Where astronauts plan to go is delightful (3,2,4,5)
I believe the answer is:
out of this world
'delightful' is the definition.
(I've seen this before)
'where astronauts plan to go is' is the wordplay.
I cannot really see how this works, but
'to' is present in the answer.
'is' is present in the answer.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for out of this world that I've seen before include "Are stars so" , "Delightful" , "Dead" , "Astronauts are sometimes" , "astronauts fired here" .)