Space flight takes one coming into sun source (9)
I believe the answer is:
stairwell
'space flight' is the definition.
(I've seen this before)
'one coming into sun source' is the wordplay.
'one' becomes 'i' (Roman numeral).
'coming into' indicates putting letters inside.
'sun' becomes 'star' (I've seen this before).
'source' becomes 'well' (well is a kind of source).
'i' inserted inside 'star' is 'stair'.
'stair'+'well'='STAIRWELL'
'takes' acts as a link.
(Other definitions for stairwell that I've seen before include "where flight is located" , "Shaft in building housing steps" , "Space flight" , "Shaft allowing access to other floors" , "Shaft for flight" .)