Orbital Elevator

On Aug 22, 2006, at 01:18 UTC, Matt Gallimore wrote:

> It would have a station on the bottom and top (or maybe just at the
bottom and
> another structure at the top) connected by cables. They would be
located
> maybe at different orbits. Between them a platform travels up and
down the
> connecting tethers. The platform has arms to help catch and hold
cargo or
> ships.
> ...
> For a low earth orbit system, the longest might be at 250 km and 750
km to
> keep the system below the lower Van Allen belt. As of present we
don't have
> much experience with extremely long tethers, do maybe a system a 200
km long
> would be beneficial.

The problem is that there simply isn't very much benefit from this.
The difference in orbital velocity over 200 km altitude is miniscule.
It'd be just enough to make docking awkward, but not enough to improve
your mass ratio, or reduce your thermal protection requirements on the
way down.

Now, if you were to take the same basic idea but rotate the tether, as
fast as you can, opposite the direction of its orbit -- then the speed
of the lower tip could be noticeably lower than orbital velocity. This
could improve your mass fraction quite a bit, as well as reduce thermal
issues. I think there's quite a lot of potential there -- as do many
others -- but the bugaboo is, of course, in the docking. You'd have a
*very* precise window in both time and space to hit, or you come right
back down instead of going on to orbit. Customers probably get mighty
annoyed when that happens.

Best,
- Joe

Joe Strout -- joe@...