Galaxy Quest (1999)

They're not astronauts... they only played them on TV. For four seasons, from 1979 to 1982, the crew of the NSEA Protector donned their uniforms and set out on thrilling and often dangerous missions in space--then their series was canceled. Nearly twenty years later, the five stars of the classic sci-fi series "Galaxy Quest" are still in costume, making appearances at science fiction conventions for legions of faithful fans...but some of those fans have a little too much faith. The Thermians, a race of aliens from Klatu Nebula, have mistaken intercepted television transmissions of the show for historical "documents." Arriving on earth, they wisk "Commander Peter Quincy Taggart" and his crew into space to help them defeat an all-too-real and very deadly adversary. With no script, no director and no clue about real space travel, the actors have to turn in the performances of their lives to become the heroes the Thermians believe them to be.