Hyperloop One Becomes ‘Virgin Hyperloop One’ • Hacker News Board

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#351

Post by sbierwagen » Thu, Oct 12, 2017, 8:51 PM UTC

JumpCrisscross wrote: post #332

sbierwagen wrote: post #330

Earlier quoted context omitted.

> "Regenerative cooling" is a rocket term. It came to mind because I used to be an aerospace engineer. There's no requirement in the definition of regenerative cooling for the coolant to be dumped. ? Regenerative cooling in rocketry uses propellant. Propellant is always dumped overboard, because it's propellant. Please show me a rocket that uses closed loop cooling of the rocket nozzle. > Filtering and then compressi…

> Please show me a rocket that uses closed loop cooling of the rocket nozzle The most famous one is the under-development SABRE [1], which includes a closed-loop helium cycle. For cryogenic rockets, closed-loop cooling of the nozzle has been explored [2] to avoid hydrogen embrittlement and oxidation of the nozzle channels, as well as to simplify plumbing. In any case, we've devolved into arguing semantics. > My turn…

>The most famous one is the under-development SABRE [1], which includes a closed-loop helium cycle.

From the linked article:

>>The 'hot' helium from the air precooler is recycled by cooling it in a heat exchanger with the liquid hydrogen fuel.

It's open-loop regenerative cooling, with helium as an intermediate coolant. The heat still ends up in the propellant, which gets dumped overboard. Not closed-loop.

That patent also specifies a heat exchanger to the propellant tank.

>I was figuring on dumping the air once done versus worrying about a reservoir.

A poorly telegraphed joke. The atmosphere, here, is the reservoir. I have edited my comment.

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#352

Post by detritus » Thu, Oct 12, 2017, 8:54 PM UTC

LowRezSkyline wrote: post #163

detritus wrote: post #128

Earlier quoted context omitted.

Yes, there we go. I'm genuinely surprised it was anything other than fairly obvious. Perhaps his reputation's different away from the UK?

How dare you be clever... don't you know that if you make the very very smart people and or the mods feel less smart you will get smacked down on HN? Or maybe it was your foolish statements of a personal nature cause that's not scientifically, rigorously provable, cause you know, personal experiences are invalid! Why... well the very very smart people know more than you! As Jobe from Arrested Development would say '…

I'm massively wary about posting chat here (with fairly good reason) but thanks.

There should be an allowance for balance and humanity in HN comments. Not everything need be ultra-violet literal on the spectrum!

x

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#353

Post by JumpCrisscross » Thu, Oct 12, 2017, 8:56 PM UTC

schiffern wrote: post #345

JumpCrisscross wrote: post #327

Earlier quoted context omitted.

> How about wrapping the tube in insulating foam At that point why not just bury it? It swaps the thermal problem for the water problem, but we know how to build tunnels.

>At that point why not just bury it? Because foam is cheaper? A nice K.I.S.S. solution. Having seemingly solved this thermal expansion problem "in the same category of problems separating us from a space elevator," I'll be expecting The Fountains of Paradise to come true soon. ;)

> We seem to have solved this thermal expansion problem

I guess I'll have to telegraph my buddies in Hawthorne and at NASA :).

Joking aside, no, foam doesn't solve the problem. You'll still have flexing. This is one of the limits on how long you can have a launch tank on the pad. Imperceptibly small flexing, but of the kind that weakens every metal we know.

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#354

Post by JumpCrisscross » Thu, Oct 12, 2017, 8:58 PM UTC

schiffern wrote: post #331

JumpCrisscross wrote: post #285

Earlier quoted context omitted.

> Note that downthread they've already moved the goalpost from "these pumps are technologically impossible" to "but they'll need a lot of them!" I never said vacuum pumps are "technologically impossible". My original comment references the Space Power Facility [1] and categorises the vacuum problem as an engineering problem. A hard one, but engineering nonetheless. The comment you link to [2] replies to someone claim…

> The comment you link to [2] replies to someone claiming the original white paper calls for a 22:1 atmosphere:tube pressure ratio. I pointed out that the figure they're referencing, Figure 11, discusses the capsule and not the tube. I happen to be that someone. :) You were talking about state-of-the-art axial compressors (the GEnx-2B67), so I assumed you were talking about the axial compressor on the front of the po…

> If that were really a problem, no pipelines of any kind could be built

The Trans-Alaska Pipeline system, which I believe is the largest at least in the United States, is 1.2m in diameter [1]. We're talking about a pipe almost 3 times wider that needs to hold itself against the atmosphere and keep capsules neatly contained.

Side note: long pipelines zig-zag to allow for thermal expansion and contraction [2]. You can't do that with the Hyperloop. (Bridges handle this with various ingenious methods, most of which will work for the Hyperloop's longitudinal expansion.)

> thermal expansion joints are the solution

Scaling pipe expansion joints where they maintain the near vacuum and deal with the structural stress of a capsule whizzing by will be difficult. By "difficult" I mean these are problems NASA (for the ISS) and Schlumberger (for pipes) have been grappling with for years and with billions of dollars in R&D.

[1] https://en.wikipedia.org/wiki/Trans-Alaska_Pipeline_System#/...

[2] https://www.quora.com/Why-do-oil-pipelines-that-transfer-oil...

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#355

Post by c22 » Thu, Oct 12, 2017, 9:11 PM UTC

Robotbeat wrote: post #323

JumpCrisscross wrote: post #305

Earlier quoted context omitted.

> Elon Musk just waltzed into the high speed rail debate and Dunning-Krugered some crazy scheme I think it's incredibly important to segregate Musk's work, i.e. SpaceX and Tesla, from his proposals, e.g. the Hyperloop, modular infrastructure and other things.

Nah, the Dunning-Kruger thing applies equally well to Tesla and SpaceX. He had no experience in either field before starting those companies. It's just that he has, in spite of all probability, succeeded and so you see them in a different light.

Maybe his experience is in building successful companies.

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#356

Post by JumpCrisscross » Thu, Oct 12, 2017, 9:12 PM UTC

kbenson wrote: post #349

hwillis wrote: post #318

Earlier quoted context omitted.

Dude, what. That's bullshit, and the size difference will be on the order of dozens or low hundreds of microns. Not only that, but the distortion will be spread evenly across the tube because it's a tube. You're just asserting that putting the tube in shadow will somehow not block heat from the sun. I'm also not sure you understand what I'm saying about an aluminum shield? Aluminum has an emissivity coefficient of .0…

I think what we have here is someone applying a known problem and solution space for one industry (rocketry) to another (civil engineering). A large vertical tube that needs to move quickly and under great stress may not allow for the same solutions that apply to a large horizontal tube that is relatively static. Fixing a large enough solar shield above a rocket hundreds of feet in the air which has to get out of the…

> I'm not sure how this problem was solved in rocketry is necessarily indicative of how hard it is to solve in other circumstances

Very fair. The advantage a rocket has is you choose when it's rolled out. You don't have to design for the worst weather because you can always hide.

You can't do that for a static structure. The Hyperloop is an attempt to marry the challenges of rocketry to the standards of civil engineering. The advantage is you don't have to think about aerodynamics, which is good, because air is the worst. (You also get civil-engineering budgets.) The bad is you can't hide from the edge cases.

If you want to grapple with this problem live, rent (or borrow) a thermal camera and make a model. Aluminum or tin foil would probably work for something on the window. I've only done this upright, to simulate storing an unfuelled vehicle outdoors in "ready-to-launch" mode, but you'll run into similar problems with a horizonatal configuration. At first, the shade works. Then thermals develop. You can foam it, and that looks like it works for a few days. Then someone instruments the inside and, lo and behold, hot spots. Turns out foam doesn't really help with heat that recurs in the same place, day after day. (Our solution: slowly rotate it.) You could completely isolate the tube, which is what NASA does in its vehicle assembly building [1], but at that point you might as well (a) bury it or (b) have a fleet of Concordes flying on loop, because either will be cheaper.

I'm not saying it's impossible. But it's much harder than the pressure problem, which is itself hard to get economical. If you want the tube above ground, I don't think it works with existing materials. My criticism of the Hyperloop One project is they didn't bother solving these issues with models. (Note: this is how Elon did it with the Falcon 1.) Instead, they decided to build a maglev track.

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

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#357

Post by JumpCrisscross » Thu, Oct 12, 2017, 9:16 PM UTC

schiffern wrote: post #337

JumpCrisscross wrote: post #316

Earlier quoted context omitted.

> I think they know that, don't you? Who's they? Hyperloop One? No--they've just punted the "hard" stuff to the end. (Kind of like the Wright Brothers designing the seats of their plane before getting it flying. Oh look! [1]) Elon Musk? Yes--I do. That's why he's waiting. > what specific problem do you see? The top heats up and the bottom doesn't. > The paper calls for 0.8-1.0 inch thick steel, which my math says is…

> No--they've just punted the "hard" stuff to the end. Citation needed. The link provided gives no support. I would be interested in seeing your calculations on the thermal side. An ANSYS multiphysics simulation (the software SpaceX uses) would show the problem, no? SpaceX has already built and used a mile-long, 11' diameter vacuum tube in Southern California, which would seem to put this matter to rest (the proof is…

> An ANSYS multiphysics simulation (the software SpaceX uses) would show the problem, no?

Yes. But SpaceX != Hyperloop One.

> SpaceX has already built and used a mile-long, 11' diameter vacuum tube in Southern California, which would seem to put this matter to rest (the proof is in the pudding, after all)

I'll go ahead and predict that the strength of that tube will have materially decreased after 1 year in the elements. I'll even posit that will occur independent of rusting, which appears to have unfortunately taken place, due to the formation of microfractures within the metal due to repeated lateral thermal flexing. That said, this was a demo track. It wasn't designed to withstand one standard atmosphere while whizzing fast, heavy capsules inside it for years on end.

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#358

Post by ant6n » Thu, Oct 12, 2017, 9:20 PM UTC

Pxtl wrote: post #343

ant6n wrote: post #213

Earlier quoted context omitted.

The average speed is governed by acceleration and dwell time - the issue for GO is lack of electrification (which increases acceleration), and lack of level boarding (which decreases dwell time). 50km/h average is actually quite fast. I mean, a radius 50km from downtown is a huge area already. We have to densify inside that radius, not sprawl people further out because the trains are so fast. This means for example w…

> This means for example we need more stations, so that more developable land is within walking distance of service That's what lrt and subways are for, not the big commuter GO trains.

That's the crux of what's wrong with commuter rail thinking in North America: "Serving the city is what the subway is for". Your original post, asking for 200km/h commuter rail, is a sign of it.

There's a meaningless separation of modes based on technology, and ascribing attributes to them. In Japan or Europe, the technologies are converging and so are the modes. Any infrastructure will have it's utilization maximized, and may function as what North Americans understand as 'commuter rail', subway' or 'light rail' all at the same time.

The result: more coverage, more service, better integration of services, more overall effectiveness, more ridership, less reliance on driving.

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#359

Post by pstuart » Thu, Oct 12, 2017, 9:25 PM UTC

Pxtl wrote: post #187

reacweb wrote: post #155

Earlier quoted context omitted.

The track should be cheaper because hyperloop has (almost) no impact on existing infrastructures. Expropriation costs for train are huge.

How could the Hyperloop not require the same expropriations? A giant tube isn't any smaller than a train track. Is it the fact that it's elevated? Rail can be elevated. Yes, rail is heavy, but so are giant evacuated steel tubes.

I think he's planning on making lots of tunnels.

https://www.wired.com/story/elon-musk-test-tunnel/

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#360

Post by dkersten » Thu, Oct 12, 2017, 9:26 PM UTC

Frondo wrote: post #335

microcolonel wrote: post #207

Earlier quoted context omitted.

I think it would be a good idea to make sure the California "high speed" rail program is never funded. It is a terrible idea. As it stands, it would be as slow as conventional rail, redundant with AmTrak, and the most expensive rail line ever built. It would be absolutely devastating for the government's relationship with at least tens of thousands of land owners, hundreds of thousands of home owners, who would see d…

It's a great idea and I can't wait to see more high speed rail built all across the country. We've already criss-crossed uncountable acres of historic, sentimental (what?? really??) land with roads, both local the state/federal highway system. HSR would be so much better use of land than roads, for moving a lot of people quickly and comfortably. Not at all redundant with Amtrak. Happily, the California project is fun…

On top of that, my experience of (southern) Californian roads is that they are muuuuuch wider and take up much more space than the coaster/amtrak train tracks take up, so roads have been much more damaging to historic sentimental land than rail is or would be.