Seminar Report 2008-2009 Space Elevator 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 non- rocket 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 Dept of E&I G.P.T.C. Koratty 1 Seminar Report 2008-2009 Space Elevator 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. Dept of E&I G.P.T.C. Koratty 2 Seminar Report 2008-2009 Space Elevator 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 1895. 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 1960. 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. Dept of E&I G.P.T.C. Koratty 3 Seminar Report 2008-2009 Space Elevator 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. Dept of E&I G.P.T.C. Koratty 4 Seminar Report 2008-2009 Space Elevator 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. Dept of E&I G.P.T.C. Koratty 5 Seminar Report 2008-2009 Space Elevator 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 Dept of E&I G.P.T.C. Koratty 6 Seminar Report 2008-2009 Space Elevator 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 Dept of E&I G.P.T.C. Koratty 7 Seminar Report 2008-2009 Space Elevator 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.