On Mon, 06 Nov 2006 14:55:05 +0000, Monte Davis wrote:

sal wrote:

you don't get a lot of help with horizontal thrust from the cable unless
it's seriously bent -- one would not expect the cable to act very "stiff"

It doesn't need to be. You're acquiring that GEO orbital velocity over
more than a week; the "sideways" acceleration is small, and easily
supplied from the restoring force that's trying to keep the ribbon
vertical and taut. People keep thinking about the flimsy part we build,
and forgetting the six-sextillion-ton flywheel at the base...

Yes, and what's more a rough BOT calculation indicates that far more than
half the energy which needs to be put in is "pure lift". (In fact I make
it something like 90% change in potential energy, 10% change in kinetic
energy, to get to geosynchronous orbit -- but I suspect my numbers may be
kind of wrong; too many places where it's easy to misplace a factor of 10...)


But again that's one of the obvious in-your-face problems which needs to
be addressed

And was, years ago. A beanstalk SE simply isn't going to happen in the
foreseeable future unless the cable can be much, much, much lighter than
the multi-billion-ton versions in Red Mars, Fountains of Paradise, and
Web Between the Worlds. IIRC, Edwards' baseline is ~800 tonnes for the
finished ~100,000-km cable. Do the math: the mass per m^2 is comparable
to newsprint or plastic food wrap.

I have lots of doubts about space elevators, but jeez, I wish we could
get past the Red Mars disaster scenario.

Yes, well, I kind of figured those two issues had been beaten to death
already, which is why I didn't raise them in the OP.


Monte Davis
http://montedavis.livejournal.com

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