Setting out to Saturn, a traveller in space (9)
I believe the answer is:
astronaut
'a traveller in space' is the definition.
I can't tell whether this defines the answer.
'setting out to saturn' is the wordplay.
'setting' becomes 'a' (I can't explain this - if you can you should give a lot more credence to this answer).
'out' indicates an anagram.
'to'+'saturn'='tosaturn'
'tosaturn' is an anagram of 'stronaut'.
'a'+'stronaut'='ASTRONAUT'
Can you help me to learn more?
(Other definitions for astronaut that I've seen before include "Space voyager" , "Skier" , "For member of high-flying mission" , "High-flier" , "Space explorer" .)