Challenges for space medicine.

Since April 1961, when Yuri Gagarin first orbited the earth about 270 astronauts (predominantly males) have lived in space. More than 90 percent of these astronauts were natives of the USA and the ex-USSR. In this commentary, the challenges confronting the discipline of space medicine are reviewed. These include, (1) space sickness, (2) wasting of the musculoskeletal system and (3) developing a longterm life support system.