope you don’t mind this.

jfindley 9y ago

It's easy to come up with reasons why something won't work. But, usually, it's more productive to start with the understanding that other people are smart too, and that they may have thought of these problems. In this particular case, I believe that the original white paper addresses these points. I'm not a structural engineer, so I've no idea if their solutions are valid and I'm not saying that it's never okay to criticize, but this reads to me as if you may have fallen into the trap of forgetting that the people who designed this are very smart people, and thus likely thought of the obvious problems.