View source for Astronomy:Space elevator

{{short description|Proposed type of space transportation system}}
[[File:Space elevator structural diagram--corrected for scale+CM+etc.svg|thumb|upright=1.15|alt=Diagram of a space elevator. At the bottom of the tall diagram is the Earth as viewed from high above the North Pole. About six earth-radii above the Earth an arc is drawn with the same center as the Earth. The arc depicts the level of geosynchronous orbit. About twice as high as the arc and directly above the Earth's center, a counterweight is depicted by a small square. A line depicting the space elevator's cable connects the counterweight to the equator directly below it. The system's center of mass is described as above the level of geosynchronous orbit. The center of mass is shown roughly to be about a quarter of the way up from the geosynchronous arc to the counterweight. The bottom of the cable is indicated to be anchored at the equator. A climber is depicted by a small rounded square. The climber is shown climbing the cable about one third of the way from the ground to the arc. Another note indicates that the cable rotates along with the Earth's daily rotation, and remains vertical. |A space elevator is conceived as a cable fixed to the equator and reaching into space. A counterweight at the upper end keeps the [[Physics:Center of mass|center of mass]] well above geostationary orbit level. This produces enough upward centrifugal force from Earth's rotation to fully counter the downward gravity, keeping the cable upright and taut. Climbers carry cargo up and down the cable.]]
[[File:Space elevator in motion viewed from above north pole.ogv|thumbtime=28|thumb|upright=1.15|Space elevator in motion rotating with Earth, viewed from above North Pole. A free-flying satellite (green dot) is shown in geostationary orbit slightly behind the cable.]]

A '''space elevator''', also referred to as a '''space bridge''', '''star ladder''', and '''orbital lift''', is a proposed type of planet-to-space transportation system,<ref>{{cite web|url=https://www.isec.org/faq/#What%20is%20it |title=What is a Space Elevator? |publisher=The International Space Elevator Consortium |year=2014 |access-date=August 22, 2020}}</ref> often depicted in science fiction. The main component would be a cable (also called a [[Engineering:Space tether|tether]]) anchored to the surface and extending into space. An Earth-based space elevator cannot be constructed with a tall tower supported from below due to the immense weight—instead, it would consist of a cable with one end attached to the surface near the equator and the other end attached to a counterweight in space beyond [[Astronomy:Geostationary orbit|geostationary orbit]] (35,786&nbsp;km altitude). The competing forces of gravity, which is stronger at the lower end, and the 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 (crawlers) could repeatedly climb up and down the tether by mechanical means, releasing their cargo to and from orbit.<ref name="Edwards">{{cite report|last=Edwards|first=Bradley Carl|title=The NIAC Space Elevator Program|url=http://www.niac.usra.edu/studies/521Edwards.html|publisher=NASA Institute for Advanced Concepts|archive-url=https://web.archive.org/web/20080512225341/http://www.niac.usra.edu/studies/521Edwards.html|archive-date=May 12, 2008|access-date=November 24, 2007|url-status=bot: unknown}}</ref> The design would permit vehicles to travel directly between a planetary surface, such as the Earth's, and orbit, [[Astronomy:Non-rocket spacelaunch|without the use of large rockets]].

The concept of a tower reaching [[Astronomy:Geosynchronous orbit|geosynchronous orbit]] was first published in 1895 by [[Biography:Konstantin Tsiolkovsky|Konstantin Tsiolkovsky]].<ref>{{cite web |title=Space Elevator Gets Lift |url=http://www.g4tv.com/techtvvault/features/35657/Space_Elevator_Gets_Lift.html |access-date=September 13, 2007 |last=Hirschfeld |first=Bob |date=January 31, 2002 |publisher=TechTV |archive-url=https://web.archive.org/web/20050608080057/http://www.g4tv.com/techtvvault/features/35657/Space_Elevator_Gets_Lift.html |archive-date=June 8, 2005|quote=The concept was first described in 1895 by Russian author K. E. Tsiolkovsky in his 'Speculations about Earth and Sky and on Vesta.'}}</ref> 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 [[Physics:Tension|tensile]] structures, with the weight of the system held up from above by centrifugal forces. In the tensile concepts, a [[Engineering:Space tether|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 [[Engineering:Plumb bob|plumb bob]]. The cable thickness is adjusted based on tension; it has its maximum at a geostationary orbit and the minimum on the ground.

Available materials are not [[Engineering:Specific strength|strong and light]] enough to make an Earth space elevator practical.<ref>{{cite web |url=http://www.bbc.com/future/story/20150211-space-elevators-a-lift-too-far |title=Should We give up on the dream of space elevators? |first=Nic |last=Fleming |date=February 15, 2015 |access-date=January 4, 2021 |publisher=BBC |quote= 'This is extremely complicated. I don't think it's really realistic to have a space elevator,' said Elon Musk during a conference at MIT, adding that it would be easier to 'have a bridge from LA to Tokyo' than an elevator that could take material into space. }}</ref><ref>{{cite web|url=https://www.smithsonianmag.com/innovation/people-are-still-trying-build-space-elevator-180957877/ |title=People Are Still Trying to Build a Space Elevator |access-date= January 4, 2020 |last=Donahue |first=Michelle Z. |date=January 21, 2016 |publisher=Smithsonian Magazine |quote= 'We understand it’s a difficult project,' YojiIshikawa says. 'Our technology is very low. If we need to be at 100 to get an elevator built – right now we are around a 1 or 2. But we cannot say this project is not possible.' }}</ref><ref>{{cite web|url=https://www.economist.com/the-economist-explains/2018/01/30/why-the-world-still-awaits-its-first-space-elevator |title=Why the world still awaits its first space elevator |access-date= January 4, 2020 |date=January 30, 2018 |publisher=The Economist |quote=The chief obstacle is that no known material has the necessary combination of lightness and strength needed for the cable, which has to be able to support its own weight. Carbon nanotubes are often touted as a possibility, but they have only about a tenth of the necessary strength-to-weight ratio and cannot be made into filaments more than a few centimetres long, let alone thousands of kilometres. Diamond nanothreads, another exotic form of carbon, might be stronger, but their properties are still poorly understood. }}</ref> Some sources expect that future advances in [[Physics:Carbon nanotube|carbon nanotube]]s (CNTs) could lead to a practical design.<ref name="Edwards"/><ref name="Smitherman" /><ref name="universetoday" /> Other sources believe that CNTs will never be strong enough.<ref>{{cite web|url=https://www.newscientist.com/article/2093356-carbon-nanotubes-too-weak-to-get-a-space-elevator-off-the-ground/ |title=Carbon nanotubes too weak to get a space elevator off the ground |access-date=January 3, 2020|last=Aron |first=Jacob |date=June 13, 2016 |publisher=New Scientist |quote= Feng Ding of the Hong Kong Polytechnic University and his colleagues simulated CNTs with a single atom out of place, turning two of the hexagons into a pentagon and heptagon, and creating a kink in the tube. They found this simple change was enough to cut the ideal strength of a CNT to 40 GPa, with the effect being even more severe when they increased the number of misaligned atoms... That’s bad news for people who want to build a space elevator, a cable between the Earth and an orbiting satellite that would provide easy access to space. Estimates suggest such a cable would need a tensile strength of 50 GPa, so CNTs were a promising solution, but Ding’s research suggests they won’t work.}}</ref><ref>{{cite web|url=https://www.space.com/2456-nanotubes-stuff.html |title=Nanotubes Might Not Have the Right Stuff |access-date= January 3, 2020 |last=Christensen |first=Billn |date=June 2, 2006 |publisher=Space.com |quote=recent calculations by Nicola Pugno of the Polytechnic of Turin, Italy, suggest that carbon nanotube cables will not work... According to their calculations, the cable would need to be twice as strong as that of any existing material including graphite, quartz, and diamond. }}</ref><ref>{{cite web|url=https://www.popsci.com/carbon-nanotubes-cant-handle-space-elevator/ |title=Carbon Nanotubes Can't Handle a Space Elevator |access-date= January 3, 2020 |last=Whittaker |first=Clay |date=June 15, 2016 |publisher=Popular Science |quote=Alright, space elevator plans are back to square one, people. Carbon nanotubes probably aren't going to be our material solution for a space elevator, because apparently even a minuscule (read: atomic) flaw in the design drastically decreases strength. }}</ref> Possible future alternatives include [[Physics:Boron nitride nanotube|boron nitride nanotube]]s, [[Chemistry:Carbon nanothread|diamond nanothreads]]<ref name="SCIAM_DN" /><ref name="Xtech_DN" /> and macro-scale single crystal [[Physics:Graphene|graphene]].<ref name="azom.com">{{Cite web |url=https://www.azom.com/article.aspx?ArticleID=16371 |title=Space Elevator Technology and Graphene: An Interview with Adrian Nixon|date=July 23, 2018}}</ref>

The concept is applicable to other planets and [[Astronomy:Astronomical object|celestial bodies]]. For locations in the Solar System with weaker gravity than Earth's (such as the [[Astronomy:Lunar space elevator|Moon]] or [[Astronomy:Mars|Mars]]), the strength-to-density requirements for tether materials are not as problematic. Currently available materials (such as [[Chemistry:Kevlar|Kevlar]]) are strong and light enough that they could be practical as the tether material for elevators there.<ref>[[Biography:Hans Moravec|Moravec, Hans]] (1978). [http://www.frc.ri.cmu.edu/~hpm/project.archive/1976.skyhook/papers/scasci.txt ''Non-Synchronous Orbital Skyhooks for the Moon and Mars with Conventional Materials'']. Carnegie Mellon University. frc.ri.cmu.edu</ref>

==History==
===Early concepts===
[[File:Константин Циолковский.jpg|thumb|left|upright|Konstantin Tsiolkovsky]]
The key concept of the space elevator appeared in 1895 when Russian scientist [[Biography:Konstantin Tsiolkovsky|Konstantin Tsiolkovsky]] was inspired by the Eiffel Tower in [[Place:Paris|Paris]]. He considered a similar tower that reached all the way into space and was built from the ground up to the altitude of {{convert|35,786|km|mi|abbr=off|sp=us}}, the height of [[Astronomy:Geostationary orbit|geostationary orbit]].<ref name="NASASci">{{cite web |url=https://science.nasa.gov/headlines/y2000/ast07sep_1.htm |title=The Audacious Space Elevator |publisher=NASA Science News |url-status=dead |access-date=September 27, 2008 |archive-url=https://web.archive.org/web/20080919070924/https://science.nasa.gov/headlines/y2000/ast07sep_1.htm |archive-date=September 19, 2008}}</ref> He noted that the top of such a tower would be circling [[Astronomy:Earth|Earth]] as in a geostationary orbit. Objects would acquire horizontal velocity due to the Earth's rotation as they rode up the tower, and an object released at the tower's top would have enough horizontal velocity to remain there in geostationary orbit. Tsiolkovsky's conceptual tower was a compression structure, while modern concepts call for a [[Engineering:Tensile structure|tensile structure]] (or “tether”).

===20th century===
Building a compression structure from the ground up proved an unrealistic task as there was no material in existence with enough compressive strength to support its own weight under such conditions.<ref name="JBIS1999">{{cite journal |author1=Landis, Geoffrey A. |author2=Cafarelli, Craig |name-list-style=amp |year = 1999 |title = The Tsiolkovski Tower Reexamined |journal = Journal of the British Interplanetary Society |volume = 52 |pages = 175–180 |others = Presented as paper IAF-95-V.4.07, 46th International Astronautics Federation Congress, Oslo Norway, October 2–6, 1995 |bibcode = 1999JBIS...52..175L}}</ref> In 1959, the Russian engineer Yuri N. Artsutanov suggested a more feasible proposal. Artsutanov suggested using a geostationary [[Astronomy:Satellite|satellite]] as the base from which to deploy the structure downward. By using a [[Physics:Counterweight|counterweight]], a cable would be lowered from geostationary orbit to the surface of Earth, while the counterweight was extended from the satellite away from Earth, keeping the cable constantly over the same spot on the surface of the Earth. Artsutanov's idea was introduced to the Russian-speaking public in an interview published in the Sunday supplement of ''Komsomolskaya Pravda'' in 1960,<ref>{{cite web |url=http://liftport.com/files/Artsutanov_Pravda_SE.pdf |archive-url=https://web.archive.org/web/20060506100948/http://liftport.com/files/Artsutanov_Pravda_SE.pdf |archive-date=May 6, 2006 |title=To the Cosmos by Electric Train |work=liftport.com |year=1960 |publisher=Young Person's Pravda |last=Artsutanov |first=Yu |access-date=March 5, 2006}}</ref> but was not available in English until much later. He also proposed tapering the cable thickness in order for the stress in the cable to remain constant. This gave a thinner cable at ground level that became thickest at the level of geostationary orbit.

Both the tower and cable ideas were proposed in David E. H. Jones' quasi-humorous ''Ariadne'' column in ''New Scientist'', December 24, 1964.

In 1966, Isaacs, Vine, Bradner and Bachus, four {{wipe|United States}} engineers, reinvented the concept, naming it a "Sky-Hook", and published their analysis in the journal ''Science''.<ref>{{cite journal |title=Satellite Elongation into a True 'Sky-Hook' |year=1966 |journal= Science |volume = 151 |doi = 10.1126/science.151.3711.682 |author=Isaacs, J. D. |author2= A. C. Vine, H. Bradner and G. E. Bachus |bibcode = 1966Sci...151..682I |issue=3711 |pages=682–3 |last3=Bradner |last4=Bachus |pmid=17813792 |s2cid=32226322 }}</ref> 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 area, and found that the [[Engineering:Specific strength|strength]] required would be twice that of any then-existing material including [[Chemistry:Graphite|graphite]], [[Chemistry:Quartz|quartz]], and [[Chemistry:Diamond|diamond]].

In 1975, an American scientist, Jerome Pearson, reinvented the concept, publishing his analysis in the journal ''Acta Astronautica''. He designed<ref>{{cite journal |author = Pearson, J. |year = 1975 |title = The orbital tower: a spacecraft launcher using the Earth's rotational energy |url = http://www.star-tech-inc.com/papers/tower/tower.pdf |journal = Acta Astronautica |volume = 2 |pages = 785–799 |doi = 10.1016/0094-5765(75)90021-1 |issue = 9–10 |bibcode = 1975AcAau...2..785P |citeseerx = 10.1.1.530.3120}}</ref> a cross-section-area altitude profile that tapered and would be better suited to building the elevator. 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 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 {{convert|144,000|km|mi|abbr=off|sp=us}} (almost half the distance to the [[Astronomy:Moon|Moon]]) as the lower sections of the elevator were built. Without a large counterweight, the upper portion of the cable would have to be longer than the lower due to the way [[Physics:Gravity|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 [[Engineering:Space Shuttle|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 [[Astronomy:Asteroid mining|asteroidal]] or lunar ore.

After the development of carbon nanotubes in the 1990s, engineer David Smitherman of [[Organization:NASA|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 [[Organization:Marshall Space Flight Center|Marshall Space Flight Center]], inviting many scientists and engineers to discuss concepts and compile plans for an elevator to turn the concept into a reality.

In 2000, another American scientist, [[Biography:Bradley C. Edwards|Bradley C. Edwards]], suggested creating a {{convert|100,000|km|mi|abbr=on}} long paper-thin ribbon using a carbon nanotube composite material.<ref name="EDWARDS_PHASE_I_2000_472Edwards.html">Bradley C. Edwards, "[http://www.niac.usra.edu/studies/472Edwards.html The Space Elevator]"</ref> He chose the wide-thin ribbon-like cross-section shape rather than earlier circular cross-section concepts because that shape would stand a greater chance of surviving impacts by meteoroids. The ribbon cross-section shape also provided large surface area for climbers to climb with simple rollers. Supported by the [[Organization:NASA Institute for Advanced Concepts|NASA Institute for Advanced Concepts]], Edwards' work was expanded to cover the deployment scenario, climber design, power delivery system, [[Astronomy:Space debris|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.<ref name="Edwards" /><ref name="Smitherman">[http://www.nss.org/resources/library/spaceelevator/2000-SpaceElevator-NASA-CP210429.pdf "Space Elevators: An Advanced Earth-Space Infrastructure for the New Millennium"], NASA/CP-2000-210429, Marshall Space Flight Center, Huntsville, Alabama, 2000 ([https://web.archive.org/web/20150328040627/http://www.nss.org/resources/library/spaceelevator/2000-SpaceElevator-NASA-CP210429.pdf archived])</ref><ref>Science @ NASA, [https://science.nasa.gov/headlines/y2000/ast07sep_1.htm "Audacious & Outrageous: Space Elevators"] {{webarchive|url=https://web.archive.org/web/20080919070924/https://science.nasa.gov/headlines/y2000/ast07sep_1.htm |date=September 19, 2008}}, September 2000</ref>

===21st century===
To speed space elevator development, proponents have organized several competitions, similar to the Ansari X Prize, for relevant technologies.<ref>{{cite web |url=http://www.nbcnews.com/id/5792719 |title=Space elevator contest proposed |first=Alan |last=Boyle |publisher=NBC News |date=August 27, 2004}}</ref><ref>{{cite web |url=http://www.elevator2010.org/ |title=The Space Elevator – Elevator:2010 |access-date=March 5, 2006 |archive-date=January 6, 2007 |archive-url=https://web.archive.org/web/20070106211508/http://www.elevator2010.org/ |url-status=dead }}</ref> Among them are [[Unsolved:Elevator:2010|Elevator]], which organized annual competitions for climbers, ribbons and power-beaming systems from 2005 to 2009, the Robogames Space Elevator Ribbon Climbing competition,<ref>{{cite web |url=http://robogames.net/rules/climbing.php |title=Space Elevator Ribbon Climbing Robot Competition Rules |access-date=March 5, 2006 |archive-url = https://web.archive.org/web/20050206100051/http://robolympics.net/rules/climbing.shtml|archive-date=February 6, 2005}}</ref> as well as NASA's [[Organization:Centennial Challenges|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.<ref>{{cite web |url=http://www.nasa.gov/home/hqnews/2005/mar/HQ_m05083_Centennial_prizes.html |title=NASA Announces First Centennial Challenges' Prizes |year=2005 |access-date=March 5, 2006 |archive-date=June 8, 2005 |archive-url=https://web.archive.org/web/20050608083813/http://www.nasa.gov/home/hqnews/2005/mar/HQ_m05083_Centennial_prizes.html |url-status=dead }}</ref><ref>{{cite web |url=http://www.space.com/news/050323_centennial_challenge.html |title=NASA Details Cash Prizes for Space Privatization |first=Robert Roy |last=Britt |work=Space.com |date=March 24, 2005 |access-date=March 5, 2006}}</ref>
The first European Space Elevator Challenge (EuSEC) to establish a climber structure took place in August 2011.<ref>{{cite web |title=What's the European Space Elevator Challenge? |url=http://eusec.warr.de/?eusec|publisher=European Space Elevator Challenge |access-date=April 21, 2011}}</ref>

In 2005, "the [[Company:LiftPort Group|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 {{convert|100,000|km|mi|abbr=on}} space elevator, this move will allow it to make money in the short term and conduct research and development into new production methods."<ref name="universetoday">{{cite news |url=http://www.universetoday.com/am/publish/liftport_manufacture_nanotubes.html?2742005 |title=Space Elevator Group to Manufacture Nanotubes |date=April 27, 2005 |first=Fraser |last=Cain |work=Universe Today |access-date=March 5, 2006}}</ref> Their announced goal was a space elevator 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 {{cvt|5|cm|in}} wide and {{cvt|1|mm|in}} (approx. 13 sheets of paper) thick, lifted with balloons.<ref>{{cite news |url=http://www.newscientistspace.com/article/dn8725.html |title=Space-elevator tether climbs a mile high |date=February 15, 2006 |work=New Scientist |first=Kimm |last=Groshong |access-date=March 5, 2006}}</ref> In April 2019, Liftport CEO Michael Laine admitted little progress has been made on the company's lofty space elevator ambitions, even after receiving more than $200,000 in seed funding. The carbon nanotube manufacturing facility that Liftport announced in 2005 was never built.<ref>{{cite web |title=If a space elevator was ever going to happen, it could have gotten its start in N.J. Here's how it went wrong |url=https://www.nj.com/cumberland/2019/04/if-a-space-elevator-was-ever-going-to-happen-it-could-have-gotten-its-start-in-nj-heres-how-it-went-wrong.html |publisher=NJ.com |date=March 28, 2019 |access-date=May 11, 2019}}</ref>

In 2007, [[Unsolved:Elevator:2010|Elevator]] held the 2007 Space Elevator games, which featured US$500,000 awards for each of the two competitions ($1,000,000 total), as well as an additional $4,000,000 to be awarded over the next five years for space elevator related technologies.<ref>[https://web.archive.org/web/20100118153108/http://www.spaceward.org/elevator2010 Elevator:2010 – The Space Elevator Challenge]. spaceward.org</ref> No teams won the competition, but a team from MIT entered the first 2-gram (0.07&nbsp;oz), 100-percent carbon nanotube entry into the competition.<ref>[https://web.archive.org/web/20071101081423/http://www.spaceward.org/games07Wrapup.html Spaceward Games 2007]. The Spaceward Foundation</ref> Japan held an international conference in November 2008 to draw up a timetable for building the elevator.<ref name="JapanUKTimes">{{cite news | title = Japan hopes to turn sci-fi into reality with elevator to the stars | url=http://www.thetimes.co.uk/tto/news/world/article1967078.ece | work=The Times | location=London | first=Leo | last=Lewis | date=September 22, 2008 | access-date=May 23, 2010}} Lewis, Leo; News International Group; accessed September 22, 2008.</ref>

In 2012, the Obayashi Corporation announced that it could build a space elevator by 2050 using carbon nanotube technology.<ref name="physorg_obayashi">{{cite news| url=http://www.physorg.com/news/2012-02-japan-builder-eyes-space-elevator.html | website=Phys.org | title=Going up: Japan builder eyes space elevator | date=February 22, 2012}}</ref> The design's passenger climber would be able to reach the GEO level after an 8-day trip.<ref>{{cite news| url=https://www.smithsonianmag.com/smart-news/researchers-take-tiny-first-step-toward-space-elevator-180970212/ | title=Japan Takes Tiny First Step Toward Space Elevator | date=September 5, 2018 |work=Smithsonian Magazine |first=Jason |last=Daley}}</ref> Further details have been published in 2016.<ref>{{cite journal |last1=Ishikawa |first1=Y. |date=2016 |title=Obayashi Corporation's Space Elevator Construction Concept |url=https://ui.adsabs.harvard.edu/abs/2016JBIS...69..227I/abstract |journal=Journal of the British Interplanetary Society |volume=69 |issue= |pages=227–239 |doi= |bibcode=2016JBIS...69..227I |access-date=January 5, 2021}}</ref>

In 2013, the [[Organization:International Academy of Astronautics|International Academy of Astronautics]] published a technological feasibility assessment which concluded that the critical capability improvement needed was the tether material, which was projected to achieve the necessary [[Engineering:Specific strength|specific strength]] within 20 years. The four-year long study looked into many facets of space elevator development including missions, development schedules, financial investments, revenue flow, and benefits. It was reported that it would be possible to operationally survive smaller impacts and avoid larger impacts, with meteors and space debris, and that the estimated cost of lifting a kilogram of payload to GEO and beyond would be $500.<ref>{{Cite book|title = Space Elevators: An Assessment of the Technological Feasibility and the Way Forward|last1 = Swan|last2 =Raitt|last3 =Swan|last4 = Penny|last5 =Knapman|first1 = Peter A.|first2 = David I.|first3 = Cathy W.|first4 = Robert E.|first5 = John M.|publisher = International Academy of Astronautics|year = 2013|isbn = 9782917761311|location = Virginia, US|pages = 10–11, 207–208}}</ref><ref>Swan, P., Penny, R., Swan, C. "Space Elevator Survivability, Space Debris Mitigation", Lulu.com Publishers, 2011{{self-published source|date=February 2020}}</ref>{{self-published inline|date=February 2020}}

In 2014, Google X's Rapid Evaluation R&D team began the design of a Space Elevator, eventually finding that no one had yet manufactured a perfectly formed [[Physics:Carbon nanotube|carbon nanotube]] strand longer than a meter. They thus decided to put the project in "deep freeze" and also keep tabs on any advances in the carbon nanotube field.<ref>{{cite web|last=Gayomali|first=Chris|title=Google X Confirms The Rumors: It Really Did Try To Design A Space Elevator|url=http://www.fastcompany.com/3029138/world-changing-ideas/google-x-confirms-the-rumors-it-really-did-try-to-design-a-space-elevat?partner=rss|work=Fast Company |date=April 15, 2014 |access-date=April 17, 2014}}</ref>

In 2018, researchers at Japan's Shizuoka University launched STARS-Me, two [[Engineering:CubeSat|CubeSat]]s connected by a tether, which a mini-elevator will travel on.<ref>{{Cite web | url=https://www.nbcnews.com/mach/science/colossal-elevator-space-could-be-going-sooner-you-ever-imagined-ncna915421 | title=A colossal elevator to space could be going up sooner than you ever imagined |work=NBC News |date=October 2, 2018 |first=Scott |last=Snowden}}</ref><ref>{{cite web |url=https://www.curbed.com/2018/9/12/17851500/space-elevator-japan-news |title=Japan is trying to build an elevator to space |publisher=Curbed.com |first=Meghan |last=Barber |date=September 12, 2018 |access-date=September 18, 2018}}</ref> The experiment was launched as a test bed for a larger structure.<ref>{{Cite web | url=https://gizmodo.com/japan-testing-miniature-space-elevator-near-the-interna-1828800558 |title = Japan Testing Miniature Space Elevator Near the International Space Station| date=September 4, 2018 }}</ref>

In 2019, the [[Organization:International Academy of Astronautics|International Academy of Astronautics]] published "Road to the Space Elevator Era",<ref>{{cite book |vauthors=Swan PA, Raitt DI, Knapman JM, Tsuchida A, Fitzgerald MA, Ishikawa Y |title=Road to the Space Elevator Era |date=May 30, 2019 |publisher=International Academy of Astronautics |isbn=978-0-9913370-3-3 |url=https://www.heinleinbooks.com/product-page/road-to-the-space-elevator-era}}</ref> a study report summarizing the assessment of the space elevator as of summer 2018. The essence is that a broad group of space professionals gathered and assessed the status of the space elevator development, each contributing their expertise and coming to similar conclusions: (a) Earth Space Elevators seem feasible, reinforcing the IAA 2013 study conclusion (b) Space Elevator development initiation is nearer than most think. This last conclusion is based on a potential process for manufacturing macro-scale single crystal [[Physics:Graphene|graphene]]<ref name="azom.com"/> with higher [[Engineering:Specific strength|specific strength]] than [[Physics:Carbon nanotube|carbon nanotube]]s.

==In fiction==
{{main|Unsolved:Space elevators in fiction}}
In 1979, space elevators were introduced to a broader audience with the simultaneous publication of [[Biography:Arthur C. Clarke|Arthur C. Clarke]]'s novel, ''[[Unsolved:The Fountains of Paradise|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 [[Biography:Robert A. Heinlein|Robert A. Heinlein]]'s 1982 novel ''Friday'', the principal character mentions a disaster at the “Quito Sky Hook” and makes use of the "Nairobi Beanstalk" in the course of her travels. In [[Biography:Kim Stanley Robinson|Kim Stanley Robinson]]'s 1993 novel ''Red Mars'', colonists build a space elevator on Mars that allows both for more colonists to arrive and also for natural resources mined there to be able to leave for Earth.  Larry Niven's book ''Rainbow Mars'' describes a space elevator built on Mars. In David Gerrold's 2000 novel, ''Jumping Off The Planet'', a family excursion up the Ecuador "beanstalk" is actually a child-custody kidnapping. Gerrold's book also examines some of the industrial applications of a mature elevator technology. The concept of a space elevator, called the Beanstalk, is also depicted in John Scalzi's 2005 novel ''Old Man's War.'' In a biological version, Joan Slonczewski's 2011 novel ''The Highest Frontier'' depicts a college student ascending a space elevator constructed of self-healing cables of anthrax bacilli. The engineered bacteria can regrow the cables when severed by space debris.

==Physics==

===Apparent gravitational field===
An Earth space elevator cable rotates along with the rotation of the Earth. Therefore, the cable, and objects attached to it, would experience upward centrifugal force in the direction opposing the downward gravitational force. The higher up the cable the object is located, the less the gravitational pull of the Earth, and the stronger the upward centrifugal force due to the rotation, so that more centrifugal force opposes less gravity. The centrifugal force and the gravity are balanced at geosynchronous equatorial orbit (GEO). Above GEO, the centrifugal force is stronger than gravity, causing objects attached to the cable there to pull ''upward'' on it. Because the counterweight, above GEO, is rotating about the Earth faster than the natural orbital speed for that altitude, it exerts a centrifugal pull on the cable and thus holds the whole system aloft.

The net force for objects attached to the cable is called the ''apparent gravitational field''. The apparent gravitational field for attached objects is the (downward) gravity minus the (upward) centrifugal force. The apparent gravity experienced by an object on the cable is zero at GEO, downward below GEO, and upward above GEO.

The apparent gravitational field can be represented this way:<ref name="aravind"/>{{rp|Table 1}}

{{block indent|The downward force of actual [[Physics:Newton's law of universal gravitation|gravity]] ''decreases'' with height: [[Physics:Newton's law of universal gravitation|<math>g r = -GM/r^2</math>]]}}
{{block indent|The upward [[Physics:Centrifugal force|centrifugal force]] due to the planet's rotation ''increases'' with height: [[Physics:Centrifugal force|<math>a = \omega^2 r</math>]]}}
{{block indent|Together, the apparent gravitational field is the sum of the two:
{{block indent|<math>g = -\frac{GM}{r^2} + \omega^2 r</math>}}}}

where
{{block indent|''g'' is the acceleration of ''apparent'' gravity, pointing down (negative) or up (positive) along the vertical cable (m s<sup>−2</sup>),}}
{{block indent|''g<sub>r</sub>'' is the gravitational acceleration due to Earth's pull, pointing down (negative)(m s<sup>−2</sup>),}}
{{block indent|''a'' is the centrifugal acceleration, pointing up (positive) along the vertical cable (m s<sup>−2</sup>),}}
{{block indent|''G'' is the [[Physics:Gravitational constant|gravitational constant]] (m<sup>3</sup> s<sup>−2</sup> kg<sup>−1</sup>)}}
{{block indent|''M'' is the mass of the Earth (kg)}}
{{block indent|''r'' is the distance from that point to Earth's center (m),}}
{{block indent|''ω'' is Earth's rotation speed (radian/s).}}

At some point up the cable, the two terms (downward gravity and upward centrifugal force) are equal and opposite. Objects fixed to the cable at that point put no weight on the cable. This altitude (r<sub>1</sub>) depends on the mass of the planet and its rotation rate. Setting actual gravity equal to centrifugal acceleration gives:<ref name="aravind"/>{{rp|p. 126}}
{{block indent|<math>r_1 = \left(\frac{GM}{\omega^2}\right)^\frac{1}{3}</math>}}

This is {{convert|35786|km|mi|0|abbr=on}} above Earth's surface, the altitude of geostationary orbit.<ref name="aravind"/>{{rp|Table 1}}

On the cable ''below'' geostationary orbit, downward gravity would be greater than the upward centrifugal force, so the apparent gravity would pull objects attached to the cable downward. Any object released from the cable below that level would initially accelerate downward along the cable. Then gradually it would deflect eastward from the cable. On the cable ''above'' the level of stationary orbit, upward centrifugal force would be greater than downward gravity, so the apparent gravity would pull objects attached to the cable ''upward''. Any object released from the cable ''above'' the geosynchronous level would initially accelerate ''upward'' along the cable. Then gradually it would deflect westward from the cable.

===Cable section===
Historically, the main technical problem has been considered the ability of the cable to hold up, with tension, the weight of itself below any given point. The greatest tension on a space elevator cable is at the point of geostationary orbit, {{convert|35786|km|mi|0|abbr=on}} above the Earth's equator. This means that the cable material, combined with its design, must be strong enough to hold up its own weight from the surface up to {{convert|35786|km|mi|0|abbr=on}}. A cable which is thicker in cross section area at that height than at the surface could better hold up its own weight over a longer length. How the cross section area tapers from the maximum at {{convert|35786|km|mi|0|abbr=on}} to the minimum at the surface is therefore an important design factor for a space elevator cable.

To maximize the usable excess strength for a given amount of cable material, the cable's cross section area would need to be designed for the most part in such a way that the [[Physics:Stress (mechanics)|stress]] (i.e., the tension per unit of cross sectional area) is constant along the length of the cable.<ref name="aravind" /><ref>Artuković, Ranko (2000). [http://www.zadar.net/space-elevator/ "The Space Elevator".] zadar.net</ref> The constant-stress criterion is a starting point in the design of the cable cross section area as it changes with altitude. Other factors considered in more detailed designs include thickening at altitudes where more space junk is present, consideration of the point stresses imposed by climbers, and the use of varied materials.<ref name="PhaseII"/> To account for these and other factors, modern detailed designs seek to achieve the largest ''[[Physics:Factor of safety#Margin of safety|safety margin]]'' possible, with as little variation over altitude and time as possible.<ref name="PhaseII"/> In simple starting-point designs, that equates to constant-stress.

For a constant-stress cable with no safety margin, the cross-section-area as a function of distance from Earth's center is given by the following equation:<ref name="aravind" />

{{CSS image crop
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{{block indent|<math>A( r ) = A_s \exp\left[ \frac{\rho g R^2}{T}\left( \frac{1}{R}+\frac{R^2}{2R_g^3}-\frac{1}{r}-\frac{r^2}{2R_g^3} \right) \right]</math>}}

where
{{block indent|''g'' is the gravitational acceleration at Earth's surface (m·s<sup>−2</sup>),}}
{{block indent|<math>A_s</math> is the cross-section area of the cable at Earth's surface (m<sup>2</sup>),}}
{{block indent|''ρ'' is the density of the material used for the cable (kg·m<sup>−3</sup>),}}
{{block indent|''R'' is the Earth's equatorial radius,}}
{{block indent|<math>R_g</math> is the radius of geosynchronous orbit,}}
{{block indent|1=''T'' is the stress the cross-section area can bear without [[Engineering:Yield (engineering)|yielding]] (N·m<sup>−2</sup>), its elastic limit.}}

Safety margin can be accounted for by dividing T by the desired safety factor.<ref name="aravind" />

===Cable materials===
Using the above formula we can calculate the ratio between the cross-section at geostationary orbit and the cross-section at Earth's surface, known as taper ratio:<ref group="note">Specific substitutions used to produce the factor {{val|4.85|e=7}}:{{block indent|<math>A(R_g)/A_s = \exp \left[ \frac{\rho \times 9.81 \times (6.378\times 10^6)^2 } {T} \left( \frac{1}{6.378\times 10^6} + \frac{(6.378\times 10^6)^2}{2 (4.2164\times 10^7)^3} - \frac{1}{4.2164\times 10^7} - \frac{(4.2164\times 10^7)^2}{2 (4.2164\times 10^7)^3}\right)\right]</math>}}</ref>{{block indent|<math>A(R_g)/A_s = \exp \left[\frac{\rho}{T}\times 4.85\times 10^7\right]</math> }}
[[File:Space Elevator Taper Ratio.svg|thumb|Taper ratio as a function of specific strength]]
{| class="wikitable" style="text-align:left"
|+Taper ratio for some materials<ref name="aravind" />
|-
!Material!!Tensile strength<br />(MPa)!!Density<br />(kg/m<sup>3</sup>)!![[Engineering:Specific strength|Specific strength]]<br />(MPa)/(kg/m<sup>3</sup>)!!Taper ratio
|-
|Steel || 5,000 || 7,900 || 0.63 ||{{val|1.6|e=33}}
|-
|[[Chemistry:Kevlar|Kevlar]] || 3,600 || 1,440 || 2.5 ||{{val|2.5|e=8}}
|-
|Single wall [[Physics:Carbon nanotube|carbon nanotube]] || 130,000 || 1,300 || 100 || 1.6
|}
The taper ratio becomes very large unless the specific strength of the material used approaches 48 (MPa)/(kg/m<sup>3</sup>). Low specific strength materials require very large taper ratios which equates to large (or astronomical) total mass of the cable with associated large or impossible costs.

==Structure==
[[Image:SpaceElevatorClimbing.jpg|thumb|right|One concept for the space elevator has it tethered to a mobile seagoing platform.]]
There are a variety of space elevator designs proposed for many planetary bodies. Almost every design includes a base station, a cable, climbers, and a counterweight. For an Earth Space Elevator the Earth's rotation creates upward [[Physics:Centrifugal force|centrifugal force]]<!--"upward" is a continuously changing direction which implies an accelerated reference frame where "c.f." is unquestionable (see http://xkcd.com/123/) --> on the counterweight. The counterweight is held down by the cable while the cable is held up and taut by the counterweight. The base station anchors the whole system to the surface of the Earth. Climbers climb up and down the cable with cargo.

===Base station===
Modern concepts for the base station/anchor are typically mobile stations, large oceangoing vessels or other mobile platforms. Mobile base stations would have the advantage over the earlier stationary concepts (with land-based anchors) by being able to maneuver to avoid high winds, storms, and [[Astronomy:Space debris|space debris]]. Oceanic anchor points are also typically in international waters, simplifying and reducing the cost of negotiating territory use for the base station.<ref name="Edwards" />

Stationary land-based platforms would have simpler and less costly logistical access to the base. They also would have the advantage of being able to be at high altitudes, such as on top of mountains. In an alternate concept, the base station could be a tower, forming a space elevator which comprises both a compression tower close to the surface, and a tether structure at higher altitudes.<ref name="JBIS1999" /> Combining a compression structure with a tension structure would reduce loads from the atmosphere at the Earth end of the tether, and reduce the distance into the Earth's gravity field the cable needs to extend, and thus reduce the critical strength-to-density requirements for the cable material, all other design factors being equal.

===Cable===
[[File:Kohlenstoffnanoroehre Animation.gif|thumb|upright|Carbon nanotubes are one of the candidates for a cable material<ref name="physorg_obayashi"/>]]
[[Image:SpaceElevatorAnchor.jpg|thumb|upright|A seagoing anchor station would also act as a deep-water seaport.]]
A space elevator cable would need to carry its own weight as well as the additional weight of climbers. The required strength of the cable would vary along its length. This is because at various points it would have to carry the weight of the cable below, or provide a downward force to retain the cable and counterweight above. Maximum tension on a space elevator cable would be at geosynchronous altitude so the cable would have to be thickest there and taper as it approaches Earth. Any potential cable design may be characterized by the taper factor – the ratio between the cable's radius at geosynchronous altitude and at the Earth's surface.<ref>{{cite web |title=NAS-97-029: NASA Applications of Molecular Nanotechnology |author=Globus, Al |display-authors=0 |publisher=NASA |url=http://www.nas.nasa.gov/assets/pdf/techreports/1997/nas-97-029.pdf |access-date=September 27, 2008 |archive-date=April 8, 2016 |archive-url=https://web.archive.org/web/20160408064557/http://www.nas.nasa.gov/assets/pdf/techreports/1997/nas-97-029.pdf |url-status=dead }}</ref>

The cable would need to be made of a material with a high [[Engineering:Specific strength|tensile strength/density ratio]]. For example, the Edwards space elevator design assumes a cable material with a tensile strength of at least 100 gigapascals.<ref name="Edwards"/> Since Edwards consistently assumed the density of his carbon nanotube cable to be 1300&nbsp;kg/m<sup>3</sup>,<ref name="EDWARDS_PHASE_I_2000_472Edwards.html"/> that implies a specific strength of 77 megapascal/(kg/m<sup>3</sup>). This value takes into consideration the entire weight of the space elevator. An untapered space elevator cable would need a material capable of sustaining a length of {{convert|4,960|km|mi|sp=us}} of its own weight ''at [[Sea level|sea level]]'' to reach a [[Astronomy:Geostationary|geostationary]] altitude of {{convert|35786|km|mi|0|abbr=on}} without yielding.<ref>This 4,960 km "escape length" (calculated by [[Biography:Arthur C. Clarke|Arthur C. Clarke]] in 1979) is much shorter than the actual distance spanned because centrifugal forces increase (and gravity decreases) dramatically with height:{{cite web |url=http://www.islandone.org/LEOBiblio/CLARK2.HTM |title=The space elevator: 'thought experiment', or key to the universe?|last=Clarke|first=A.C.|year=1979|access-date=January 5, 2010|archive-date=January 3, 2014|archive-url=https://web.archive.org/web/20140103033306/http://www.islandone.org/LEOBiblio/CLARK2.HTM|url-status=dead}}</ref> Therefore, a material with very high strength and lightness is needed.

For comparison, metals like titanium, steel or aluminium alloys have [[Engineering:Specific strength|breaking lengths]] of only 20–30&nbsp;km (0.2–0.3 MPa/(kg/m<sup>3</sup>)). Modern fiber materials such as [[Chemistry:Kevlar|kevlar]], fiberglass and carbon/graphite fiber have breaking lengths of 100–400&nbsp;km (1.0–4.0 MPa/(kg/m<sup>3</sup>)). Nanoengineered materials such as carbon nanotubes and, more recently discovered, [[Physics:Graphene|graphene]] ribbons (perfect two-dimensional sheets of carbon) are expected to have breaking lengths of 5000–6000&nbsp;km (50–60 MPa/(kg/m<sup>3</sup>)), and also are able to conduct electrical power.{{Citation needed|date=April 2014}}

For a space elevator on Earth, with its comparatively high gravity, the cable material would need to be stronger and lighter than currently available materials.<ref name="Huff.3353697" /> For this reason, there has been a focus on the development of new materials that meet the demanding specific strength requirement. For high specific strength, carbon has advantages because it is only the sixth element in the [[Chemistry:Periodic table|periodic table]]. Carbon has comparatively few of the protons and neutrons which contribute most of the dead weight of any material. Most of the interatomic [[Chemistry:Chemical bond|bonding forces]] of any element are contributed by only the [[Physics:Valence electron|outer few]] electrons. For carbon, the strength and stability of those bonds is high compared to the mass of the atom. The challenge in using carbon nanotubes remains to extend to macroscopic sizes the production of such material that are still perfect on the microscopic scale (as microscopic defects are most responsible for material weakness).<ref name="Huff.3353697">{{cite news |first=Jillian |last=Scharr |title=Space Elevators On Hold At Least Until Stronger Materials Are Available, Experts Say |newspaper=Huffington Post |date=May 29, 2013 |url=https://www.huffingtonpost.com/2013/05/29/space-elevators-stronger-materials_n_3353697.html}}</ref><ref>{{cite journal |last=Feltman |first=R. |title=Why Don't We Have Space Elevators? |journal=Popular Mechanics |date=March 7, 2013 |url=http://www.popularmechanics.com/science/space/nasa/why-dont-we-have-space-elevators-15185070}}</ref><ref>{{cite news |last=Templeton |first=Graham |url=http://www.extremetech.com/extreme/176625-60000-miles-up-geostationary-space-elevator-could-be-built-by-2035-says-new-study |title=60,000 miles up: Space elevator could be built by 2035, says new study |work=Extreme Tech |date=March 6, 2014 |access-date=April 14, 2014}}</ref> As of 2014, carbon nanotube technology allowed growing tubes up to a few tenths of meters.<ref>{{cite journal| first1=X.| last1=Wang| title=Fabrication of Ultralong and Electrically Uniform Single-Walled Carbon Nanotubes on Clean Substrates| volume=9| pages=3137–3141| year=2009| doi=10.1021/nl901260b| journal=Nano Letters| last2=Li| first2=Q.| last3=Xie| first3=J.| last4=Jin| first4=Z.| last5=Wang| first5=J.| last6=Li| first6=Y.| last7=Jiang| first7=K.| last8=Fan| first8=S.| issue=9| pmid=19650638| bibcode=2009NanoL...9.3137W| url=http://www.chem.pku.edu.cn/page/liy/labhomepage/publications/2009/2009NL.pdf| url-status=dead| archive-url=https://web.archive.org/web/20170808164154/http://www.chem.pku.edu.cn/page/liy/labhomepage/publications/2009/2009NL.pdf| archive-date=August 8, 2017| citeseerx=10.1.1.454.2744}}</ref>

In 2014, [[Chemistry:Carbon nanothread|diamond nanothreads]] were first synthesized.<ref name="SCIAM_DN">{{cite magazine |url=http://www.scientificamerican.com/article/liquid-benzene-squeezed-to-form-diamond-nanothreads/ |title=Liquid Benzene Squeezed to Form Diamond Nanothreads |first=Julia |last=Calderone |date=September 26, 2014 |magazine=Scientific American |access-date=July 22, 2018}}</ref> Since they have strength properties similar to carbon nanotubes, diamond nanothreads were quickly seen as candidate cable material as well.<ref name="Xtech_DN">{{cite news |url=http://www.extremetech.com/extreme/190691-new-diamond-nanothreads-could-be-the-key-material-for-building-a-space-elevator |title=New diamond nanothreads could be the key material for building a space elevator |first=Sebastian |last=Anthony |date=September 23, 2014 |publisher=Zeff Davis, LLC |newspaper=Extremetech |access-date=July 22, 2018}}</ref>

===Climbers===
[[Image:SpaceElevatorInClouds.jpg|thumb|upright|A conceptual drawing of a space elevator climber ascending through the clouds.]]

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 at 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.

Climbers would need to be paced at optimal timings so as to minimize cable stress and oscillations and to maximize throughput. Lighter climbers could be sent up more often, with several going up at the same time. This would increase throughput somewhat, but would lower the mass of each individual payload.<ref name="LangGTOSS">{{cite web |url=http://spaceelevatorwiki.com/wiki/images/2/2b/Paper_Lang_Climber_Transit.pdf |last=Lang |first=David D. |title=Space Elevator Dynamic Response to In-Transit Climbers |access-date=February 9, 2016 |archive-date=May 28, 2016 |archive-url=https://web.archive.org/web/20160528232403/http://spaceelevatorwiki.com/wiki/images/2/2b/Paper_Lang_Climber_Transit.pdf |url-status=dead }}</ref>

[[File:Space elevator balance of forces--circular Earth--more accurate force vectors.svg|thumb|upright=1.15|As the car climbs, the cable takes on a slight lean due to the Coriolis force. The top of the cable travels faster than the bottom. The climber is accelerated horizontally as it ascends by the Coriolis force which is imparted by angles of the cable. The lean-angle shown is exaggerated.]]
The horizontal speed, i.e. due to orbital rotation, of each part of the cable increases with altitude, proportional to distance from the center of the Earth, reaching low [[Astronomy:Orbital speed|orbital speed]] at a point approximately 66 percent of the height between the surface and geostationary orbit, or a height of about 23,400&nbsp;km. A payload released at this point would go into a highly eccentric elliptical orbit, staying just barely clear from atmospheric reentry, with the periapsis at the same altitude as LEO and the apoapsis at the release height. With increasing release height the orbit would become less eccentric as both periapsis and apoapsis increase, becoming circular at geostationary level.<ref>{{cite web |first=Blaise |last=Gassend |title=Falling Climbers |url=http://gassend.net/spaceelevator/falling-climbers/index.html |access-date=December 16, 2013}}</ref><ref>{{cite web |title=Space elevator to low orbit? |url=http://www.endlessskyway.com/2010/05/space-elevator-to-low-orbit.html |date=May 19, 2010 |website=Endless Skyway |access-date=December 16, 2013 |archive-url=https://web.archive.org/web/20131216184533/http://www.endlessskyway.com/2010/05/space-elevator-to-low-orbit.html |archive-date=December 16, 2013 |url-status=dead}}</ref>

When the payload has reached GEO, the horizontal speed is exactly the speed of a circular orbit at that level, so that if released, it would remain adjacent to that point on the cable. The payload can also continue climbing further up the cable beyond GEO, allowing it to obtain higher speed at jettison. If released from 100,000&nbsp;km, the payload would have enough speed to reach the asteroid belt.<ref name="PhaseII" />

As a payload is lifted up a space elevator, it would gain not only altitude, but horizontal speed (angular momentum) as well. The angular momentum is taken from the Earth's rotation. As the climber ascends, it is initially moving slower than each successive part of cable it is moving on to. This is the [[Physics:Coriolis force|Coriolis force]]: the climber "drags" (westward) on the cable, as it climbs, and slightly decreases the Earth's rotation speed. The opposite process would occur for descending payloads: the cable is tilted eastward, thus slightly increasing Earth's rotation speed.

The overall effect of the <!--n.b. the elevator is in a non inertial reference frame, so centrifugal is correct--->centrifugal force acting on the cable would cause it to constantly try to return to the energetically favorable vertical orientation, so after an object has been lifted on the cable, the counterweight would swing back toward the vertical, a bit like a pendulum.<ref name="LangGTOSS" /> Space elevators and their loads would be designed so that the center of mass is always well-enough above the level of geostationary orbit<ref>{{cite web |url=http://gassend.net/spaceelevator/center-of-mass/index.html |title=Why the Space Elevator's Center of Mass is not at GEO |first=Blaise |last=Gassend |access-date=September 30, 2011}}</ref> to hold up the whole system. Lift and descent operations would need to be carefully planned so as to keep the pendulum-like motion of the counterweight around the tether point under control.<ref>{{cite journal|doi=10.1016/j.actaastro.2008.10.003|title=The effect of climber transit on the space elevator dynamics|year=2009|last1=Cohen|first1=Stephen S.|last2=Misra|first2=Arun K.|journal=Acta Astronautica|volume=64|issue=5–6|pages=538–553|bibcode=2009AcAau..64..538C}}</ref>

Climber speed would be limited by the Coriolis force, available power, and by the need to ensure the climber's accelerating force does not break the cable. Climbers would also need to maintain a minimum average speed in order to move material up and down economically and expeditiously.<ref>{{Cite web|last=Courtland|first=Rachel|title=Space elevator trips could be agonisingly slow|url=https://www.newscientist.com/article/dn16223-space-elevator-trips-could-be-agonisingly-slow/|access-date=2021-05-28|website=New Scientist|language=en-US}}</ref> At the speed of a very fast car or train of {{convert|300|km/h|mph|abbr=on}} it will take about 5 days to climb to geosynchronous orbit.<ref>{{cite book|author1=Bill Fawcett, Michael Laine |author2=Tom Nugent jr. |name-list-style=amp |title=LIFTPORT|date=2006|publisher=Meisha Merlin Publishing, Inc.|location=Canada|isbn=978-1-59222-109-7|page=103}}</ref>

===Powering climbers===
Both power and energy are significant issues for climbers – the climbers would need to gain a large amount of potential energy as quickly as possible to clear the cable for the next payload.

Various methods have been proposed to get that energy to the climber:
* Transfer the energy to the climber through wireless energy transfer while it is climbing.
* Transfer the energy to the climber through some material structure while it is climbing.
* Store the energy in the climber before it starts – requires an extremely high [[Physics:Specific energy|specific energy]] such as nuclear energy.
* Solar power – After the first 40&nbsp;km it is possible to use solar energy to power the climber<ref>{{cite web |url = http://isec.org/pdfs/isec_reports/2013_ISEC_Design_Considerations_for_Space_Elevator_Tether_Climbers_Final_Report.pdf |title = Design Consideration for Space Elevator Tether Climbers |last1 = Swan, P. A. |last2 = Swan, C. W. |last3 = Penny, R. E. |last4 = Knapman, J. M. |last5 = Glaskowsky, P. N. |publisher = ISEC |quote = During the last ten years, the assumption was that the only power available would come from the surface of the Earth, as it was inexpensive and technologically feasible. However, during the last ten years of discussions, conference papers, IAA Cosmic Studies, and interest around the globe, many discussions have led some individuals to the following conclusions: • Solar Array technology is improving rapidly and will enable sufficient energy for climbing • Tremendous advances are occurring in lightweight deployable structures |url-status = dead |archive-url = https://web.archive.org/web/20170116175959/http://isec.org/pdfs/isec_reports/2013_ISEC_Design_Considerations_for_Space_Elevator_Tether_Climbers_Final_Report.pdf |archive-date = January 16, 2017}}</ref>

Wireless energy transfer such as laser power beaming is currently considered the most likely method, using megawatt-powered free electron or solid state lasers in combination with adaptive mirrors approximately {{convert|10|m|ft|abbr=on}} wide and a photovoltaic array on the climber tuned to the laser frequency for efficiency.<ref name="Edwards" /> For climber designs powered by power beaming, this efficiency is an important design goal. Unused energy would need to be re-radiated away with heat-dissipation systems, which add to weight.

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 conductivity of carbon nanotubes to provide power.<ref name="JapanUKTimes" />

===Counterweight===
[[File:Nasa space elev.jpg|thumb|Space Elevator with Space Station]]
Several solutions have been proposed to act as a counterweight:
* a heavy, captured [[Astronomy:Asteroid|asteroid]];<ref name="NASASci" /><ref>{{cite web|url=https://www.popsci.com/building-hanging-from-an-asteroid/ |title=This building hanging from an asteroid is absurd – but let's take it seriously for a second |work=Popular Science |first=Sara |last=Chodosh |date=March 29, 2017 |language=en|access-date=September 4, 2019}}</ref>
* a [[Engineering:Space dock|space dock]], space station or spaceport positioned past geostationary orbit
* a further upward extension of the cable itself so that the net upward pull would be the same as an equivalent counterweight;
* parked spent climbers that had been used to thicken the cable during construction, other junk, and material lifted up the cable for the purpose of increasing the counterweight.<ref name="PhaseII">Edwards BC, Westling EA. (2002) ''The Space Elevator: A Revolutionary Earth-to-Space Transportation System.'' San Francisco: Spageo Inc. {{ISBN|0-9726045-0-2}}.</ref>
Extending the cable has the advantage of some 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. Its disadvantage is the need to produce greater amounts of cable material as opposed to using just anything available that has mass.

==Applications==
===Launching into deep space===
An object attached to a space elevator at a radius of approximately 53,100&nbsp;km would be at [[Astronomy:Escape velocity|escape velocity]] when released. Transfer orbits to the L1 and L2 [[Astronomy:Lagrangian point|Lagrangian point]]s could be attained by release at 50,630 and 51,240&nbsp;km, respectively, and transfer to lunar orbit from 50,960&nbsp;km.<ref>{{cite web|url=http://www.spaceelevator.com/docs/iac-2004/iac-04-iaa.3.8.3.04.engel.pdf |title=IAC-04-IAA.3.8.3.04 Lunar transportation scenarios utilising the space elevator |author=Engel, Kilian A. |publisher=www.spaceelevator.com |url-status=dead |archive-url=https://web.archive.org/web/20120424230830/http://www.spaceelevator.com/docs/iac-2004/iac-04-iaa.3.8.3.04.engel.pdf |archive-date=April 24, 2012}}</ref>

At the end of Pearson's {{convert|144,000|km|mi|abbr=on}} cable, the tangential velocity is 10.93 kilometers per second (6.79&nbsp;mi/s). That is more than enough to [[Astronomy:Escape velocity|escape]] Earth's gravitational field and send probes at least as far out as [[Astronomy:Jupiter|Jupiter]]. Once at Jupiter, a gravitational assist maneuver could permit solar escape velocity to be reached.<ref name="aravind">{{cite journal|title=The physics of the space elevator |author=Aravind, P. K.|year=2007|journal=American Journal of Physics|volume=45|issue=2|doi=10.1119/1.2404957|page=125 |url=http://users.wpi.edu/~paravind/Publications/PKASpace%20Elevators.pdf |bibcode=2007AmJPh..75..125A|access-date=January 7, 2013|archive-url=https://web.archive.org/web/20181221130720/http://users.wpi.edu/~paravind/Publications/PKASpace%20Elevators.pdf |archive-date=December 21, 2018|url-status=dead}}</ref>

===Extraterrestrial elevators===
A space elevator could also be constructed on other planets, asteroids and moons.

A [[Astronomy:Mars|Martian]] tether could be much shorter than one on Earth. Mars' surface gravity is 38 percent of Earth's, while it rotates around its axis in about the same time as Earth. Because of this, Martian [[Astronomy:Areostationary orbit|stationary orbit]] is much closer to the surface, and hence the elevator could be much shorter. Current materials are already sufficiently strong to construct such an elevator.<ref>Forward, Robert L. and Moravec, Hans P. (March 22, 1980) [http://www.frc.ri.cmu.edu/~hpm/project.archive/1976.skyhook/1982.articles/elevate.800322 Space Elevators]. Carnegie Mellon University. "Interestingly enough, they are already more than strong enough for constructing skyhooks on the moon and Mars."</ref> Building a Martian elevator would be complicated by the Martian moon [[Astronomy:Phobos (moon)|Phobos]], which is in a low orbit and intersects the Equator regularly (twice every orbital period of 11&nbsp;h 6&nbsp;min). Phobos and Deimos may get in the way of an areostationary space elevator; on the other hand, they may contribute useful resources to the project. Phobos is projected to contain high amounts of carbon. If carbon nanotubes become feasible for a tether material, there will be an abundance of carbon near Mars. This could provide readily available resources for future colonization on Mars.

[[File:Space elevator Phobos.jpg|thumb|upright=1.35|Space elevator Phobos]]
[[File:Earth vs Mars gravity at elevation.webp|thumb|upright=1.35|[[Physics:Gravity of Earth|Earth]] vs Mars vs Moon gravity at [[Elevation|elevation]]]]
[[Astronomy:Phobos (moon)|Phobos]] is [[Astronomy:Tidal locking|tide-locked]]: one side always faces its primary, Mars. An elevator extending 6,000&nbsp;km from that inward side would end about 28 kilometers above the [[Astronomy:Martian surface|Martian surface]], just out of the denser parts of the [[Astronomy:Atmosphere of Mars|atmosphere of Mars]]. A similar cable extending 6,000&nbsp;km in the opposite direction would counterbalance the first, so the center of mass of this system remains in Phobos. In total the space elevator would extend out over 12,000&nbsp;km which would be below [[Astronomy:Areostationary orbit|Areostationary orbit]] of Mars (17,032&nbsp;km). A rocket launch would still be needed to get the rocket and cargo to the beginning of the space elevator 28&nbsp;km above the surface. The surface of Mars is rotating at 0.25 km/s at the equator and the bottom of the space elevator would be rotating around Mars at 0.77&nbsp;km/s, so only 0.52&nbsp;km/s (1872&nbsp;km/h) of [[Astronomy:Delta-v|Delta-v]] would be needed to get to the space elevator. Phobos orbits at 2.15&nbsp;km/s and the outermost part of the space elevator would rotate around Mars at 3.52&nbsp;km/s.<ref>{{cite journal |last1=Weinstein |first1=Leonard M. |title=Space Colonization Using Space-Elevators from Phobos |journal=AIP Conference Proceedings |date=January 2003 |volume=654 |pages=1227–1235 |doi=10.1063/1.1541423 |s2cid=1661518 |bibcode=2003AIPC..654.1227W |hdl=2060/20030065879 |url=https://space.nss.org/wp-content/uploads/2003-Space-Colonization-Using-Space-Elevators-From-Phobos.pdf |access-date=23 December 2022 |language=en}}</ref><ref>{{cite conference |last1=Weinstein |first1=Leonard |title=AIP Conference Proceedings |chapter=Space Colonization Using Space-Elevators from Phobos |conference=AIP Conference Proceedings|year=2003 |volume=654 |pages=1227–1235 |doi=10.1063/1.1541423 |bibcode=2003AIPC..654.1227W |hdl=2060/20030065879 |hdl-access=free}}</ref>

The Earth's [[Astronomy:Moon|Moon]] is a potential location for a [[Astronomy:Lunar space elevator|Lunar space elevator]], especially as the [[Engineering:Specific strength|specific strength]] required for the tether is low enough to use currently available materials. The Moon does not rotate fast enough for an elevator to be supported by centrifugal force (the proximity of the Earth means there is no effective lunar-stationary orbit), but differential gravity forces means that an elevator could be constructed through [[Astronomy:Lagrangian point|Lagrangian point]]s. A near-side elevator would extend through the Earth-Moon L1 point from an anchor point near the center of the visible part of Earth's Moon: the length of such an elevator must exceed the maximum L1 altitude of 59,548&nbsp;km, and would be considerably longer to reduce the mass of the required apex counterweight.<ref name="Pearson 2005" />
A far-side lunar elevator would pass through the L2 Lagrangian point and would need to be longer than on the near-side: again, the tether length depends on the chosen apex anchor mass, but it could also be made of existing engineering materials.<ref name="Pearson 2005">{{cite web| url=http://www.niac.usra.edu/files/studies/final_report/1032Pearson.pdf| year= 2005| title=Lunar Space Elevators for Cislunar Space Development Phase I Final Technical Report| last1=pearson |first1=Jerome| first2=Eugene |last2=Levin |first3=John |last3=Oldson |first4=Harry |last4=Wykes}}</ref>

[[File:16 Psyche space elevator.webp|thumb|300px|[[Astronomy:16 Psyche|16 Psyche]] space elevator concept <br> The [[Physics:Surface gravity|surface gravity]] is less than 2% of earths at ~{{val|0.144|u=m/s2}}<ref name=Shepard-Richardson-etal-2017>
{{cite journal
 |last1=Shepard    |first1=Michael K.
 |last2=Richardson  |first2=James
 |last3=Taylor      |first3=Patrick A.
 |display-authors=0
 |year=2017
 |title=Radar observations and shape model of asteroid 16&nbsp;Psyche
 |journal=Icarus
 |volume=281  |pages=388–403
 |bibcode=2017Icar..281..388S
 |doi=10.1016/j.icarus.2016.08.011 |doi-access=free
}}
</ref>]]
[[File:Ceres space elevator.webp|thumb|[[Astronomy:Ceres (dwarf planet)|Ceres]] space elevator concept <br> Surface gravity is  {{ubl|{{Gr|0.938|469.7|3}} [[Physics:Acceleration|m/s{{sup|2}}]]{{refn|groupname=lower-alpha|name="known parameters"|Calculated based on known parameters:
* Surface area: 4πr{{sup|2}}
* Surface gravity: {{sfrac|GM|r{{sup|2}}}}
* Escape velocity: {{sqrt|{{sfrac|2GM|r}}}}
* Rotation velocity: {{sfrac|rotation period|circumference}}}}|0.029 [[Physics:G-force|''g'']]}} less than 3% of [[Astronomy:Earth|Earth]]'s]]
Rapidly spinning asteroids or moons could use cables to eject materials to convenient points, such as Earth orbits;<ref>Ben Shelef, the Spaceward Foundation [http://www.spaceward.org/documents/papers/ASE.pdf Asteroid Slingshot Express - Tether-based Sample Return] {{Webarchive|url=https://web.archive.org/web/20130806051254/http://www.spaceward.org/documents/papers/ASE.pdf |date=August 6, 2013 }}</ref> or conversely, to eject materials to send a portion of the mass of the asteroid or moon to Earth orbit or a [[Astronomy:Lagrangian point|Lagrangian point]]. [[Biography:Freeman Dyson|Freeman Dyson]], a physicist and mathematician, has suggested{{Citation needed|date=September 2008}} using such smaller systems as power generators at points distant from the Sun where solar power is uneconomical.

A space elevator using presently available engineering materials could be constructed between mutually tidally locked worlds, such as [[Astronomy:Pluto|Pluto]] and [[Astronomy:Charon (moon)|Charon]] or the components of binary asteroid [[Astronomy:90 Antiope|90 Antiope]], with no terminus disconnect, according to Francis Graham of Kent State University.<ref>{{cite book|author=Graham FG |title=45th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit|doi=10.2514/6.2009-4906|chapter=Preliminary Design of a Cable Spacecraft Connecting Mutually Tidally Locked Planetary Bodies|year=2009|isbn=978-1-60086-972-3}}</ref> However, spooled variable lengths of cable must be used due to ellipticity of the orbits.

==Construction==
{{Main|Engineering:Space elevator construction}}

The construction of a space elevator would need reduction of some technical risk. Some advances in engineering, manufacturing and physical technology are required.<ref name="Edwards" /> Once a first space elevator is built, the second one and all others would have the use of the previous ones to assist in construction, making their costs considerably lower. Such follow-on space elevators would also benefit from the great reduction in technical risk achieved by the construction of the first space elevator.<ref name="Edwards" />

Prior to the work of Edwards in 2000,<ref name="EDWARDS_PHASE_I_2000_472Edwards.html" /> most concepts for constructing a space elevator had the cable manufactured in space. That was thought to be necessary for such a large and long object and for such a large counterweight. Manufacturing the cable in space would be done in principle by using an [[Astronomy:Asteroid|asteroid]] or [[Astronomy:Near-Earth object|Near-Earth object]] for source material.<ref>D.V. Smitherman (Ed.), [http://www.nss.org/resources/library/spaceelevator/2000-SpaceElevator-NASA-CP210429.pdf Space Elevators: An Advanced Earth-Space Infrastructure for the New Millennium] {{Webarchive|url=https://web.archive.org/web/20150328040627/http://www.nss.org/resources/library/spaceelevator/2000-SpaceElevator-NASA-CP210429.pdf |date=March 28, 2015 }}, NASA/CP-2000-210429, Marshall Space Flight Center, Huntsville, Alabama, 2000</ref><ref>Hein, A.M., [https://www.academia.edu/2111184/A.M._Hein_Producing_a_Space_Elevator_Tether_using_a_NEO_A_Preliminary_Assessment_ Producing a Space Elevator Tether Using a NEO: A Preliminary Assessment], International Astronautical Congress 2012, IAC-2012, Naples, Italy, 2012</ref> These earlier concepts for construction require a large preexisting space-faring infrastructure to maneuver an asteroid into its needed orbit around Earth. They also required the development of technologies for manufacture in space of large quantities of exacting materials.<ref name="ISEC_SE_way_forward_2013">Space Elevators: An Assessment of the Technological Feasibility and the Way Forward, Page 326, http://www.virginiaedition.com/media/spaceelevators.pdf {{Webarchive|url=https://web.archive.org/web/20140516231842/http://www.virginiaedition.com/media/spaceelevators.pdf |date=May 16, 2014 }}</ref>

Since 2001, most work has focused on simpler methods of construction requiring much smaller space infrastructures. They conceive the launch of a long cable on a large spool, followed by deployment of it in space.<ref name="Edwards" /><ref name="EDWARDS_PHASE_I_2000_472Edwards.html" /><ref name="ISEC_SE_way_forward_2013" /> The spool would be initially parked in a geostationary orbit above the planned anchor point. A long cable would be dropped "downward" (toward Earth) and would be balanced by a mass being dropped "upward" (away from Earth) for the whole system to remain on the geosynchronous orbit. Earlier designs imagined the balancing mass to be another cable (with counterweight) extending upward, with the main spool remaining at the original geosynchronous orbit level. Most current designs elevate the spool itself as the main cable is payed out, a simpler process. When the lower end of the cable is long enough to reach the surface of the Earth (at the equator), it would be anchored. Once anchored, the center of mass would be elevated more (by adding mass at the upper end or by paying out more cable). This would add more tension to the whole cable, which could then be used as an elevator cable.

One plan for construction uses conventional rockets to place a "minimum size" initial seed cable of only 19,800&nbsp;kg.<ref name="Edwards" /> This first very small ribbon would be adequate to support the first 619&nbsp;kg climber. The first 207 climbers would carry up and attach more cable to the original, increasing its cross section area and widening the initial ribbon to about 160&nbsp;mm wide at its widest point. The result would be a 750-ton cable with a lift capacity of 20 tons per climber.

===Safety issues and construction challenges===
{{Main|Unsolved:Space elevator safety}}
For early systems, transit times from the surface to the level of geosynchronous orbit would be about five days. On these early systems, the time spent moving through the Van Allen radiation belts would be enough that passengers would need to be protected from radiation by shielding, which would add mass to the climber and decrease payload.<ref>{{cite web|url=https://www.newscientist.com/article/dn10520 |title=Space elevators: 'First floor, deadly radiation!' |access-date=January 2, 2010 |date=November 13, 2006|work=New Scientist |publisher=Reed Business Information Ltd.}}</ref>

A space elevator would present a navigational hazard, both to aircraft and spacecraft. Aircraft could be diverted by air-traffic control restrictions. All objects in stable orbits that have perigee below the maximum altitude of the cable that are not synchronous with the cable would impact the cable eventually, unless avoiding action is taken. One potential solution proposed by Edwards is to use a movable anchor (a sea anchor) to allow the tether to "dodge" any space debris large enough to track.<ref name="Edwards" />

Impacts by space objects such as meteoroids, micrometeorites and orbiting man-made debris pose another design constraint on the cable. A cable would need to be designed to maneuver out of the way of debris, or absorb impacts of small debris without breaking.{{Citation needed|date=July 2022}}

===Economics===
{{Main|Finance:Space elevator economics}}
With a space elevator, materials might be sent into orbit at a fraction of the current cost. As of 2022, conventional rocket designs cost about US$12,125 per [[Kilogram|kilogram]] (US$5,500 per [[Pound (mass)|pound]]) for transfer to geostationary orbit.<ref>{{cite web|url=https://www.spacex.com/rideshare/#:~:text=%24275k%20for%2050kg%20to,LEO%2C%20GTO%2C%20and%20TLI.|title=Smallsat Rideshare Program|date=March 1, 2022|work=SpaceX|access-date=May 1, 2023}}</ref> Current space elevator proposals envision payload prices starting as low as $220 per kilogram ($100 per [[Pound (mass)|pound]]),<ref>{{cite web|url=http://www.spaceward.org/elevator-faq |title=The Space Elevator FAQ |access-date=June 3, 2009 |author=The Spaceward Foundation |location=Mountain View, CA |archive-url=https://web.archive.org/web/20090227115101/http://www.spaceward.org/elevator-faq |archive-date=February 27, 2009 |url-status=dead}}</ref> similar to the $5–$300/kg estimates of the [[Physics:Launch loop|Launch loop]], but higher than the $310/ton to 500&nbsp;km orbit quoted to Dr. Jerry Pournelle for an orbital airship system.<ref>{{cite web |first=Jerry |last=Pournelle |date=April 23, 2003 |url=http://www.jerrypournelle.com/archives2/archives2view/view306.html#Friday |title=Friday's VIEW post from the 2004 Space Access Conference |access-date=January 1, 2010}}</ref>

Philip Ragan, co-author of the book ''Leaving the Planet by Space Elevator'', states that "The first country to deploy a space elevator will have a 95 percent cost advantage and could potentially control all space activities."<ref>{{cite news |url=http://www.news.com.au/news/race-to-build-worlds-first-space-elevator/story-fna7dq6e-1111118059040 |title=Race on to build world's first space elevator |date=November 17, 2008|work=news.com.au|first=Andrew |last=Ramadge|author2=Schneider, Kate|access-date=January 14, 2016|url-status=dead|archive-date=September 13, 2015 |archive-url=https://web.archive.org/web/20150913204538/http://www.news.com.au/news/race-to-build-worlds-first-space-elevator/story-fna7dq6e-1111118059040}}</ref>

==International Space Elevator Consortium (ISEC)==
The International Space Elevator Consortium (ISEC) is a US Non-Profit [[Organization:501(c)(3) organization|501(c)(3)]] Corporation<ref>{{Cite web|title=ISEC IRS filing |url=https://apps.irs.gov/app/eos/displayAll.do?dispatchMethod=displayAllInfo&Id=4984679&ein=800302896&country=US&deductibility=all&dispatchMethod=searchAll&isDescending=false&city=&ein1=80-0302896&postDateFrom=&exemptTypeCode=al&submitName=Search&sortColumn=orgName&totalResults=1&names=&resultsPerPage=25&indexOfFirstRow=0&postDateTo=&state=IL|website=apps.irs.gov |access-date=February 9, 2019}}</ref> formed to promote the development, construction, and operation of a space elevator as "a revolutionary and efficient way to space for all humanity".<ref name="isec">{{cite web |url=http://www.isec.org/index.php/what-is-isec |work=ISEC |title=What is ISEC? : About Us |access-date=June 2, 2012 |url-status=dead |archive-url=https://web.archive.org/web/20120707201835/http://www.isec.org/index.php/what-is-isec |archive-date=July 7, 2012}}</ref> It was formed after the Space Elevator Conference in Redmond, Washington in July 2008 and became an affiliate organization with the [[Organization:National Space Society|National Space Society]]<ref>{{Cite web|title=NSS Affiliates|website=www.nss.org |url=http://www.nss.org/about/affiliates.html|access-date=August 30, 2015|archive-date=October 16, 2015 |archive-url=https://web.archive.org/web/20151016040656/http://www.nss.org/about/affiliates.html|url-status=dead}}</ref> in August 2013.<ref name="isec" /> ISEC hosts an annual Space Elevator conference at the Seattle Museum of Flight.<ref>{{Cite web |url=https://www.space.com/27225-space-elevator-technology.html|title=Space Elevator Advocates Take Lofty Look at Innovative Concepts |first=Leonard |last=David |date=September 22, 2014 |website=Space.com |language=en|access-date=February 13, 2019}}</ref><ref>{{Cite web|url=https://space.nss.org/the-international-space-elevator-consortium-isec-2017-space-elevator-conference/ |title=The International Space Elevator Consortium (ISEC) 2017 Space Elevator Conference |date=August 14, 2017|publisher=National Space Society |language=en-US|access-date=February 13, 2019}}</ref><ref>{{Cite web |url=http://spaceref.com/space-elevator/annual-space-elevator-conference-set-for-august-25-27.html |title=Annual Space Elevator Conference Set for August 25–27 |website=SpaceRef |first=Marc |last=Boucher |date=July 17, 2012 |access-date=February 13, 2019 }}{{Dead link|date=December 2023 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

ISEC coordinates with the two other major societies focusing on space elevators: the Japanese Space Elevator Association<ref>{{Cite web|title = Japan Space Elevator Association|url = http://www.jsea.jp/links/|script-website = ja:一般｜JSEA 一般社団法人 宇宙エレベーター協会|access-date = August 30, 2015}}</ref> and EuroSpaceward.<ref>{{cite web|url = http://www.eurospaceward.org/|title = Eurospaceward|date = August 30, 2015|access-date = August 30, 2015|website = Eurospaceward}}</ref> ISEC supports symposia and presentations at the International Academy of Astronautics<ref>{{Cite web|url = http://iaaweb.org/content/view/624/823/|title = Homepage of the Study Group 3.24, Road to Space Elevator Era|date = October 2, 2014|access-date = August 30, 2015|website = The International Academy of Astronautics (IAA)|last = Akira|first = Tsuchida}}</ref> and the International Astronautical Federation Congress<ref>{{Cite web|url = http://www.iafastro.org/events/iac/iac-2014/meetings/|title = IAC 2014 Meeting Schedule|access-date = August 30, 2015|website = International Astronautical Federation|archive-date = September 24, 2015|archive-url = https://web.archive.org/web/20150924032203/http://www.iafastro.org/events/iac/iac-2014/meetings/|url-status = dead}}</ref> each year.

==Related concepts==
The conventional current concept of a "Space Elevator" has evolved from a static compressive structure reaching to the level of GEO, to the modern baseline idea of a static tensile structure anchored to the ground and extending to well above the level of GEO. In the current usage by practitioners (and in this article), a "Space Elevator" means the Tsiolkovsky-Artsutanov-Pearson type as considered by the International Space Elevator Consortium. This conventional type is a static structure fixed to the ground and extending into space high enough that cargo can climb the structure up from the ground to a level where simple release will put the cargo into an [[Physics:Orbit|orbit]].<ref>"CLIMB: The Journal of the International Space Elevator Consortium", Volume 1, Number 1, December 2011, This journal is cited as an example of what is generally considered to be under the term "Space Elevator" by the international community. [http://www.isec.org/index.php?option=com_content&view=article&id=28&Itemid=31] {{Webarchive|url=https://web.archive.org/web/20131218085857/http://www.isec.org/index.php?option=com_content&view=article&id=28&Itemid=31|date=December 18, 2013}}</ref>

Some concepts related to this modern baseline are not usually termed a "Space Elevator", but are similar in some way and are sometimes termed "Space Elevator" by their proponents. For example, [[Biography:Hans Moravec|Hans Moravec]] published an article in 1977 called "A Non-Synchronous Orbital [[Engineering:Skyhook (structure)|Skyhook]]" describing a concept using a rotating cable.<ref>{{cite journal |author=Moravec, Hans P. |title=A Non-Synchronous Orbital Skyhook|journal=Journal of the Astronautical Sciences|volume=25 |date=October–December 1977|bibcode=1977JAnSc..25..307M|pages=307–322}}</ref> The rotation speed would exactly match the orbital speed in such a way that the tip velocity at the lowest point was zero compared to the object to be "elevated". It would dynamically grapple and then "elevate" high flying objects to orbit or low orbiting objects to higher orbit.

The original concept envisioned by Tsiolkovsky was a compression structure, a concept similar to an [[Engineering:Radio masts and towers|aerial mast]]. While such structures might reach space (100&nbsp;km, 62&nbsp;mi), they are unlikely to reach geostationary orbit. The concept of a Tsiolkovsky tower combined with a classic space elevator cable (reaching above the level of GEO) has been suggested.<ref name="JBIS1999"/> Other ideas use very tall compressive towers to reduce the demands on launch vehicles.<ref name="TorontoProposal"/> The vehicle is "elevated" up the tower, which may extend as high as above the atmosphere, and is launched from the top. Such a tall tower to access near-space altitudes of {{cvt|20|km|mi}} has been proposed by various researchers.<ref name="TorontoProposal">{{cite journal |doi=10.1016/j.actaastro.2009.02.018 |title=A free-standing space elevator structure: A practical alternative to the space tether|year=2009 |last1=Quine |first1=B.M. |last2=Seth |first2=R.K. |last3=Zhu |first3=Z.H. |journal=Acta Astronautica |volume=65 |issue=3–4 |page=365 |citeseerx=10.1.1.550.4359 |bibcode=2009AcAau..65..365Q |url=http://pi.library.yorku.ca/dspace/bitstream/handle/10315/2587/AA_3369_Quine_Space_Elevator_Final_2009.pdf}}</ref><ref>{{Cite book |doi = 10.2514/6.1998-3737|chapter = Compression structures for Earth launch |title = 34th AIAA/ASME/SAE/ASEE Joint Propulsion Conference and Exhibit|year = 1998|last1 = Landis|first1 = Geoffrey}}</ref><ref>Hjelmstad, Keith, [http://hieroglyph.asu.edu/wp-content/uploads/2014/08/Hjelmstad-on-Stephenson-Structural-Design-of-the-Tall-Tower.pdf "Structural Design of the Tall Tower"], ''Hieroglyph'', November 30, 2013. Retrieved September 1, 2015.</ref>

The aerovator is a concept invented by a Yahoo Group discussing space elevators, and included in a 2009 book about space elevators. It would consist of a >1000 km long ribbon extending diagonally upwards from a ground-level hub and then levelling out to become horizontal. Aircraft would pull on the ribbon while flying in a circle, causing the ribbon to rotate around the hub once every 13 minutes with its tip travelling at 8 km/s. The ribbon would stay in the air through a mix of aerodynamic lift and centrifugal force. Payloads would climb up the ribbon and then be launched from the fast-moving tip into orbit.<ref>{{Citation |last=Van Pelt |first=Micheal |title=Space Elevators |date=2009 |url=https://doi.org/10.1007/978-0-387-76556-3_6 |work=Space Tethers and Space Elevators |pages=143–178 |editor-last= |editor-first= |access-date=2023-12-27 |place=New York, NY |publisher=Springer |language=en |doi=10.1007/978-0-387-76556-3_6 |isbn=978-0-387-76556-3}}</ref>

Other concepts for [[Astronomy:Non-rocket spacelaunch|non-rocket spacelaunch]] related to a space elevator (or parts of a space elevator) include an [[Astronomy:Orbital ring|orbital ring]], a [[Astronomy:Space fountain|space fountain]], a [[Physics:Launch loop|launch loop]], a [[Engineering:Skyhook (structure)|skyhook]], a [[Engineering:Space tether|space tether]], and a buoyant "SpaceShaft".<ref>[http://ksj.mit.edu/tracker/2009/07/space-shaft-or-story-would-have-been-bit/ Space Shaft: Or, the story that would have been a bit finer, if only one had known...], "Knight Science Journalism Tracker (MIT)", July 1, 2009.</ref>

==Notes==
{{reflist|group=note}}

==See also==
*Gravity elevator
*[[Astronomy:Orbital ring|Orbital ring]]

==References==
{{reflist|1=25em}}

==Further reading==
{{Refbegin}}
* [http://www.nss.org/resources/library/spaceelevator/2000-SpaceElevator-NASA-CP210429.pdf A conference publication based on findings from the Advanced Space Infrastructure Workshop on Geostationary Orbiting Tether "Space Elevator" Concepts] {{Webarchive|url=https://web.archive.org/web/20150328040627/http://www.nss.org/resources/library/spaceelevator/2000-SpaceElevator-NASA-CP210429.pdf |date=March 28, 2015 }} (PDF), held in 1999 at the NASA Marshall Space Flight Center, Huntsville, Alabama. Compiled by D.V. Smitherman Jr., published August 2000.
* "The Political Economy of Very Large Space Projects" [http://www.jetpress.org/volume4/space.htm HTML] [http://www.jetpress.org/volume4/space.pdf PDF], John Hickman, Ph.D. ''Journal of Evolution and Technology'' Vol. 4 – November 1999.
* [https://spectrum.ieee.org/aerospace/space-flight/a-hoist-to-the-heavens A Hoist to the Heavens] By Bradley Carl Edwards
* Ziemelis K. (2001) "Going up". In New Scientist '''2289''':&nbsp;24–27. [http://www.spaceref.com/news/viewnews.html?id=337 Republished in SpaceRef] {{Webarchive|url=https://web.archive.org/web/20220112075348/http://www.spaceref.com/news/viewnews.html?id=337 |date=January 12, 2022 }}. Title page: "The great space elevator: the dream machine that will turn us all into astronauts."
* [https://web.archive.org/web/20101104104658/http://www.space.com/businesstechnology/technology/space_elevator_020327-1.html The Space Elevator Comes Closer to Reality]. An overview by Leonard David of space.com, published March 27, 2002.
* Krishnaswamy, Sridhar. Stress Analysis – [https://web.archive.org/web/20060519133820/http://www.cqe.northwestern.edu/sk/C62/OrbitalTower_ME362.pdf The Orbital Tower] (PDF)
* LiftPort's Roadmap for Elevator To Space [https://web.archive.org/web/20070710032602/http://www.liftport.com/papers/SE_Roadmap_v1beta.pdf SE Roadmap] (PDF)
* {{cite news |date=March 28, 2008 |first=David |last=Shiga |url=https://www.newscientist.com/article/dn13552-space-elevators-face-wobble-problem/ |title=Space elevators face wobble problem |work=New Scientist }}
* Alexander Bolonkin, "[https://archive.org/details/Non-rocketSpaceLaunchAndFlight Non Rocket Space Launch and Flight]". Elsevier, 2005. 488 pgs. {{ISBN|978-0-08044-731-5}}.
{{Refend}}

==External links==
* [http://economist.com/science/tq/displayStory.cfm?story_id=7001786 The Economist: Waiting For The Space Elevator] (June 8, 2006 – subscription required)
* [https://web.archive.org/web/20060806021241/http://www.radio.cbc.ca/programs/quirks/archives/01-02/nov0301.htm CBC Radio Quirks and Quarks November 3, 2001] ''Riding the Space Elevator''
* [http://www.timesonline.co.uk/tol/driving/features/article5529668.ece Times of London Online: Going up ... and the next floor is outer space]
* [http://www.islandone.org/LEOBiblio/CLARK1.HTM ''The Space Elevator: 'Thought Experiment', or Key to the Universe?''] {{Webarchive|url=https://web.archive.org/web/20200201205032/http://www.islandone.org/LEOBiblio/CLARK1.HTM |date=February 1, 2020 }}. By Sir Arthur C. Clarke. Address to the XXXth International Astronautical Congress, Munich, September 20, 1979.
* [https://www.isec.org/ International Space Elevator Consortium Website]
* [http://www.sf-encyclopedia.com/entry/space_elevator Space Elevator] entry at ''[[The Encyclopedia of Science Fiction]]''

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{{Non-rocket spacelaunch}}
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[[Category:Space elevator| ]]
[[Category:Exploratory engineering]]
[[Category:Hypothetical technology]]
[[Category:Space access]]
[[Category:Spacecraft propulsion]]
[[Category:Vertical transport devices]]

{{Sourceattribution|Space elevator}}