It's been 22 years since U.S. President Ronald Reagan proposed building the International Space Station, but its mission has since radically changed.

Initially the ISS was conceived as a laboratory for developing medicines and experimenting with a wide variety of substances, The Washington Post reported Monday.

Today, while only half finished, the station's primary mission has been shifted by President George W. Bush to support his plan of sending astronauts to the moon, Mars and beyond.

"As it was originally planned, the space station would be a facility for all users," Donald Thomas, NASA's space station program scientist, told the Post. He said any researcher with an interesting experiment would have been welcomed aboard the ISS.

Today, said Thomas, the ISS is being used to study such problems as how to keep kidney stones -- as well as bone and muscle loss -- from developing in astronauts and why astronauts' immune systems deteriorate while they are in space.

And experiments planned at the ISS include learning how to control bowling-ball-sized satellites that might be used in space missions.

Copyright 2006 by United Press International