Re: New (?) take on orbital elevators (perhaps dumb!)
- From: "nunya@xxxxxxx" <Alien8752@xxxxxxxxx>
- Date: 28 Mar 2007 02:38:06 -0700
On Mar 28, 1:49 am, Richard Burke <i...@xxxxxxxxxxxxxxxxxx> wrote:
This almost certainly a really dumb idea,
Yep. Well, sorta.
but I don't have the maths or
the engineering knowledge to know for sure, so here goes... (Also, if
you have dealt with the idea before, then I apologise.)
As I understand it, there are four main technical obstacles to
constructing an orbital elevator out to geosynch:
- developing materials with sufficient tensile strength to 'hang' 22,000
miles, and also to deal with the tensile pull of the necessary
counterweight.
- safety. What happens if the structure snaps - or if someone plants a
bomb? Presumably the Earth-tethered end would smash down into the
atmosphere and wrap itself around the equator. (Might fly outwards
first, I guess.)
- how to construct it. Build it in orbit and drop an end down? Feed it
up from Earth with some bizarre rocket system to keep the end vertical?
- money.
So, I got to thinking, why are these things problems? And the answer is
that it has to be 22,000 miles long and tethered to a point on the
equator. If it was shorter and *not* on the equator, could it perhaps be
less strong, safer, easier to build and cheaper...?
So here's the probably-dumb bit:
How about building a structure at one of the poles with two opposite
lines that rotate to provide centrifugal 'force'? (Think of a helicopter
rotor with 1,000 mile blades and you get the idea.) Would this work? I
can see all sorts of potential problems:
No. Just having a thing rotate doesn't keep it from falling; objects
in orbit _are_ falling; that's why it's called freefall. They keep
doing it because their velocity toward the horizon exactly equals
their downward velocity.
But an orbit isn't a "free" orbit if its center isn't congruent with
the Earth's center. Circling or hovering over the Earth's pole isn't a
free orbit, you have to force it.
Fortunately, there's a way to do that with a thing called a statite:
http://en.wikipedia.org/wiki/Statite
With a big enough sail, you can build a beanstalk from anywhere you
can park a statite, including near/at a pole. Unlike an equatorial
beanstalk it has to be actively steered to keep the ground end steady
or it'll drift. That might be a bad thing, or a good thing. It might
make a dandy really-heavy-lift system for moving, say, whole cities.
OTOH I wouldn't ever want to heat the pilot say "oops".
Mark L. Fergerson
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