Strainers in firm spacecraft (9)
I believe the answer is:
colanders
'strainers' is the definition.
(colander is a kind of strainer)
'in firm spacecraft' is the wordplay.
'in' is an insertion indicator.
'firm' becomes 'cos' (I am not sure about this - if you are sure you should believe this answer much more).
'spacecraft' becomes 'lander' (eg a moon lander).
'cos' going around 'lander' is 'COLANDERS'.
Can you help me to learn more?
(Other definitions for colanders that I've seen before include "Culinary strainers" , "Can solder manufacture perforated utensils?" , "they'll be in the kitchen" , "Bowl-shaped strainers" .)