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The Hyperloop: BUSTED

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Tepe:

--- Quote from: ogden on January 17, 2018, 08:51:02 am ---
--- Quote from: Tepe on January 17, 2018, 08:16:55 am ---Think of the Tsiolkovsky rocket equation. You have to lift the fuel you are going to need for the landing

--- End quote ---

Yes. Think of it. When landing comes, payload and 2nd stage is already lifted and fuel which were used to lift all that is already gone - meaning not that much fuel is needed to decelerate remaining mass for safe reentry speed. After all they are doing it now, so nothing much to discuss here.

--- End quote ---
You missed the point. The fuel needed for landing is equivalent to a larger payload that must be lifted.

There are two possibilities for why it appears to work out for SpaceX:

1) It truly is cheaper to spend more fuel lifting fuel to be able to recover the booster than to build a new booster.

or

2) Their booster is just so much cheaper than their competitors' more expensive systems that they can afford it anyway and still be the cheapest alternative.

That they are doing it now doesn't automatically entail that it is optimal or even a good idea. Just that it works.

Tepe:

--- Quote from: HalFET on January 17, 2018, 08:52:22 am ---So take anything a European space agency says with a serious grain of salt, the feasibility analysis is often based in politics and not physics.

--- End quote ---
Ideally feasibility studies should be grounded in both physics and economics.

HalFET:
Tepe, if it were just economics I wouldn't see any issue with it, but it is heavily based in politics. The theoretical application process for research grants and projects from ESA should be:
a) Check list of open calls.
b) Submit proposal with consortium based on skills.
c) Choose best candidate

The actual process seems to be more like this:
a) Contact the local representative to get the call modified to target a subject you're already working on.
b) Submit a proposal with a consortium based on geographical divisions and political favour.
c) Hope that no one has more friends than you and your project partners.

But to get back to the original topic:

--- Quote from: amspire on January 17, 2018, 09:10:52 am ---I listen to a bit of some of the hype. Lots of talk about building Hyperloop in tunnels and underwater - that is going to make rescue easy. The ideas are all based on some sort of super computerised network that means you capture a driverless vehicle to the station and when you get out, your seat in a hyperloop is waiting - no time wasted. The thing is they will need the same security as airports. Perhaps more since the concept is just so vulnerable.
--- End quote ---
We also run high speed trains without security, and someone setting of a small explosive charge near a link between carriages or the locomotive would also cause a massacre most likely... The only place where I've seen the type of outrageous security you suggest is in the US really, and the security for aeroplanes is still a joke at the end of the day.


--- Quote ---You fire a tiny charge that pierces the skin of a passenger carriage at the 900 Km mark of a 1000Km pipe and they have to immediately flood the whole tube with air. They then have to rescue the thousands of people in the tube which could mean some have to drive 900Km at a slow speed back to the starting point. The Hyperloop is down probably for the day.
--- End quote ---
Wouldn't it be 100 km to the other end point, just to be a bit pedantic  :-DD

And you'd have to segment the tunnel with airlocks anyway, to have a realistic chance of maintaining a vacuum in the majority of the tunnel when you have to do maintenance for example. So you wouldn't have to pressurise the entire tunnel. Honestly there are enough holes in this thing that you don't have to poke at it with these weak arguments. Pretty much every argument I hear against the hyperloop can be categorised as the following:

* The entire tube will collapse if there is a single dent.
* The vehicle is very fragile and we'll need outrageous security measures to keep everyone safe since they'll be killed instantly otherwise.Both are issues you can design around, they feel more like emotional arguments than based in fact. If you want to bash it at least go for something that is more into the ballpark of actual concerns (construction cost, energy expenditure, ...) and not a simplistic assumption. By the same logic and demonstrations I can claim a submarine is going to implode instantly when it touches the water, and an aeroplane will explode the moment it goes above the clouds.


--- Quote ---They are now only talking of a 2/3 cost saving over high speed trains, and so by the time it is implemented, the reality could be 3 times the cost of high speed trains. They know what trains cost. The Hyperloop costs are fictional at this stage.

--- End quote ---
No company is going to release their actual cost estimations since it'd make them vulnerable to the competition if there would ever be an actual project call for it. But no matter what it'd run massively over cost, see the average monorail project to get an idea of how bad these things can get.

jonovid:

--- Quote from: Tepe on January 17, 2018, 09:23:50 am ---
--- Quote from: HalFET on January 17, 2018, 08:52:22 am ---So take anything a European space agency says with a serious grain of salt, the feasibility analysis is often based in politics and not physics.

--- End quote ---
Ideally feasibility studies should be grounded in both physics and economics.

--- End quote ---

japanese maglev trains have fully working prototypes that the public can ride on.
as full-sized non-working structural models imaginary, simulated, or theoretical do not cut it.
scientific calculations must be tested in the real world. elon musk needs put his money where your mouth is.
a working prototype, not a lot of test jigs.  prove that it works. have it top out at 670 mph (1080 km/h) in the tube
over range of 263 miles (or 424 kilometers) simulated range of Los Angeles to Las vegas.

ogden:

--- Quote from: Tepe on January 17, 2018, 09:21:45 am ---You missed the point. The fuel needed for landing is equivalent to a larger payload that must be lifted.

--- End quote ---

Indeed it can be payload in place of landing fuel/gear. I did not miss any point, Mr.Obvious, I just said that not that much fuel is needed for deceleration. Anyway if it would not be feasible, then they would not even try. After all they are leading rocket scientists, not you or me :)


--- Quote ---1) It truly is cheaper to spend more fuel lifting fuel to be able to recover the booster than to build a new booster.

--- End quote ---

For sure initial cost of booster refurbishment is much higher as stated, but it will go down w/o doubt:

http://spacenews.com/spacex-says-reusable-stage-could-cut-prices-by-30-plans-first-falcon-heavy-in-november/

Shotwell said it was too early to set precise prices for a reused Falcon 9, but that if the fuel on the first stage costs $1 million or less, and a reused first stage could be prepared for reflight for $3 million or so, a price reduction of 30 percent – to around $40 million – should be possible.


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