Starcrash

Starcrash is a movie starring Marjoe Gortner, Caroline Munro, and Christopher Plummer. An outlaw smuggler and her alien companion are recruited by the Emperor of the Galaxy to rescue his son and destroy a secret weapon by the evil...
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.