National Geographic | Astrobiology & Space Travel - Documentary 720p
Scientists speculate on how life originated on earth based on the range of conditions where life survives today and the conditions that existed on the early earth. They then look for those conditions, past or present, that may exist on other planets or moons. The many and various hazards to space travel are explained. But solving that problem better propulsion systems are need to travel anywhere beyond the moon. Some possibilities, both realistic and speculative, are described.