- published: 12 Apr 2009
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The term micro-g environment (also µg, often referred to by the term microgravity) is more or less a synonym of weightlessness and zero-G, but indicates that g-forces are not quite zero, just very small. The symbol for microgravity, µg, was used on the insignia of Space Shuttle flight STS-87 because this flight was devoted to microgravity research.
Comparison of boiling of water under earth's gravity (1 g, left) and microgravity (right). The source of heat is in the lower part of the photograph.
A comparison between the combustion of a candle on Earth (left) and in a microgravity environment, such as that found on the ISS (right).
Colourized gray-scale composite image of the individual frames from a video of a backlit fuel droplet burning in microgravity.
Multiple overlays of three separate microgravity flame images.
A "stationary" micro-g environment would require travelling far enough into deep space so as to reduce the effect of gravity by attenuation to almost zero. This is the simplest in conception, but requires traveling an enormous distance, rendering it most impractical. For example, to reduce the gravity of the Earth by a factor of one million one needs to be at a distance of 6 million km from the Earth, but to reduce the gravity of the Sun to this amount one has to be at a distance of 3700 million km. (The gravity due to the rest of the Milky Way is already smaller than one millionth of the gravity on Earth, so we need not move away further from its center.) Thus it is not impossible, but it has only been achieved by a few spaceships such as Voyager 1, which do not return to Earth. To reduce the gravity to one thousandth of that on Earth one needs to be at a distance of 200,000 km.