Film with established actor ultimately going into space (7)
I believe the answer is:
western
'film' is the definition.
(I know that Western is a type of film)
'with established actor ultimately going into space' is the wordplay.
'with' becomes 'w' (short for with).
'established' becomes 'est' (abbreviation).
'ultimately' says to take the final letters.
'going into' is an insertion indicator.
'space' becomes 'en' (in printing, a space as wide as a letter 'n').
The final letter of 'actor' is 'r'.
'r' placed inside 'en' is 'ern'.
'w'+'est'+'ern'='WESTERN'
(Other definitions for western that I've seen before include "Cowboy film of occidental origin" , "The Occident" , "Spaghetti film?" , "direction?" , "Cowboys and Indians film" .)