It excludes nothing, a spacecraft's task? (8)
I believe the answer is:
omission
'it excludes' is the definition.
(to omit something is to leave it out)
'nothing a spacecraft's task?' is the wordplay.
'nothing' becomes 'o' (looks like zero - 0).
'a spacecraft's task?' becomes 'mission' (a spacecraft might have a mission).
'o'+'mission'='OMISSION'
(Other definitions for omission that I've seen before include "cut?" , "task not done" , "Something left out or forgotten" , "Something lacking" , "Deficiency" .)