How does the human body respond to long-duration spaceflight? Does radiation present a problem? How about long periods of weightlessness? And what about the isolation? We're about to find out. NASA's "One-Year Mission" launches at 3:42 p.m. EDT tomorrow, when American astronaut Scott Kelly and Russian cosmonaut Mikhail Kornienko blast off from the Baikonur Cosmodrome in Kazahkstan for the International Space Station. A new perspective.