Elated -- but can't we try for Mars now? (4,3,4)

I believe the answer is:

over the moon

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'elated' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Other definitions for over the moon that I've seen before include "those Apollo chose walked here?" , "Pleased" , "cock-a-hoop" , "Where a jumped-up cow went" , "a long way into space?" .)

I've seen this clue in The Telegraph.

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