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comment by am_Unition
am_Unition  ·  1017 days ago  ·  link  ·    ·  parent  ·  post: Hyperloop Competition

That's a very interesting theory.

Presuming that people should be able to survive the journey, whatever structure it is you're considering for a mag-lev launch would have to be absolutely MASSIVE (they have solved the problem in your above picture with an infinitely long cantilever beam, nice!). The scale of this project could potentially dwarf the LHC, and certainly in cost, as human life enters the equation. The only place worth building such a thing would be so far removed from active tectonic zones that selecting a candidate site would take years, geopolitics aside (continental US doesn't look good for a ~100 year investment, northern Alaska looks OK though - EDIT: sorry, the best places in the US are the northern great plains, Texas, and Florida). They might even finance strategically dyanmite'ing nearby fault lines as a precaution.

The main problem is that if you were to shoot out of an evacuated tube anywhere close to the Earth's surface near escape velocity, that's about like hitting the surface of the ocean falling at terminal velocity. You'll have to make sure the shock of hitting atmosphere doesn't kill your passengers. So put a very long tapering nose to ease the transition? That's mass, and it's gonna cost you a shitton of energy to accelerate. So build it high and have a gradually increasing pressure as the vessel ascends in the tube until you exit the tube? That's gonna make the Burj Khalifa look like child's play.

All other speculations aside, the most obvious design feature is to have the thing be totally vertical. How much of the structure would be above the ground vs. subsurface is the only debate in that vein.

Not sayin' you're wrong, but it's a huge challenge with today's capabilities.




kleinbl00  ·  1017 days ago  ·  link  ·  

I want you to watch this fucker. Not because he's entirely relevant, but because he's kinda relevant (and awesome).

That's John Stapp, going ragged edge of mach the hard way. Asshole went 570mph in an open-topped jet just to see if it was safe.

This one's not much better:

Same track, 50 years later, NASA hitting 2800 m/s. Aerodynamics still not really factoring that much. There's no substitute for cubic inches, as they say. Still, we're less than halfway there.

Riddle me this - didja read?

    The Gen-1 system proposes to accelerate unmanned craft at 30 g through a 130-kilometer (81 mi) long tunnel, with a plasma window preventing vacuum loss when the exit's mechanical shutter is briefly open, evacuated of air with an MHD pump. (The plasma window is larger than prior constructions, 2.5 MW estimated power consumption itself for 3 metres (9.8 ft) diameter).[12] In the reference design, the exit is on the surface of a mountain peak of 6,000 metres (20,000 ft) altitude, where 8.78 kilometres per second (5.46 mi/s) launch velocity at a 10 degree angle takes cargo capsules to low earth orbit when combined with a small rocket burn providing 0.63 kilometres per second (0.39 mi/s) for orbit circularization. With a bonus from Earth's rotation if firing east, the extra speed, well beyond nominal orbital velocity, compensates for losses during ascent including 0.8 kilometres per second (0.50 mi/s) from atmospheric drag.

131 km. The SSC was 87km; you wouldn't even need to go 'round twice. The optimization is for centrifugal force vs. circumference; that's the sort of thing one would want to test at small scale, I reckon.

    So build it high and have a gradually increasing pressure as the vessel ascends in the tube? That's gonna make the Burj Khalifa look like child's play.

I think that messing with the pressure (positive or negative) is a great reason to do some testing. Either way, you're leaving the heavy shit on the ground. Besides, I know some of the guys who worked on the Burj. It's just a tall damn building.

If you're in the mood to investigate magnetic tube launch, the best place to start is to build a magnetic tube launcher. Reusable rockets are nice, but Elon has to have known from the beginning that they're an interim technology at best.

This is a guy who wants to colonize Mars. He ain't doin' that with hydrox.

am_Unition  ·  1017 days ago  ·  link  ·  

    The SSC was 87km

Check your verb tense (I don't know what I mean here). But as a Texan, if you EVER mention the SSC again, I will be forced to de-fund you to the point of reckless abandonment. I know that they actually built the tunnels and some facilities, but the Higgs could have been found here in the states 10 years ago. Seriously, talk about it again, and I'll stop paying you nothing. For free.

I don't think we need empirical testing to tell us what will happen with the hydrodynamics of a mag-lev. It's not terribly difficult to simulate, relatively small contributions from turbulence aside. Such is why I don't think it's feasible, at least in the short term; there is a lack of announced solutions to the problem. Hell, some nerds probably simulate this kind of thing in their free time (/entrepreneurship?). If someone actually leaked the slightest hint of R&D from a muskompany of potentially monolithic structures, I'd be more inclined to get excited. And boiiiii do I want to hear exactly that.

Now it's time for the Mars rant! You put "Mars" in italics; I salivated.

Andy Weir spoke fairly candidly about Mars colonization to SEDS the other day in a Google Hangouts. Super pessimistic, and proceeded to thoroughly trash talk Mars One. It was a good time for me. He doesn't think NASA will have anyone on Mars before the 2050's, and although he didn't say anything explicitly about doubting Musk's Mars bid for the 2030's, I'm inclined to share his general pessimism on the timescale within the next few decades.

A Mars mission launched within the foreseeable future must answer this question: How can any large organization knowingly send people to their deaths? The only way to justify a Mars venture is by ensuring either the return of the astronauts or offering a guarantee of long, rewarding, extraterrestrial life; AKA, a sustainable colony. And we're not even close to meeting either of those challenges, but I totally agree that Musk is looking like one figurehead who could make it happen the quickest.

Anyway, cheers to a first stage mag-lev. I want to see it too... why not?

kleinbl00  ·  1017 days ago  ·  link  ·  

Dude, my best friend's dad was one of two project managers on the SSC. I probably know more about it than you do.

I think it's naive of you to presume that a completely unbuilt and untested high-mach system can be modeled using the data we already have. Modeling is where you extend a known body of knowledge into a tiny corner of the unknown so that you can be assured of success when you test it. How many car crashes have there been in the world? How robust is that model? Yet safety boards all over the world still require crash testing of every new model. And those are just cars, not hypersonic vacuum tunnels shooting transport quantities of superconductors into space.

Andy Weir is charming, but he's a computer scientist. He has less space training than you. He has less space training than I. And he's a year behind on trash-talking Mars One.

That doesn't mean Elon Musk doesn't want to go there. There's a poster of Mars at SpaceX. He's on Colbert talking about terraforming it (using a technique I first read about in Analog back in '88 - nothing new here). And SpaceX was formed primarily because no one would take Elon's ideas to Mars so he built himself a space launch company.

I appreciate your opinions, but stop trying to block my facts with them.