question: How realistic are spaceships with Earth-like gravity in the future?
comment: It's actually pretty easy to create fake gravity. You've just got to spin the spaceship really fast and the centrifugal force inside would be identical to Earth's gravity.
passages: Space stations in science fiction can employ both existing and speculative technologies. One of the earliest images was the rotating wheel space station (such as the Stanford torus), the inertia and centripetal force of which would theoretically simulate the effects of gravity. Stations using artificial gravity are still purely speculative.
   Section::::Centripetal.:Manned spaceflight.:Proposals.
  
  A number of proposals have incorporated artificial gravity into their design:
  
  BULLET::::- 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.
   In many science fiction stories, there are artificial gravity generators that create a gravitational field based on a mass that does not exist. It helps the story by creating a more Earth-like spaceship, and in the case of a movie or television program, it helps the production because it is a lot cheaper than the special effects needed to simulate weightlessness.
  
  In the "Star Trek" universe, artificial gravity is achieved by the use of "gravity plating" embedded in a starship's deck.
   Astrophysicist Neil deGrasse Tyson, astronomer and skeptic Phil Plait, and veteran NASA astronaut and spacewalker Scott E. Parazynski have offered comments about some of the most "glaring" inaccuracies. "The Dissolve" characterized these complaints as "absurd", problems "only an astrophysicist would find".
  
  Examples of differences from reality include:
   BULLET::::- 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-ring centrifuge would utilize both standard metal-frame and inflatable spacecraft structures and would provide 0.11 to if built with the diameter option.
   BULLET::::- The Multi-Generation Ship
  
  A generation ship is a slower-than-light spaceship housing some hundreds of people which takes several human generations to complete its journey. It could in principle be built using known technology.
  
  BULLET::::- Gravity
  
  Niven can conceive of four ways of generating artificial gravity in a spaceship: (1) centrifugal force; (2) adding mass, e.g. neutronium or a black hole (this would incur serious penalties in fuel consumption); (3) gravity waves; and (4) continuous linear acceleration to the midway point of a journey, followed by continuous deceleration.
  
  BULLET::::- Flying Cities
   This imagined spaceship could offer round trips to Proxima Centauri lasting about 7.1 traveler years (~12 years on Earth clocks), round trips to the Milky Way's central black hole of about 40 years (~54,000 years elapsed on earth clocks), and round trips to Andromeda Galaxy lasting around 57 years (over 5 million years on Earth clocks). Unfortunately, sustaining 1-gee acceleration for years is easier said than done, as illustrated by the maximum payload to launch mass ratios shown in the figure at right.
  
  Section::::In curved spacetime.
   In science fiction, artificial gravity (or cancellation of gravity) or "paragravity" 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 "gravitomagnetic field", but there has been no verification or even negative results from third parties. In 2006, a research group funded by ESA claimed to have created a similar device that demonstrated positive results for the production of gravitomagnetism, although it produced only 0.0001"g". This result has not been replicated. String theory predicts that gravity and electromagnetism unify in hidden dimensions and that extremely short photons can enter those dimensions.
   In general, with the limited health effects present in shorter spaceflights, as well as the high cost of research, application of artificial gravity is often stunted and sporadic.
  
  Section::::Centripetal.:Manned spaceflight.:In science fiction.
  
  Several science fiction novels, films and series have featured artificial gravity production. In the movie , a rotating centrifuge in the "Discovery" spacecraft provides artificial gravity. 
   They have, however, been employed on projects such as Genesis. This spacecraft visited the Earth-Sun point and returned using very little propellant.
  
  Section::::See also.
  
  BULLET::::- Aerodynamics
  
  BULLET::::- Aerospace Engineering
  
  BULLET::::- Astrophysics
  
  BULLET::::- Canonical units
  
  BULLET::::- Celestial mechanics
  
  BULLET::::- Chaos theory
  
  BULLET::::- Kepler orbit
  
  BULLET::::- Lagrangian point
  
  BULLET::::- Mechanical Engineering
  
  BULLET::::- N-body problem
  
  BULLET::::- Orbit
  
  BULLET::::- Orders of magnitude (speed)
  
  BULLET::::- Roche limit
  
  BULLET::::- Spacecraft propulsion
  
  BULLET::::- Tsiolkovsky rocket equation
  
  BULLET::::- Universal variable formulation
  
  Section::::Further reading.
  
  Many of the options, procedures, and supporting theory are covered in standard works such as:
  
  Section::::External links.
  
  BULLET::::- ORBITAL MECHANICS (Rocket and Space Technology)
   Section::::Gravity model for Earth.
  
  The type of gravity model used for the Earth depends upon the degree of fidelity required for a given problem. For many problems such as aircraft simulation, it may be sufficient to consider gravity to be a constant, defined as:
  
  based upon data from "World Geodetic System 1984" (WGS-84), where formula_15 is understood to be pointing 'down' in the local frame of reference.
  
  If it is desirable to model an object's weight on Earth as a function of latitude, one could use the following ( p. 41):
  
  where
  
  BULLET::::- formula_17 = per s
   Section::::Requirements.:Artificial gravity.
   In a more general sense, "artificial gravity" may also refer to the effect of linear acceleration, e.g. by means of a rocket engine. 
  
  Rotational simulated gravity has been used in simulations to help astronauts train for extreme conditions. 
  
  Rotational simulated gravity has been proposed as a solution in manned spaceflight to the adverse health effects caused by prolonged weightlessness. 
   As such, low-impulse but long-term linear acceleration has been proposed for various interplanetary missions. For example, even heavy (100 ton) cargo payloads to Mars could be transported to Mars in and retain approximately 55 percent of the LEO vehicle mass upon arrival into a Mars orbit, providing a low-gravity gradient to the spacecraft during the entire journey.
   Section::::Technology used to compensate for the negative effects.:Artificial gravity.
  
  Artificial gravity (AG) is the increase or decrease of gravitational force on an object or person by artificial means. Different types of forces, including linear acceleration and centripetal force, can be used to generate this artificial gravitational force.
   From the point of view of people rotating with the habitat, artificial gravity by rotation behaves in some ways similarly to normal gravity but with the following differences:
   The flight dynamics of spacecraft differ from those of aircraft in that the aerodynamic forces are of very small, or vanishingly small effect for most of the vehicle's flight, and cannot be used for attitude control during that time. Also, most of a spacecraft's flight time is usually unpowered, leaving gravity as the dominant force.
   Section::::Centripetal.:Manned spaceflight.:Gemini missions.
  
  The Gemini 11 mission attempted 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 g, by firing their side thrusters to slowly rotate the combined craft like a slow-motion pair of bolas.
  
  The resultant force was too small to be felt by either astronaut, but objects were observed moving towards the "floor" of the capsule.
   Whatever design is chosen, it would be necessary for the spacecraft to possess some means to quickly transfer ballast from one section to another, otherwise even small shifts in mass could cause a substantial shift in the spacecraft's axis, which would result in a dangerous "wobble." One possible solution would be to engineer the spacecraft's plumbing system to serve this purpose, using drinking water and/or waste water as the ballast. 
   Even in the case of an airless body, there is a limit to how close a spacecraft may approach. The magnitude of the achievable change in velocity depends on the spacecraft's approach velocity and the planet's escape velocity at the point of closest approach (limited by either the surface or the atmosphere.)
   Several studies have suggested that artificial gravity might be an adequate countermeasure for prolonged space flight, especially if combined with other countermeasures. A conceptual design entitled ViGAR (Virtual Gravity Artificial Reality) was proposed in 2005 by Kobrick et al. and it details a device that combines artificial gravity, exercise and virtual reality to counter the negative effects of prolonged spaceflight. It includes a bicycle on a centrifuge as well as an integrated virtual reality system.
  
  Section::::Technology used to compensate for the negative effects.:Exercise methods.
  
  Section::::Technology used to compensate for the negative effects.:Exercise methods.:Treadmill Vibration Isolation and Stabilization (TVIS).
   Section::::See also.
  
  BULLET::::- Artificial gravity
  
  BULLET::::- Clinostat
  
  BULLET::::- Effect of spaceflight on the human body
  
  BULLET::::- European Low Gravity Research Association (ELGRA)
  
  BULLET::::- Micro-g environment
  
  BULLET::::- Microgravity University
  
  BULLET::::- Space adaptation syndrome
  
  BULLET::::- Space medicine
  
  BULLET::::- Vomit Comet
  
  Section::::External links.
  
  BULLET::::- Weightlessness Flight with Zero-Gravity airplane
  
  BULLET::::- Microgravity Centre
  
  BULLET::::- Microgravity Flight with Zero-G aircraft
  
  BULLET::::- maniacworld.com "NASA Reduced Gravity Aircraft", videos of the NASA Reduced Gravity Aircraft and of participants in a flight on that aircraft.
  
  BULLET::::- How Weightlessness Works at HowStuffWorks
  
  BULLET::::- NASA - SpaceResearch - Human Physiology Research and the ISS: Staying Fit Along the Journey
   A common conception about spacecraft orbiting the earth is that they are operating in a gravity free environment. Although there is a way of making sense of this within the physics of Einstein's general relativity, within Newtonian physics, this is technically inaccurate .
   Flight calculations are made quite precisely for space missions, taking into account such factors as the Earth's oblateness and non-uniform mass distribution; gravitational forces of all nearby bodies, including the Moon, Sun, and other planets; and three-dimensional flight path. For preliminary performance analysis, some simplifying assumptions can be made: the planet is spherical and uniform; the vehicle can be simulated as a point mass; flight path assumes a two-body patched conic approximation; and the local flight path lies in a single plane) with reasonably small loss of accuracy.
   It is not yet known whether 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 at countering the adverse effects on health of weightlessness. Artificial gravity at 0.1"g" and a rotating spacecraft period of 30 s would require a radius of only . Likewise, at a radius of 10 m, a period of just over 6 s would be required to produce standard gravity (at the hips; gravity would be 11% higher at the feet), while 4.5 s would produce 2"g". If brief exposure to high gravity can negate the harmful effects of weightlessness, then a small centrifuge could be used as an exercise area.
  
presuppositions: Earth-like gravity is not realistic to create.
corrections: Gravity is already easy to create.
raw_presuppositions: Earth-like gravity is not realistic to create. It's not currently realistic to replicate Earth-like gravity.
raw_corrections: Gravity is already easy to create. It's already easy to replicate Earth-like gravity.