English: A 1969 station concept, to be assembled on-orbit from spent Apollo program stages.The station was to rotate on its centralaxis to produce artificial gravity. The majority of early space station concepts created artificial gravity one way or another in order to simulate a more natural or familiar environment for the health of the astronauts. After returning micro-gravity environment, astronauts find their muscles weak because they have not been using them. Long-term exposure to micro-gravity could generate long-term health problems for astronauts who do not utilize their muscles (tThis is why there are exercise machines on space shuttles and on the International Space Station).