Slightly crazy orbit, perhaps incomplete? Mine wasn't (7)
I believe the answer is:
gagarin
'incomplete? mine wasn't' is the definition.
The definition suggests a singular noun which matches the answer.
'slightly crazy orbit' is the wordplay.
'slightly crazy' becomes 'gaga' (I've seen this before).
'orbit' becomes 'rin' (I can't explain this - if you can you should give a lot more credence to this answer).
'gaga'+'rin'='GAGARIN'
'perhaps' acts as a link.
Can you help me to learn more?
(Other definitions for gagarin that I've seen before include "Yuri --, cosmonaut" , "Yuri ....... first man in space" , "Astronaut" , "old spaceman" , "Yuri ......, first Russian into space" .)