A realer elevator to space?

Arthur C.Clarke popularized the notion of drawing a cable from a
geosynchronous satellite to the Earth and then using it as an elevator
cable. In real life such a cable would be torn apart by forces. If
we imagine an indestructable cable, the geosynchronous satellite would
swiftly be pulled from the sky by the cable's weight.

The question is really what combination of (indestructable) cable and
satellite would summate to a functioning geosynchronous arrangement.
If the satellite were (say) at twice the natural geosynchronous
distance, the pull of the Earth-attached cable might sling it so the
centripital force balances against the combination of gravity and the
cable's tug. The cable would not be straight up-down in this
scenario, of course, but a spiraling connection from Earth to
satellite.

I wonder if anyone has calculated out what actual configuration would
work to establish a working geosynchronous cable-satellite combination
like this, assuming an indestructable cable. I can't imagine that any
known cable material could survive the forces involved, but would be
pleased to be informed differently.

Eric

Thus spake Eric Flesch
Arthur C.Clarke popularized the notion of drawing a cable from a
geosynchronous satellite to the Earth and then using it as an elevator
cable. In real life such a cable would be torn apart by forces. If
we imagine an indestructable cable, the geosynchronous satellite would
swiftly be pulled from the sky by the cable's weight.

The question is really what combination of (indestructable) cable and
satellite would summate to a functioning geosynchronous arrangement.
If the satellite were (say) at twice the natural geosynchronous
distance, the pull of the Earth-attached cable might sling it so the
centripital force balances against the combination of gravity and the
cable's tug. The cable would not be straight up-down in this
scenario, of course, but a spiraling connection from Earth to
satellite.

I wonder if anyone has calculated out what actual configuration would
work to establish a working geosynchronous cable-satellite combination
like this, assuming an indestructable cable. I can't imagine that any
known cable material could survive the forces involved, but would be
pleased to be informed differently.


I do not know any of the details, but I do know that there are people
working on this. My source is only a TV programme, presented by James
May. There is a million dollar prize (to be awarded by NASA, if memory
serves) for the design of a prototype car which can climb the cable.
James May showed a bunch of very reputable engineers working on it as a
spare time project. They had a buggy which climbed a cable using solar
power (actually the power was provided by a spotlight, but same
principle).

Calculating the orbit for a satellite of given mass and given density of
cable seems like a straightforward enough problem. The answer depends on
how much tension you want in the cable. I don't see why you would think
the cable is not straight down. If you swing a mass attached to the end
of a rope, is the rope not straight?

I know little of materials, but since this problem is being taken
seriously, I can only assume that people have done the calculations and
believe either that it is possible, at least in principle, to construct
a sufficiently strong cable, or that it will become possible in the
foreseeable future.

Regards

--
Charles Francis
moderator sci.physics.foundations.
charles (dot) e (dot) h (dot) francis (at) googlemail.com (remove spaces and
braces)

http://www.teleconnection.info/rqg/MainIndex

On Mon, 02 Mar 09 10:30:08 GMT, (Eric Flesch) wrote:

Arthur C.Clarke popularized the notion of drawing a cable from a
geosynchronous satellite to the Earth and then using it as an elevator
cable.
The question is really what combination of (indestructable) cable and
satellite would summate to a functioning geosynchronous arrangement.
If the satellite were (say) at twice the natural geosynchronous
distance, the pull of the Earth-attached cable might sling it so the
centripital force balances against the combination of gravity and the
cable's tug.

I wonder if anyone has calculated out what actual configuration would
work to establish a working geosynchronous cable-satellite combination
like this, assuming an indestructable cable.

Calculations are given in this article by Pearson--The orbital tower
9/17/1974 http://www.star-tech-inc.com/papers/tower/tower.pdf

In the article, Pearson concluded that conventional materials would
not work but possibly some carbon based material might just.

The next episode in the history is that carbon nano-tube composites
were developed and appear to meet Pearson's criteria:
http://www.niac.usra.edu/files/studi...472Edwards.pdf
The Space Elevator by Bradley Edwards, which covers a variety of
aspects of the challenges--manufacture of the ribbon, boosting it into
orbit, dodging space debris, whatever!

Microsoft (!) is sponsoring a 4 day conference on the space elevator
August 13 to 16 http://www.spaceelevatorconference.org/

Casting about in this morass of incredible numbers--how much does the
22,000 miles of ribbon we must boost into orbit weigh??!!! You get a
sense of how the Frenchman in the street felt when they set off to dig
not one but two trenches called the Suez and Panama canals.

On Mon, 02 Mar 09, John Bailey wrote:
Calculations are given in this article by Pearson--The orbital tower
9/17/1974 http://www.star-tech-inc.com/papers/tower/tower.pdf

Thanks for the great response. It's worth presenting his abstract:

"The theoretical possibility is examined of constructing a tower to
connect a geostationary satellite to the ground. The 'orbital tower'
could be built only by overcoming the three problems of buckling,
strength, and dynamic stability. The buckling problem could be solved
by building the tower outward from the geostationary point so that it
remains balanced in tension and stabilized by the gravity gradient
until the lower end touches the Earth and the upper end reaches
144,000 km altitude. The strength problem could be solved by tapering
the crosssectional area of the tower as an exponential function of the
gravitational and inertial forces, from a maximum at the geostationary
point to a minimum at the ends. The strength requirements
are extremely demanding, but the required strength-to-weight ratio is
theoretically available in perfect-crystal whiskers of graphite. The
dynamic stability is investigated and the tower is found to (be)
stable under the vertical forces of lunar tidal excitations and under
the lateral forces due to payloads moving along the tower. By
recovering the excess energy of returning spacecraft, the tower would
be able to launch other spacecraft into geostationary orbit with no
power required other than frictional and conversion losses. By
extracting energy from the Earth’s rotation, the orbital tower would
be able to launch spacecraft without rockets from the geostationary
orbit to reach all the planets or to escape the solar system."

Microsoft (!) is sponsoring a 4 day conference on the space elevator
August 13 to 16 http://www.spaceelevatorconference.org/

Best hypothetical use of the Gates billions I have seen (presuming
curing cancer to be an insoluble problem).

Eric

On Mon, 02 Mar 09, Oh No wrote:
Thus spake Eric Flesch
... The cable would not be straight up-down in this scenario,
of course, but a spiraling connection from Earth to satellite.

I don't see why you would think
the cable is not straight down. If you swing a mass attached to the end
of a rope, is the rope not straight?

No, of course it is not straight. There must be a traverse force to
pull the mass forward, and this is supplied by the traverse component
of the rope angle which may be very slight but must be present.

Eric

Thus spake Eric Flesch
On Mon, 02 Mar 09, Oh No wrote:
Thus spake Eric Flesch
... The cable would not be straight up-down in this scenario,
of course, but a spiraling connection from Earth to satellite.

I don't see why you would think
the cable is not straight down. If you swing a mass attached to the end
of a rope, is the rope not straight?

No, of course it is not straight. There must be a traverse force to
pull the mass forward, and this is supplied by the traverse component
of the rope angle which may be very slight but must be present.


There is no of course about it. We have known there is no transverse
force on an orbiting body, since the time of Newton. Planets do not
require angels to push them round their orbits. Why should your
satellite be any different?

Regards

--
Charles Francis
moderator sci.physics.foundations.
charles (dot) e (dot) h (dot) francis (at) googlemail.com (remove spaces and
braces)

http://www.teleconnection.info/rqg/MainIndex