The condition of zero-gravity (zero-g) or microgravity
experienced by all spacecraft and their occupants when in orbit, in any
other state of free fall, or traveling through space at constant speed.
Weightlessness can be of great benefit in certain areas of research and
manufacturing, and large construction work in space. Large masses in orbit
do not require support, and their movement is restricted only by inertia.
Structures can be designed without provision for support against the forces
of gravity – in free space there is no such thing as a static load.
On the other hand, long-term exposure to weightlessness has adverse health
effects, including muscular deconditioning and bone
The first person to write about the possibility of weightlessness may have
been Bishop Francis Godwin in his book The
Man in the Moone (1638).