Who would make up the research team for a trans-Atlantic tunnel?

Scott T. Jensen wrote: >It would contain a vacuum inside it and the

I should think that the first thing that needs to happen is a mag-lev needs to go into service someplace (or 4..)... then an underground-evacuated supersonic one...

Then we might be ready to decide who is qualified to undertake such a project...

Al...

An interesting link; it prompted some thoughts.

A speed in excess of 5,000 km/h is, well, _fast_. Assuming a lateral acceleration of 0.5g, the train would need five minutes or so just to get up to cruise speed.

Continuous acceleration (still assuming 0.5g) would cut the travel time between London and New York City to slightly over half an hour. The train's speed at turnover would be approximately 18,000 km/h--an appreciable fraction of orbital speed, so passengers would be light on their feet for a while.

What _are_ the speed limitations of a maglev, assuming operation in a reasonable-grade vacuum? If 5,000 km/h is okay (as the above link suggests), why not 18,000?

Cutting the travel time between London and NYC by half an hour may not be worth the extra trouble in any case. But upend the maglev and attach it to an orbital tower: At 5,000 km/h the trip to geosynch takes about seven hours; continuous acceleration cuts that to an hour and a half (at

Speed at turnover: 47,000 km/h....

{mucho snippage}

To celebrate the occasion, we're giving 100 people the chance to make history by winning an all expense return trip to New York on the first train through the Tunnel."

Another site brought to you by Those With Too Much Time On Their Hands.

The site is saying it would take only 54 minutes. The fastest time set by the Concorde was 2 hours, 52 minutes, and 59 seconds.

Scott Jensen

Normal jets like 747 take 7 - 7 & half hours to get from New York to London and 8 - 8 & half hours to get from London to New York. The difference in the two flight times is due to headwinds and tailwinds.

Scott Jensen

Yes. At 0.5g continuous acceleration it would take (assuming a distance of 5000km, which is close enough for our purposes) slightly under 34 minutes. At 1g, travel time would be 24 minutes. But even without continuous acceleration, the acceleration and deceleration would be an appreciable fraction of the travel time.

Sorry, I misread your statement. When I read "cut" in your original reply, I took it as cutting the current time by that amount. Interesting that your numbers put it at 34 minutes and the link I gave puts it at 54 minutes. I wonder if they were calculating no perceivable g force on the passengers.

Scott Jensen

Scott T. Jensen opined

The concept of supersonic in a vacuum is interesting.

-ash Cthulhu for President! Why vote for a lesser evil?

Wouldn't be much of a problem (unless I messed up my spreadsheet something terrible). At 0.5g horizontal acceleration you'd have a bit over five minutes at each end, with the passengers experiencing 1.12g (ignoring changes in vertical acceleration). 0.2g of continuous acceleration would get you there in 54 minutes.

I just noticed this thread is cross-posted; follow-ups hereby set to rec.arts.sf.science, which is where I came in.

I believe even if you had long bucky tubes for support a mag rail to geosynch would be too heavy.

Some recent Clarke tower threads discuss power transmission by laser beam. I think this could move an elevator cart, but don't know what kind of acceleration is doable.

I'd like to see rails on some of the mountains of Ecuador. At the equator the earth is moving about .5 km/s. A tube ending at the top of an 8 km summit would eject its payload into an atmosphere about 1/3 as dense as sea level.

It's been around for a very long time. First time I read about it was in the 1970's in something like Popular Science. Then it was to be done in an underground tunnel cut through solid rock.

Scott Jensen

I think he's being a wise ass. Supersonic means faster than sound. And how fast does sound travel in a vacuum?

Dear Hop David:

It is calculable: v = sqrt( C * gamma / V^ (gamma - 1)) vacuum should be really close to an ideal gas, so 1.4 should be a reasonable value. C is some finite constant, and is gas-dependent. V is the inverse of density, and pretty much increases without bound in a vacuum... so the square root of something really close to zero, isn't a very big number either. A few meters per second, near Earth...

I agree, I think he is being clever. I think the intent was "supersonic at STP, and not in vacuum".

David A. Smith

The tunnel can't be a perfect vacuum. Even with extremely low densities, at 18,000km/hr you're looking at some extreme heating.

Remember, the shuttle is at it's worst part of re-entry (reaching

Not only that, but with a tunnel, you might have some problems letting the trace air (compressed on the front surface of the train) get around.

Dave

Hmmm....the speed of sound in the atmosphere varies only with temperature. Think of it as depending on pressure waves promulgated by air molecules travelling at a speed proportional to temperature.

Brian Whatcott Altus OK

I agree, but that (c=sqrt(gamma*R*T)) is one equation that frequently inpsires dissent. It is 'obvious' that density should be involved.

The reason that the density is not the controlling factor is demonstrated by a billiard ball model of the air. The more air molecules there are, sure the number of collisions is higher, but the mean path before a collision is a lot shorter, and you have to get a lot more balls moving on average. This also shows why gas temperature, which is proportional to the RMS speed for the billiard balls, controls the rate of translation of a pressure wave.

It is worth pointing out that this definition of temperature is useless and misleading in a near vacuum, and even on Earth, overnight, on a cloudless night. The classic example of that is why your car gets so cold overnight - it is facing a very large heatsink at not much more than 4K.

But you already knew that, I just think it is neat.

Cheers

Greg

Change research to engineering team. Research would not include actually building it.

Fair point.

Project is too big. It'd take multiple engineering companies to do it.

Sounds like an ideal terrorist target!

Agreed.

But wouldn't there at least be one "master" engineering company that all the others answer to and work with? If so, what engineering firm(s) in the world could be that guiding body?

Scott Jensen