Spaceship deposited carbon on floating platform (5)
I believe the answer is:
craft
'spaceship' is the definition.
(thesaurus)
'carbon on floating platform' is the wordplay.
'carbon' becomes 'C' (C is the chemical symbol for carbon).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'floating platform' becomes 'raft' (I've seen this before).
'c'+'raft'='CRAFT'
'deposited' is the link.
This may not be correct. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for craft that I've seen before include "Create" , "Boat - mastery" , "Workmanship" , "Dexterity" , "Guile" .)