A complex physical structure specifically designed to serve as a multipurpose platform in low Earth orbit. Functioning independently and often without a crew actively involved in onboard operations, a space station contains the structures and mechanisms to operate and maintain such support systems as command and data processing, communications and tracking, motion control, electrical power, and thermal and environmental control. Evolving together with technology and increasing in scope and complexity, the space station has a history in which each program was based upon the developments and achievements of its predecessor.