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How Space Elevators Will Work
by Kevin Bonsor

Photo courtesy NASA
A space elevator would allow space travel without the need for rocket fuel.
Since 1961, when Russian cosmonaut Yuri Gagarin became the first person to ride into space, fewer than 1,000 people have experienced the thrill of space travel and less than 20 have walked on the moon. The rest of us have watched, waiting for the day when space travel might become as commonplace as airplane travel. Looking at recent odds, the chance that you or I will make it into space seems fairly slim -- in 1998, only 32 of the 6 billion people on Earth made trips into space. That gives you about a 200,000,000:1 shot, which means you have a better chance of winning the lottery than riding into space.

There are several reasons why space hasn't opened up as a tourist destination where we might spend a week at a lunar hotel or take a celestial cruise. The main reason is the shipping costs. With today's technology, it costs about $10,000 per pound ($22,000/kg) to put anything into orbit. At those prices, a 150-pound person would have to pay $1,500,000 for a ticket to space. Getting the necessary materials into space to build a hotel there would cost in the hundreds of billions of dollars, at least.

However, while today's technology is hampering our plans to hike up Martian mountains, there are several solutions under development that could make mass space transit a reality in this century. Our best bet is NASA's idea to build a space elevator. In this edition of How Stuff Will Work, we'll take a look at space elevators and find out how they might be your ticket into orbit.

The Basics
The basic idea behind a space elevator is pretty simple. Here are the key components involved in constructing one:

  • An extremely tall base tower on Earth
  • A heavy weight orbiting the Earth
  • A cable that connects the tower to the weight
  • A spacecraft that can ride the cable into orbit
To better understand the concept of a space elevator, think of the game tetherball. In this game, a ball is attached to a pole by way of a rope. Think of the rope as the cable, the pole as Earth and the ball as the weight. Now, imagine that the ball is put into perpetual spin around the pole, so fast that it keeps the rope taut. This is generally how a space elevator would work. The weight at the end of the cable spins around the Earth, keeping the cable taut. The spacecraft would simply ride up the cable as a train rolls over tracks.

If this type of transport system could be built, we would see a rapid decline in the cost of boosting a spacecraft into orbit. The largest single cost in launching the space shuttle is the rocket fuel, but there are other costs, such as building and maintaining the vehicle and building expendable rocket boosters.

To get into low Earth orbit, the space shuttle burns approximately 4 million pounds (1.8 million kg) of fuel in eight minutes. That's a huge amount of fuel for a 200-mile (322-km) trip. With a space elevator, the need for rocket fuel is eliminated completely. The elevator draws its initial launch energy from an electrical-power station on the ground.

As the vehicle rides farther up the cable it requires less electrical energy, relying more on the centrifugal force produced by the spinning counterweight to pull it into orbit. By the time the vehicle reaches the end of the cable, it could be moving as fast as 6.79 miles per second (10.93 kps)! At these speeds, a vehicle could detach from the cable and fly off into space at speeds fast enough to reach Mars in days or weeks instead of months.

World's Largest Construction Project
So, if this space elevator is such a simple concept and could save billions or trillions of dollars, why isn't it being built already? The main reason is that technology is just now reaching the point where a space elevator could be turned into a reality. When this idea was first thought of more than 100 years ago, the Wright brothers hadn't even gotten their plane off the ground yet.

Photo courtesy NASA
Space elevators could generate speeds that would shorten the time it takes to reach Mars.
A space elevator would be the largest and most difficult construction project we'd have ever undertaken. The base tower built on Earth would be 31 mi (50 km) tall. Given that the world's tallest structure -- the CN Tower in Toronto, Canada -- is just barely one-third of a mile in height (about 0.5 km), such a space tower is hard to conceive of. The extreme height of this tower would be necessary to anchor the cable to the Earth.

While this tower is built, scientists would also have to work on the cable itself, which would extend more than 89,000 mi (144,000 km) from the equator into space. By the time it is finished, the cable would cover a third of the distance to the moon. Both the tower and the cable would have to be constructed out of a material strong enough to span that large distance without being pulled apart by the Earth and the counterweight. Scientists think that a specially-equipped satellite could be sent into orbit to build the cable using nanomachines. Nanotechnology would enable the cable to basically construct itself one molecule at a time. It would extend down toward Earth to attach to the tower and up into space to attach to the counterweight.

NASA is proposing that this counterweight be an asteroid that would somehow be moved into a precise position and placed into orbit thousands of miles from Earth. If everything went as planned, this asteroid would orbit Earth, pulling the cable tight to allow a vehicle to slide up and down it.

Today, scientists are developing the components and designs that could allow for the construction of such a space elevator before the year 2100. It will likely take years to build the massive structure. According to NASA researchers, here are the key technologies that are being developed for space-elevator construction:

  • Carbon nanotube (CNT) - A lightweight material 100 times stronger than steel. Until recently, scientists lacked a strong material light enough to build a cable that could span more than 100,000 mi (160,934 km) into space. The development of carbon nanotube makes the space elevator a viable option. Carbon nanotubes are pure-carbon cylinders that were first created about a decade ago by zapping graphite with lasers. It has a tensile strength of 200 gigapascals (GPa); for comparison, graphite, quartz and alumina each have a tensile strength of just over 20 GPa. NASA has said that a material used to build a space tether would need a tensile strength of 62 GPa.

  • Tether technology - Long cables that can transfer momentum from one object to another. Currently, tethers are used to attach astronauts to the space shuttle during space walks. Tethers attaching a spacecraft to a satellite could be used to pull the spacecraft up and then sling it into space with more velocity and fuel efficiency than current launch methods -- once this is successful, scientists can further pursue the idea of an Earth-to-space tether.

  • Electromagnetic propulsion - Electromagnetic propulsion currently allows a train to hover on a cushion of air, enabling the vehicle to travel at high speeds by eliminating friction. Magnetic levitation trains that can travel at more than 310 mph (500 kph) are already being developed in several countries. These trains use powerful superconducting magnets that give off a great deal of heat. Scientists are already searching for room-temperature superconductors that require no cooling and could be used to create maglev trains that require little energy.

The idea would be to combine all of these technologies to construct four to six maglev tracks that would run the length of the cable into space. The space vehicles would either stop at different stages to float satellites or other payloads into space or would use the track as a high-speed launching ramp. Such a space-transportation system could also allow you to take trips into space for about the same price as a plane trip.

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