The Collaborative International Dictionary of English v.0.48:

space station \space" sta`tion\, n.
   a manned artificial satellite orbiting the earth designed for
   extended occupation and use by multiple crews in succession.
   [PJC]

WordNet (r) 3.0 (2006):

space station
    n 1: a manned artificial satellite in a fixed orbit designed for
         scientific research [syn: space station, space
         platform, space laboratory]