Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Hyperloop One Becomes ‘Virgin Hyperloop One’

techcrunch.com

Post reply on HN
Print view View original

241–250 of 517 posts

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#241

Post by JumpCrisscross »

thearn4 wrote: post #211
JumpCrisscross wrote: post #168

The original Hyperloop paper quotes its design pressure as “about 1/6 the pressure of the atmosphere on Mars” [1]. Martian atmospheric pressure is “about 0.6% of Earth's mean sea level pressure” [2]. So 0.1% of Earth’s surface pressure, or a 1,000:1 pressure change. To put that in perspective, the Boeing 787’s GEnx-2B67, the most powerful GEnx engine variant, generates a 43:1 pressure ratio [3]. To get a sense of the…

Some colleagues of mine also did a short feasibility assessment of the original white paper, and came to some similar conclusions. The propulsion system also made some assumptions about compressor performance that seemed too optimistic compared to existing turbomachinery. That said, I have not followed closely enough to know if the hyperloop startups out there are following the original conception or if it has signif…

> Some colleagues of mine also did a short feasibility assessment of the original white paper, and came to some similar conclusions

Likewise. It sounds like above-surface (on Earth) is probably unfeasible given (a) security and (b) thermal concerns.

For security, we just contemplated debris from the track (or a bullet from an errant rifle) puncturing the tube. Hyperloop One is testing an 3.3m diameter and 500m long track [1]. That's 4,276 cubic meters [a]. "At sea level and at 15 °C air has a density of approximately 1.225 kg/m3" [2]. The air in the Hyperloop One test track thus weighs about 5,200 kg.

If we use the Hyperloop's original design spec [3], a puncture means air on one side at 1 atm expanding into the space on the other at 1/1,000 atm. This simplifies to a wall of air moving at just below the speed of sound. Since the speed of sound is about 330 m/s [4], the end of the tunnel will could hit with a pulse with about 140 megajoules of energy [b]. That's the energy in about 30 kg of TNT [5][c].

> I hear that they've ditched the compressor altogether, but that's got to have a pretty big impact on expected speeds

It currently sounds like a vactrain [1] with magnetic levitation [2].

[1] https://arstechnica.com/cars/2017/03/hyperloop-one-shows-pho...

[a] pi * (3.3 / 2) ^ 2 * 500

[2] https://en.wikipedia.org/wiki/Density_of_air

[3] http://www.spacex.com/sites/spacex/files/hyperloop_alpha-201...

[4] https://en.wikipedia.org/wiki/Speed_of_sound

[b] (1/2) * (5200 / 2) * 330 ^ 2

[5] https://en.wikipedia.org/wiki/TNT_equivalent

[c] (140 * 10^6 / 4.184 * 10^9) * 10^3

[1] https://en.wikipedia.org/wiki/Vactrain

[2] https://en.wikipedia.org/wiki/Maglev

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#243

Post by matt4077 »

thearn4 wrote: post #211
JumpCrisscross wrote: post #168

The original Hyperloop paper quotes its design pressure as “about 1/6 the pressure of the atmosphere on Mars” [1]. Martian atmospheric pressure is “about 0.6% of Earth's mean sea level pressure” [2]. So 0.1% of Earth’s surface pressure, or a 1,000:1 pressure change. To put that in perspective, the Boeing 787’s GEnx-2B67, the most powerful GEnx engine variant, generates a 43:1 pressure ratio [3]. To get a sense of the…

Some colleagues of mine also did a short feasibility assessment of the original white paper, and came to some similar conclusions. The propulsion system also made some assumptions about compressor performance that seemed too optimistic compared to existing turbomachinery. That said, I have not followed closely enough to know if the hyperloop startups out there are following the original conception or if it has signif…

Weren't there published papers by NASA scientists proving, without a doubt, that it's impossible to construct a booster rocket with the structural stability to return to earth?

I'm willing to give this guy the benefit of the doubt considering his track record. It's also instructive to read the comments when the original Hyperloop idea was published. Even the people thinking Musk would fail were in the minority, because everyone was certain he had no plans of even trying.

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#244

Post by zardo »

imron wrote: post #169
Pxtl wrote: post #147

Earlier quoted context omitted.

That's impressively cynical, but Musk obviously stands to gain a lot if people keep California using roads. California wants to go green and he sells the best technology for green road-based transportation.

To be fair, he also stands a lot to gain if Hyperloop becomes a reality.

How does that work? He had an idea and promoted it. No one's going to be paying him royalties for it.

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#245

Post by JumpCrisscross »

schiffern wrote: post #235
Robotbeat wrote: post #218

Earlier quoted context omitted.

Wait, who said that they need to compress the air all the way to Earth pressure? None of your critique makes sense without that assumption, and nowhere in your post do you say where that comes from.

> Wait, who said that they need to compress the air all the way to Earth pressure? No one. The Hyperloop alpha paper explicitly contradicts this assumption on page 18, where the flow diagram gives the compressor input at 99 Pa and the output at 2.1 kPa (a 21:1 pressure ratio). http://www.spacex.com/sites/spacex/files/hyperloop_alpha-201...

> The Hyperloop alpha paper explicitly contradicts this assumption on page 18, where the flow diagram gives the compressor input at 99 Pa and the output at 2.1 kPa (a 21:1 pressure ratio)

One standard atmosphere (atm) is defined at over 100,000 Pa [1]. The 21:1 pressure ratio in Figure 11 on page 18 is for the "passenger plus vehicle capsule" [2]. I'm talking about the tube.

Going from 99 to 2.1 isn't hard. Going from 100,000 to 100 and then keeping it there is.

[1] https://en.wikipedia.org/wiki/Atmosphere_(unit)

[2] http://www.spacex.com/sites/spacex/files/hyperloop_alpha-201...

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#246

Post by chipotle_coyote »

nradov wrote: post #226
valas wrote: post #219

Earlier quoted context omitted.

"it would be as slow as conventional rail" - citation? Even Reason Foundation (which is as biased as it gets - it's funded by Koch brothers and ideological critic of almost any government investment) claim SF to LA times will be 3:30 to 4:40, which is faster than any train today.

That's barely faster than driving, once you account for the time spent moving between your origin/destination and the train station as well as transferring luggage.

An under-four-hour train trip still sounds like a win over a six-hour-with-good-traffic drive. Especially for people who don't really like making that drive, which I suspect is a substantial subset of the population. (I like driving, personally, but that trip is decidedly less than a thrill.)

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#247

Post by dvanduzer »

jey wrote: post #220
daemin wrote: post #182

Earlier quoted context omitted.

Isn't that because the freight companies are the ones that actually built, own, and operate the tracks? If Amtrak or another passenger company owned the tracks, their trains would get priority.

No, Amtrak supposedly has priority by law: https://www.washingtonpost.com/news/powerpost/wp/2016/04/29/...

Based on this article, I'm under the impression that the law was overturned. The most recent article I can find about the status of adjudication suggests that Amtrak will have a very difficult time upholding that law: http://lyldenlawnews.com/2016/09/22/u-s-faces-a-choice-on-am...

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#248

Post by Twirrim »

daemin wrote: post #165

Just as a thought experiment, could the promotion of these "hyperloop" projects be a clever political ploy to misdirect/divert attention and prevent a viable high speed rail network from being built? Elon's main business is electric cars and (one of) Branson's is airlines. So a reasonable competitor to both is fast and cheap(er) public transport along a major travel corridor in the USA. This means that by promoting t…

All Branson has left is a partial holding of Virgin Atlantic on the flying business side of things. Virgin is in the train business, and has 100% holdings there, so if anything he has more business interest in seeing high speed rail come about.

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#249

Post by Brakenshire »

mseebach wrote: post #223
Brakenshire wrote: post #188

Earlier quoted context omitted.

We're just building a new major high speed line in the UK, and you'd be surprised how often you hear people say that it shouldn't be built because the technology will be superseded by the hyperloop, or autonomous cars, or whichever. It's one of the major talking points, even if it isn't one of the major blocks.

Meh. The imminency of "Major New Technology Just Around The Corner" has always been a favourite argument for the anti-progress crowd. EDIT to add: Before Hyperloop, it was Maglev. And frankly, a significantly better argument against HS2 is that it's an impossibly expensive boondoggle.

> a significantly better argument against HS2 is that it's an impossibly expensive boondoggle.

Nah, it connects most of England's largest cities, and will be 2/3rds of the network which will connect all of the cities of the North of England into something approaching a single labour market. Liverpool, Leeds, Sheffield, Manchester, Birmingham will be all be within 30-50 minutes of each other, with London within an hour and a half, with trains running between destinations 2 or 3 times an hour. The value of that is enormous.

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#250

Post by JumpCrisscross »

hwillis wrote: post #231
JumpCrisscross wrote: post #168

The original Hyperloop paper quotes its design pressure as “about 1/6 the pressure of the atmosphere on Mars” [1]. Martian atmospheric pressure is “about 0.6% of Earth's mean sea level pressure” [2]. So 0.1% of Earth’s surface pressure, or a 1,000:1 pressure change. To put that in perspective, the Boeing 787’s GEnx-2B67, the most powerful GEnx engine variant, generates a 43:1 pressure ratio [3]. To get a sense of the…

> The Hyperloop’s thermal issues are a hard enough problem that they alone put this in the domain of materials science. That’s the same category of problems separating us from a space elevator. What? What are you even talking about?? That's a completely ridiculous statement. The pressure inside and outside the lunar landing module was 1,000,000,000,000,000x. 100 kPa to 10^-10 Pa. It makes zero sense to apply this kin…

> The pressure inside and outside the lunar landing module was 1,000,000,000,000,000x. 100 kPa to 10^-10 Pa

We didn't pump air into the lunar module from the Moon. We carried it from Earth pre-pressurized. Unless you're proposing we build and seal the Hyperloop tubes in space before bringing them down, the analogy isn't appropriate.

Also, consider a soda can. It's stronger when pressurized from the inside. Modern nuclear attack submarines collapse around 730m [1]. Since for "every 33 feet (10.06 meters) you go down, the pressure increases by 14.5 psi," we're talking about water pressure of about 1,000 psi or about 72 atm.

[1] https://en.wikipedia.org/wiki/Submarine_depth_ratings

[2] https://oceanservice.noaa.gov/facts/pressure.html

Post reply on HN