Wednesday, March 01, 2006

Geek Musings: Mile High x20

The Liftport Group has had another success: a sustained robot climb to a mile high. This has prompted me to lay out a possibly absurd idea that has been bubbling away for a while now. Like most ideas, it won't do much good in the back room. So, here it is, for all to pillage and chortle over...

  • space elevators,
  • the stresses the ribbon has to be able to withstand,
  • how to reduce those stresses.

  • revenue streams.
  • high altitude balloons.
  • supplying those balloons with robots climbing up ribbons.

The irony being that:
  • only the first twenty miles of the ultimate journey is covered.
  • wind shear is likely to be a substantial fraction of the stresses to consider: especially when a category 5 hurricane drops by.
  • all wind shear occurs in the troposphere (ie the first twenty miles).

So, why not:
  • start the real journey *from* twenty miles?
  • place the base station/anchor above the troposhere?
  • suspend it from... balloons?
This gives you:
  • freedom from wind shear stresses
  • freedom to move around

Apart from the kneejerk 'that's a silly idea', I can think of more serious objections, like:
  • that's one big balloon!
  • that's a lot of (expensive) helium!
  • that's a long way to climb!

No problem:
  • a nominal 1000 tonne anchor weighs as much a 1E7 cubic metres of air at that altitude (I estimate pressure to be ~0.1atm). Think a cube of ~200m to a side: about the same dimensions as a city block. Big, but at 20 miles up, who's being crowded? Besides, use several balloons.
  • Yes, even at that altitude, that's a *lot* of expensive helium! So? Why use helium? Why use anything at all?
  • Since there are serious proposals to supply balloons at this altitude with robots climbing up ribbons anyway (or by visits from other balloons), I think this one is solved.
Err... suspending 1000 tonnes with nothing at all?
  • Nope, use a vacuum! You see, it's a matter of bouyancy, and an envelope whose interior pressure is 10% exterior pressure is as bouyant as if it were filled with hydrogen!
  • Pumping down to that pressure is a no-brainer, although the envelope needs to be braced to prevent it from collapsing.
  • The envelope material is the issue. Given that a one atmosphere pressure differential is something like 10 tonnes/m2, it needs to be something non-porous, very strong, and very light. Something like...ribbon cable!
  • One question arises, though: does one still refer to such an envelope as a 'balloon'?
It may not be feasible, it may not be practical. Hell, it may not even be original! (certainly I'm not the only one to have thought of vacuum bouyancy). Still, it's my idea, and it might be worth a short sf story. Just remember you heard it from me on this date*!

My opinions regarding patents was aired a while back so, yes, Liftport folks, if you find this through the wonders of Technorati before I post it to you, you can use it.
So can anyone else for that matter.

OK. Somebody can bring me back down to Earth now.
*Update: Tom Nugent of Liftport has kindly replied to my query. He tells me he's heard it all before, but that the notion has merit. I'm not really surprised it's been thought of before (dare I say: 'it's not rocket science'?...oooh! that one's probably done the rounds as well;-). Still, it's nice to find I'm off with the same load of pixies as a few other people!


At 7:36 AM , Blogger Brian Dunbar said...

Warning - I am not an engineer, I am just the IT guy and a layman. I think people have talked about putting the ribbon head at altitude and for the reason you cite.

Some problems

Getting there is a problem. Expensive as well.

And yes these problems are solveable and might well be solved by 2018 but .. we're trying to keep costs down. One gee whiz hand-wavium component (the CNT composite) is enough.

At 9:52 AM , Blogger Tony Fisk said...

Thanks, Brian.
I'm not an engineer either, just a software engineer with an M. Sc. majoring in physics.
I was simply speculating on the possibilities and jotting them down. Economic reality took a back seat!

I'm pleased, indeed relieved, to hear that these ideas have been considered before. (After all, wouldn't it be awful if the best CNT ribbon you could produce was *just* short of the loading requirements, and no one had come up with alleviating strategies?)

While I find the feedback wrt feasability is encouraging, I fully understand that Liftport needs to concentrate on practicalities and the main item.


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