A free standing tower is one for which the tension drops to zero at both ends, requiring no restraint at either end to keep the tower in place. In contrast, for an element above the geostationary height, the centrifugal force F C exceeds the weight W and hence F U < F D for equilibrium, implying that the tension in the tower decreases as a function of height past the geostationary height. These two preceding statements imply that the tension in the tower increases with height from ground level to geostationary height. For an element below geostationary height, the weight force W exceeds the centrifugal force F C and one must have F U > F D for equilibrium. The vector sum of these four forces must vanish if the element is in equilibrium.įor an element at geostationary height (that is, at a distance from the Earth’s center equal to the radius of geostationary orbit) the weight and centrifugal forces are equal ( W = F C ), and therefore the tension forces at the two ends must also be equal ( F U = F D ) for equilibrium. 1(b), which shows the four forces acting on a small element of the tower: an upward force F U due to the portion of tower above the element, a downward force F D due to the portion of tower below the element, a downward force W due to the weight of the element, and a (fictitious) upward centrifugal force F C on the element due to its presence on the rotating Earth. This point can be understood by looking at Fig. A free standing tower is in tension along its entire length, with the tension adjusting itself so that each element of the tower is in equilibrium under the action of the gravitational, centrifugal, and tension forces acting on it. What is the height of a free standing tower of constant density and constant cross sectional area at the Earth’s equator? A free standing tower is one whose weight is counterbalanced by the outward centrifugal force on it, so that it exerts no force on the ground beneath it. Despite this publicity, the idea of the elevator did not really catch on among scientists because an analysis of its structure showed that no known material was strong enough to build it. In 1978 Arthur Clarke brought the idea to the attention of the general public through his novel Fountains of Paradise 5 and at about the same time Charles Sheffield, a physicist, wrote a novel 6 centered on the same concept. ![]() 3 The concept was rediscovered by the American engineer, Jerome Pearson, 4 in 1975. In more recent times the concept of the space elevator was first proposed by the Russian physicist Konstantin Tsiolkovsky in 1895 and then again by the Leningrad engineer, Yuri Artsutanov, in 1960. The earliest mention of anything like the elevator seems to have been in the book of Genesis, which talks of an attempt by an ancient civilization to build a tower to heaven (the “Tower of Babel”) that came to naught because of a breakdown of communication between the participants. As such, it is well worth studying and thinking about for all the possibilities it has to offer.īefore discussing the physics of the space elevator, we recall some of the more interesting facts of its history. Whether that happens or not, the space elevator represents an application of classical mechanics to an engineering project on a gargantuan scale that would have an enormous impact on humanity if it is realized. Liftport’s website features a timer that counts down the seconds to the opening of its elevator on 12 April 2018. ![]() 1 Partly as a result of this study, a private organization called Liftport 2 was formed in 2003 with the goal of constructing a space elevator and enlisting the support of universities, research labs, and businesses that might have an interest in this venture. ![]() NASA commissioned some studies of the elevator in the 1990s that concluded that it would be feasible to build one and use it to transport payload cheaply into space and also to launch spacecraft on voyages to other planets. Although the idea of such a structure is quite old, it is only within the last decade or so that it has attracted serious scientific attention. A space elevator is a tall tower rising from a point on the Earth’s equator to a height well above a geostationary orbit, where it terminates in a counterweight.
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