Manned spacecraft are vehicles with the capability of maintaining life outside of Earth's atmosphere. Partially in recognition of the fact that women as well as men are active participants in space travel programs, manned spacecraft are now frequently referred to as crewed spacecraft.

In its earliest stages, crewed space flight was largely an exercise in basic research. Scientists were interested in collecting fundamental information about the Moon, the other planets in our solar system, and outer space. Today, crewed space flight is also designed to study a number of practical problems, such as the behavior of living organisms and inorganic materials in zero gravity conditions.

A very large number of complex technical problems must be solved in the construction of spacecraft that can carry humans into space. Most of these problems can be classified in one of three major categories: communication, environmental and support, and re-entry...