Fifty years ago it was not even certain that humans could survive the experience of spaceflight. With his one-orbit flight, Yuri Gagarin demonstrated that they could. Since that April 12, 1961, feat, (only) 522 people have gone into orbit, an orbiting space laboratory has been continually inhabited since 1998, and 12 astronauts walked on the surface of the moon. Even with this record of accomplishment, the future of 21st century spaceflight remains uncertain. Will humans stay close to planet Earth, or will they some day in the next decades once again set out for distant destinations? Cold War competition sent Americans to the moon. What will be the compelling rationale for this century's human space exploration? The answer is not clear.
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