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 quite understand how this works, but
an anagram of 'had' is 'dah' which is within the answer.
'moon' could be 'io' (moon of Jupiter) and 'io' is found in the leftover letters.
This accounts for all the letters.
This explanation may well be incorrect...
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" .)