Micro-g environment

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).

A micro-g environment (also µg, often referred to by the term microgravity) is one where the acceleration induced by gravity has little or no measurable effect - gravity itself does not change.^[1] The only three methods of creating a micro-g environment are to travel far enough into deep space so as to reduce the effect of gravity by attenuation, by falling, and by orbiting a planet. The terms weightlessness and Zero-G refer to this same environment.

The first method is the simplest in conception, but requires traveling an enormous distance, rendering it most impractical. Even during the coasting phase to the Moon, the astronauts only experienced micro-g because they were orbiting the sun and free falling within the combined gravitational fields of the Earth, moon, and Sun.

The second method, falling, is very common but approaches micro-g only when the fall is in a vacuum, as air resistance will provide some resistance to free fall acceleration. Also it is difficult to fall for long enough periods of time to do much experimentation or to support any commercial activity. There are also problems which involve avoiding too sudden of a stop at the end. However, it is still used as training for astronauts and for some experiments. Drop towers, sounding rockets, and airplanes (such as used by NASA's Reduced Gravity Research Program, aka the Vomit Comet) provide short term weightlessness.

The third is orbiting a planet, which is really just falling with sufficient forward (tangential) speed so as to follow the curvature of the planet. The effect is perpetual free-fall. This is the environment commonly experienced in the space shuttle, International Space Station, Mir (no longer in orbit), etc. While this scenario is the most suitable for scientific experimentation and commercial exploitation, it is still quite expensive to operate in, mostly due to launch costs.

Commercial applications

Metal spheres

In a shot tower (now obsolete), molten metal (such as lead or steel), was dripped through a sieve into free fall. With sufficient height (several hundred feet), the metal would be solid enough to resist impact (usually in a water bath) at the bottom of the tower. While the shot may have been slightly deformed by its passage through the air and by impact at the bottom, this method produced metal spheres of sufficient roundness to be used directly in shotgun shells or to be refined by further processing for applications requiring higher accuracy.

High quality crystals

While not yet a commercial application, there has been much interest in growing crystals in micro-g, as in a space station or automated artificial satellite, in an attempt to reduce crystal lattice defects. Such defect-free crystals may prove useful for certain microelectronic applications and also to produce crystals for subsequent X-ray crystallography.

Low quality crystals

Are a commercial application, there has been no interest in growing them in micro gravity as they are deep under earth.

See also

• μFluids@Home is a distributed computing project that models the behavior of liquid rocket propellants in micro-g.
• Weightlessness

References

External links

Wikimedia Commons has media related to: Weightlessness

• Overview of microgravity applications and methods
• Criticism of the terms "Zero Gravity" and "Microgravity", a persuasion to use terminology that reflects accurate physics (Sci.space post).
• Space Biology Research at AU-KBC Research Centre