"Joe Delphi" wrote in
ink.net:

Well, I learn something new everyday. I am a technical person
although I don't work in the aerospace industry and, at first, I
thought this was a joke, I didn't know that people were seriously
studying it.

Not surprising; many people still consider it a joke. One of the biggest
obstacles is that no existing material is strong enough to construct one.
But a lot of folks have stopped laughing since the discovery of carbon
nanotubes, which shows some promise *if* it can be fabricated economically
in the quantities required, and can be integrated into a composite material
without losing too much of its theoretical strength. Another obstacle is
that the elevator would become a navigation hazard for low-orbiting
spacecraft, and may need the capability to "dodge" detectable space debris,
plus shielding to protect against undetectable space debris. This is
solvable, but far from trivial.

British SF author Arthur C. Clarke is a leading advocate of space
elevators. When asked when one might actually be built, he replied, "about
ten years after everyone stops laughing." Other sources give a different
number of years; they are probably all accurate quotes, given Clarke's
propensity for embellishing his own quotes as he ages.

I can imagine how it might work up to geo-sync orbit, but the website
said that people are also investigating how it can be used to lift
payolads to the moon and other planets - not sure how that would work.

A space elevator in geostationary orbit (GSO), by definition, rotates at an
angular velocity equal to that required by a spacecraft in GSO. Angular
velocity for a circular orbit decreases with altitude. So if a spacecraft
climbing a space elevator "jumps off" at an altitude below GSO, it will be
travelling too slow to remain at the jump-off altitude, and will wind up in
an elliptical orbit with apogee equal to the jump-off altitude, and a lower
perigee altitude (possibly lower than the surface of the earth, if it
doesn't climb high enough...).

On the other hand, if the space elevator extends significantly above GSO,
the spacecraft could continue to climb above GSO. If the spacecraft jumps
off above GSO, it will be travelling too fast to remain at the jump-off
altitude, and will wind up in an orbit with perigee at the jump-off point,
and a higher apogee altitude. If the jump-off altitude is high enough, the
spacecraft will be travelling faster than Earth escape velocity. Careful
choice of jump-off altitude and timing will result in a translunar or
interplanetary trajectory, though small propulsive corrections may still be
required afterward.

--
JRF

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