here is a different one.
The story of Jack and the Beanstalk is starting to sound more and more possible every day:a huge,tall structure comes out of the ground and goes straight up through the clouds; at the end is a wonderful,mysterious castle.Developers at NASA's Advanced Projects office at the Marshall Space Flight Center in Alabama have more or less the same idea.It's called the Space Elevator.
"We could have a satellite orbiting above the Earth,and string a line from it down to Earth," says David Smitherman,technical manager at the Advanced Projects Office."That line would be used to pull vehicles up to space.From there they could be easily launched into other orbits."
Why do it that way?Smitherman and many space propulsion experts agree that the biggest drain of energy takes place when a vehicle blasts off.Pushing through Earth's gravitational pull requires great amounts of fuel,but once they get out of our atmosphere,the rest is easy.If you could cut out that "blast off" portion,space travel would be easier and much more fuel-efficient.
In the beanstalk story,Jack shimmied up the giant plant using muscle-power.In a Space Elevator scenario,magnetic levitation vehicles would zoom up the side of an exceedingly tall structure and end up at a transfer point where they'd then board a craft to the moon,Mars,or any other distant destination.If it all sounds like too much science fiction,take a look at the requirements for making the Space Elevator a reality.
There are several key concepts to master before this can all happen,Smitherman says.The first is how to anchor the elevator.The starting point will be on Earth-obviously-perhaps originating on a platform at sea.But it will end up attached to a satellite orbiting our world.But you know satellites; their orbits can be quite erratic."The only type of satellite that will work is one in geostationary Earth orbit," Smitherman says.
"Satellites orbit at many altitudes," he continues."To stay in orbit,the satellite needs speed,because it's actually in a free fall around earth.If it goes fast enough,it won't hit ground.Imagine throwing a rock from a mountaintop.The harder and faster you throw it,the farther out from the mountain it will go.The Earth is round,so conceivably,if you throw that rock hard enough and fast enough,it will circle the earth and come back to you.That's an orbit,and that's what satellites do.In a geostationary orbit,the satellite is at the point high enough above Earth,where the rock you throw from the mountain is going the same speed as the Earth's rotation.Because they're traveling very fast at the same speed,at this high altitude,the satellite appears to be staying still over the same point above the Earth's equator."
Another issue is how the structure that guides the cable and the magnetic levitation vehicle will be built.In order to reach a geostationary satellite,the tower will have to reach 36,000 kilometers (22,000 miles) above Earth.Any structure we currently use would have to be enormous in size in order to support the weight of a structure that tall."If you made the tower out of steel," Smitherman says,"it would be massive in diameter.It would be miles thick.That's totally impractical.A new material has been developed,however,called carbon nanotubes,that is 100 times as strong as steel but with only a fraction of the weight.Carbon nanotubes is an idea that makes this all sound much more achievable."
"This is not a new concept," Smitherman says."Author Arthur C.Clarke coined the term "space elevator" in his book "Fountains of Paradise," written in the late 1970s.But building a tower to the sky has been in mythology and culture for centuries.I won't see a Space Elevator in my lifetime,but my children may.Kids who are in school right now are the ones who can make this happen by the end of our century."
Courtesy of NASA's Aeronautics Mission Directorate
Published by NASAexplores:January 30,2001
Decaying Orbit
Subject:Science
