Artificial gravity

Artificial gravity is an acceleration resulting from the application of a force. In the context of manned spaceflight, artificial gravity may alleviate the adverse health effects of prolonged weightlessness. Astronauts routinely experience intermittent linear accelerations caused by the force of a rocket engine. However, the term artificial gravity usually refers to a sustained Normal force provided by a rigid structure in uniform circular motion. Practical outer space applications of artificial gravity for humans have not yet been built and flown, principally because of the large size of the spacecraft required to produce a useful centripetal acceleration, comparable to little g.

Zero gravity causes health problems in humans the severity of which depend on the length of exposure. Space adaptation syndrome affects some astronauts but usually passes within 2 - 4 days. However, months or years of exposure to zero gravity causes a long list of health problems including bone density loss, muscle atrophy, a compromised vestibular system, impaired eyesight, impaired mental ability, fatigue caused by loss of sleep, and a diminished immune system. There is an equally long list of maladies facing the astronauts when they return home, as they try to re-adjust to gravity on Earth. Astronauts and cosmonauts who have been weightless for 6 months or more are too weak support their own body weight and have to be carried from their spacecraft. The vast majority of astronauts and cosmonauts returning to Earth from a long duration space mission lasting 6 months or more are susceptible to dangerously low blood pressure, a condition known as Orthostatic Hypotension. This is caused in part by dehydration but is also symptomatic of their weakened heart muscle which struggles against the force of gravity to maintain blood flow to the brain. This condition causes astronauts to feel dizzy or risk passing out. This presents a serious problem for which there is no immediate cure. Additionally, the astronauts report problems with hand-eye coordination. They fail hand-eye coordination tests that they had previously aced before going into space. The bone density loss mentioned previously may not be reversible, despite the 2 hours per day of load bearing exercise that the astronauts do whilst they are in orbit. Astronauts returning to Earth following a long duration spaceflight enter a rehabilitation program that can last up to a year. The purpose of the program is to help them rebuild their muscle strength. During this long recovery time, they feel extremely vulnerable to bone fractures in particular. According to the testimony of these astronauts, it takes 1 to 3 days to recover for every day spent weightless in space.

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