Space Elevators

When Sputnik 1 reached space and orbited the Earth, it was an event that would change the world. The Soviet Unions satellite launched on October 4th 1957 and it was the first artificial object to ever be launched into Earth’s orbit. Since then the frontier of space has been a field of countless research. Among the many topics is the means of transporting people, equipment, and cargo into orbit. We have relied on rocket-propulsion as our way of breaking out of Earth’s atmosphere, but there are many other ways.

Rocket-propulsion looks good on television, seeing a huge cloud of smoke, a thunderous roar, and that iconic countdown, it’s all dandy, but it is very inefficient from both a cost and time perspective. It costs approximately $22,000 per kilogram for rocket-propulsion endeavors. Each launch must be heavily planned and coordinated. There are thousands of variables for any rocket-propulsion launch, from safety of citizens on the ground, the return trip, and the landing of jettisoned parts.

The majority of problems in rocket-propulsion would be eliminated with space elevators. In the past this was truly a dream of even the wackiest science fiction, but modern developments have revealed that it is possible. A space elevator is basically a long cable with a counterweight in space (geostationary orbit) and it’s anchored to the Earth. It is like a tetherball installation on playgrounds, except the pole is the Earth.

However the components in a space elevator are not simple, fishing line and a bowling bowl won’t get the job done. A highly flexible and tensile material is needed to form the ribbon, while the counterweight could technically be anything, as long as it is of appropriate weight. Early plans were going to utilize an asteroid as the counterweight, but it would be easier to simply use an artificial creation. Anchoring the ribbon wouldn’t be much of a hassle either. An offshore mobile platform would most likely be the anchor for the ribbon.

In fact every aspect of the space elevator is ready to go, except the ribbon. The mechanical lifters that ride the ribbon are far into design already. Lifters will climb the ribbon using traction-treads and go up to 200 km/hour. These will vary in size and payload with the proposed highest max at a 20-ton capacity. The lifter will be powered by a free-electron laser system at the anchor point. It will beam 2.4 megawatts of energy to photovoltaic cells, probably made of gallium arsenide attached to the lifters. Lifters will convert it to electricity to be used by niobium-magnet DC electric motors. Essentially lifters would be capable of climbing the space elevator every day.

The ribbon is the one major drawback so far for space elevators. This tether must be both strong and light. The only conceivable material to form this highly flexible and tensile ribbon is carbon nanotube fibers. These can be 100 times stronger than steel and as flexible as plastic. Carbon nanotubes internal structure is similar to a network of soccer balls, which gives it unbelievable strength. The ribbon would need to be 100,000 km, but the longest carbon nanotubes developed so far have only been a few centimeters long.

Space elevator ribbons are kept taut by the counterweight’s perpetual orbit motion. The counterweight swings around the Earth thereby keeping the ribbon constantly taut. Centripetal force as well as Earth’s gravity would both be counterbalanced by the centrifugal force of the counterweight’s orbit. Once the counterweight, the ribbon, and the anchor are all set up, then lifters would be attached to the ribbon, powered up, and space elevators would become a reality.

Konstantin Tsiolkovsky first conceived space elevators in 1895. He proposed a ‘tower’ that connects Earth’s surface to its orbit after he saw the Eiffel Tower in Paris, France. Originally early ‘lifters’ would climb the ribbon by orbital velocity. However, Tsiolkovsy’s concept was a compression structure and totally impractical from both a design and construction standpoint. There have been many other concepts throughout time by several scientists. But David Smitherman and Bradley C. Edwards were the first to propose the idea of using carbon nanotube’s as the ribbon material.

From the Moon to the Earth is a whopping 382500 km, yet the ribbon for the space elevator is planned to be more than one-fourth that distance. Having an extremely easy method of traveling one-fourth to the Moon would be invaluable to further space research. A space station could easily be maintained, with daily supplies delivered and quick transportation of materials. Whatever the space exploring vessels of the future will be, they will still benefit from the space elevator; refueling/recharging, swapping crews, doing quick material drops, all these things would be so simple and easy. Also space elevators bypass Earth’s atmosphere, and space shuttles use up the most fuel breaking out of the atmosphere and re-entering is a costly event as well. Not only would scientific research benefit, but commercial space tours would be more practical with a space elevator.

Space elevators are still being researched and perfected. If a way to quickly make long carbon nanotube fibers is discovered, then space elevators could be setup up in the very near future. However space elevators are threatened by three problems. Firstly, weather, this is uncontrollable and the only negative effect it could have is to delay a lifter. Secondly, terrorism, malfunctioning, and sabotage are all factors that can affect anything, including space elevators. Lastly, orbital debris poses a threat. While there most likely isn’t any debris that could sever a carbon nanotube fiber ribbon, it still poses a problem.

Cost wise a space elevator station would be a fraction of current space shuttle programs. As mentioned earlier, it costs $22,000 per kilogram for a traditional rocket-propulsion shuttle launch, but space elevators would lower that cost to a max cost of $880 per kilogram. Construction costs for one space elevator are projected at around $6 billion with legal and regulatory costs being about $4 billion. These cosmological railroads are far less expensive than conventional rocket-propulsion methods.
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Simple space elevator diagram

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Free-body diagram of forces on a space elevator

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Offshore mobile platform anchor


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Mechanical lifter/climber

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Space elevator


Sources:
http://en.wikipedia.org/wiki/Space_elevator
http://science.howstuffworks.com/space-elevator.htm

Questions:
Are there any other materials that could be used as the ribbon except for carbon nanotube fibers?
How does a space elevator benefit average civilians?
Would you ride a space elevator?


Sonia Bansal- What would the weight of the counterweight be?
Depends on the length and mass of the ribbon.
Nauma Haider - How much money and kilograms are necessary for a rocket-propulsion launch?
I'm not sure I understand; do you mean is there a minimum payload for a rocket-propulsion launch to be greenlit?
Greg Sturm - How fast would this elevator presumably go? For a 22,000 mile trip to be commercialized sometime in the future it would probably have to be really fast, right?
Yes Greg, it'll be 'really fast'. 190 km/hour is the projected speed of the lifters. So it'll take about half an hour to go the whole ribbon length. Also, it's 62,000 miles, not 22,000 miles.
Robert Lopez - How long would the creation of a space elevator take? What kind of problems might they encounter once it is built?
Construction would be a matter of weeks. There are a few problems, mainly weather and orbital debris.
Brandon Siegenfeld- Why is it necessary for the platform on Earth to be mobile?
The anchor actually doesn't have to be mobile, it just has more advantages of being so. This way the space elevator can be moved as the mobile platform could drag the ribbon to a new location.
Sam Edwards - Do we currently have lasers powerful enough to use to power a space elevator?
They are being developed at the moment.
Will Chan - After getting to the top of the space elevator, what happens if something breaks and you can't get down?
Well most space elevators will actually detach from the ribbon and re-enter the atmosphere down to the surface, naturally letting gravity pull it back. It is possible to come back down on the ribbon however. If something breaks though, then I wouldn't worry about it. Firstly, as mentioned, most lifters will be capable of returning by themselves. Secondly, the counterweight will most likely a spacestation, so there'll most likely be a solution to return there.
Kevin Norris - Can the lifter take advantage of centripetal force/inertia (must it be powered to go up)?
Lifters do indeed take advantage of the ribbon's centripetal force, but it is not enough, so the lifters must be externally powered.
James Song- What physical effects would occur if a person were to move too quickly in a space elevator?
They would still experience the same forces if they were stationary. Like in a normal elevator, if the cable snaps and you jump just before it slams into the botom of the shaft, you're still going to hit the floor just as hard.