Replying to myself. Apparently Google discontinued the secret question method so honestly I have no idea what happens when you try to recover your account and I'm not in the mood to try it:)
Yes, the article (and summary) confused me. On my Google account, to do a password recovery I believe they'd need to compromise my second email account and know a security question to recover my Gmail account. If they do all that, then yeah I'm screwed but frankly that is a lot of work and they could just steal my identity instead:)
Agreed. That's what I was trying to say. It's a force measurement, not mass measurement. My problem is that this ignores momentum - which in a train is significant. If the front of the train is strong enough to withstand the pressure - and this is very feasible - then the rest of the train will follow unharmed. Bypasses would help equalize the pressure on either side. The speed at which it will slow to a stop is entirely dependent on the mass of the train. If the G forces are too great, then increase the mass of the train.
Thunderfoot's demonstration of the train going rocketing out of the tube is simply unrealistic. He should repeat the experiment with progressively smaller projectiles to show the effect of a bypass.
loss of vacuum results in 10t per square metre of air rushing at you at ~700mph.
10t per square meter? What? How does the air have more mass than the train? You mean the 14 psi? That does not equal mass - that's pressure, in units of force. The train simply needs more mass than the air has (which is easy) and it needs the strength to resist a sudden 14psi pressure increase. Certainly airplanes demonstrate that this is feasible. Finally, you can open up bypasses to let air rush past the train.
I assure you that a 15 ton train has a lot more momentum at 700MPH than a comparable volume of air. If you want a gentler deceleration profile, make it heavier.
Agreed, but it sounds pretty survivable. No people turning into jelly. And the point is you can engineer it to stop in any amount of time you wish, staying under whatever acceleration profile you want.
14.7 PSI is easily handled by a combination of brakes (that already need to stop a 700MPH train!) and bypasses for the air. Thunderfoot's demonstration is a bit absurd.
Maybe, but it lacks the ability to scale. Perhaps the massive capital cost can be justified on a direct route from LA to SF with maybe a stop in Silicon Valley. But a stop in Sacramento? Oh, lord, no. I don't know what the SF-to-LA air traffic is, and maybe it is indeed doomed - but I'm extremely skeptical as air travel is very scalable.
The original proposal was to have tubes using existing highway right-of-way - and all of the test track is above ground. So I understand people's criticism.
Aren't we talking about the survive-ability of a worst-case failure? In that case, some injuries or deaths would be expected. The point of the graphs I linked to is to show that the number of Gs is not by itself instructive - it is Gs over time. You have to stay under those curves. A roller coaster can exceed 6 Gs. The point is, it is a very straightforward engineering problem to properly weight and shape the sled such that it will stay under the curve necessary to keep most passengers safe. It will not instantaneously stop unless it has zero mass, and it's stopping distance will increase with mass. If the stopping distance is too short? Make it heavier.
I agree that sabotage is a legitimate security concern, though rail also has this weakness and it - for whatever reason - is not often exploited.
But I'd be careful about using the test track to infer what the final tracking would look like. For one thing, it'll almost certainly be far more complex: expansion joints, hatches, vents, etc. I'm also not as worried about earthquakes - the tubing is bound to be very flexible. Earthquakes go on for dozens of seconds to minutes - they are not instantaneous. I think there would be time to slow or stop the passenger cars if the system encountered failure. And like Fukushima, it would be a tragedy - but far smaller in scale than the larger loss of life from the earthquake.
I don't think it's feasible at all from an economic standpoint, but some of the criticisms are from people who watched a YouTube video or something and are not that well thought through. There's not a lot of impossible physics being proposed - just very expensive engineering that, IMHO, is doomed to be too costly and too complex (and thus unreliable) for practical use. Holding vacuum economically is a huge challenge - tubes crinkling up is not.
The clearance between the pod and the tube wall is very much part of the system design
But that clearance can be shuttered. At simplest, imagine a slightly-pressurized cylinder that has plugs on both ends. The plugs are held in place with pressure such that if the pressure equalizes, the plugs fall away (well, one would fall away and the other ejected) and the cylinder becomes a pass-through tube. This is a system would safely pass air through if there was a sudden (or even gradual) depressurization. If needed, you could do this to the entire passenger compartment, which would suddenly get a little breezy:)
I'm sure you could do something much more clever using the fact that small amounts of rarefied air will behave much differently than large amounts of atmospheric air and have different bypass paths depending on the pressure.
Yeah, it's a wall of air - but it's a wall of... air. Highly compressible, soft and squishy. If your sled has any mass at all compared to the air, it won't be a sudden halt. Bonus points if it is streamlined. You can decelerate a human body from 700MPH pretty darned quickly.
First, look at this chart to see where human tolerances lie. You can see that - forward facing - humans can take quite a bit of instantaneous acceleration of around 19 G. At 19G you could decelerate in:
t = 700 mph / 19 G = 1.68 s.
That's an oversimplification, but I'm very confident that the system could be designed to fit within the envelope on that chart. That's exactly what they do with trains today in the US - they keep adding mass until the train is heavy enough to plow through anything they are likely to encounter at a grade crossing... efficiency be damned.
Tanker cars are designed to keep the contents inside, not contain a vacuum. The forces are literally the opposite of what was designed. You might as well claim that the pyramids are a poor design because they'd fly apart if turned on their side.
I like Thunderfoot and subscribe to his channel. I'm not an advocate for hyperloop and think it is not economically feasible.
But the failure mode he demonstrates with an air hose is silly. Thunderfoot should try progressively smaller projectiles in the same-size tube to see how dramatically the velocities fall off. The hyperloop sled does not need to fill the entire cross-sectional area of the tube, and in fact that would make it very oddly-shaped for human occupation. I just don't see this as a problem that is beyond a technical engineering solution - just one that will cost too much to be viable.
Don't believe everything you see in a YouTube video. I subscribe to Thunderfoot, too, but while he's very smart he's not an expert on EVERYTHING.
While technically true that the air would rush in at the "speed of sound", this is actually to the advantage of the system. The reason is that the shockwave will limit the mass of air flowing in and reduce the severity of the leak. So, yeah, there will be some turbulent "supersonic" air coming through the leak, but it will immediately go laminar once it hits the much larger volume of the tube.
think of the pressure wave of air rushing in and what that will do to any near by vehicle
There are engineering solutions to that - the most obvious would be emergency vents that open up in the event that pressure is lost in any part of the tube. You can also make the tube larger than it needs to be to let air circulate around the car (like in a regular subway) rather than pushing it like a piston through a tight cylinder. Even a total vacuum is only 1 atm, 14lbs sq in, or 100 kPa lower than ambient - so it's not like we're developing pressures beyond what large brakes could not overcome.
My critique is that the engineering solutions are all going to be complex, expensive and make the thing a white elephant - but it's completely feasible from a technical standpoint.
Yes, I used to live in NYC, and I'm familiar with Grado. They do indeed hand-make their headphones (out of wood!) and if those are what you have, then yeah, you paid for the old-school craftsmanship. Many of the audiophile-class stuff is wholly or in part made in China, though (cough, Bowers & Wilkins, cough) - and if they use modern processes even highfalutin headphones will have less than $100 in parts. It's just wood, metal, and plastic. And while this is all very subjective, I personally haven't experienced anything better than the tried and true MDR 7506, which go for around $100.
I wouldn't get too cocky. Wanna bet your $900 pair didn't cost much more than the Beats to manufacture? I'm glad they make you happy (and I'm envious that you have hours to lay in bed quietly!). I'm glad your sister finds happiness in $250 sunglasses, even if I'm completely satisfied by the ones I get from the guy on the street corner selling them for $5. I also spend my money on things that make me happy. It's a wonderful world.
I don't fly as much as I used to, but I've switched from noise cancelling headphones to Sennheiser CX150 RT earbuds. I even wear them when I'm not listening to music, just to block the sound. They might not be quite up to the best noise cancelling headphones, but they are darned close. Actually, the Panasonic RPHJE120G headphones aren't bad, either - though definitely not as good as the Sennheisers. I got the Sennheisers for $15 on sale and the Panasonic buds were $6.50 on sale so I bought several.
Sort of... the generics were estimated to cost $16.89 vs $20.19 for the real. Sure, they are $200 headphones, but that's a 20% increase in COGS. The counterfeit is "almost identical" because by definition it has to be a pretty believable copy in order to pass for the real thing.
Anyway, my point wasn't that Beats headphones are a good deal - they aren't. My point was to support the parent's implication that the headphones could be fake - they even fooled an expert. Secondarily, my point was that the author is knowingly exaggerating and misleading.
Slashdot Mirror
Replying to myself. Apparently Google discontinued the secret question method so honestly I have no idea what happens when you try to recover your account and I'm not in the mood to try it :)
Yes, the article (and summary) confused me. On my Google account, to do a password recovery I believe they'd need to compromise my second email account and know a security question to recover my Gmail account. If they do all that, then yeah I'm screwed but frankly that is a lot of work and they could just steal my identity instead :)
So... still better than password-only. That's probably good enough for my purposes.
same value.
Agreed. That's what I was trying to say. It's a force measurement, not mass measurement. My problem is that this ignores momentum - which in a train is significant. If the front of the train is strong enough to withstand the pressure - and this is very feasible - then the rest of the train will follow unharmed. Bypasses would help equalize the pressure on either side. The speed at which it will slow to a stop is entirely dependent on the mass of the train. If the G forces are too great, then increase the mass of the train.
Thunderfoot's demonstration of the train going rocketing out of the tube is simply unrealistic. He should repeat the experiment with progressively smaller projectiles to show the effect of a bypass.
loss of vacuum results in 10t per square metre of air rushing at you at ~700mph.
10t per square meter? What? How does the air have more mass than the train? You mean the 14 psi? That does not equal mass - that's pressure, in units of force. The train simply needs more mass than the air has (which is easy) and it needs the strength to resist a sudden 14psi pressure increase. Certainly airplanes demonstrate that this is feasible. Finally, you can open up bypasses to let air rush past the train.
I assure you that a 15 ton train has a lot more momentum at 700MPH than a comparable volume of air. If you want a gentler deceleration profile, make it heavier.
This thing still makes no economic sense.
Agreed, but it sounds pretty survivable. No people turning into jelly. And the point is you can engineer it to stop in any amount of time you wish, staying under whatever acceleration profile you want.
14.7 PSI is easily handled by a combination of brakes (that already need to stop a 700MPH train!) and bypasses for the air. Thunderfoot's demonstration is a bit absurd.
Maybe, but it lacks the ability to scale. Perhaps the massive capital cost can be justified on a direct route from LA to SF with maybe a stop in Silicon Valley. But a stop in Sacramento? Oh, lord, no. I don't know what the SF-to-LA air traffic is, and maybe it is indeed doomed - but I'm extremely skeptical as air travel is very scalable.
The original proposal was to have tubes using existing highway right-of-way - and all of the test track is above ground. So I understand people's criticism.
Aren't we talking about the survive-ability of a worst-case failure? In that case, some injuries or deaths would be expected. The point of the graphs I linked to is to show that the number of Gs is not by itself instructive - it is Gs over time. You have to stay under those curves. A roller coaster can exceed 6 Gs. The point is, it is a very straightforward engineering problem to properly weight and shape the sled such that it will stay under the curve necessary to keep most passengers safe. It will not instantaneously stop unless it has zero mass, and it's stopping distance will increase with mass. If the stopping distance is too short? Make it heavier.
I didn't see a Musk quote on there.
I agree that sabotage is a legitimate security concern, though rail also has this weakness and it - for whatever reason - is not often exploited.
But I'd be careful about using the test track to infer what the final tracking would look like. For one thing, it'll almost certainly be far more complex: expansion joints, hatches, vents, etc. I'm also not as worried about earthquakes - the tubing is bound to be very flexible. Earthquakes go on for dozens of seconds to minutes - they are not instantaneous. I think there would be time to slow or stop the passenger cars if the system encountered failure. And like Fukushima, it would be a tragedy - but far smaller in scale than the larger loss of life from the earthquake.
I don't think it's feasible at all from an economic standpoint, but some of the criticisms are from people who watched a YouTube video or something and are not that well thought through. There's not a lot of impossible physics being proposed - just very expensive engineering that, IMHO, is doomed to be too costly and too complex (and thus unreliable) for practical use. Holding vacuum economically is a huge challenge - tubes crinkling up is not.
The clearance between the pod and the tube wall is very much part of the system design
But that clearance can be shuttered. At simplest, imagine a slightly-pressurized cylinder that has plugs on both ends. The plugs are held in place with pressure such that if the pressure equalizes, the plugs fall away (well, one would fall away and the other ejected) and the cylinder becomes a pass-through tube. This is a system would safely pass air through if there was a sudden (or even gradual) depressurization. If needed, you could do this to the entire passenger compartment, which would suddenly get a little breezy :)
I'm sure you could do something much more clever using the fact that small amounts of rarefied air will behave much differently than large amounts of atmospheric air and have different bypass paths depending on the pressure.
Yeah, it's a wall of air - but it's a wall of... air. Highly compressible, soft and squishy. If your sled has any mass at all compared to the air, it won't be a sudden halt. Bonus points if it is streamlined. You can decelerate a human body from 700MPH pretty darned quickly.
First, look at this chart to see where human tolerances lie. You can see that - forward facing - humans can take quite a bit of instantaneous acceleration of around 19 G. At 19G you could decelerate in:
t = 700 mph / 19 G = 1.68 s.
That's an oversimplification, but I'm very confident that the system could be designed to fit within the envelope on that chart. That's exactly what they do with trains today in the US - they keep adding mass until the train is heavy enough to plow through anything they are likely to encounter at a grade crossing... efficiency be damned.
Tanker cars are designed to keep the contents inside, not contain a vacuum. The forces are literally the opposite of what was designed. You might as well claim that the pyramids are a poor design because they'd fly apart if turned on their side.
I like Thunderfoot and subscribe to his channel. I'm not an advocate for hyperloop and think it is not economically feasible.
But the failure mode he demonstrates with an air hose is silly. Thunderfoot should try progressively smaller projectiles in the same-size tube to see how dramatically the velocities fall off. The hyperloop sled does not need to fill the entire cross-sectional area of the tube, and in fact that would make it very oddly-shaped for human occupation. I just don't see this as a problem that is beyond a technical engineering solution - just one that will cost too much to be viable.
Don't believe everything you see in a YouTube video. I subscribe to Thunderfoot, too, but while he's very smart he's not an expert on EVERYTHING.
While technically true that the air would rush in at the "speed of sound", this is actually to the advantage of the system. The reason is that the shockwave will limit the mass of air flowing in and reduce the severity of the leak. So, yeah, there will be some turbulent "supersonic" air coming through the leak, but it will immediately go laminar once it hits the much larger volume of the tube.
think of the pressure wave of air rushing in and what that will do to any near by vehicle
There are engineering solutions to that - the most obvious would be emergency vents that open up in the event that pressure is lost in any part of the tube. You can also make the tube larger than it needs to be to let air circulate around the car (like in a regular subway) rather than pushing it like a piston through a tight cylinder. Even a total vacuum is only 1 atm, 14lbs sq in, or 100 kPa lower than ambient - so it's not like we're developing pressures beyond what large brakes could not overcome.
My critique is that the engineering solutions are all going to be complex, expensive and make the thing a white elephant - but it's completely feasible from a technical standpoint.
But they don't get used to read other people's grocery lists.
Yes, I used to live in NYC, and I'm familiar with Grado. They do indeed hand-make their headphones (out of wood!) and if those are what you have, then yeah, you paid for the old-school craftsmanship. Many of the audiophile-class stuff is wholly or in part made in China, though (cough, Bowers & Wilkins, cough) - and if they use modern processes even highfalutin headphones will have less than $100 in parts. It's just wood, metal, and plastic. And while this is all very subjective, I personally haven't experienced anything better than the tried and true MDR 7506, which go for around $100.
I wouldn't get too cocky. Wanna bet your $900 pair didn't cost much more than the Beats to manufacture? I'm glad they make you happy (and I'm envious that you have hours to lay in bed quietly!). I'm glad your sister finds happiness in $250 sunglasses, even if I'm completely satisfied by the ones I get from the guy on the street corner selling them for $5. I also spend my money on things that make me happy. It's a wonderful world.
My "good" headphones cost $15, so yeah I'm not even touching a $200 pair.
I don't fly as much as I used to, but I've switched from noise cancelling headphones to Sennheiser CX150 RT earbuds. I even wear them when I'm not listening to music, just to block the sound. They might not be quite up to the best noise cancelling headphones, but they are darned close. Actually, the Panasonic RPHJE120G headphones aren't bad, either - though definitely not as good as the Sennheisers. I got the Sennheisers for $15 on sale and the Panasonic buds were $6.50 on sale so I bought several.
Sort of... the generics were estimated to cost $16.89 vs $20.19 for the real. Sure, they are $200 headphones, but that's a 20% increase in COGS. The counterfeit is "almost identical" because by definition it has to be a pretty believable copy in order to pass for the real thing.
Anyway, my point wasn't that Beats headphones are a good deal - they aren't. My point was to support the parent's implication that the headphones could be fake - they even fooled an expert. Secondarily, my point was that the author is knowingly exaggerating and misleading.