After the space
shuttle Columbia lifted off on April 12, 1981 from Kennedy Space Center, to
start the first space shuttle mission, the dream of a reusable spacecraft was realized.
Since that time, NASA has launched more than 100 missions. Each mission was
done by launching a large rocket that has to be built from a scratch. It surely
cost a lot to make even a single rocket, and the additional cost to launch the
rocket (approximately $10,000) would be a very burdensome budget.
Considering the
cost and the time to make and launch the rocket, scientists have to figure out
how to send people or machines into space at a low cost and the spacecraft has
to be reusable. By borrowing the Russian scientist, Konstantin Tsiolkovsky’s
concept about the tower that reach the earth’s geostationary orbit, they have
come out with a concept of a new space transportation system that could make
travel to Geostationary Earth Orbit (GEO) a daily event and transform the
global economy. The space transportation system is called the “Space Elevator”.
space elevator
is a proposed type of space transportation system. Its main component is a
ribbon-like cable (also called a tether) anchored to the surface and extending
into space. It is designed to permit vehicle transport along the cable from a
planetary surface, such as the Earth's, directly into space or orbit, without
the use of large rockets.
To better understand the concept of a space
elevator, think of the game tetherball in which a rope is attached at one end
to a pole and at the other to a ball. In this analogy, the rope is the carbon
nanotubes composite ribbon, the pole is the Earth and the ball is the
counterweight. Now, imagine the ball is placed in perpetual spin around the
pole, so fast that it keeps the rope taut. This is the general idea of the
space elevator. The counterweight spins around the Earth, keeping the cable
straight and allowing the robotic lifters to ride up and down the ribbon.
The
centerpiece of the elevator will be the carbon nanotubes composite ribbon that
is just a few centimeters wide and nearly as thin as a piece of paper. Carbon
nanotubes, discovered in 1991, are what make scientists believe that the space
elevator could be built. Carbon nanotubes have the potential to be 100 times
stronger than steel and are as flexible as plastic. The strength of
carbon nanotubes comes from their unique structure, which resembles soccer
balls. Once scientists are able to make fibers from carbon nanotubes, it will
be possible to create threads that will form the ribbon for the space elevator.
Previously available materials were either too weak or inflexible to form the
ribbon and would have been easily broken.
Once
a long ribbon of nanotubes is created, it would be wound into a spool that
would be launched into orbit. When the spacecraft carrying the spool reaches a
certain altitude, perhaps Low Earth Orbit, it would begin unspooling, lowering
the ribbon back to Earth. At the same time, the spool would continue moving to
a higher altitude. When the ribbon is lowered into Earth's atmosphere, it would
be caught and then lowered and anchored to a mobile platform in the ocean.
The
ribbon would serve as the tracks of a sort of railroad into space. Mechanical
lifters would then be used to climb the ribbon to space.
While the ribbon is still a conceptual
component, all of the other pieces of the space elevator can be constructed
using known technology, including the robotic lifter, anchor
station and power-beaming system.
Lifter
The
robotic lifter will use the ribbon to guide its ascent into space.
Traction-tread rollers on the lifter would clamp on to the ribbon and pull the
ribbon through, enabling the lifter to climb up the elevator.
The
space elevator will originate from a mobile platform in the equatorial Pacific,
which will anchor the ribbon to Earth.
Counterweight
At
the top of the ribbon, there will be a heavy counterweight. Early plans
for the space elevator involved capturing an asteroid and using it as a
counterweight. However, more recent plans like those of LiftPort and the
Institute for Scientific Research (ISR) include the use of a man-made
counterweight. In fact, the counterweight might be assembled from equipment
used to build the ribbon including the spacecraft that is used to launch it.
Power Beam
The
lifter will be powered by a free-electron laser system located on or
near the anchor station. The laser will beam 2.4 megawatts of energy to
photovoltaic cells, perhaps made of Gallium Arsenide (GaAs) attached to
the lifter, which will then convert that energy to electricity
to be used by conventional, niobium-magnet DC electric motors,
according to the ISR.
Once
operational, lifters could be climbing the space elevator nearly every day. The
lifters will vary in size from five tons, at first, to 20 tons. The 20-ton
lifter will be able to carry as much as 13 tons of payload and have 900 cubic
meters of space. Lifters would carry cargo ranging from satellites
to solar-powered panels and eventually humans up the ribbon at a
speed of about 118 miles per hour (190 km/hour).
If
the space elevator is realized later in the years forward, in addition to seeing from the technological point of view, we also have to look from the standpoint of the impact on
society. Space elevator is a great yet a very dangerous
technology, because it involves not only the environment on the earth, but on
the space which is mostly unreachable and unpredictable. If we look at the
bigger point of view, we can see that the space elevator compared to the earth
is only a tiny fragile string attached to a ball, so it is very easy for it to
break up if anything happened inside or near the earth. For example, the
lightning stroke can damage the cable; meteors can easily break the cable or destroy
the elevator although the chance is tiny; Wind loading study that can vibrate
the cable; atomic oxygen in the upper atmosphere which is extremely corrosive and will etch
the epoxy in our cable and possibly the carbon nanotubes; radiation damage; and
the possibility of environmental impact during the construction.
Besides
its impact to the environment, the space elevator gives society a great amount
of contribution that gives the advantage for the people. First, space elevator
has the potential to transform the global economy. It helps the economy such as
reducing the cost needed to make a spacecraft and it may bring us to a new
world of economy. Second, it gives us a bigger chance to study about the space.
It also helps the scientists to collect data, real-time, without using any kind
of robots/special devices. And the last but not least, it gives all the people
in the world a chance to go to the outer space and see what’s going on above
our earth, to know, and to study all things outside the earth.
Name : Hans Chandra
Lecturer Name : Aditya Pratomo
Campus : Surya University
http://en.wikipedia.org/wiki/Space_elevator
http://science.howstuffworks.com/space-elevator.htm
http://www.mill-creek-systems.com/HighLift/chapter10.html
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