Knowing times for space mission (5)
I believe the answer is:
flyby
'space mission' is the definition.
(flyby is a type of space mission)
'knowing times' is the wordplay.
'knowing' becomes 'fly'.
'times' becomes 'by' (both can mean 'multiplied by').
'fly'+'by'='FLYBY'
'for' is the link.
(Other definitions for flyby that I've seen before include "Part of probe's track closest to the observed planet" , "Low pass at air display" .)