written by Kevin Reimund on August 29, 2003 | contact me
number of views: 77020 | printable version (text) (PDF)
"...and she's buying a stairway to heaven."
The space elevator is a concept, so magnificent, so huge and so daunting that it may seem like an impossible task from the future. But in reality, the concept of the space elevator has existed since 1895 when a Russian scientist, Konstantin Tsiolkovsky who was inspired by the Eiffel Tower, envisioned a tower that stretched all the way into space. The idea was quietly forgotten over the turmoil that arose in the world as militarism and imperialism grew popular in the early 1900's. However, in 1957, another Russian scientist, Yuri Artsutanov drew up a more feasible plan in which a cable was lowered toward Earth while a counterweight was extended from Earth, keeping the cable's center of gravity at the geosynchronous point. The task was not forgotten and in 1966, four American scientists did tests and found that the cable would require a strength twice that of any known material, including diamond. In 1975, Jerome Pearson did a lot of work regarding the physics of the tower, determining how much material would be needed. He even accounted for fluctuations, such as lunar gravity and winds. The idea was picked up by the legendary eccentric Sci-Fi writer Arthur C. Clarke and publicized 1978. His book, The Fountains of Paradise had a space elevator that was connected at the island of Taprobane, an equatorial island near Sri Lanka. In 1999, David Smitherman retouched the subject in "Space Elevators: An Advanced Earth-Space Infrastructure for the New Millennium" Throughout the years, the concept has grown from a diamond composite to a nanotube structure. It has changed from a thick beam to a paper-thin cable, but the space elevator is still the same task. It may seem daunting at first, a 30,000 mile long cable into the heavens and I will be frank with you, it would not be an easy task to accomplish, but the potential rewards far outweigh any doubts. A cable stretching into space would allow people to hop on a car and arrive, six days later, on an orbiting space station. Such a system would allow raw materials to be brought up to space for processing and return to the Earth at a 100 billion dollar profit per year. People could easily be transported up into space and materials could easily be shipped back down to Earth. But such a task is so daunting that no one even knows where to begin. There are many designs, and each of them is good, relying on the intense finesse and etiquette, both required and acquired from space, from suspending a cable in the high atmosphere to making the cable an integral part of the Earth itself. And of course, such a system would cost somewhere in the 500 billion dollar range, more than the national debt of the United States, and that is saying a lot. So how do I begin this small story on this monumental task? By bringing you back to the roots of the space elevator concept, all the way back to Paris 1895...
"Construction of it will begin 50 years after everyone stops laughing."
As I said before, the space elevator concept (hereby referred to as the cable) had its roots in Paris, where the Eiffel Tower inspired by Konstantin Tsiolkovsky. The idea was refined many times and each time, the results were not encouraging. It was presented as a mere speculation that a cable of some strong material could be suspended from orbit and used for mass transportation from Earth to geosynchronous orbit. Such a material would have to be incredibly durable, strong, hard and flexible, yet have a tensile strength 10,000 times more that of steel. And at the time, researching such a material was out of the question. The concept was quietly shelved, except for word, which reached Arthur C. Clarke's inventive ear. His book, The Fountains of Paradise reinserted the cable concept into the scientific community and made the public aware of the potentials of the space elevators. Clarke came up with a number of different ideas including "sky hooks" where cables hung from the orbit. A person merely had to latch their plane onto the hooks and the elevator would lift them to the orbiting station. This kept the dream of the cable alive, yet, for the moment, all work was halted.
"Such a monumental task is not readily achievable, and yet, because of the difficulties surrounding it's construction, we see fit to continue research upon what most would call a lost cause. This both compliments the human ingenuitive spirit and the industrialistic nature of the best nation on our world."
New Horizons for a Forgotten Topic
In 1991, a new hope for the space elevator was born. A Japanese electron microscopist, Sumio Iijima, who discovered thin filaments on specimens when he was studying the material deposited on the cathode during the arc-evaporation synthesis of fullerenes. Fullerenes are cage-like structures of molecular carbon containing 60-500 atoms. They are commonly referred to and known as buckyballs, due to their shape. They closely resemble the expanding plastic balls that you see at science shops, yet due to their size and the materials used to make them, they are incredibly strong. And while I'm not going to go through the entire history of the nanotube (although I will retouch upon it in section III), you now know how the nanotube was discovered and that's all I wanted.
"The ladder made access to the roof or a second floor possible. The stairs made access to larger buildings. The lift made building 30 floors high. The full-fledged elevator made the skyscraper possible. A space elevator could make a "sky broacher" possible."
Thank You NASA
As NASA grew, NASA began to take an interest in the space elevator concept. They produced lab results and determined the exact tensile strength for the cable material. The found that the aforementioned carbon nanotubes had 30 times the tensile strength of the required material, but, alas, no material is perfect. Nanotubes tend to be short, on the range of 2 or so nanometers. Nobody feels that it is practical or possible to build the cable out of layer after layer of 2 nanometer long wires. It would take 500 million layers to make a single meter and making a layer might cost 10 million dollars. Also, nanotubes tended to deform and slip out of the shape that they were supposed to make. A bundle, designed to look like a cable, can easily be squashed into a flatter shape, like a collection of plastic wires in a circle or the bottom of a broom. Needless to say, it is quite difficult to climb something that keeps on changing shape to conform with stress.
"It's impossible to destroy the cable itself so we planted charges on Clarke's surface. When they go off, the rock will soften and Clarke will be shot out to Saturn."
Nanotubes are expensive and scientists have looked for substitutes for them. The single most important requirement is the tensile strength or the self-height; the height at which the tower becomes too heavy to support itself. Steel tops out at about 3 miles. Titanium at about 5.5 miles. If the steel and titanium is compressed to form crystalline steel and titanium, then they would be able to reach about 300 and 550 miles, respectively. A special composite developed by researchers to present to a conference that was to be designing space elevators came up with a material with pressurized bubbles in it to support the material. The self-height of this material was 1150 miles, about one thirty-thousandth the required self-height. And, as I said before, nanotubes exceeded this requirement by 30 times. Obviously, we have no choice but to conquer the problems of the nanotube.
Section II: Dimensions of the Cable
"The cable would be 30,000 miles long and have an asteroid anchor at the end of it. Anything approaching the end would have enough speed to reach Saturn."
The Base Station
The base station is usually envisioned as a cable descending into the rock of an equatorial mountain, bolted by high-strength composite bolts, or floating suspended in the air over a floating platform in the middle of the Pacific. No matter what, the cable base would have to meet requirements rivaling that of the cable itself. It would have to have an airport larger than any ever dreamed of to ferry constant traffic of people departing to space. It would have to have a harbor, also larger than any other. The quickest way to transport goods from space is through the cable down to a ship or plane. The interior transportation system would make it rival that of a large city and the maintenance required would require a population of around 10,000. Also needed would be immense medical facilities because with the number of people, accidents would occur quite frequently. Also, accommodations would be needed. Full size houses for employees and large and luxurious hotels for the extravagant passengers on their way to space. A floating city 30 miles in diameter (circular) would be needed at least to house the transportation, production, refinement and population demands. If on land, a large harbor out to sea and a large airport would still be needed, though people could be housed in the less restrictive pleasures of a South American city. Regardless of whatever happens, such a large complex would require at least 20 years of construction and billions upon billions of dollars in construction costs.
"Such a system pales in insignificance to our highway system,"
The cable itself has had a variety of remakes, just as the concept itself has. In some concepts, the cable is more like a ribbon, 3 feet wide and thinner than a sheet of paper. Some people envision a more rope sized cable, maybe 1 foot by 1 foot. Some more industrialistic people envision a 15 foot thick cable and I think that in the near future, a half mile might not seem so unreasonable. Obviously, the more space you have, the more you can do. A half-mile cable might fit a hundred cars and maybe even some trains, that is, assembly lines from space. Large mass produced goods, such as cars and boats and such might be put on trains from space. The manufactured good would be put on a train like device designed to move on the cable. A fleet of cars, trucks, boats, ships, and such could descend and the trains could return to space carrying trash and wastes for recycling and reprocessing. Most people seem to envision the elevator as a normal elevator with cars. They go down until they're called up. This is incredibly restrictive. Rather, these cars will act more like trains. A single shaft will be devoted to going up. At the bottom, the cars are switched to the other track to go back up. This allows a much larger volume of traffic for these cars, since hundreds can be called down depending on the amount of traffic. All in all, the cable would be between 30,000 and 45,000 miles long, be at most half a mile wide. An average guess assumes that a cable would weigh between 100 and 1,000,000 tons.
The structure of the cable changes as well. At the ground, the cable is very compact, but, further from the atmosphere, stresses are less and the cable naturally expands. At the base of the cable, stresses are very light because the cable is just hanging and is bolted into place. At the end, however, stresses are very heavy. The cable has to be held upright. The weight of the cable is counterbalanced by a small asteroid as an anchor. The weight of the cable tries to pull the cable down towards the earth, since only a small portion of it is in true orbit at 30,000 miles. The majority of the cable is below the geosynch point, and therefore acts like any other tower. The cable there has weight and this immense weight must be counter balanced. At the other end of the cable, the cable is above orbital velocity, and therefore, anything on the cable is in danger of falling up, away from the Earth. A perfectly weighted asteroid must counterbalance the pull. It need not even weigh the entire weight of the cable, since the lower levels of the cable will be a building and the upper atmospheric level would be self-supporting (explained in Section III). The total weight of the asteroid might even be more than the cable, which, in a sense is good. This extra weight is counterbalanced by the base station, either pulling the entire weight of the Earth if it's land based or pulling on the floating platform, which would weigh a lot of megatons. A carefully measured segment of the cable would be allowed to rest below the base station at sea. As the asteroid is mined, the weight and stress becomes less and the cable can be allowed to slide up until an equilibrium is reached at ground level, at which the mining is stopped.
"Don't ever hit all the buttons on this elevator; you'd be dead long before you got to the top."
The production station at the geosynch point is something I envision in two parts. It doesn't make any sense to restrict building to the cable alone. At the geosynch point, a simple rotating ring 500 feet in diameter and a large docking bay for orbital spacecraft is all that is needed. People simply take a ferry to the main station. Mass transit freighters load items directly onto the cable for lowering. Bulk ferries transport masses of people back and forth. The station on the cable would be very simple, leaving the complex orbital building to occur at the main station, a large orbiting metropolis.
"When the occupants of the elevator car Bangkok Friend learned that Clarke had broken away from the cable and was falling, the hurried to the foyer and the locker room and pulled on emergency spacesuits as fast as the could, and for a wonder there was no panic, it all happened in the heart, on the surface everyone was businesslike and attentive to the small group at the lock door who were trying to determining where exactly they were, and when they should abandon the car."
The most important part of the cable is the car. Without the car, the elevator is nothing more than a large thread hanging in space. The car has to masterfully fulfill a variety of roles. The passenger car will most likely be furnished as a 0-gee hotel, a full 6 stories high and designed with a definite "up" for when the car was up or accelerating upward. A luxury car might rotate on its chassis, allowing the deceleration to cause the sensation of gravity as well, saving richer passengers from the 3 days of deceleration that they would normally have to go through. Cargo cars would be much more utilitarian. Most wouldn't even have to be pressurized or manned, since most industrial cargo from the station would be mechanical. The method of propulsion for the cars would come from self contained nuclear reactors that generated an electrical push on magnetic repulsers mounted inside the cable itself. These repulsers would be self contained devices receiving power from massive solar power farms mounted at the geosynch point. Power would be transferred to them by the nanotubes themselves. This system also would generate a magnetic field for the cable, shielding it's occupants from the harsh radiation in space. The sheer size of the cable means that a total of +1,585,800 repulsers mounted in the cable, mounted every 100 feet.
"Now Mars has a little black line going around it's equator like the one I thought Earth had when I was a kid."
I have provided an illustration of the basic cable structure from a great distance (though it's not much to look at). The purpose of the anchor (which I believe is described sketchy at best in my writing) is explained here. Also, realize that the cable does not maintain an "even strain". As it expands outward, the cable must grow larger to have more strength. At the bottom, the cable is being pulled down toward the ground. A single nanotube stretched 30,000 miles could do that. On the other end, about 5 through 15 thousand miles of thread (extremely short) must support a few million tons of asteroid weight. The cable naturally expands with the stress and new nanotube material must be "strung in-between the cracks" to relieve the tension of the "outer cable", lest the asteroid break away and the cable wrap around the world a few times.
Section III: Modern Advances and Speculations of the Author
"...people will want a cheap fast, reliable way to get to space, now that the space shuttle has exploded and lost its glow with the public."
Modern Developments in the 21st Century
As the clock stuck midnight and old man time was greeted by the new year, but also the new millennium. Now, the past seems insignificant, but I've seen a number of developments perfect for the space elevator. For example, a company called Liquid Metal Technologies Limited is designing an alloy. Their proprietary process allows the metal to melt and be molded at much lower temperatures. Also, it has a higher elasticity and a higher energy-return weight of any metal, not to mention being extremely light, stronger and harder than steel or titanium and being extremely easy to shape. New construction methods allow nanotubes to do things they could never do before. For example, scientists at Purdue University have found ways to string nanotubes around a single straight strand, rather like a shoelace, with a nylon core and a cotton ropelike structure on the outside. This makes the nanotube even stronger. Also, new methods of producing nanotubes allow them to be made at an estimated length of 100 meters, still a far off dream for a space elevator, but, not a bad start.
"The future of space is small."
New Twists to Old Ideas
As capitalists begin to realize the potential benefits of a space elevator, they have begun to make plans. These plans rang from wild ideas in which twenty tons of cable is sent up into space to be reeled down like lowering a rope into a hole and pulling people up to having a bunch of sheets fly up and flip themselves onto the edge of the ribbon and become another 5 feet of the cable. Some of these ideas deserve merit and I think that I shall take the time to mention some. The first and most direct approach includes launching a reel of twenty tons of cable. As the cable is lowered, another reel comes up and attaches itself onto it. When the cable reaches the ground, it has the capability to lift up to 20 tons of cargo into orbit. Not as crazy as it sounds. A corporation called HighLift Systems wants to lower a ribbon of nanotubes, 3 feet wide, 30,000 miles long and maybe a few microns across onto the ground. While I don't see the point of making a ribbon rather than a cable, HighLift does. Another system even involves a set of "climbers" or little climbing components that attach to the end of the cable. This corporation envisions that after 2-and-a-half years and 300 of these climbers adding onto a base constructed on Earth, mounted at the geosynch point, the cable would beat it's full height.
Speculations by the Author
The past year, I have seen numerous ideas for space elevators themselves, components, various base stations, various propulsion methods and even additions to nullify the weight effects of the cable up to 120,000 feet using vacuum chambers. I see the first elevator not so much as a true elevator as much as a lift, more like tying a string onto a small hotel and lifting it into orbit and, essentially, that's what I envision the first elevator as. A reel in orbit that lifts a small hotel sized car into orbit for loading and unloading. It would start with about 100 tons of cargo launched into orbit on a Russian Energia booster. The cable would drop down and be bolted to the floor using a buckyball "hook" with a holding capacity of 100 tons or more. Then a single 20 ton weight would attach to the other end of the reel in orbit, on the other side of the geosynch point. Because this weight would be faster than orbital velocity, it would try to slingshot away from the world with a pull of about 50 tons. This pulls the cable taught and makes a stable working platform. Now, 4 other cables are hard bolted both to the 4 corners of the circular reel that's anchored in space and to high strength bolts at ground level. To make the cable stiff so that the car does not scrape against the edges, a simple rail holds onto the 4 other cables and uses them for support. Now, the elevator is complete. To increase the holding capacity of the elevator, you simply increase the weight. A 20 ton weight might pull 50 tons. Bring up another 20 ton weight and you can bring up 100 tons next time. Then you can bring up 250 tons until you can carry huge cargoes, limited only to the strength of the cable (which can also be doubled by adding more thread). Eventually, just below the geosynch point, a you can find a full terran gee in orbit, caused because everything below the geosynch point will be moving slower than orbital velocity. The weight on the other hand makes a nice spot for a full terran gee facing outward, with the sun at your feet and the Earth at your head. The geosynch point allows for large space stations to be built. This system can be expanded until a full fledged elevator can be built. However, even with this new full fledged elevator, the lift would still remain important for many decades afterwards.
I have included a second illustration that shows a quintuple lift and reel system and a single lift and reel cable. Black lines are supports and red lines are lift cables. The little black spot near the single lift elevator is a proposed geosynch space station. The thick cable that attaches to the quintuple lift connects to a large asteroidal anchor.
This, however, just covers the lift systems. My ideas stretch into the full sized elevator too. My design sees a large half mile wide cable that extends from a large 100 mile tower. The base, either built into the land or the sea, would extend some feet under the actual boarding and departing areas. This would make room for a toroidal turnaround area. Cars would come down, unload and then go down a tunnel where they would automatically turn around and shift onto the other track to go back up. As I said earlier, having set tracks going up and down allow traffic to be increased a hundredfold.
Possibly the most innovative idea I've ever had when talking about space elevators was my idea that, if workable, could make the first 120,000 feet of the cable (and tower) "weightless". Simply attaching balloons onto the side of the cable would lift the building and nullify its weight. Now, no balloon could counteract the weight of 120,000 feet of cable, so rather than have a balloon, we have no balloon whatsoever. Actually, what we would use is a high-strength (probably nanotube) material that is extremely light to house vacuums. Nothing floats better than nothing and the larger the area of the "nothing" the greater the lift. A 1x1x1' box of vacuum out of nanotube might provide the lift to pull a child into the air. Lots of these chambers spread out over the entire side of the cable that's in the atmosphere might be able to nullify and even counteract the force of gravity.
Section IV: Possible Effects on the Industry of Terra and Luna
"When you do the math, this comes out to be about the 15,858,000th floor."
I cannot even begin to express my feeling on the effects of a space elevator on Lunar/Terran industry. A few tons of algae could go up one day and return a month later as some miracle cure for cancer. After the basic cable is constructed, which would have the capability of lifting space station components of about 200 tons, a large scale manufacturing plant could be constructed. Prefabricated systems could be developed on Earth and transported up. Complex or heavy components could be built on Earth. Eventually, the space station could grow into a large sprawling city, with a central shaft about 50 feet wide, a large rotating ring habitat, a large shipbuilding facility in orbit, a large industrial complex, large manufacturing centers and even a huge research park full of research modules connected to a main grid of transfer tubes. Later on, other elevators could be constructed. With the advent of the quintuple lift elevator, a space station up to three miles wide could be passed through into orbit. The industry would be very well developed by the time a full scale lunar lift would be constructed. There are two ways to go about this. The selenosynch point (the geosynchronous point over Luna) is about 1/6 the distance from the lunar surface, so it would make an ideal short elevator. Another design proposes stretching the elevator a few hundred thousand miles to the Earth/Luna lagrange point and suspending the cable there. This would allow lunar materials to be shipped farther out into space before being picked up by a tug and being brought back to Earth. Also, this would lessen the time to get to Luna itself. A shipment of 100 tons of lunar ore might fetch 10 million dollars on a 2070+ market. With the space elevator, it might cost 100,000 dollars to get from Luna to Earth with 100 tons of ore. That's 9.9 million dollars return, excluding the drastically reduced price of setting up a mining station.
"You see that train? That's the war machine. All sorts of weapons come down there from full size battleships to tanks and artillery pieces. I even saw a submarine come down once. All this industry is making ZzapWorks a great power along the equator."
With the prices of ore and manufacturing decreasing, one must look at this from a militaristic point of view. To a general planning an assault, this is too good to be true. The space elevator has the potential to be turned into a very potent weapons. If every manufacturing plant was devoted toward building an army and all of the trains going down carried military pieces, then you could amass an army, navy and air force larger than anything ever seen on the planet in a month. You could have enough to be considered a "respectable adversary" in a week. So therefore, he who controls the elevator could control the world. After finding enough men, the owner of the elevator has the capability to make a planet dominating army in a few weeks. Simply put, once some strategist realizes this in 2080 or so, people are going to be scrambling for the equator. You wouldn't be able to stop nations from building their own elevators just for the sole purpose of maintaining the ability to compete with the owner of the first one. As people realize that space based elevators are extremely vulnerable to space based attacks, they will begin to develop space based weapons and this new space race would cause a boost in technology. Of course, the large number of weapons would undoubtedly work as a deterrent to full scale war, at least among more logical and methodical countries, such as Canada, America, Russia, France and England. However, African nations might fight over control rights and wars would very well erupt over control of a cable or two. However, this is just our violent nature and cannot be prevented. A cable will lead to war eventually.
"I look up at that cable every day. I tell myself, we made it, it's Earthly. It's made out of buckyballs and such, but I can't help but think of the tower of Babel. And Led Zepplin. It reminds me of him to. " And my spirit is crying for reason..." But that's a different story."
On To Mars
While I talk about the effects of a space elevator on Mars in the next section, I talk about using a Terran one to get to Mars in this section. Now, in order for for it to take 6 days to reach the geosynchronous point, the car on the cable has to move at a constant speed of 208 miles per hour. Rather than suddenly accelerate people to this velocity (about 268 feet per second) and create Space Elevator's Patent Strawberry Jam, we would slowly accelerate to more than 208 miles per hour until we reached 15,000 miles per hour. The result is that it take the same amount of time because the slow acceleration fills in the time gap. Now, a spacecraft being launched on the cable going to Mars would just continue to accelerate. By the time it reached the bottom, it might be going 17,000 miles per hour, enough to reach Mars in about 2 years, yet carrying everything needed to create a research and exploration base on the planet. Because the elevator knows no bounds, a whole fleet of spacecraft could be flung out toward Mars. After braking, some would land on the surface and some would begin a Martian elevator, which would only need to be about 20,000 miles high.
Section V: Terraforming and Colonization Effects on Mars
"I think since 2100, exactly 10 people have landed on the Martian surface. I think the other 10 or so billion walked."
Building the Martian Lift
Building a Martian lift system, much like the primitive lift that I described earlier in section III could very well make for the rapid exploration of Mars. A single reel of tether with four other anchoring reels to anchor it might cost 10 billion dollars. The effects of such a system at early stages during Mars exploration would be very beneficial. Large pieces of equipment could be moved down to the planet very quickly and cheaply. Bulky life-support and mining equipment could be sent down and a huge city might develop around the base of this elevator. But these are only effects. Actually transporting these materials to Martian orbit, deploying them and bringing in the supplies to use the elevator would cost more than a few hundred billion dollars and, except for the corporation or country that owns the Terran space elevator, it might be all but out of reach.
However, despite all of these monetary problems, the Martian elevator would be fairly simple. The tether and reel system mentioned before would be extremely easy to construct. Just drop the anchors down onto the planet, have the robots place them accordingly and drop a habitat and you're ready to begin.
"Congratulations Gossamer Albatross, you've just become the bridge to the new world."
The Effect Two weeks after the first elevator is constructed on Mars, I imagine that
we could have a habitat for 100 people in a large pressurized dome, air mining, a temporary gas flow (for oxygen/water), exploration via heavy two story rovers and dirigibles. Virtually any type of heavy equipment from a large jet engine mining water and oxygen from the atmosphere to a fleet of nuclear reactors could be deposited on Mars and moved. First, I imagine that we would need to create a human presence. A small habitat for 5 people could be lowered down to the surface and these 5 people would supervise the deposit of all materials, then, a temporary shelter for 30 would be erected while automated robots were at work creating a dome habitat. Eventually, after two weeks, about the time it takes to drop off two loads, we could have a permanent human base ready to begin the exploration, colonization and eventual terraforming of Mars.
"There were three ships ahead of them, the Soaring Albatross, the Wandering Albatross and the Royal Albatross, all carrying equipment, the Soaring, the elevator equipment, the Wandering, the sustanance for two years, the Royal, the heavy machinery. The Gossamer Albatross carried the most important cargo of all, the human drones to supervise the machines."
It will take quite an effort to construct the estimated four ships needed to bring all of the materials to Mars. The first three ships would be extended versions of the STS external fuel tanks, approximately 100 meters long, hollow, containing guidance systems, ion engines and large cargo holds. One would carry the space elevator parts, one would carry the foodstuffs required for an extended stay and the other would carry the heavy machinery for setting up base. These would all be slow ships, launched approximately one year before the crew ship would be launched, utilizing a faster means of propulsion (VASIMR? M2P2? Magnetoplasma? Fission/Fusion?) and arrive a little after 5 months after the first ships entered orbit.
Although it may not seem relevant to this topic, the means of getting the elevator material to Mars is almost as important as the elevator itself. Without materials to work with, a building a Martian elevator is impossible, as I'm sure you can see.
"It's like a disease. We build this huge spike and stuck it in Mars and everywhere around it, these humans are ripping up the land. Look at it in a fast-paced footage from the Albatross' footage. You can see it. In ten years, humanity has spread like... Like E. Coli on room temperature canadian bacon—maple cured."
This is the biggie. With a true dedicated space elevator running a train system, not a lift, we could truly change the face of Mars.
For one, gasses essential to terraforming could be funneled down the elevator and released from cars at exactly the right altitude, or they could be placed in storage at the base and distributed evenly among the planet. Carbon dioxide could be moved up the cable for processing into methane and oxygen, one of which can be used as a greenhouse gas, the other of which can be inhaled. Terraforming equipment (miners, laboratories and factory equipment) could be moved down to Mars with ease and terraforming might take years less than would normall be required.
On my personal uneducated (to the moment) estimate, I would say that the high end estimate for terraforming with a cable and without a cable would be about 200 years to 150 years, with a cable. I would say, on the low end, that with a cable, terraforming would take 40 years, without a cable, 80. Even to an unaided eye, the potential benifits for colonization and terraforming are plainly obvious. I would like to say...
"I wanted it to be on Mars. I wanted it to be on Mars."
Anybody who says we don't have any use for a space elevator is clearly wrong. Anybody who says that space elevators are uneconomical, or laboratory marvels that have no real applications are clearly wrong. I accept that, in some respects, other launch systems would be better than a space elevator. A person in a hurry might take a rocket rather than a car, which would take 6 days to the rocket's 15 minutes. Heavy cargoes that are not really delicate (solar power satelites, ores) might be better served on a large railgun. But such advocates of these systems commonly forget that no system is good for everything and that having closed minds got us in the sorry state we are in now.
But dollar for dollar, a space elevator is simply the most economical space transportation system that there is, and there is no arguing about that.
3) Space.com Space Elevator article
4) Space.com Carbon Nanotubes article