The most common and most likely answer to this crossword clue is the 7 letter word APOLUNE
A
P
O
L
U
N
E
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The straight part
We know that "Outer limit for spacecraft" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case outer limit for spacecraft = apolune.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does APOLUNE mean?
APOLUNE noun- The point of an elliptical lunar orbit where the distance between the satellite and the Moon is at its maximum.