OT: SABRE engine

Seems a lot more conceptually sound than some Elon Musk vacuum-tube pod-transporter!

Reply to
bitrex
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Elon Musk's vacuum-tube pod transporter predates Telsa by a few decades.

It depends on the observation that railways could go a lot faster without a ir resistance, and was spelled out in a Proceedings of the IEEE article som e decades ago.

The capital cost of digging a smoothly curved air-tight tunnel between popu lar destinations is pretty much all that stops it from happening.

The original article envisaged quite deep tunnels, and calculated optimal t rajectories between a number of places, on the basis that you tipped the po d into the tunnel at one end, let it accelerate under gravity only so that it was travelling maximally fast at the lowest point in the tunnel and was progressively decelerated by gravity as it went up the other side, to arriv e - stationary - at it's destination some forty minutes later.

Cute idea. The author did acknowledge that there would be frictional losses that would have to be made up, and that the pod would require some sort of get-you-home power if the nominal velocities became impractical.

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wanted to throw his linear motor with magnetic suspension (it's that old), though the original proposal had been happy with steel wheels on steel rail s.

Scam-jet satellite launchers had been imagined at least as far back. As an undergraduate (1961) I wanted to see power lasers (which didn't happen to e xist back then) used to to heat the air in the scam-jet duct ...

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Bill Sloman, Sydney
Reply to
bill.sloman

Well you could say that about building a space probe to Alpha Centauri, it isn't that it isn't at all possible with present-day technology...

Reply to
bitrex

In this case though it sounds like the innovation is a lightweight heat exchanger possibly made possible by advances in materials science that weren't feasible in the 60s.

Reply to
bitrex

You can't make money out of a space probe to Alpha Centauri.

There's a market for rapid transit between major cities, but rapid transport through air-tight tunnels doesn't look as it could be sold cheaply enough and frequently enough to cover the capital cost of those tunnels.

Air transport is already pretty capital intensive, and burns a lot more energy per trip, but at least you can move the planes to some other route if some ghastly mistake (like Brexit or Trump) kills the traffic on one particular route.

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Bill Sloman, Sydney
Reply to
bill.sloman

There are also other issues. Like what effort (energy) would it cost to get and keep the entire tube at near-vacuum and what would happen when the sealing is suddenly undone or the tube structurally fails because of a material fault or an external action from an adversary. Or what would happen to the passengers when the vehicle develops a leak due to a fault or action.

Reply to
Rob

a conventional open-air maglev (aside from a relatively short tunnel under the Bering Straight) that ran east to west from North America to Paris or London operating at say 400 mph seems a more practical project. Most of the route would be essentially uninhabited. It would take a bit longer for the trip than a flight west to east but still less than a day.

Reply to
bitrex

Not much. Places like CERN and the LIGO gravitational wave detector have been doing it for many years.

Air gets in and the trains or pods have to limp home much more slowly.

Aircraft already have to deal with this problem.

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Bill Sloman, Sydney
Reply to
bill.sloman

A much smaller volume, and much better controlled. (no places where vehicles have to enter or leave the system with people inside)

Air would get in at the speed of sound and apply very large forces on the vehicles that are used to operate without much headwind.

Aircraft operate in much less of a vacuum and when depressurization occurs the system only has to provide oxygen for a short period, while the pilot executes an emergency descend.

There is no such thing as an emergency descend in the hyperloop and the pressure is so low that the blood of the passengers would boil away immediately. Emergency oxygen is not enough to cover that.

Reply to
Rob

there's the thermal issue as well, cooling things to around 20C in a vacuum is not entirely trivial.

NT

Reply to
tabbypurr

snipped-for-privacy@ieee.org wrote in news: snipped-for-privacy@googlegroups.com:

I had this idea decades ago in 1971 at age 11.

I still have design ideas surrounding high speed package delivery.

The "track" would go alongside the high speed passenger rail (or above or beside).

My high speed system is mag lev and linear motor driven, and as a backup it is mag-lev'd and riding right, or it sits/gets suspended by an overhead gantry rail pair. This allows negotiation thru turns sans the mag lev as well. It is a fully tunnellized system. No "scenic route" or "scenic views". The 'sealed' "vac track" package system is separate tube on the same main.

Reply to
DLUNU

That's what heat pumps are for. Radiation transfer increases with the fourth power of temperature, and the tunnel walls are going to stay cool.

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Bill Sloman, Sydney
Reply to
bill.sloman

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You were about a century too late to claim priority.

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Bill Sloman, Sydney
Reply to
bill.sloman

des.

thout air resistance, and was spelled out in a Proceedings of the IEEE arti cle some decades ago.

en popular destinations is pretty much all that stops it from happening.

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e been doing it for many years.

nside)

It's called an airlock. You need two sets of doors that can be made vacuum- tight and a high capacity pump to empty it.

Assuming that there weren't airlock doors (usually left open) spread around the system to let you isolate segments of track for maintenance and repair .

Buried tunnels have the advantage that there isn't a lot of air buried deep underground to flow into the tunnel if the structure stops being airtight. What air might get in could flow rapidly, but there wouldn't be much of it . "Very large forces" seem improbable.

Earthquakes collapsing the tunnels would be a bigger risk, and you might ne ed a double tunnel structure in geologically risky areas to isolate the ai r-tight tunnel from possible geological movement.

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Trains could carry a lot more oxygen than planes.

And the tunnels would be set up to allow repressurisation of individual seg ments for maintenance work. In an emergency the tunnel segment wouldn't be evacuated for long.

But there would be emergency repressurisation of segments of the tunnel.

In a hyperloop you blast a hole in a fraction of a second.

Arthur C Clarke went into the effects of short term exposure to a vaccuum a very long time ago. Blood might "boil" at room temperature, but this would cool the surface from which it would be boiling off, so it isn't going to blast anybody apart.

The vapour pressure of water at 38C is 49.7 torr - about 6.5% of atmospheri c pressure, and it cools the surface its evaporating from. You'd need to ge t that much oxygen pressure in the lung just to keep the passengers alive, and positive pressure oxygen masks (as used by stratospheric pilots in time s past) do exactly that.

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Bill Sloman, Sydney
Reply to
bill.sloman

Why not just put the package on the high-speed train? The value-add from cutting say 2 hours off delivery of a package seems like it would hardly justify the cost of construction

Reply to
bitrex

The Paris pneumatic package distribution system had automatic routing from 1931.

It did save a lot of progressively more expensive human labour.

Amazon now seems to have automated pick and place for putting things onto pallets for shipping, and taking them off again at their destinations.

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Bill Sloman, Sydney
Reply to
bill.sloman

Sure, but the size of the room you need to empty for each trip is about the same as the size of the largest vacuum chamber now existing. And it has to be emptied in a few seconds, all delay there is going to add to the length of the trip. (as usual the trip time is compared between raw trip time on the new service and net trip time including adjacend travel and boarding procedures of existing services, any additional time is reducing the claimed advantage or parity)

It would not be a good idea to close doors when there are vehicles travelling at 1000 km/h through the system.

The ground above the tunnel would not hold back the atmospheric pressure for very long I think. Maybe when it is drilled through rock, but we don't have that here.

That would be quite some extra effort. Not only do you need a (much) larger tunnel, you also re-introduce the risk of the inner tube getting filled with air very quickly in case of failure.

Filling the tunnel with air in a short time (given the volume) will be a highly energetic event that will not be survivable. Like an exploding bomb, only the other way around.

So designing the hyperloop passenger facilities is just like designing spacecraft for hundreds of people. Either you accept the risk that a failure results in loss of the passengers or you have a very big task ahead.

Reply to
Rob

What are you smoking? Those statements don't even pass cursory sanity checks!

There are plenty of reasons why hyperloops aren't the most viable options for transport, without inventing Trump-worthy "reasons".

Reply to
Tom Gardner

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ecades.

without air resistance, and was spelled out in a Proceedings of the IEEE a rticle some decades ago.

tween popular destinations is pretty much all that stops it from happening.

st to

have been doing it for many years.

e inside)

uum-tight and a high capacity pump to empty it.

Never heard of the vaccuum chambers they use for testing satellites?

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It would be nice if it were, but the last plane flight you were on should h ave cured you of any idea that you have to hold loading delays down to a fe w seconds.

It seems to take half an hour to get everybody aboard an aircraft and settl ed before the aircraft can even get in the queue to take off.

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Perhaps, but a few seconds is drawing a very long bow.

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Much the same as happen on aircraft and high speed trains under comparable conditions. Quite a lot of trouble is taken to make sure that it doesn't ha ppen often, but that's it.

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ound the system to let you isolate segments of track for maintenance and re pair.

You are going to know where each vehicle is in the system, and they are goi ng to know the state of all the airlock doors. High speed rail system deal with much the same problems today. And it will be easier to keep drunk driv ers off the track when that track is totally enclosed in a vacuum system.

deep underground to flow into the tunnel if the structure stops being airti ght. What air might get in could flow rapidly, but there wouldn't be much o f it. "Very large forces" seem improbable.

't

Think air flow rates through compacted soil and clay.

t need a double tunnel structure in geologically risky areas to isolate th e air-tight tunnel from possible geological movement.

That would follow from one way of doing it. There are others.

leak

segments for maintenance work. In an emergency the tunnel segment wouldn't be evacuated for long.

Twaddle.

.

um a very long time ago. Blood might "boil" at room temperature, but this w ould cool the surface from which it would be boiling off, so it isn't going to blast anybody apart.

heric pressure, and it cools the surface its evaporating from. You'd need t o get that much oxygen pressure in the lung just to keep the passengers ali ve, and positive pressure oxygen masks (as used by stratospheric pilots in times past) do exactly that.

Or like designing aircraft. A jet flying at 40,000 feet is in an atmosphere that is at about 20% of sea level atmospheric pressure.

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Bill Sloman, Sydney
Reply to
bill.sloman

The main short-term danger of exposure to vacuum is lack of oxygen

Reply to
bitrex

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