Moon's associate space-probe at the centre of the earth! (5)
I believe the answer is:
lunar
'moon's' is the definition.
'associate space-probe at the centre of the earth' is the wordplay.
'associate space probe' becomes 'luna' (I can't explain this - if you can you should believe this answer much more).
'at the centre' indicates the central letters.
'of the earth' becomes 'terrene' (I've seen this in another clue).
The middle of 'terrene' is 'r'.
'luna'+'r'='LUNAR'
Can you help me to learn more?
(Other definitions for lunar that I've seen before include "One sort of month" , "that could describe landscape with more than one mare" , "Selenic" , "Related to the moon" , "Kind of eclipse" .)