Space elevators | Wikipedia audio article
Channel: wikipedia tts
Date: 2018-12-28

This is an audio version of the Wikipedia Article:
https://en.wikipedia.org/wiki/Space_elevator


00:02:57 1 History
00:03:05 1.1 Early concepts
00:04:00 1.2 20th century
00:08:20 1.3 21st century
00:12:54 2 In fiction
00:14:28 3 Physics
00:14:37 3.1 Apparent gravitational field
00:17:04 3.2 Cable section
00:19:57 3.3 Cable material
00:23:10 4 Structure
00:23:46 4.1 Base station
00:25:04 4.2 Cable
00:28:20 4.3 Climbers
00:31:59 4.4 Powering climbers
00:33:35 4.5 Counterweight
00:34:35 5 Launching into deep space
00:35:35 6 Extraterrestrial elevators
00:37:54 7 Construction
00:40:49 7.1 Safety issues and construction challenges
00:42:05 7.2 Economics
00:43:06 8 International Space Elevator Consortium (ISEC)
00:44:58 9 Related concepts



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SUMMARY
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A space elevator is a proposed type of planet-to-space transportation system.  The main component would be a cable (also called a tether) anchored to the surface and extending into space. The design would permit vehicles to travel along the cable from a planetary surface, such as the Earth's, directly into space or orbit, without the use of large rockets. An Earth-based space elevator would consist of a cable with one end attached to the surface near the equator and the other end in space beyond geostationary orbit (35,786 km altitude). The competing forces of gravity, which is stronger at the lower end, and the outward/upward centrifugal force, which is stronger at the upper end, would result in the cable being held up, under tension, and stationary over a single position on Earth.  With the tether deployed, climbers could repeatedly climb the tether to space by mechanical means, releasing their cargo to orbit.  Climbers could also descend the tether to return cargo to the surface from orbit.The concept of a tower reaching geosynchronous orbit was first published in 1895 by Konstantin Tsiolkovsky.  His proposal was for a free-standing tower reaching from the surface of Earth to the height of geostationary orbit. Like all buildings, Tsiolkovsky's structure would be under compression, supporting its weight from below. Since 1959, most ideas for space elevators have focused on purely tensile structures, with the weight of the system held up from above by centrifugal forces. In the tensile concepts, a space tether reaches from a large mass (the counterweight) beyond geostationary orbit to the ground. This structure is held in tension between Earth and the counterweight like an upside-down plumb bob.
To construct a space elevator on Earth, the cable material would need to be both stronger and lighter (have greater specific strength) than any known material. Development of new materials that meet the demanding specific strength requirement must happen before designs can progress beyond discussion stage. Carbon nanotubes (CNTs) have been identified as possibly being able to meet the specific strength requirements for an Earth space elevator. Other materials considered have been boron nitride nanotubes, and diamond nanothreads, which were first constructed in 2014.A prototype was launched in 2018 to tether to future stations as well as the International Space Station. It is a miniature version to be further examined before making the decision to build up a large structure in the coming years. 
The concept is applicable to other planets and celestial bodies. For locations in the solar system with weaker gravity than Earth's (such as the Moon or Mars), the strength-to-density requirements for tether materials are not as problematic. Currently available materials (such as Kevlar) are strong and light enough that they could be used as the tether material for elevators there.