The most common and most likely answer to this crossword clue is the 9 letter word ARMSTRONG
I've seen this crossword clue in The Times
A
R
M
S
T
R
O
N
G
More clues leading to the result ARMSTRONG
- Jazz leader — one requesting “Fly me to the moon”?
- Astronaut packing some punch, it's implied?
- Member blowing hard, renowned trumpeter
- Adventurer who packs a punch?
- Rider penalised, prepares for a fight: conduct ultimately improper, they say
- A jolly powerful cyclist?
- Moon-walker like Bahubali or Bhujbal in India?
- Bully gets gun moved to the front for astronaut
- If so, lifting of dumb-bell might be easy for man on moon
- Member meeting powerful old American high-flyer
Buddy explains!

The straight part
We know that "Astronaut" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case astronaut = armstrong.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.