"Gravity" refers to the force exerted by the Earth on objects in its vicinity; standing on the surface of the earth an object behaves within the environment of this force. Conversely, a “microgravity” or “micro-g” environment is one in which gravity has a minuscule effect on a mass and represents a material reduction in the gravitational forces under which objects behave on Earth.
The myth that a satellite remains in orbit because it operates far enough from Earth’s gravitational pull is untrue. Gravity still exists in orbit. A satellite stays suspended because its location and speed work together to create a centrifugal equilibrium that counteracts Earth’s gravitational pull. A state of microgravity is achieved because the object in orbit is in a constant state of free fall. In this environment objects are not subject to sedimentation, gravity-drive convection or hydrostatic pressure. For particular projects these and other micro-g conditions create research settings far superior to those we can establish on Earth.
The first micro-g experiments took place on the Apollo spacecraft in 1957 when the first men went into space. Since then scientists have conducted thousands of experiments that have helped build our understanding of microgravity and the benefits of conducting research within its environments.