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Asteroids are constantly threatening Earth, with thousands lurking too close to our planet for comfort. We travel to Arizona to meet the team who spend every night scanning the heavens for asteroids that could threaten earth, and reveal how scientists test an intense laser beam they hope could one day deflect an asteroid away from Earth . But is there more to these deadly space rocks than the next Armageddon? At NASA we see astronauts train in weightless conditions for the first manned mission to an asteroid, and discover how asteroids could become cosmic gas stations ...