Someone setting out unto a star! (9)
I believe the answer is:
astronaut
'someone' is the definition.
(astronaut is a kind of someone)
'out unto a star' is the wordplay.
'out' indicates anagramming the letters.
'unto'+'a'+'star'='untoastar'
'untoastar' is an anagram of 'ASTRONAUT'.
'setting' is the link.
(Other definitions for astronaut that I've seen before include "Santa tour for space traveller" , "heavenly voyager" , "high flier" , "Armstrong or Sharman, say" , "spaceman" .)