Moon landing had upset state (5)
I believe the answer is:
idaho
'state' is the definition.
(US state)
'moon landing had upset' is the wordplay.
I cannot really understand how this works, but
an anagram of 'had' is 'dah' which is located in the answer.
'moon' could be 'io' (moon of Jupiter) and 'io' is present in the leftover letters.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for idaho that I've seen before include "US state, capital Boise" , "The Gem State, known for its potatoes" , "State of NW US" , "My Own Private -- (1991 film)" , "Pertaining to the Bard" .)