Editing Space elevator (section)

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

A [[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 [[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. (22 March 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 [[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 (moon)|Phobos]]]]
[[File:Earth vs Mars gravity at elevation.webp|thumb|upright=1.35|[[Gravity of Earth|Earth]] vs [[Gravity of Mars|Mars]] vs [[Moon]] [[gravity]] at [[elevation]]]]
[[Phobos (moon)|Phobos]] is [[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 [[Martian surface]], just out of the denser parts of the [[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 [[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 [[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 [[Moon]] is a potential location for a [[Lunar space elevator]], especially as the [[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 [[Lagrangian point]]s. A near-side elevator would extend through the Earth-Moon [[Inner lagrangian point|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 |last1=Pearson |first1=Jerome |last2=Levin |first2=Eugene |last3=Oldson |first3=John |last4=Wykes |first4=Harry |year=2005 |title=Lunar Space Elevators for Cislunar Space Development Phase I Final Technical Report |url=http://www.niac.usra.edu/files/studies/final_report/1032Pearson.pdf}}</ref>

[[File:16 Psyche space elevator.webp|thumb|upright=1.4|[[16 Psyche]] space elevator concept—the [[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=etal
 |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|upright=1.4|[[Ceres (dwarf planet)|Ceres]] space elevator concept –<br />[[Surface gravity]] is  {{ubl|{{Gr|0.938|469.7|3}} [[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 [[g-force|''g'']]}} less than 3% of [[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=6 August 2013}}.</ref> or conversely, to eject materials to send a portion of the mass of the asteroid or moon to Earth orbit or a [[Lagrangian point]]. [[Freeman Dyson]], a physicist and mathematician, 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 [[Pluto]] and [[Charon (moon)|Charon]] or the components of binary asteroid [[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.