using high speed lifts travellers go vertical straight up 5klms into the sky to skyports tethered from the earth. Low gravity and velocities matching the surface of the earth and constant refuelling mean high altitude and low gravity planes mean planes only touchdown for maintenence and are otherwise in constant flight.

would this actually work? i mean the skyport would need to 'pull' on the tether to keep it vertical so the lifts can traverse - so it has to be high enough to want to 'fly off' into space and hence pull on the tether. how high is this? what forces are we talking? could cables / steel really hold that force? How long would it take a high-speed lift to travel up to it? I think the world's fastest lift is 12.5m/s or 45klm/h. If it was 10 klms up that means a lift trip of about 15 minutes - how high does the elevator actually have to go?

I've heard somewhere that the vertical tether is actaully now being used as a cheaper way to get payload into space. As with a commercial airliner almost all of its fuels are used on take off, for a spacecraft overcoming earth's gravity is the hardest part. Using a low speed lightweight object (such as a lift) would require relatively no energy which could easily be provided by solar panels on the floating airport.

The hardest part would be getting the actual airport into space. each building component would need to be sent up. but maybe the tether could be installed first and allow progressive delivery and assemblage of parts into the final design.

each city would have a skyport and the actual flying craft would just bounce across the atmosphere flying only directly north or south, with the earth orbitting below. for example, it takes me 24hrs plus stopover time to get to england from sydney, as the plane is fighting the atmosphere and gravity the whole way. the earth rotates thru to london in just 11 hrs. if the distance of travel is only from the exact longitude of syndey, then directly north until it aligns with London's latitude (there is a clever way of saying this but I don't know what that is) and given at that altitude there is only enough atmosphere to control the flight direction, so fuel consumption could be massively reduced.
-- williamsmatt, Sep 04 2008

Spaceward Foundation http://spaceward.org/elevator
The Space Elevator Competition [swimr, Sep 06 2008]

Cable Taper Formula http://en.wikipedia...levator#Cable_taper
Cable must be thickest in the middle, really thin at the ends. [swimr, Sep 06 2008]

Interesting, the tether concept you mention is actually called a space elevator. I'm actually part of a University engineering team trying to compete in the Spaceward Games [Link].

One of the problems with these tethers is that they have to go out far, really far. The quote from the website is 25000-60000 miles. For comparison, the ISS is only about 200 miles(?) above ground level.

Cable technology is quite a ways off also, with some of the longest Nanotubes being only a centimeter or so long (Nanotubes may be the only current material capable of building such a device out of).

But I suppose the elevator could be built long, and carry small reentry aircraft ~200 miles up for transcontinental flight... [+]

Oh, and the aircraft would have to travel more than North/South, as they will be spinning at the same rate as the Earth.
-- swimr, Sep 04 2008


All in due time... all in due time... [+]
-- xxobot, Sep 04 2008


did i mention.... skyhooks?

60,000 miles. that's way out!
-- williamsmatt, Sep 04 2008


//carbon nanotubes// I thought technically you could make the tether out of kevlar, but the taper was crazy.
-- MisterQED, Sep 04 2008


The taper is actually a really cool subject. [Link]

Skyhooks ?.....
-- swimr, Sep 05 2008


Niether of those links will open.
-- 2 fries shy of a happy meal, Sep 06 2008


Whoops, try those two.
-- swimr, Sep 06 2008


Commercial aircraft normally fly at something like 10km, which gives you an idea. You're out by, alas, orders of magnitude.
-- MaxwellBuchanan, Sep 07 2008


// travellers go vertical straight up 5klms// So, somewhat lower than the peak of Mt Everest?
//Low gravity //
Err, no, alas, gravity will be still over 90% of what it was at sea level.

As has been pointed out, you're orders of magnitude out, and bear in mind, that even travelling at Mach 2 all the way (obviously not possible), you'd still take over seventeen hours to reach the necessary geostationary orbit.
-- coprocephalous, Oct 13 2008


[wm] your space science is pretty dodgy, but if you change the premise to atmospheric travel you would have something pretty neat (tethered airports 10km up)
-- FlyingToaster, Oct 13 2008


You might find Zeppelins a better solution to keeping your ports aloft.

The USS Akron (239m) was used briefly as an aircraft carrier for the F9C Sparrowhawk (6m). All you need do is scale that up to handle an A380 (73m) and build an airship 3564m long, or more. Maybe an airstrip supported by four 1km airships might do the job better.
-- wagster, Oct 14 2008


I'd go with the sailing thing. Much more relaxing.
-- wagster, Oct 14 2008



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