1. Introduction. Fig1. This shows the basic structure of a space elevator

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1 1. Introduction A space elevator is a proposed mega structure designed to transport material from a celestial body s surface into space as a way of nonrocket space launch. The term most often refers to a structure that reaches from the surface of the Earth to geosynchronous orbit (GSO). The concept of a structure reaching to geosynchronous orbit was first conceived by Konstantin Tsiolkovsky. Who proposed a compression structure or Tsiolkovsky Tower. Space elevators have also sometimes been referred to as beanstalks, space bridges, space ladders, skyhooks, orbital towers, or orbital elevators. Fig1. This shows the basic structure of a space elevator The key concept of the space elevator appeared in 1895 when Russian Scientist Konstantin Tsiolkovsky was inspired by the Eiffel Tower in Paris to consider a tower that reached all the way into s0pace, built from the 1

2 ground up to an altitude of 35,790 kilometers above sea level (geostationary orbit). Tsiolkovsky s tower would be able to launch objects into orbit without a rocket. Unlike more recent concepts for space elevators. Tsiolkovsky s (conceptual) tower was a compression structure, rather than tension (or tether ) structure. Fig2. This shows Eiffel tower in Paris What is the need of a space elevator: - It is to move pay loads and people into the orbit of earth and asteroid mars and beyond with low cost. 2

3 2. History The idea of building a tower from the surface of the Earth into space, the sky, or the heavens dates back to some of the very earliest known manuscripts in existence. The writings Moses, about 1450 B.C. in his book Genesuis, chapter 11, reference an earlier civilization that in about 2100 B.C. tried to build a tower to heaven out of brick and tar. This stricture is commonly called the Tower of Mesopotamia. Later in chapter 28, about 1900B.C Jacob had a dream about a staircase or ladder built to heaven, commonly called Jacob s ladder. More contemporary writings on the subject date back to K.E. Tsiolkovski in his manuscript Speculations about Earth and Sky and on Vesta, published in The idea for building a tower from surface of the Earth into space has been dreamed of invented and reinvented many times throughout modern civilization. The first published a account describing a space elevator that recognized the utility of geosynchronous orbit did not occur until In 1975 Jerome Pearson working at the Air Force Research Laboratory, also independently in invented the space elevator and published a technical paper Acta Astronautica. This publication brought the concept to the attention of the space flight community. Pearson later participated in the NASA Marshall Tether workshops beginning in 1983, and brought the space elevator concept into the space tether technical community. 3

4 3. Primary Technology Thrust There are five primary technology thrusts as critical to the development of the elevator:- First was the development of high-strength materials for the both the cables and the tower. In a Researcher noted that maximum stress (on space elevator cable) is at geosynchronous altitude so the cable must be thickest there and taper exponentially as it approaches Earth. Fiber materials such as graphite, alumina, and quartz have exhibited tensile strengths greater than 20 Pa (Giga-Pascals, a unit of measurements for tensile strength) during testing for cable tethers. The desired strength for the space elevator is about 62 GPa. Carbon nanotubes have exceeded all other materials and appear to have a theoretical strength far above the desired range for space elevator structures. Second technology thrust was the continuation of tether technology development to gain experience in the deployment and control of such long structures in space. Third was the introduction of lightweight, composite structural materials to the general construction industry for the development of taller towers and buildings. Fourth was the development of high-speed, electromagnetic propulsion for mass-transportation systems, launch systems, launch assist systems and high-velocity launch rails. These are, basically, higher speed version of the Trans now used at airports to carry passengers between terminals. They would float above the track, propelled by magnets, using no moving parts. This feature would allow the space elevator to attain high vehicle speeds without the wear and tear that wheeled vehicles would put on the structure. 4

5 Fifth was the development of transportation, utility and facility infrastructures to support space constriction and industrial development from Earth out to GEO. The high cost of constructing a space elevator can only be justified by high usage, by passengers and payload, tourists and space dwellers. 5

6 4. Ideas of development of space elevator Twentieth century Building a compression structure from the ground up proved an unrealistic task; there was no material in existence with enough compressive strength to support its own weight under such condition. In 1959 another Russian scientist Yuri N Artsutanov suggested a more feasible proposal. Artsutanov suggested using a geosynchronous satellite as the base from which to deploy the structure downward. By using a counterweight, a cable will be lowered from geosynchronous orbit 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. Artsutanov's idea was introduced to the Russian-speaking public in an interview published in the Sunday supplement of Komsomolskaya Pravda (usually named in English, "Young Person's Pravda") in 1960, but was not available in English until much later. He also proposed tapering the cable thickness so that the tension in the cable was constant this gives a thin cable at ground level, thickening up towards GEO. Making a cable over 35,000 kilometers long is a difficult task. In 1966, Isaacs, Vine, Bradner and Bachus, four American engineers, reinvented the concept, 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, assuming it would be a straight cable with no variations in its cross section, and found that the strength required would be twice that of any existing material including graphite, quartz, and diamond. In 1975 an American scientist, Jerome Pearson, reinvented the concept yet again, publishing his analysis in the journal Acta Astronautica. He designed a tapered cross section that would be better suited to building the elevator. The completed cable would be thickest at the geosynchronous 6

7 orbit, where the tension was greatest, and would be narrowest at the tips to reduce the amount of weight per unit area of cross section that any point on 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. In 1977, Hans Moravec published an article called "A Non- Synchronous Orbital Skyhook", in which he proposed an alternative space elevator concept, using a rotating cable, in which the rotation speed exactly matches the orbital speed in such a way that the instantaneous velocity at the point where the cable was at the closest point to the Earth was zero. This concept is an early version of a space tether transportation system. In 1979, space elevators were introduced to a broader audience with the simultaneous publication of Arthur C. Clarke's novel, The Fountains of Paradise, in which engineers construct a space elevator on top of a mountain peak in the fictional island country of Taprobane (loosely based on Sri Lanka, albeit moved south to the equator), and Charles Sheffield's first novel, The Web Between the Worlds, also featuring the building of a space elevator. Three years later, in Robert A. Heinlein's 1982 novel Friday the principal character makes use of the "Nairobi Beanstalk" in the course of her travels. Kim Stanley Robinson's Mars trilogy chronicles the fictional settlement and terraforming of Mars and a space elevator is a focus point for one of the plotlines. In 1999, Larry Niven authored the book Rainbow Mars which contained a "Hanging Tree" - an organic 'Skyhook' which was capable of interstellar travel. The book skillfully discussed several 7

8 merits/demerits of such an approach to the Beanstalk - the primary demerit being that the water necessary to sustain such an enormous 'tree' would require the drying up of all of its host planet's water bodies - which is used as a plot device to explain the drying up of Mars. Twenty first century 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 an orbital skyhook 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, "s: An Advanced Earth-Space Infrastructure for the New Millennium", provides an introduction to the state of the technology at the time, and summarizes the findings. Another American scientist, Bradley C. Edwards, suggested creating a 100,000 km long paper-thin ribbon using nanotube fibers, suggesting that this structure would stand a greater chance of surviving impacts by meteoroids. Supported by the NASA Institute for Advanced Concepts, the work of Edwards was expanded to cover the deployment scenario, climber design, power delivery system, orbital debris avoidance, anchor system, surviving atomic oxygen, avoiding lightning and hurricanes by locating the anchor in the western equatorial Pacific, construction costs, construction schedule, and environmental hazards. The largest holdup to Edwards' proposed design is the technological limits of the tether material. His calculations call for a fiber composed of epoxy-bonded carbon nanotubes with a minimal tensile strength of 130 GPa (including a safety factor of 2); however, tests in 2000 of individual single-walled carbon nanotubes (SWCNTs), which should be notably stronger than an epoxy-bonded rope, indicated the strongest measured as 52 GPa. Multi-walled carbon nanotubes have been measured with tensile strengths up to 63 GPa. 8

9 In order to speed development of space elevators, proponents are planning 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 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 has announced that it will be building a carbon nanotube manufacturing plant in Millville, New Jersey, to supply various glasses, 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 group also announced that they had obtained permission from the Federal Aviation Administration to use airspace to conduct preliminary tests of its high altitude robotic lifters. The experiment was successful. 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. On August 24, 2006 the Japanese National Museum of Emerging Science and Technology in Tokyo has started to show the animation movie '', based on ATA Project, also directed and edited by project leader, Dr. Serkan Anilir. This movie shows a possible image about the cities of future, placing the space elevator tower as a new infrastructure into the city planning, and aims to contribute children education. Currently, the movie is shown in all science museums in Japan. The x-tech Projects Company has also been founded to pursue the prospect of a commercial. In 2007, Elevator:2010 held the 2007 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. 9

10 5. Structure of space elevator For constructing a space elevator there should be a structure for it. Therefore the space elevator has a structure they are listed below Base station:- Ψ Base station Ψ Cable Ψ Lifter Ψ Anchor station Ψ Counter weight Ψ Power beam The base station designs typically fall into two categories mobile and stationary. Mobile stations are typically large oceangoing vessels, though airborne stations have 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. 10

11 Fig3. This shows a mobile base station which will be situated in the ocean. Cable:- The cable must be made of a material with a large tensile strength/density ratio. Carbon nanotubes would be a highly useful material for creating a space elevator By comparison, most steel has a tensile strength of less than 2 GPa, and the strongest steel resists no more than 5.5 GPa, but steel is dense. The much lighter material Kevlar has a tensile strength of GPa, while quartz fiber and carbon nanotubes can reach upwards of 20 GPa; the tensile strength of diamond filaments would theoretically be minimally higher. 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. Even the strongest fiber made of nanotubes is likely to have notably less strength than its components. Carbon nanotubes have the potential to be 100 times stronger than steel and are as flexible as plastic. The strength of carbon nanotubes comes from their unique structure which resembles like a soccer ball. 11

12 Fig4. This shows the structure of a carbon nanotube. Fig5. This shows the structure of many carbon nanotubes joined together. The cost of carbon nanotubes will be $25/gram. 12

13 Lifter:- The robotic lifter will use the ribbon to guide its ascent into space. Traction-tread rollers on the lifter would clamp on to the ribbon and pull the ribbon through, enabling the lifter to climb up the elevator. Anchor Station:- The space elevator will originate from a mobile platform in the equator Pacific, which will anchor the ribbon to Earth. Counterweight:- At the top of the ribbon, there will be a heavy counterweight. Early plans the space elevator involved capturing an asteroid and using it as a counterweight. However, more recent plans like those of LiftePort and the institute for Scientific Research (ISR) include the use of a man-made counterweight. In fact the counterweight might be assembled from equipment used to build the ribbon including the spacecraft that is used to launch it. 13

14 Fig6. This figure shows the counter weight fixed at the top Power Beam:- The lifter will powered by a free-electron laser system located on or near the anchor station. The laser will beam 2.4 megawatts of energy to photovoltaic cells, p[perhaps made of Gallium Arsenide (GaAS) attached to the lifter, which will then convert that energy to electricity to be used by conventional, niobium-magnet DC electric motors, according to the ISR. 14

15 6. Launching into outer space The velocities that might be attained at the end of Pearson s 144,000km cable cab are determined. The tangential velocity is kilometers per second which is more than enough to escape Earth s gravitational field and send probes as far out as Saturn. If an object were allowed to slide freely along the upper part of the tower, a velocity high enough to escape the solar system entirely would be attained. This is accomplished by trading off overall angular momentum of the tower for velocity of the launched object, in much the same way one snaps a towel or throws a lacrosse ball. After such an operation a cable would be left with less angular momentum than required to keep its geostationary position, the rotation of the Earth would them pull on the cable increasing its angular velocity, leaving the cable swinging backwards and forwards about its starting point. For higher velocities, the cargo can be electromagnetically accelerated, or the cable could be extended, although that would require additional strength in the cable. 15

16 7. Failure modes, safety issues and construction difficulties As with any structure, there are a number of ways in which things could go wrong. A space elevator would present a considerable navigational hazard both to aircraft and spacecraft. Aircraft could be dealt with by means of simple air-traffic control restriction but impacts by space objects pose a more difficult problem. Satellites:- In nothing were done, essentially all satellites with perigees below the top of the elevator would eventually collide with the elevator cable. Twice per day each orbital plane intersects the elevator, as the rotation of the Earth swings the cable around the equator. Corrosion:- Corrosion is a major risk to any thinly built tether (which most designs call for). In the upper atmospheres, atomic oxygen steadily eats away at most materials. A tether will consequently need to either be made from a corrosion-resistant material or have corrosionresistant coating, adding to weigh. Radiation:- The effectiveness of the magnetosphere to deflect radiation emanating from the sun decreases dramatically after rising several earth radii above the surface. This ionizing radiation may cause damage to materials within both the tether and climbers. Materials defects:- Any structure as large as a space elevator will have massive numbers of tiny defects in the construction material. It has been suggested, that because large structures have more defects than small structures, that large strictures are inherently weaker than small, giving an estimated carbon nanotube strength of only 24 GPa down to only 1.7 GPa in millimeter-scale sample. 16

17 Weather:- In the atmosphere the risk factors of wind and lightning come into play. The basic mitigation is location. As long as the tether s anchor remains within two degrees of the equator, it will remain in the quiet zone between the Earth s Hadley cells, where there is relatively little violent weather. Vibration harmonics:- A final risk of structural failure comes from the possibility of vibration harmonics within the cable. Like the shorter and more familiar strings of stringed musical instruments, the cable of a space elevator has a natural resonant frequency. If the cable is excited at this frequency, for example by the travel of elevators up and down it, the vibrational energy could build up to dangerous levels and exceed the cable s tensile strength. This can be avoided by the use of suitable damping systems within the cable, and by scheduling travel up and down the cable keeping its resonant frequency in mind. Cut near the anchor point:- If the elevator is cut at its anchor point on Earth s surface, the outward force exerted by the counterweight would cause the entire elevator to rise upward into an unstable orbit Cut to about 25,000 km:- If the break occurred at the higher altitude, up to about 25,000 km, the lower portion of the elevator would descend to Earth and drape itself along the equator east of the anchor point, while the now unbalanced upper portion would rise to a higher orbit. Political issues:- One potential problem with a space elevator would be the issue of ownership and control. Such an elevator would require significant investment (estimate start at about US$5 billion for a very primitive tether), and it could take at least a decade to recoup such expenses. 17

18 Terrorist attack:- Another major problem is the terrorist attack. Once they have attacked the world trade center. Here the terrorist may attack the space elevator. 18

19 8. Other concepts * Low-Earth orbit space elevator concept [LEO] * Mars space elevator concept * Moon space elevator concept LEO space elevator concept:- The LEO space elevator concept is an intermediate version of the earth surface to GEO space elevator concept, and appears to be feasible today using high strength materials and space technology Mars space elevator concepts:- At mars, proposal have been studied for tethered elevator type structures in a low-mars orbit, and extended from the moon in orbit around the planet Phobos and Deimos. Both moons in orbital plane around mars at near equatorial inclinations. 19

20 Fig7. The structure of LEO space elevator concept 20

21 Fig8. A mars space elevator concept model 21

22 9. Some of the pictures related to space elevator Fig9. Carbon nano tubes rolled to form its structure 22

23 Carbon nanotubes Power beam Base station Fig10. The space elevator 23

24 Fig11. Different types of carbon nanotubes 24

25 Working model Accenting to the top of the building Fig12. Working models of space elevator 25

26 10. Conclusion We know that space elevator is a proposed mega structure designed to transport material from a celestial body s surface into space as a way of non-rocket space launch. So imagine such a structure which could move payloads and people into the orbit of earth with low cost other than using much hydrogen fuel as the propulsion. The entry of space elevator will change the world. The entry will lead to the space tourism, the launching of space satellites etc. Let us pray to god for the better future of the development of space elevator and the soon arrival of space elevator and the dream of many astronauts and scientist come into the near future. 26

27 11. Reference