Spacecraft for heartless brute (5)
I believe the answer is:
probe
'spacecraft' is the definition.
(I've seen this before)
'for heartless brute' is the wordplay.
'for' becomes 'pro' (as in being 'pro' something).
'heartless' says to hollow out the word (remove centre letters).
'brute' with its middle taken out is 'be'.
'pro'+'be'='PROBE'
(Other definitions for probe that I've seen before include "Explore, examine" , "Question or examine thoroughly" , "(Crime) investigation" , "Closely enquire into" , "Examine searchingly" .)