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| {{for|artificial gravity in fiction|Artificial gravity (fiction)}}
| | Nice to meet you, my title is Ling and I totally dig that name. Delaware is the location I love most but I require to move for my family members. Bookkeeping is what I do for a living. Playing crochet is a thing that I'm completely addicted to.<br><br>Also visit my website - [http://Hansolblueauction.com/hsa/board_OsQS27/77961 hansolblueauction.com] |
| {{lead too short|date=May 2013}}
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| {{Use mdy dates|date=June 2012}}
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| [[Image:Gemini 11 Agena.jpg|thumb|[[Gemini 11]] Agena tethered operations]]
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| [[File:Nautilus-X ISS demo 1.png|thumb|Proposed [[Nautilus-X]] International space station centrifuge demo]]
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| '''Artificial gravity''' is the varying (increase or decrease) of apparent [[gravitation|gravity]] ([[g-force]]) via artificial means, particularly in space, but also on Earth. It can be practically achieved by the use of different forces, particularly the [[centripetal force]] and [[linear acceleration]].
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| The creation of artificial gravity is considered desirable for long-term space travel or habitation, for ease of mobility, for in-space fluid management, and to avoid the adverse long-term [[Effects of low gravity on humans|health effects of weightlessness]].
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| A number of methods for generating artificial gravity have been proposed for many years, as well as an even larger number of [[Science fiction|sci-fi]] approaches using both real and [[fictitious force]]s. Practical [[Outer space|in-space]] applications of artificial gravity for humans have not yet been built and flown, principally due to the large size of the full-scale spacecraft that would be required to allow [[centripetal acceleration]] rotating spacecraft, such that they have not been selected as funded missions for the various large national [[space agency|space agencies]] that have developed the vast majority of space hardware in the early decades of [[human spaceflight]].<ref name=pm20130503>
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| {{cite news |last=Feltman|first=Rachel |title=Why Don't We Have Artificial Gravity? |url=http://www.popularmechanics.com/science/space/rockets/why-dont-we-have-artificial-gravity-15425569 |accessdate=2013-05-21 |newspaper=Popular Mechanics |date=2013-05-03 }}</ref>
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| ==Requirement for gravity==
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| Without [[g-force]], [[space adaptation syndrome]] occurs in some humans and animals. Many adaptations occur over a few days, but over a long period of time bone density decreases, and some of this decrease may be permanent. The minimum g-force required to avoid bone loss is not known—nearly all current experience is with g-forces of 1 [[Standard gravity|g]] (on the surface of the Earth) or 0 g in orbit. There has been insufficient time spent on the Moon to determine whether lunar gravity is sufficient.
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| A limited amount of experimentation has been done by Dr. Alfred Smith, of the [[University of California]], with chickens, since they are [[biped]]s, and mice experiencing high g-force over long periods in large [[centrifuges]] on the Earth.<ref>Great Mambo Chicken And The Transhuman Condition: Science Slightly Over The Edge</ref><ref>{{cite news| url=http://www.time.com/time/magazine/article/0,9171,897495,00.html | work=Time | title=Science: High-G Life | date=9 May 1960}}</ref>
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| Rats have been exposed to continuous artificial gravity of 1 g during Russian biosatellite missions lasting two weeks. The muscle and bone loss in these animals was found to be less than rats in 0 g. Astronauts were exposed to artificial gravity levels ranging from 0.2 to 1 g for a few minutes during several spaceflight missions, using linear sleds or rotating chairs. They did not perceive any changes in their spatial orientation when the g level was lower than 0.5 g at the [[inner ear]] level, where the sensory receptors for gravity perception are located.<ref name="Clément G 2007">Clément G, Bukley A (2007) Artificial Gravity. Springer: New York</ref>
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| ==Methods for generating artificial gravity==
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| Gravity can be simulated in numerous ways:
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| ===Rotation===
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| [[File:Artificial Gravity Space Station - GPN-2003-00104.jpg|thumb|Artificial gravity space station.1969 Nasa concept]]
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| [[File:Hegagonal inflatable space station 1962.jpg|thumb|Hexagonal inflatable rotating space station.1962 Nasa concept.]]
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| A rotating spacecraft will produce the feeling of gravity on its inside hull. The rotation drives any object inside the spacecraft toward the hull, thereby giving the appearance of a gravitational pull directed outward. Often referred to as a [[centrifugal force]], the "pull" is actually a manifestation of the objects inside the spacecraft attempting to travel in a straight line due to inertia. The spacecraft's hull provides the [[centripetal force]] required for the objects to travel in a circle (if they continued in a straight line, they would leave the spacecraft's confines). Thus, the gravity felt by the objects is simply the reaction force of the object on the hull reacting to the centripetal force of the hull on the object, in accordance with [[Newton's Third Law]].
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| From the [[rotating reference frame|point of view of people rotating with the habitat]], artificial gravity by rotation behaves in some ways similarly to normal gravity but has the following effects:
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| *[[Centrifugal force]]: Unlike real gravity which pulls towards a center, this pseudo-force that appears in rotating reference frames gives a rotational 'gravity' that pushes away from the axis of rotation. Artificial gravity levels vary proportionately with the distance from the centre of rotation. With a small radius of rotation, the amount of gravity felt at one's head would be significantly different from the amount felt at one's feet. This could make movement and changing body position awkward. In accordance with the [[Centripetal force#Formula|physics involved]], slower rotations or larger rotational radii would reduce or eliminate this problem.{{citation needed|date=December 2011}}
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| *The [[Coriolis effect]] gives an apparent force that acts on objects that move relative to a rotating reference frame. This apparent force acts at right angles to the motion and the rotation axis and tends to curve the motion in the opposite sense to the habitat's spin. If an [[astronaut]] inside a rotating artificial gravity environment moves towards or away from the axis of rotation, he will feel a force pushing him towards or away from the direction of spin. These forces act on the inner ear and can cause [[dizziness]], [[nausea]] and disorientation. Lengthening the period of rotation (slower spin rate) reduces the Coriolis force and its effects. It is generally believed that at 2 [[Revolutions per minute|rpm]] or less, no adverse effects from the Coriolis forces will occur; at higher rates some people can become accustomed to it and some do not; but at rates above 7 rpm few if any can become accustomed.<ref name=hecht2002>{{cite web |url=http://adsabs.harvard.edu/full/2002ESASP.501..151H |title=Adapting to artificial gravity (AG) at high rotational speeds |author=Hecht, H., Brown, E. L., & Young, L. R., et al. |publisher=Proceedings of "Life in space for life on Earth". 8th European Symposium on Life Sciences Research in Space. 23rd Annual International Gravitational Physiology Meeting |date=June 2–7, 2002 |accessdate=2011-02-07}}</ref> It is not yet known if very long exposures to high levels of Coriolis forces can increase the likelihood of becoming accustomed. The nausea-inducing effects of Coriolis forces can also be mitigated by restraining movement of the head.
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| This form of artificial gravity gives additional system issues:{{citation needed|date=November 2011}}
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| *Kinetic energy: Spinning up parts or all of the habitat requires energy. This would require a propulsion system and propellant of some kind to spin up (or spin down) or a motor and counterweight of some kind (possibly in the form of another living area) to spin in the opposite direction.
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| *Extra strength is needed in the structure to keep it from flying apart due to the rotation. However, the amount of structure needed over and above that to hold a breathable atmosphere (10 tonnes force per square metre at 1 atmosphere) is relatively modest for most structures.
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| *If parts of the structure are intentionally not spinning, [[friction]] and similar [[torque]]s will cause the rates of spin to converge (as well as causing the otherwise-stationary parts to spin), requiring motors and power to be used to compensate for the losses due to friction.
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| {| style="float:right; margin-left:5mm;" class="wikitable"
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| |-
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| !Calculations
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| |<br><center><math>g = \frac{R(\frac{\pi \times \mathrm{rpm}}{30})^2}{9.81}</math></center><br>
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| <center>or</center><br>
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| <center><math>R = \frac{9.81g}{(\frac{\pi \times \mathrm{rpm}}{30})^2}</math></center><br>
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| <center>where:</center>
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| ''g'' = Decimal fraction of Earth gravity<br>
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| ''R'' = Radius from center of rotation in meters<br>
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| <math>\pi\approx</math> [[Pi|3.14159]]<br>
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| rpm = revolutions per minute
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| |}
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| [[File:Calculated_rotation_speed_of_a_centrifuge.png|thumbnail|Rotation of a spacecraft to achieve a given gravity]]
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| [[File:Properties of spin graviity (1g).png|thumb|right|The size{{clarify|date=November 2011}}<!-- the units for radius are not given in the graphic: meters? feet? other? --> and speeds and period of different radii of space station]]
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| The engineering challenges of creating a rotating spacecraft are comparatively modest to any other proposed approach. Theoretical spacecraft designs using artificial gravity have a great number of variants with intrinsic problems and advantages. To reduce Coriolis forces to livable levels, a rate of spin of 2 rpm or less would be needed. To produce 1[[g-force|''g'']], the radius of rotation would have to be 224 m (735 ft) or greater, which would make for a very large spaceship. To reduce mass, the support along the diameter could consist of nothing but a cable connecting two sections of the spaceship, possibly a habitat module and a counterweight consisting of every other part of the spacecraft. It is not yet known if exposure to high gravity for short periods of time is as beneficial to health as continuous exposure to normal gravity. It is also not known how effective low levels of gravity would be to countering the adverse effects on health of weightlessness. Artificial gravity at 0.1''g'' would require a radius of only 22 m (74 ft). Likewise, at a radius of 10 m, about 10 rpm would be required to produce Earth gravity (at the hips; gravity would be 11% higher at the feet), or 14 rpm to produce 2''g''. If brief exposure to high gravity can negate the health effects of weightlessness, then a small centrifuge could be used as an exercise area.
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| The [[Gemini 11]] mission attempted to produce artificial gravity by rotating the capsule around the [[Agena Target Vehicle]] which it was attached to by a 36-meter tether. They were able to generate a small amount of artificial gravity, about 0.00015 g, by firing their side thrusters to slowly rotate the combined craft like a slow-motion pair of [[bolas]].<ref name=Gatland1976>
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| {{Cite book
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| | first = Kenneth| last = Gatland
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| | title = Manned Spacecraft, Second Revision
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| | place = New York, NY, USA
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| | publisher = MacMillan Publishing Co., Inc
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| | year = 1976
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| | pages = 180–182
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| | isbn = 0-02-542820-9 }}
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| </ref>
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| 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"/>
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| 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''g'' ([[Mars]] gravity) was to be produced by rotation (32 rpm, radius of ca. 30 cm). Fifteen mice would have orbited Earth ([[Low Earth orbit]]) for five weeks and then land alive. However the program was canceled on June 24, 2009 due to lack of funding and shifting priorities at NASA.<ref>[http://www.marstoday.com/news/viewsr.rss.html?pid=31612 ]{{dead link|date=August 2013}}</ref>{{full|date=November 2012}}
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| ===Linear acceleration===
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| Linear acceleration, even at a low level, can provide sufficient [[g-force]] to provide useful benefits. Any spacecraft could continuously accelerate in a straight line, forcing objects inside the spacecraft in the opposite direction of the direction of acceleration.
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| Most [[Rocket engine#Chemically powered|chemical]] [[Spacecraft propulsion#Reaction engines|reaction rockets]] already accelerate at a sufficient rate to produce several times Earth's g-force but can only maintain these accelerations for several minutes because of a limited supply of fuel.
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| A propulsion system with a very high [[specific impulse]] (that is, good efficiency in the use of [[reaction mass]] that must be carried along and used for propulsion on the journey) could accelerate more slowly producing useful levels of artificial gravity for long periods of time. A variety of [[Spacecraft propulsion#Electromagnetic propulsion|electric propulsion]] systems provide examples. Two examples of this long-duration, [[thrust-to-weight ratio|low-thrust]], high-impulse propulsion that have either been practically used on spacecraft or are planned in for near-term in-space use are [[Hall effect thruster]]s and [[Variable Specific Impulse Magnetoplasma Rocket]]s (VASIMR). Both provide very high [[specific impulse]] but relatively low thrust, compared to the more typical chemical reaction rockets. They are thus ideally suited for long-duration firings which would provide limited amounts of, but long-term, milli-g levels of artificial gravity in spacecraft.{{Citation needed|date=February 2011}}.
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| Low-impulse but long-term linear acceleration has been proposed for various interplanetary missions. For example, even heavy (100 [[tonne]]) cargo payloads to Mars could be transported to Mars in {{nowrap|27 months}} and retain approximately 55 percent of the [[low-Earth orbit|LEO]] vehicle mass upon arrival into a Mars orbit, providing a low-gravity gradient to the spacecraft during the entire journey.<ref name=fiso20110119>[http://spirit.as.utexas.edu/~fiso/telecon/Glover_1-19-11/Glover_1-19-11.pdf VASIMR VX-200 Performance and Near-term SEP Capability for Unmanned Mars Flight], Tim Glover, Future in Space Operations (FISO) Colloquium, pages 22 and 25, 2011-01-19. Retrieved 2011-02-01.</ref>
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| Constant linear acceleration could theoretically provide relatively short flight times around the solar system. If a propulsion technique able to support 1''g'' of acceleration continuously were available, a spaceship accelerating (and then decelerating for the second half of the journey) at 1''g'' would reach [[Mars]] within a few days.<ref>{{cite book
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| |title=Artificial Gravity
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| |first1=Gilles
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| |last1=Clément
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| |first2=Angelia P.
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| |last2=Bukley
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| |publisher=Springer New York
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| |year=2007
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| |isbn=0-387-70712-3
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| |page=35
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| |url=http://books.google.com/books?id=YUcjOsG0hi0C}}, [http://books.google.com/books?id=YUcjOsG0hi0C&pg=PA35 Extract of page 35]
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| </ref>
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| In a number of science fiction plots, acceleration is used to produce artificial gravity for [[Interstellar travel|interstellar]] spacecraft, propelled by as yet [[theoretical]] or [[Spacecraft propulsion#Hypothetical methods|hypothetical]] means.
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| This effect of linear acceleration is very well understood, and is routinely used for 0''g'' cryogenic fluid management for post-launch (subsequent) in-space firings of [[upper stage]] rockets.<ref name=goff2009>{{cite web |url=http://selenianboondocks.com/wp-content/uploads/2009/09/NearTermPropellantDepots.pdf |title=Realistic Near-Term Propellant Depots |author=Jon Goff, et al. |publisher=American Institute of Aeronautics and Astronautics |year=2009 |accessdate=2011-02-07 quote=''developing techniques for manipulating fluids in microgravity, which typically fall into the category known as settled propellant handling. Research for cryogenic upper stages dating back to the Saturn S-IVB and Centaur found that providing a slight acceleration (as little as 10<sup>−4</sup> to 10<sup>−5</sup> g of acceleration) to the tank can make the propellants assume a desired configuration, which allows many of the main cryogenic fluid handling tasks to be performed in a similar fashion to terrestrial operations. The simplest and most mature settling technique is to apply thrust to the spacecraft, forcing the liquid to settle against one end of the tank.''}}</ref>
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| ===Mass===
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| Another way artificial gravity may be achieved is by installing an ultra-high density mass in a spacecraft so that it would generate its own gravitational field and pull everything inside towards it. Technically this is not artificial gravity—it is natural gravity, gravity in its original sense. An extremely large amount of mass would be needed to produce even a tiny amount of noticeable gravity. A large asteroid could exert several thousandths of a ''g'' and, by attaching a propulsion system of some kind, would qualify as a space ship, though gravity at such a low level might not have any practical value. An advantage of such system was proposed in [[Charles Sheffield]]'s McAndrew Chronicles, where a disc of 100 m diameter and 1 m thickness of [[degenerate matter]] weighting 1,300 billion tons have 1 [[g-force|g]] 246 m away for gravity at zero acceleration, and can be used to cancel out the acceleration of 50 g at 0 m.<ref>こなにヘンだそ！「空想科学読本」 ISBN 4-87233-659-3, p 230.</ref> The disadvantage of such system is that the mass would obviously need to move with the spacecraft; if the spacecraft is to be accelerated significantly, this would greatly increase fuel consumption. Because gravitational force is inversely proportional to the square of the distance from the center of mass, it would be possible to have significant levels of gravity with much less mass than such an asteroid if this mass could be made much denser than current materials like degenerate matter. In principle, small charged black holes could be used and held in position with electromagnetic forces. However, carrying a sufficient quantity of mass to form significant gravity fields in a spacecraft is well beyond current technology.{{citation needed|date=November 2011}}
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| ===Magnetism===
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| [[File:Frog diamagnetic levitation.jpg|right|thumb|200px|A live frog levitates inside a 32 mm [[diameter]] vertical bore of a [[Bitter solenoid]] in a magnetic field of about 16 [[tesla (unit)|teslas]]]]
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| A similar effect to gravity has been created through [[diamagnetism]]. It requires magnets with extremely powerful magnetic fields. Such devices have been made that were able to levitate at most a small mouse<ref>{{cite news| url=http://www.reuters.com/article/scienceNews/idUSTRE58A02G20090911 | work=Reuters | title=U.S. scientists levitate mice to study low gravity | date=11 September 2009}}</ref> and thus produced a 1 ''g'' field to cancel the Earth's. Sufficiently powerful magnets require either expensive [[cryogenics]] to keep them [[superconductive]], or require several megawatts of power.<ref>{{cite web|url=http://web.archive.org/web/20070320120553/http://www.hfml.ru.nl/20t-magnet.html |title=20 tesla Bitter solenoid – Archived link |publisher=Web.archive.org |date=2007-03-20 |accessdate=2013-08-06}}</ref>
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| With such extremely strong magnetic fields, safety for use with humans is unclear. In addition, it would involve avoiding any ferromagnetic or paramagnetic materials near the strong magnetic field required for diamagnetism to be evident.
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| Facilities using diamagnetism may prove workable for laboratories simulating low gravity conditions here on Earth. The mouse was levitated against Earth's gravity, creating a condition similar to [[microgravity]]. Lower forces may also be generated to simulate a condition similar to lunar or Martian gravity with small [[model organisms]].
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| ===Gravity generator/gravitomagnetism===
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| In science fiction, artificial gravity (or cancellation of gravity) or "paragravity"<ref>''Collision Orbit'', 1942 by [[Jack Williamson]]</ref><ref>''[[Pale Blue Dot (book)|Pale Blue Dot]]: A Vision of the Human Future in Space'' by [[Carl Sagan]], Chapter 19</ref> is sometimes present in spacecraft that are neither rotating nor accelerating. At present, there is no confirmed technique that can simulate gravity other than actual mass or acceleration. There have been many claims over the years of such a device. [[Eugene Podkletnov]], a Russian engineer, has claimed since the early 1990s to have made such a device consisting of a spinning superconductor producing a powerful [[Gravitomagnetism|gravitomagnetic]] field, but there has been no verification or even negative results from third parties. In 2006, a research group funded by [[European Space Agency|ESA]] claimed to have created a similar device that demonstrated positive results for the production of gravitomagnetism, although it produced only 100 millionths of a ''[[standard gravity|g]]''.<ref>{{cite web|url=http://www.esa.int/SPECIALS/GSP/SEM0L6OVGJE_0.html |title=Towards a new test of general relativity? |publisher=Esa.int |date= |accessdate=2013-08-06}}</ref> [[String theory]] predicts that gravity and electromagnetism unify in hidden dimensions and that extremely short photons can enter those dimensions.<ref>The Elegant Universe: Superstrings, Hidden Dimensions and the Quest for The Ultimate Theory, by Brian Greene</ref>
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| ==Training for high or low gravitational environments==
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| ===Centrifuge===
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| {{main|High-G training}}
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| '''High-G training''' is done by aviators and astronauts who are subject to high levels of acceleration ('G') in large-radius centrifuges. It is designed to prevent a ''g-induced Loss Of Consciousness'' (abbreviated [[G-LOC]]), a situation when [[g-force#Human g-force experience|''g''-forces]] move the blood away from the brain to the extent that [[consciousness]] is lost.
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| Incidents of acceleration-induced loss of consciousness have caused fatal accidents in aircraft capable of sustaining high-''g'' for considerable periods.
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| ===Parabolic flight===
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| {{main|Vomit Comet}}
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| ''Weightless Wonder'' is the nickname for the NASA aircraft that flies parabolic trajectories and briefly provides a nearly weightless environment in which to train [[astronaut]]s, conduct research, and film motion pictures.<ref>[http://www.nasaexplores.com/show2_articlea.php?id=03-008 NASA "Weightless Wonder"]{{dead link|date=September 2009}}</ref> The parabolic trajectory creates a vertical linear acceleration which matches that of gravity, giving [[zero-g]] for a short time, usually 20–30 seconds, followed by approximately 1.8g for a similar period. The nickname [[Vomit Comet]] is also used to refer to motion sickness that is often experienced by the aircraft passengers during these parabolic trajectories. Such [[reduced gravity aircraft]] are nowadays operated by several organizations world wide.
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| ===Neutral buoyancy===
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| {{main|Neutral Buoyancy Laboratory}}
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| [[Image:NASA Neutral Buoyancy Laboratory Astronaut Training.jpg|thumb|right|An astronaut training in the NBL]]
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| [[Image:NASA Neutral Buoyancy Laboratory control area.jpg|thumb|Simulation control area]]
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| A '''Neutral Buoyancy Laboratory''' (NBL) is an [[astronaut]] training facility, such as the Sonny Carter Training Facility at the [[NASA Johnson Space Center]] in [[Houston, Texas]].<ref name="pmid18619137">{{cite journal|author=Strauss S|title=Space medicine at the NASA-JSC, neutral buoyancy laboratory|journal=Aviat Space Environ Med|volume=79|issue=7|pages=732–3|date=July 2008|pmid=18619137|url=}}</ref> The NBL is a large indoor pool of water, the largest in the world,<ref>{{cite web |url=http://spaceflight.nasa.gov/shuttle/support/training/nbl/facilities.html |title=Behind the scenes training |publisher=NASA |date=May 30, 2003 |accessdate=March 22, 2011}}</ref> in which astronauts may perform simulated [[Extra-vehicular activity|EVA]] tasks in preparation for space missions. The NBL contains full-sized mock-ups of the [[Space Shuttle]] cargo bay, flight payloads, and the [[International Space Station]] (ISS).<ref name="pmid15892545">{{cite journal|author=Strauss S, Krog RL, Feiveson AH|title=Extravehicular mobility unit training and astronaut injuries|journal=Aviat Space Environ Med|volume=76|issue=5|pages=469–74|date=May 2005|pmid=15892545|url=http://www.ingentaconnect.com/content/asma/asem/2005/00000076/00000005/art00008|accessdate=2008-08-27}}</ref>
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| The principle of [[neutral buoyancy]] is used to simulate the weightless environment of space.<ref name="pmid18619137" /> The suited astronauts are lowered into the pool using an [[overhead crane]] and their weight is adjusted by support divers so that they experience no [[buoyancy|buoyant]] force and no [[Moment (physics)|rotational moment]] about their [[center of mass]].<ref name="pmid18619137" /> The suits worn in the NBL are down-rated from fully flight-rated [[Extravehicular Mobility Unit|EMU]] suits like those in use on the space shuttle and International Space Station.
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| The NBL tank itself is {{convert|202|ft|m}} in length, {{convert|102|ft|m}} wide, and {{convert|40|ft|6|in|m}} deep, and contains 6.2 million gallons (23.5 million litres) of water.<ref name="pmid15892545" /><ref>{{cite web|title=NBL Characteristics|work=About the NBL|publisher=NASA|date=June 23, 2005|url=http://dx12.jsc.nasa.gov/about/index.shtml}}</ref> Divers breathe [[nitrox]] while working in the tank.<ref>{{cite journal|author=Fitzpatrick DT, Conkin J|title=Improved pulmonary function in working divers breathing nitrox at shallow depths|journal=Undersea and Hyperbaric Medicine|volume=30|issue=Supplement|year=2003|url=http://archive.rubicon-foundation.org/1273|accessdate=2008-08-27}}</ref><ref>{{cite journal|author=Fitzpatrick DT, Conkin J|title=Improved pulmonary function in working divers breathing nitrox at shallow depths|journal=Aviat Space Environ Med|volume=74|issue=7|pages=763–7|date=July 2003|pmid=12862332|url=http://www.ingentaconnect.com/content/asma/asem/2003/00000074/00000007/art00011|accessdate=2008-08-27}}</ref>
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| Neutral buoyancy in a pool is not [[weightlessness]], since the balance organs in the inner ear still sense the up-down direction of gravity. Also, there is a significant amount of [[Drag (physics)|drag]] presented by water.<ref name="pmid15796314">{{cite journal|author=Pendergast D, Mollendorf J, Zamparo P, Termin A, Bushnell D, Paschke D|title=The influence of drag on human locomotion in water|journal=Undersea and Hyperbaric Medicine|volume=32|issue=1|pages=45–57|year=2005|pmid=15796314|url=http://archive.rubicon-foundation.org/4037|accessdate=2008-08-27}}</ref> Generally, drag effects are minimized by doing tasks slowly in the water. Another difference between neutral buoyancy simulation in a pool and actual EVA during spaceflight is that the temperature of the pool and the lighting conditions are maintained constant.
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| ==Proposals==
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| [[File:Nasa mars artificial gravity 1989.jpg|thumb|Rotating mars spacecraft.1989 Nasa concept.]]
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| There have been a number of proposals that have incorporated artificial gravity into their design.
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| *Discovery II: Was a 2005 vehicle proposal capable of delivering 172 mt to Jupiter's orbit in only 118 days. A very small portion of the 1,690 mt craft would incorporate a centrifuge where the crew would reside.<ref>{{cite web|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050160960_2005161052.pdf|title=Realizing "2001: A Space Odyssey": Piloted Spherical Torus Nuclear Fusion Propulsion|author1=Craig H. Williams |author2=Leonard A. Dudzinski |author3=Stanley K. Borowski |author4=Albert J. Juhasz|date=March 2005|publisher=NASA|accessdate=September 28, 2011|location=Cleveland, Ohio}}</ref>
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| *[[Nautilus-X|Multi-Mission Space Exploration Vehicle]] (MMSEV): this 2011 [[NASA]] proposal for a long-duration crewed space transport vehicle includes 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 duration. The [[gravity|partial-g]] [[torus|torus-ring]] [[centrifuge]] would utilize both standard metal-frame and [[Inflatable space habitat|inflatable]] spacecraft structures and would provide 0.11 to {{nowrap|0.69[[Standard gravity|g]]}} if built with the {{convert|40|ft}} diameter option.<ref name=fiso20110126b>
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| [http://spirit.as.utexas.edu/~fiso/telecon/Holderman-Henderson_1-26-11/Holderman_1-26-11.ppt NAUTILUS – X: Multi-Mission Space Exploration Vehicle], Mark L. Holderman, ''Future in Space Operations (FISO) Colloquium'', 2011-01-26. Retrieved 2011-01-31.</ref><ref name=stn20110128>
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| [http://www.hobbyspace.com/nucleus/index.php?itemid=26786 NASA NAUTILUS-X: multi-mission exploration vehicle includes centrifuge, which would be tested at ISS], ''RLV and Space Transport News'', 2011-01-28. Retrieved 2011-01-31.</ref>
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| *[[Nautilus-X#ISS centrifuge demonstration|ISS Centrifuge Demo]]: Also proposed in 2011 as 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 {{convert|30|in}} ring interior cross-section diameter and would provide 0.08 to {{nowrap|0.51g}} partial gravity. This test and evaluation centrifuge would have the capability to become a Sleep Module for ISS crew.<ref name=fiso20110126b/><!-- the ISS Centrifuge Demo is described in pages 15-21 of the fiso20110126b ref -->
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| *[[Mars Direct]]: A plan for a manned [[Mars]] mission created by NASA engineers [[Robert Zubrin]] and [[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.{{citation needed|date=November 2011}}
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| * Gen1 Enterprise: An experienced engineer who goes by BTE-Dan created a website outlining in great detail how, with current technology, we could build the first generation of a full-sized spaceship Enterprise that could carry 1,000 people all over our solar system in reasonable amounts of time. The conceptual design is complete with a centrifugal gravity wheel to provide spacious comfortable living spaces for the crew.<ref>{{cite web|url=http://buildtheenterprise.org/gravity-wheel |title=Gravity Wheel |publisher=BuildTheEnterprise |date= |accessdate=2013-08-06}}</ref><ref>{{cite web|url=http://btewiki.org/index.php?title=Gravity_Wheel |title=Gravity Wheel |publisher=Bte Wiki |date=2012-09-06 |accessdate=2013-08-06}}</ref><ref>{{cite web|url=http://www.buildtheenterprise.org/category/gravity-wheel |title=Gravity Wheel |publisher=BuildTheEnterprise |date= |accessdate=2013-08-06}}</ref><ref>{{cite web|author=Eddie Wrenn |url=http://www.dailymail.co.uk/sciencetech/article-2144147/Lets-build-Enterprise-Star-Trek-fan-unveils-bold-plan-make-Captain-Kirks-space-ship-20-years.html |title=Let's build the Enterprise! Star Trek fan unveils bold plan to make Captain Kirk's space ship within 20 years |publisher=Dailymail.co.uk |date=2012-05-14 |accessdate=2013-08-06}}</ref><ref>{{cite web|url=http://www.startrek.com/boards-topic/33379071/buildtheenterprise-petition |title=Star Trek BuildTheEnterprise petition |publisher=Startrek.com |date= |accessdate=2013-08-06}}</ref><ref>{{cite web|url=http://www.space.com/19110-starship-enterprise-white-house-petition.html |title=Engineer Petitions White House for Real-Life Starship Enterprise |publisher=Space.com |date=2013-01-04 |accessdate=2013-08-06}}</ref><ref>{{cite web|url=http://www.universetoday.com/95099/engineer-thinks-we-could-build-a-real-starship-enterprise-in-20-years/ |title=Engineer Thinks We Could Build a Real Starship Enterprise in 20 Years |publisher=Universetoday.com |date=2012-05-11 |accessdate=2013-08-06}}</ref><ref>{{cite web|url=http://www.universetoday.com/99164/white-house-petition-could-we-build-the-starship-enterprise/ |title=White House Petition: Could we Build the Starship Enterprise? |publisher=Universetoday.com |date=2012-12-27 |accessdate=2013-08-06}}</ref>
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| {{Expand section|date=February 2011}}
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| ==See also==
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| {{Commons category|Artificial gravity}}
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| *[[Accelerated reference frame]]
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| *[[Anti-gravity]]
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| *[[Artificial gravity (fiction)|Artificial gravity in fiction]]
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| *[[Centrifugal force]]
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| *[[Centrifuge Accommodations Module]]
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| *[[Coriolis force]]
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| *[[Fictitious force]]
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| *[[Rotating wheel space station]]
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| *[[Space habitat]]
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| *[[Stanford torus]]
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| ==References==
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| {{reflist|colwidth=30em}}
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| ==External links==
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| *[http://www.artificial-gravity.com/ List of peer review papers on artificial gravity]
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| *[http://www.marsgravity.org/ Mars gravity experiment homepage]{{dead link|date=December 2009}}
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| *[http://www.artificial-gravity.com/sw/SpinCalc/SpinCalc.htm Revolving artificial gravity calculator]
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| *[http://www.projectrho.com/rocket/rocket3u.html Overview of artificial gravity in Sci-Fi and Space Science]
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| *[http://www.nas.nasa.gov/About/Education/SpaceSettlement/teacher/materials/ringworld/ringworld.html NASA's Java simulation of artificial gravity]
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| *[http://selenianboondocks.com/2010/11/variable-gravity-research-facility-xgrf/ Variable Gravity Research Facility (xGRF)], concept with tethered rotating satellites, perhaps a [[Bigelow Aerospace|Bigelow]] [[BA-330|expandable module]] and a spent [[upper stage]] as a counterweight.
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| {{Space medicine}}
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| {{DEFAULTSORT:Artificial Gravity}}
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| [[Category:Fictional technology]]
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| [[Category:Gravitation]]
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| [[Category:Space colonization]]
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| [[Category:Scientific speculation]]
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| [[Category:Space medicine]]
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