Overcoming the zero-g challenge of space
Zero-g is the absence of sensible gravity. In nature, prolonged zero-g occurs in deep space beyond the solar system where the gravitational attraction of the surrounding stars is effectively zero.
Within the solar system, prolonged zero-g is experienced by natural or man-made objects in orbit about the sun or the planets. Objects free-falling within a gravity field, but not in orbit, also experience zero-g, at least until the object impacts the surface or atmosphere.
While zero-g has many engineering advantages, it has known biomedical effects that include loss of bone mass and muscle strength and changes in internal fluid distribution. A decrease in the body’s ability to fight infection is also suspected. Prolonged bed rest on the Earth also produces similar physiological changes, such as bone mass and muscle strength loss. Despite these issues, lengthy stays in zero-g of up to a year have been successfully undertaken by Russian cosmonauts.
Zero-g also leads to difficulties in some aspects of daily living including personal hygiene, clothes and habitat cleaning, cooking, and emergency medical treatment. While manageable for small numbers of people who follow the rules, lengthy zero-g living by large numbers of people, consistent with industrial space operations, may not be practical. The better approach is to create artificial gravity in the space habitats used for personnel housing and, in some cases, for scientific and industrial processes while using zero-g in logistics support facilities, specialized habitats, and spaceships.
A primary question that requires further investigation is what level of artificial gravity is needed to maintain adequate health. Is 1 g required or can adequate human health be maintained at the lower levels of the Moon (1/6th g) and Mars (1/3rd g)? Since sustained lower g levels are not possible on the Earth and any level of artificial gravity is not practical with current space logistics capabilities, this issue will only be able to be resolved once the initial artificial gravity facilities are built in space.