Editing Artificial gravity (section)

===Human spaceflight===
The [[Gemini 11]] mission attempted in 1966 to produce artificial gravity by rotating the capsule around the [[Agena Target Vehicle]] to which it was attached by a 36-meter tether. They were able to generate a small amount of artificial gravity, about 0.00015&nbsp;''g'', by firing their side thrusters to slowly rotate the combined craft like a slow-motion pair of [[bolas]].<ref name=" Gatland1976">{{Cite book|first=Kenneth|last=Gatland|title=Manned Spacecraft, Second Revision|place=New York, NY, USA|publisher=MacMillan|year=1976|pages=180–182|isbn=978-0-02-542820-1}}</ref> The resultant force was too small to be felt by either astronaut, but objects were observed moving towards the "floor" of the capsule.<ref name="Clément G 2007">{{Cite book |editor-last=Clément |editor-first=Gilles |editor-last2=Bukley |editor-first2=Angie |title=Artificial Gravity |date=May 28, 2007 |isbn=978-0-387-70714-3 |series=Space Technology Library |location=New York |doi=10.1007/0-387-70714-X |eissn=2542-8896 |issn=0924-4263 |publisher=[[Springer Science+Business Media|Springer]] }}</ref>

==== Health benefits ====
[[File:Jsc2004e18862.jpg|thumb|Artificial gravity has been suggested for interplanetary journeys to Mars]]
Artificial gravity has been suggested as a solution to various health risks associated with spaceflight.<ref name="ncbi.nlm.nih.gov" /> In 1964, the [[Soviet]] space program believed that a human could not survive more than 14 days in space for fear that the [[heart]] and [[blood vessels]] would be unable to adapt to the weightless conditions.<ref>{{cite journal|jstor=3947769|title=Weightlessness Obstacle to Space Survival|date=April 4, 1964|journal=The Science News-Letter|volume=86|issue=7|pages=103}}</ref> This fear was eventually discovered to be unfounded as spaceflights have now lasted up to 437 consecutive days,<ref>{{cite news|url=https://www.npr.org/sections/thetwo-way/2017/04/24/525374569/astronaut-peggy-whitson-sets-new-nasa-record-for-most-days-in-space|title=Astronaut Peggy Whitson Sets NASA Record For Most Days In Space|newspaper=NPR|date=April 24, 2017|access-date=April 4, 2018|last1=Chappell|first1=Bill}}</ref> with missions aboard the International Space Station commonly lasting 6 months. However, the question of human safety in space did launch an investigation into the physical effects of prolonged exposure to weightlessness. In June 1991, the Spacelab Life Sciences 1 on the [[Space Shuttle]] flight [[STS-40]] flight performed 18 experiments on two men and two women over nine days. In an environment without gravity, it was concluded that the response of [[white blood cells]] and [[muscle]] mass decreased. Additionally, within the first 24 hours spent in a weightless environment, [[blood volume]] decreased by 10%.<ref name="jstor.org">{{cite journal|jstor=1311819|title=Artificial Gravity and Space Travel|first=Leonard|last=David|date=April 4, 1992|journal=BioScience|volume=42|issue=3|pages=155–159|doi=10.2307/1311819}}</ref><ref name="popularmechanics.com"/><ref name="iaaweb.org"/> Long periods of weightlessness can cause brain swelling and eyesight problems.<ref>{{Cite web | url=https://phys.org/news/2012-03-prolonged-space-brain-eye-abnormalities.html |title = Prolonged space travel causes brain and eye abnormalities in astronauts}}</ref> Upon return to Earth, the effects of prolonged weightlessness continue to affect the human body as fluids pool back to the lower body, the [[heart rate]] rises, a drop in [[blood pressure]] occurs, and there is a reduced tolerance for [[exercise]].<ref name="jstor.org"/>

Artificial gravity, for its ability to [[mimic]] the behavior of gravity on the human body, has been suggested as one of the most encompassing manners of combating the physical effects inherent in weightless environments. Other measures that have been suggested as symptomatic treatments include exercise, diet, and [[Pingvin exercise suit|Pingvin suits]]. However, criticism of those methods lies in the fact that they do not fully eliminate health problems and require a variety of solutions to address all issues. Artificial gravity, in contrast, would remove the weightlessness inherent in space travel. By implementing artificial gravity, space travelers would never have to experience weightlessness or the associated side effects.<ref name="iaaweb.org"/> Especially in a modern-day six-month journey to [[Mars]], exposure to artificial gravity is suggested in either a continuous or intermittent form to prevent extreme debilitation to the astronauts during travel.<ref name="ncbi.nlm.nih.gov" />

====Proposals====
[[File:Nasa mars artificial gravity 1989.jpg|thumb|Rotating Mars spacecraft – 1989 NASA concept]]
Several proposals have incorporated artificial gravity into their design:
* Discovery II: a 2005 vehicle proposal capable of delivering a 172-metric-ton crew to Jupiter's orbit in 118 days. A very small portion of the 1,690-metric-ton craft would incorporate a centrifugal crew station.<ref>{{cite web|access-date=2011-09-28|author1=Craig H. Williams|author2=Leonard A. Dudzinski|author3=Stanley K. Borowski|author4=Albert J. Juhasz|date=March 2005|location=Cleveland, Ohio|publisher=NASA|title=Realizing "2001: A Space Odyssey": Piloted Spherical Torus Nuclear Fusion Propulsion|url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050160960_2005161052.pdf}}</ref>
* [[Nautilus-X|Multi-Mission Space Exploration Vehicle]] (MMSEV): a 2011 [[NASA]] proposal for a long-duration crewed space transport vehicle; it included a rotational artificial gravity [[space habitat]] intended to promote crew health for a crew of up to six persons on missions of up to two years in duration. The [[torus|torus-ring]] [[centrifuge]] would utilize both standard metal-frame and [[Inflatable space habitat|inflatable]] spacecraft structures and would provide 0.11 to 0.69&nbsp;[[Standard gravity|''g'']] if built with the {{convert|40|ft}} diameter option.<ref name=fiso20110126b>[http://spirit.as.utexas.edu/~fiso/telecon/Holderman-Henderson_1-26-11/Holderman_1-26-11.ppt NAUTILUS – X:  Multi-Mission Space Exploration Vehicle] {{Webarchive|url=https://web.archive.org/web/20110304044259/http://spirit.as.utexas.edu/~fiso/telecon/Holderman-Henderson_1-26-11/Holderman_1-26-11.ppt |date=March 4, 2011 }}, Mark L. Holderman, ''Future in Space Operations (FISO) Colloquium'', 2011-01-26. Retrieved 2011-01-31</ref><ref name=stn20110128>
[http://www.hobbyspace.com/nucleus/index.php?itemid=26786 NASA NAUTILUS-X: multi-mission exploration vehicle includes a centrifuge, which would be tested at ISS] {{webarchive|url=https://web.archive.org/web/20110225085854/http://hobbyspace.com//nucleus/index.php?itemid=26786 |date=February 25, 2011 }}, ''RLV and Space Transport News'', 2011-01-28. Retrieved 2011-01-31</ref>
* [[Nautilus-X#ISS centrifuge demonstration|ISS Centrifuge Demo]]: a 2011 NASA proposal for a demonstration project preparatory to the final design of the larger torus centrifuge space habitat for the Multi-Mission Space Exploration Vehicle. The structure would have an outside diameter of {{convert|30|ft}} with a ring interior cross-section diameter of {{convert|30|in}}. It would provide 0.08 to 0.51&nbsp;''g'' partial gravity. This test and evaluation centrifuge would have the capability to become a Sleep Module for the ISS crew.<ref name=fiso20110126b/><!-- the ISS Centrifuge Demo is described on pages 15–21 of the fiso20110126b ref -->
[[Image:Tempo-3-0003.jpg|thumb|right|Artist’s rendering of TEMPO³ in orbit]]
* [[Mars Direct]]: A plan for a crewed [[Mars]] mission created by NASA engineers [[Robert Zubrin]] and [[David Baker (aerospace engineer)|David Baker]] in 1990, later expanded upon in Zubrin's 1996 book ''[[The Case for Mars]]''. The "Mars Habitat Unit", which would carry astronauts to Mars to join the previously launched "Earth Return Vehicle", would have had artificial gravity generated during flight by tying the spent upper stage of the booster to the Habitat Unit, and setting them both rotating about a common axis.<ref>{{cite web|url=http://www.nss.org/resources/books/non_fiction/NF_037_caseformars.html|title=NSS Review: The Case for Mars|website=www.nss.org|access-date=April 4, 2018|archive-date=January 11, 2018|archive-url=https://web.archive.org/web/20180111165837/http://www.nss.org/resources/books/non_fiction/NF_037_caseformars.html|url-status=dead}}</ref>
* The proposed [[Tempo3]] mission rotates two halves of a spacecraft connected by a tether to test the feasibility of simulating gravity on a crewed mission to Mars.<ref>[http://members.marssociety.org/TMQ/TMQ-V1-I1.pdf The Mars Quarterly] {{Webarchive|url=https://web.archive.org/web/20170421044642/http://members.marssociety.org/TMQ/TMQ-V1-I1.pdf|date=April 21, 2017}} pg15-Tom Hill</ref>
* The [[Mars Gravity Biosatellite]] was a proposed mission meant to study the effect of artificial gravity on mammals. An artificial gravity field of 0.38&nbsp;''g'' (equivalent to [[Mars]]'s surface gravity) was to be produced by rotation (32 rpm, radius of ca. 30&nbsp; cm). Fifteen mice would have orbited Earth ([[Low Earth orbit]]) for five weeks and then land alive.<ref name="iac07">Korzun, Ashley M.; Wagner, Erika B.; et al. (2007). [http://smartech.gatech.edu/bitstream/1853/26717/1/IAC-07-A1.9.-A2.7.05.pdf Mars Gravity Biosatellite: Engineering, Science, and Education]. 58th [[International Astronautical Congress]].</ref> However, the program was canceled on 24 June 2009, due to a lack of funding and shifting priorities at NASA.<ref>{{cite web|url=http://www.spaceref.com/news/viewsr.html?pid=31612|archive-url=https://archive.today/20120914085936/http://www.spaceref.com/news/viewsr.html?pid=31612|url-status=dead|archive-date=September 14, 2012|title=The Mars Gravity Biosatellite Program Is Closing Down|website=www.spaceref.com|date=June 24, 2009|access-date=April 4, 2018}}</ref>
* Vast Space is a private company that proposes to build the world's first artificial gravity space station using the rotating spacecraft concept.<ref>{{Cite web |last=Werner |first=Debra |date=2022-09-15 |title=Vast Space to develop artificial-gravity space station |url=https://spacenews.com/vast-space-intro/ |access-date=2023-09-17 |website=SpaceNews |language=en-US}}</ref>

==== Issues with implementation ====
Some of the reasons that artificial gravity remains unused today in [[spaceflight]] trace back to the problems inherent in [[implementation]]. One of the realistic methods of creating artificial gravity is the centrifugal effect caused by the [[centripetal force]] of the floor of a rotating structure pushing up on the person. In that model, however, issues arise in the size of the spacecraft. As expressed by John Page and Matthew Francis, the smaller a spacecraft (the shorter the radius of rotation), the more rapid the rotation that is required. As such, to simulate gravity, it would be better to utilize a larger spacecraft that rotates slowly. 

The requirements on size about rotation are due to the differing forces on parts of the body at different distances from the axis of rotation. If parts of the body closer to the rotational axis experience a force that is significantly different from parts farther from the axis, then this could have adverse effects. Additionally, questions remain as to what the best way is to initially set the rotating motion in place without disturbing the stability of the whole spacecraft's orbit. At the moment, there is not a ship massive enough to meet the rotation requirements, and the costs associated with building, maintaining, and [[launching]] such a craft are extensive.<ref name="popularmechanics.com"/>

In general, with the small number of negative health effects present in today's typically shorter spaceflights, as well as with the very large cost of [[research]] for a technology which is not yet really needed, the present day development of artificial gravity technology has necessarily been stunted and sporadic.<ref name="iaaweb.org"/><ref name="jstor.org"/>  

As the length of typical space flights increases, the need for artificial gravity for the passengers in such lengthy spaceflights will most certainly also increase, and so will the knowledge and resources available to create such artificial gravity, most likely also increase.  In summary, it is probably only a question of time, as to how long it might take before the conditions are suitable for the completion of the development of artificial gravity technology, which will almost certainly be required at some point along with the eventual and inevitable development of an increase in the average length of a spaceflight.<ref>[https://www.nasa.gov/podcasts/houston-we-have-a-podcast/artificial-gravity/ Artificial Gravity, Houston We Have a Podcast] NASA.gov. By Gary Jordan and Bill Paloski. March 26, 2021. Retrieved February 11, 2024.</ref>

====In science fiction====
Several science fiction novels, films, and series have featured artificial gravity production.

* In the movie ''[[2001: A Space Odyssey (film)|2001: A Space Odyssey]]'', a rotating centrifuge in the ''Discovery'' spacecraft provides artificial gravity. 
* The 1999 television series ''[[Cowboy Bebop]]'', a rotating ring in the ''Bebop'' spacecraft creates artificial gravity throughout the spacecraft.
* In the novel ''[[The Martian (Weir novel)|The Martian]]'', the ''Hermes'' spacecraft achieves artificial gravity by design; it employs a ringed structure, at whose periphery forces around 40% of Earth's gravity are experienced, similar to Mars' gravity.
** In the novel ''[[Project Hail Mary]]'' by the same author, weight on the titular ship ''Hail Mary'' is provided initially by engine thrust, as the ship is capable of constant acceleration up to {{math|2 ''ɡ''}} and is also able to separate, turn the crew compartment inwards, and rotate to produce {{math|1 ''ɡ''}} while in orbit.
* The movie ''[[Interstellar (film)|Interstellar]]'' features a spacecraft called the ''Endurance'' that can rotate on its central axis to create artificial gravity, controlled by retro thrusters on the ship.
* The 2021 film ''[[Stowaway (2021 film)|Stowaway]]'' features the upper stage of a launch vehicle connected by 450-meter long [[Space tether|tethers]] to the ship's main hull, acting as a counterweight for [[inertia]]-based artificial gravity.<ref>{{cite web |last1=Kiang |first1=Jessica |title=Review: Anna Kendrick is lost, and found, in space in smart sci-fi 'Stowaway' |url=https://www.latimes.com/entertainment-arts/movies/story/2021-04-22/stowaway-netflix-review |website=Los Angeles Times |date=April 22, 2021 |access-date=25 April 2021}}</ref>
* The series [[The Expanse (TV series)|The Expanse]] utilizes both rotational gravity and linear thrust gravity in various space stations and spaceships. Notably, Tycho Station and the [[Generation ship]] ''LDSS Nauvoo'' use rotational gravity. Linear gravity is provided by a fictitious 'Epstein Drive', which killed its creator Solomon Epstein during its maiden flight due to high gravity injuries. 
* In the television series ''[[For All Mankind (TV series)|For All Mankind]]'', the space hotel ''Polaris'', later renamed ''Phoenix'' after being purchased and converted into a space vessel by Helios Aerospace for their own Mars mission, features a wheel-like structure controlled by thrusters to create artificial gravity, whilst a central axial hub operates in zero gravity as a docking station.