S1, E4: A mission to Mars may seem like the stuff of science fiction, but NASA is working to make it a reality. But one big question remains: can the human body withstand this 34-million-mile odyssey? See how modern science is preparing today's astronauts for our next adventures into the deadly void of outer space. The experiences of our first astronauts are helping engineers create new technology to overcome the biggest obstacle to long-term space travel: our human bodies.