Idiot about to make ingredient of rocket fuel (5)
I believe the answer is:
nitre
'ingredient of rocket fuel' is the definition.
(chemical used in rocket fuel)
'idiot about to' is the wordplay.
'idiot' becomes 'nit' (I've seen this before).
'about to' becomes 're' (I've seen this in other clues).
'nit'+'re'='NITRE'
'make' is the link.
(Other definitions for nitre that I've seen before include "Sodium nitrate" , "Inert kind of saltpetre" , "Mineral used in gunpowder" , "explosive ingredient" , "Inert (anag) - saltpetre" .)