Crossword Genius

Astronaut best among stars when rotated (8)

Ross

I believe the answer is:

spaceman

I'm a little stuck... Click here to teach me more about this clue!

'astronaut' is the definition.
(I know that astronaut can be written as spaceman)

'best among stars when rotated' is the wordplay.
I cannot quite see how this works, but
'best' could be 'ace' (ace can informally mean very good) and 'ace' is found in the answer.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for spaceman that I've seen before include "NASA PC, me! (anag)" , "one requiring a supply of oxygen?" , "Armstrong, say" , "High flier" , "Distant traveller" .)

I've seen this clue in The Sun.
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