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' or in favour of something).
'heartless' suggests removing the centre.
'brute' with its centre 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" .)