Starcrash(1978)

A galactic adventure beyond your wildest dreams!

A pair of smugglers manage to pick up a castaway while running from the authorities, who turns out to be the only survivor from a secret mission to destroy a mysterious superweapon designed by the evil Count Zartharn. The smugglers are soon recruited by the Emperor to complete the mission, as well as to rescue the Emperor's son, who has gone missing.