Re: New (?) take on orbital elevators (perhaps dumb!)

"Mike Williams" <nospam@xxxxxxxxxxxxxxxxxx> wrote in message
news:KpVxFIAmJODGFw5Z@xxxxxxxxxxxxxxxxxxxxx
Wasn't it Richard Burke who wrote:

Actually, like my helicopter rotor analogy, I was assuming the structure
would rotate, and that the ends would necessarily be going at or near
orbital velocity...

Don't the ends have to move faster than orbital velocity? If the ends
move at less than orbital velocity then the rotor blade is in
compression. I can't imagine a 300 kilometre rotor that wouldn't buckle
under compression.

The ends have to move faster than orbital velocity, but not for that reason.
The aerodynamic lift can help to keep it up.(although it gets tricky at
supersonic velocities), but the ends need to move near orbital velocity in
order to actually fling things into orbit.

One big snag is that if the ends are moving at near orbital speed, and
the rotor is only a few hundred kilometres long, then there's going to
be some part of the rotor that's moving at a significant percentage of
orbital speed through atmosphere. That's going to cause drag, so you
have to keep adding energy to the system to keep it going.

Fortunately, you already have to have a mechanism for adding energy after
each launch, so it's simply a matter of scaling up.

Also, the friction from moving through the atmosphere at near orbital
speed is going to cause heating. So you need a material that copes with
such heating, and doesn't need to be replaced quite as often as the
tiles on a NASA Shuttle heat shield.

Less of a problem if you get out of the lower atmosphere as quickly as
possible. Build a steeply climbing section near the pivot, supported by
aerodynamic lift, and just keep the end from going much above 1000km/h to
avoid having to deal with supersonic aerodynamics and excessive heating and
stuff. Then let it level out and have most of the length of the rotor
residing in the mesosphere or thermosphere. Lift on the inner segment would
also pull it inwards, keeping the whole thing from flattening out under the
apparent weight of the much longer outer segment.

-l.
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