[wordup] the space elevator

[Adam Shand]

this is great, i'm surprised it took me this long to stumbled across
this as i've always wondered about this.  ever since i was a little kid
reading science fiction :)

anyway they think that it's now possible to build an elevator to a
satelite in geosynchronous orbit, or maybe even the moon.  the break
though that makes the the difference it super strong carbon nanotubes that
are about 100 times stronger then steel.

if you're interested the original pdf is better then the enclosed text and
has pictures. :)

URL:  http://www.elevator-world.com/magazine/archive01/0101-002.html-ssi
PDF:  http://elevator-world.com/magazine/pdf/0101-002.pdf

SPACE ELEVATOR: MORE SCIENCE THAN FICTION
by Terri Wagner

We live in a world where science fiction, with the march of time, becomes
more science than fiction. In this case, the "celestial tower" of the 19th
century may become a reality in the 21st century. Although there are no
current projects on the subject, the National Aeronautics and Space
Administration (NASA) has revived an idea once considered infeasible.
Referred to as a celestial tower, space elevator, rotavator or space
tether, the concept is a way to hoist people and cargo into space without
using rockets or rocket fuel. NASA has dusted off plans set aside in the
early 1970s as improbable, and Otis Elevator Co. has responded that it has
"the right stuff" to help NASA achieve its dream of building a space
elevator.

The idea of a space tower with an elevator in it has been around since at
least 1895. Russian scientist Konstantin Tsiolkovsky, inspired by the
Eiffel Tower, wrote about what he called a "celestial castle." He proposed
building a tower up to 35,800 kilometers (km). Inside a spindle-shaped
cable would terminate in a castle-like structure which would orbit the
earth remaining at the same spot, called a geosynchronous orbit (see
Figure 1).

Time travel to 1960, a second Russian scientist changes the concept a
little by suggesting the use of a geosynchronous satellite as the base
from which to build the tower. In Y.N. Artsutanov's suggestion, a cable
would be lowered to the earth from a satellite, while another cable
stretched out to a counterweight in space (see Figure 2).

Just six years later, American engineers began to look around for what
type of material would be needed for a cable 35,000-km long. It was
assumed the cable would be straight with no variations in its cross
section. The conclusion in this mid-1960s study was that the strength
required will be twice that of any existing material, including graphite,
quartz or diamond.

American scientist Jerome Pearson devoted time in the early 1970s to
refining the concept. He designed a tapered cross section, slowly
extending a counterweight out to 144,000 km, half the distance to the moon
while the lower part of the tower was being built. However, the logistics
did not add up it would take 24,000 Space Shuttle trips just to transport
part of the material needed to construct the tower.

Not giving up, Pearson then reversed the idea why not build from the moon
to the earth. Using the Lagrangian method of defining special stable
points that exist about any two orbiting bodies where gravitational forces
are balanced, Pearson determined that the cable length for that center of
gravity needed to be L1 or L2 (Lagrangian points). For L1, the cable would
need to be 291,901 km, and for L2, 525,724 km. Obviously, one drawback was
the length of the cables, not to mention the material would have to be
gathered and possibly manufactured on the moon.

However, the idea just would not go away. To use an elevator to launch
objects into space without the risks of a rocket was too good to give up
on. Since the elevator would attain orbit velocity as it rode up the
cable, an object released there would also have the proper orbital
velocity. It was the building from the ground up that seemed the most
improbable aspect of the task.

Enter the late 20th century. The space elevator or the space tethered
transportation system or "Skyhook" began receiving renewed consideration.
Take one 36,000-km-long cable going down to earth and one 110,000-km-long
cable going out to a ballast weight and you would have in effect a skyhook
a cable strong enough to hold its own weight with the ballast weight
helping to keep the center of mass of the system at a geostationary
altitude orbit.

Now, if the Skyhook used a number of cables arranged in a hollow
structure, then electrified tracks could be built inside the structure and
you would have a hoistway. Add cars that climb the skyhook from the
earth's surface into geostationary orbit and you have the space elevator.
However, it would consume an appreciable amount of electrical energy. Cars
continuing beyond the orbital point would have to brake to keep from
flying out too fast. If the braking were done by an electric motor, the
braking energy could be turned into electricity and used to raise the next
cable car from the ground. On reaching the ballast mass, the car would be
150,000 km from earth and moving with a tangential velocity of 11km/s.
Taking this concept back into the science fiction realm, if the car were
to let go of the cable at just the right time, the car (now spacecraft)
could coast to Saturn on a minimum energy orbit or travel rapidly to other
planets.

A second version of the Skyhook is a Rotavator, which uses a cable that is
much shorter than the geostationary orbit. The Rotavator rotates as it
orbits the earth with the ends of the cable touching near the surface of
the earth.

The Moravec design for this concept shortens the length of the cable to
4,000-km long, one-third the diameter of the earth and one-ninth the
length of the 36,000-km Skyhook. The taper for the aderated graphite cable
would be 10:1. The central portion of the cable would be in a
2,000-km-high orbit and set to spinning at one revolution every 40
minutes. Six times each orbit, once every 20 minutes, one of the cable
ends would touch down to the upper regions of the earth's atmosphere.
Total liftoff acceleration would have be 2.4 g's, less than the shuttle
launch. In 20 minutes, the load would reach the peak of the trajectory,
traveling at 13km/s. The science fiction aspect of this concept
theoretically, with this velocity, you could reach a Mars orbit in 72 days
and Venus in 41.

Following Pearson's reverse idea, a lunar Rotavator could be built. Take
the concept further and you could have a series of spinning cables with
enough velocity to transfer you to any planet in the solar system.
However, a serious drawback to spinning cables is spinning asteroids and
space debris.

Science fiction, maybe, maybe not.

In an August 2000 report, NASA detailed the first serious concept of
building a space elevator that would hum along a thin diamond fiber and
extend 22,000 miles above the earth's equator. Why the equator? It is a
region almost devoid of hurricanes and tornadoes and in alignment with
geostationary orbit.

David Smitherman, a scientist at the Advanced Projects office of NASA's
Marshall Space Flight Center in Alabama, claims "current construction
materials are already good enough to build a tower 15 km high. That way
more than 80% of atmospheric forces affecting the cable could be avoided."

To keep the extremely long cable from tumbling back to earth, a mass could
be attached to the far end. The pull of the mass trying to spin off into
deep space would counter the pull of gravity that would tug the cable.
Both forces would keep the connecting cable taut and allow it to escort
electromagnetic cars shuttling back and forth through tunnels in the
cable.

"It's like building a skyscraper in reverse," Pearson explained. "At the
top, you have the thickest point and below there's a cable hanging."

Making the space elevator a reality relies on recent developments in
nanotechnology. The key is an extremely strong cable that can extend
thousands of kilometers into space. The answer could lie in carbon
nanotubes which are lightweight but 100 times stronger than steel,
according to Smitherman.

"In regards to elevator mechanisms, it was noted that a high speed
electromagnetic elevator would be needed. It is not exactly clear how to
integrate an electromagnetic vehicle system into a vertical structure to
make the high speed elevator. Perhaps this is a technology challenge that
the elevator industry could consider."  David Smitherman

In other words, NASA believes the 19th century space elevator is feasible.

Otis believes it has the ability to make the technology happen. John
Thackrah, vice president of engineering for Otis, said that based on Otis'
current capabilities for creating transportation systems for skyscrapers
several miles high, a space elevator may be more fact than fantasy.

"Today, we have the technology to create elevator systems for a
five-mile-high tower," Thackrah added. "At the rate of our development
efforts, we could apply the technology we are working on for today's
existing market to the NASA concept within the next 10 years."

Otis already has a range of technological applications to address the
structural, dispatching, control and maintenance issues associated with
such an undertaking.

Otis also designs equipment for efficient use of hoistway space through
multi-deck car frames. Multi-deck elevators would be important for food
preparation areas, sleeping quarters, sanitary facilities and cargo
storage for a journey from the earth's surface to orbit.

Otis projects under development for release to earthbound markets are
self-propelled and lightweight vehicles; stackable- or multi-deck-car
frames; ride-quality components including aerodynamic cabs, door and cab
seals; electromagnetic-field guideshoes; and intelligent door systems that
maintain the same open and close profiles under standard pressure or zero
g's.

In addition, control systems that enable vehicles to "see" each other and
avoid collision are used today on Otis' horizontal people mover systems,
which typically share horizontal hoistways or "guideways"  at airports.

Otis also factors in repairs to such a system. Routine maintenance would
have to be minimized. The system would require on-board diagnostics that
could not only warn maintenance personnel on earth of potential problems,
but also enable repairs from a remote in this case very remote location.

Currently, Otis' REM monitoring system can detect software as well as
electro-mechanical degradation on microprocessor-based systems and
automatically alerts a service dispatcher. In addition, the company is
developing diagnostics for "maintenance-free" earthbound elevators.

In other words, Otis believes it has the technology to make the 19th
century space elevator a reality.

REFERENCES:

* NASA Academy. "Space Towers."
  - http://astro-2.msfc.nasa.gov/Academy/TETHER/SPACETOWERS/html

* Transorbital Library. "Tethered Space Transportation Systems."
  - http://www.transorbital.net/ Library/D001_S03.html

* "NASA Needs Extremely Tall Tower for Space Elevator Concept." Civil
  Engineering News. November 2000.

* Onion, Amanda. "Celestial Lift." ABCNEWS.com

* Otis News Release. "Twinkle, Twinkle, little star, was that an elevator
  car?" October 26, 2000.
  - http://www.otis.com/