You might think of this section as science fiction. A Space Elevator? Read on. You'll be surprised. You can also skip over some of this if it gets too technical. Just get the main points.
I believe it was Sir Arthur C Clarke who coined the term -- The Space Elevator. The idea is this: It is very costly and dangerous to ferry people and stuff out of Earth's atmosphere -- just to Low Earth Orbit (LEO). We need to travel up to 17,500 mph (25,000 kph), to get there. As we bitterly know, we have lost two Space Shuttles, and a lot of people trying to hone our way into LEO. Further, the fuel expended to carry us to orbit is enormous. Large rockets and booster rockets. And LEO is only between 100 and 1200 miles above the Earth. (While LEO is stated to be up to 1200 miles, we have no vehicles that can reach that altitude. Isn't that a shame).
Once in LEO, it's actually not too tough to move lots of stuff and people with very little fuel.
So what if there was an easier way?
Enter the idea of a Space Elevators. These vehicles would ferry people and supplies above the atmosphere. From there, ferries would not have to spend much fuel to carry people and things to Space Stations, to the moon, and beyond.
So, science fiction? Read on.
At MIT and at Cambridge, in private industry in he US and around the world, this concept of Space Elevators is being taken very seriously. In fact manufacturing techniques are being invented and built as I write this.
Before you scoff, remember we have built tunnels under the Alps and the English Channel. We are only limited by our imagination.
There are several techniques being devised for an Elevator. One requires mass production of artificial diamonds -- imagine looking up on a moonlit night and seeing a diamond studded line to the heavens. A second technique involves the large-scale creation of "nanotubes". These are tiny -- microscopic -- chains that are linked together like a christmas decoration.
Let me tell you how this idea came about, and what is being worked on and thought about today:
In 1959 another Russian scientist, Yuri N. Artsutanov, resurrected the idea with a more feasible proposal. Artsutanov suggested using a geostationary satellite as the base from which to deploy the structure downward. By using a counterweight, a cable would be lowered from geostationary orbit (GSO) to the surface of Earth, while the counterweight was extended from the satellite away from Earth, keeping the center of gravity of the cable motionless relative to Earth. He further proposed to taper the cable thickness so that the tension in the cable was constant—this gives a thin cable at ground level, thickening up towards GSO. Artsutanov's idea was introduced to the Russian-speaking public in an interview published in the Sunday supplement of Komsomolskaya Pravda in 1960, but was not available in English until much later.
As you can imagine, making a cable over 35,000 kilometers long is a difficult task.
In 1966, four American engineers (Isaacs, Vine, Bradner and Bachus), reinvented the concept in the west, naming it a "Sky-Hook," and published their analysis in the journal Science. They decided to determine what type of material would be required to build a space elevator. However, they found that the strength required would be twice that of any existing material including graphite, quartz, and diamond. That seemed to doom the idea.
In 1975 an American scientist, Jerome Pearson, reinvented the concept yet again, publishing his analysis in the journal Acta Astronautica. He proposed a tapered cross section. The completed cable would be thickest at the geostationary orbit, where the tension was greatest, and would be narrowest at the tips to reduce the amount of weight that the cable would have to bear.
He suggested using a counterweight that would be slowly extended out to 144,000 kilometers (almost half the distance to the Moon) as the lower section of the elevator was built. Without a large counterweight, the upper portion of the cable would have to be longer than the lower due to the way gravitational and centrifugal forces change with distance from Earth. His analysis included disturbances such as the gravitation of the Moon, wind, and moving payloads up and down the cable. The weight of the material needed to build the elevator would have required thousands of Space Shuttle trips, although part of the material could be transported up the elevator when a minimum strength strand reached the ground or be manufactured in space from asteroidal or lunar ore. This was a grand idea but beyond our reach. If only it had been looked on as a global enterprise. Anyway....
In 1977, Hans Moravec published an article called "A Non-Synchronous Orbital Skyhook", in which he proposed an alternative scheme, using a rotating cable, in which the rotation speed exactly matches the orbital speed. At the point where the cable was at the closest point to the Earth there would be no rotation. This concept is an early version of the current space tether transportation system ideas.
To hear Dr. Fuller in his own words, click on his picture.
Here is a grand example. The Eden Project
Bucky, as he liked to be called, then took his concept to the molecular level, where he and others designed incredibly strong molecules that bond together originally called Buckyballs. Nanotubes are a refinement to Buckyballs or as they are called nowadays -- Fullerines. It is these nanotubes that could make Space Elevators a reality.
Most recent discussions focus on tensile structures (specifically, tethers) reaching from geostationary orbit (approximately 23,000 miles high) to the ground. These structures would be held in tension between Earth and counterweights in space like a guitar string held taut. Note that in the literature, space elevators have also sometimes been referred to as beanstalks, space bridges, space lifts, space ladders, skyhooks, orbital towers, or orbital elevators.
After the development of carbon nanotubes in the 1990s, engineer David Smitherman of NASA/Marshall's Advanced Projects Office realized that the high strength of these materials might make the concept of a Space Elevator feasible, and put together a workshop at the Marshall Space Flight Center, inviting many scientists and engineers to discuss concepts and compile plans for an elevator to turning the concept into a reality. The publication he edited compiling information from the workshop, "Space Elevators: An Advanced Earth-Space Infrastructure for the New Millennium" summarized the state of the technology at the time.
When he started, the largest impediment to Edwards' proposed design was the technological limits of the tether material. His calculations called for a fiber, composed of epoxy-bonded carbon nanotubes. However, tests in 2000 of individual single-walled carbon nanotubes (SWCNTs), indicated that even the nanotube technology of that time would be up to the task.
In order to speed development of space elevators, proponents, including Dr. Edwards, have organized several competitions, similar to the Ansari X Prize, for relevant technologies.
Among them are Elevator:2010 which will organize annual competitions for climbers, ribbons and power-beaming systems, the Robolympics Space Elevator Ribbon Climbing competition, as well as NASA's Centennial Challenges program which, in March 2005, announced a partnership with the Spaceward Foundation (the operator of Elevator:2010), raising the total value of prizes to US $400,000.
In 2005, the LiftPort Group of space elevator companies announced that it will be building a carbon nanotube manufacturing plant in Millville, New Jersey, to supply various glass, plastic and metal companies with these strong materials. Although LiftPort hopes to eventually use carbon nanotubes in the construction of a 100,000 km (62,000 mile) space elevator, this move will allow it to make money in the short term and conduct research and development into new production methods.
The first space elevator is proposed to launch in 2010. On February 13, 2006, the LiftPort Group announced that, earlier the same month, they had tested a mile of "space-elevator tether" made of carbon-fiber composite strings and fiberglass tape measuring 5 cm wide and 1 mm (approx. 6 sheets of paper) thick, lifted with balloons.
The US is now not alone with this research and development.
On August 24, 2006, the Japanese National Museum of Emerging Science and Technology in Tokyo started showing the animation movie 'Space Elevator', based on the ATA Space Elevator Project, also directed and edited by the project leader, Dr. Serkan Anilir. This movie shows a possible image of the cities of the future, placing the space elevator tower in the context of a new infrastructure in city planning, and aims to contribute to children's education. From November 2006, the movie is being shown in all science museums in Japan.
The x-Tech Projects company has also been founded to pursue the prospect of a commercial Space Elevator.
In 2007, Elevator:2010 held the 2007 Space Elevator games which featured US $500,000 awards for each of the two competitions, (US $1,000,000 total) as well as an additional US $4,000,000 to be awarded over the next five years for space elevator related technologies. No teams won the competition, but a team from MIT entered the first 2-gram, 100% carbon nanotube entry into the competition.
Japan held an international conference in November of 2008 to draw up a timetable for building the elevator.
In 2008 the book "Leaving the Planet by Space Elevator" by Dr. Edwards and Philip Ragan, was published in Japanese and entered the Japanese best seller list. This has led to a Japanese announcement of intent to build a Space Elevator at a projected price tag of $8 billion. In a report by Leo Lewis, Tokyo correspondent of The Times newspaper in England, plans by Shuichi Ono, chairman of the Japan Space Elevator Association, are unveiled.
Lewis says: "Japan is increasingly confident that its sprawling academic and industrial base can solve the construction issues, and has even put the astonishingly low price tag of a trillion yen (£5 billion) on building the elevator. Japan is renowned as a global leader in the precision engineering and high-quality material production without which the idea could never be possible."
As you can see, this amazing concept is starting to leave the world of science fiction, and is gaining corporate and government financial support.
So, how will it work?
The centrifugal force of earth's rotation is the main principle behind the elevator. As the earth rotates the centrifugal force tends to align the nanotube in a stretched manner. There are a variety of tether designs. Almost every design includes a base station, a cable, climbers, and a counterweight.
The base station designs typically fall into two categories—mobile and stationary. Mobile stations are typically large oceangoing vessels, though airborne stations have also been proposed as well.
Stationary platforms would generally be located in high-altitude locations, such as on top of mountains, or even potentially on high towers.
Mobile platforms have the advantage of being able to maneuver to avoid high winds, storms, and space debris. While stationary platforms don't have these advantages, they typically would have access to cheaper and more reliable power sources, and require a shorter cable. While the decrease in cable length may seem minimal (typically no more than a few kilometers), the cable thickness could be reduced over its entire length, significantly reducing the total weight.
The cable must be made of a material with a large tensile strength/mass ratio. A space elevator can be made relatively economically feasible if a cable with a density similar to graphite can be mass-produced at a reasonable price. Carbon nanotubes would be a highly useful material for creating a space elevator. Carbon nanotubes' theoretical tensile strength has been estimated between 140 and 177 GPa (depending on plane shape), and its observed tensile strength has been variously measured from 63 to 150 GPa, close to the requirements for space elevator structures.
Nihon University professor of engineering Yoshio Aoki, the director of the Japan Space Elevator Association, has stated that the cable would need to be four times stronger than the strongest carbon nanotube fiber as of 2008, or about 180 times stronger than steel.
Improving tensile strength depends on further research on purity and different types of nanotubes.
By comparison, most steel has a tensile strength of under 2 GPa, and the strongest steel resists no more than 5.5 GPa.
The much lighter material Kevlar has a tensile strength of 2.6–4.1 GPa, while quartz fiber and carbon nanotubes can reach upwards of 20 GPa; the tensile strength of diamond filaments would theoretically be minimally higher.
A seagoing anchor station would incidentally act as a deep-water seaport.
The technology to spin regular VdW-bonded yarn from carbon nanotubes is just in its infancy: the first success in spinning a long yarn, as opposed to pieces of only a few centimeters, was reported in March 2004, but the strength/weight ratio was not as good as Kevlar due to the inconsistent quality and short length of the tubes being held together by VdW.
As of 2006, carbon nanotubes cost $25/gram, and even a minimal, very low payload space elevator "seed ribbon" could have a mass of at least 18,000 kg.
However, this price is declining, and large-scale production could result in strong economies of scale.
Carbon nanotube fiber is an area of energetic worldwide research because the applications go much further than space elevators.
Other suggested application areas include suspension bridges, new composite materials, lighter aircraft and rockets, armor technologies, and computer processor interconnects. This is good news for space elevator proponents because it is likely to push down the price of the cable material further.
A newly discovered type of carbon nanotube called the colossal carbon tube may be strong and light enough to support a space elevator. Its tensile strength is only 6.9 GPa, but its density is only .116 g/cm3, making its specific strength sufficient for a space elevator. In addition, it has been fabricated in lengths on the scale of centimeters, a headstart on the thousands of kilometers needed for a space elevator.
Due to its enormous length a space elevator cable must be carefully designed to carry its own weight as well as the smaller weight of climbers. The required strength of the cable will vary along its length, since at various points it has to carry the weight of the cable below, or provide a centripetal force to retain the cable and counterweight above.
In a 1998 report, NASA researchers noted that: "the maximum stress on a space elevator cable is at geosynchronous altitude so the cable must be thickest there and taper exponentially as it approaches Earth."
Most space elevator designs call for a climber to move autonomously along a stationary cable.
A space elevator cannot be an elevator in the typical sense (with moving cables) due to the need for the cable to be significantly wider at the center than the tips. While various designs employing moving cables have been proposed, most cable designs call for the "elevator" to climb up a stationary cable.
Climbers cover a wide range of designs.
On elevator designs whose cables are planar ribbons, most propose to use pairs of rollers to hold the cable with friction (as in the header image on this page). Usually, elevators are designed for climbers to move only upwards, because that is where most of the payload goes. For returning payloads, atmospheric reentry on a heat shield remains a very competitive option, which also avoids the problem of docking to the elevator in space.
Climbers must be paced at optimal timings so as to minimize cable stress and oscillations and to maximize throughput. Lighter climbers can be sent up more often, with several going up at the same time. This increases throughput somewhat, but lowers the mass of each individual payload.
As the car climbs, the elevator takes on a 1 degree lean, due to the top of the elevator traveling faster than the bottom around the Earth.
The horizontal speed of each part of the cable increases with altitude, proportional to distance from the center of the Earth, reaching orbital velocity at geostationary orbit. Therefore as a payload is lifted up a space elevator, it needs to gain not only altitude but angular momentum (horizontal speed) as well. This angular momentum is taken from the Earth's own rotation.
As the climber ascends it is initially moving slightly more slowly than the cable that it moves onto (Coriolis force) and thus the climber "drags" on the cable.
The overall effect of the centrifugal force acting on the cable causes it to constantly try to return to the energetically favourable vertical orientation, so after an object has been lifted on the cable the counterweight will swing back towards the vertical like an inverted pendulum. Provided that the Space Elevator is designed so that the center of weight always stays above geostationary orbit for the maximum climb speed of the climbers, the elevator cannot fall over. Lift and descent operations must be carefully planned so as to keep the pendulum-like motion of the counterweight around the tether point under control.
By the time the payload has reached GEO the angular momentum (horizontal speed) is enough that the payload is in orbit.
The opposite process would occur for payloads descending the elevator, tilting the cable eastwards and insignificantly increasing Earth's rotation speed.
Both power and energy are significant issues for climbers -- the climbers need to gain a large amount of potential energy as quickly as possible to clear the cable for the next payload.
Nuclear energy and solar power have been proposed, but generating enough energy to reach the top of the elevator in any reasonable time without weighing too much is not feasible.
The proposed method is laser power beaming, using megawatt powered lasers in combination with adaptive mirrors approximately 10 m wide and a photovoltaic array on the climber tuned to the laser frequency for efficiency. A major obstacle for any climber design is the dissipation of the substantial amount of waste heat generated due to the less than perfect efficiency of any of the power methods.
Yoshio Aoki, a professor of precision machinery engineering at Nihon University and director of the Japan Space Elevator Association, suggested including a second cable and using the superconductivity of carbon nanotubes to provide power. There are now annual conferences on this technology.
There have been several methods proposed for dealing with the counterweight need: a heavy object, such as a captured asteroid or a space station, positioned past geostationary orbit, or extending the cable itself well past geostationary orbit. The latter idea has gained more support in recent years due to the relative simplicity of the task and the fact that a payload that went to the end of the counterweight-cable would acquire considerable velocity relative to the Earth, allowing it to be launched into interplanetary space.
Additionally, Brad Edwards has proposed that initially elevators would be up-only, and that the elevator cars that are used to thicken up the cable could simply be parked at the top of the cable and act as a counterweight.
LAUNCHING INTO OUTER SPACE
The velocities that might be attained at the end of Pearson's 144,000 km cable would be more than enough to escape Earth's gravitational field and send probes at least as far out as Jupiter.
Once at Jupiter a gravitational assist manoeuvre permits solar escape velocity to be reached.
Space elevator could also be constructed on other planets, asteroids and moons.
A Martian tether could be much shorter than one on Earth. Mars' surface gravity is 38% of Earth's, while it rotates around its axis in about the same time as Earth. Because of this, Martian areostationary orbit is much closer to the surface, and hence the elevator would be much shorter. Exotic materials might not be required to construct such an elevator. However, building a Martian elevator would be a unique challenge because the Martian moon Phobos is in a low orbit, and intersects the equator regularly (twice every orbital period of 11 h 6 min).
A lunar space elevator can possibly be built with currently available technology about 50,000 kilometers long extending though the Earth-moon L1 point from an anchor point near the center of the visible part of Earth's moon.
On the far side of the moon, a lunar space elevator would need to be very long (more than twice the length of an Earth elevator) but due to the low gravity of the Moon, can be made of existing engineering materials.
Rapidly spinning asteroids or moons could use cables to eject materials in order to move the materials to convenient points, such as Earth orbits or conversely, to eject materials in order to send the bulk of the mass of the asteroid or moon to Earth orbit or a Lagrangian point. This was suggested by Russell Johnston in the 1980s.
Freeman Dyson, a physicist and mathematician, has suggested using such smaller systems as power generators at points distant from the Sun where solar power is uneconomical. For the purpose of mass ejection, it is not necessary to rely on the asteroid or moon to be rapidly spinning.
Instead of attaching the tether to the equator of a rotating body, it can be attached to a rotating hub on the surface. This was suggested in 1980 as a "Rotary Rocket" by Pearson and described very succinctly on the Island One website as a "Tapered Sling".
The construction of a space elevator would be a vast project requiring advances in engineering, manufacturing, and physical technology.
One early plan involved lifting the entire mass of the elevator into geostationary orbit, and simultaneously lowering one cable downwards towards the Earth's surface while another cable is deployed upwards directly away from the Earth's surface.
Alternatively, if nanotubes with sufficient strength could be made in bulk, a single hair-like 18-metric ton (20 short ton) 'seed' cable could be deployed in the traditional way then progressively heavier cables would be pulled up from the ground along it, repeatedly strengthening it until the elevator reaches the required mass and strength. This is much the same technique used to build suspension bridges.
A space elevator would present a considerable navigational hazard, both to aircraft and spacecraft. Aircraft could be diverted by air-traffic control restrictions, but impacts by space objects such as meteoroids and micrometeorites pose a more difficult problem.
With a space elevator, materials might be sent into orbit at a fraction of the current cost. As of 2000, conventional rocket designs cost about US $11,000 per kilogram for transfer to (very) low earth or geostationary orbit. Current proposals envision payload prices starting as low as $220 per kilogram.
West Australian co-author of the book "Leaving the Planet by Space Elevator", Philip Ragan, states that "The first country to deploy a space elevator will have a 95 per cent cost advantage and could potentially control all space activities."
Alternatives to geostationary tether concepts
Many different types of structures ("space elevators") for accessing space have been suggested; However, As of 2004, concepts using geostationary tethers seem to be the only space elevator concept that is the subject of active research and commercial interest in space.
The original concept envisioned by Tsiolkovsky was a compression structure, a concept similar to an aerial mast. While such structures might reach the agreed altitude for space (100 km), they are unlikely to reach geostationary orbit (35,786 km).
The concept of a Tsiolkovsky tower combined with a classic space elevator cable has been suggested.
Other uses for the technology created to build a space elevator include an orbital ring and space tether.
So, a fascinating subject and one that the business and scientific world is taking quite seriously.
If you'd like to follow up on this, I suggest you subscribe to The Space Elevator Blog.
Finally, I'd like to thank my friend Bill Fletcher, for enlightening me to the possibilities of this technology.