Passenger on a space probe (7)

I believe the answer is:

voyager

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'passenger' is the definition.
(thesaurus)

I don't understand how the rest of the clue works.

(Other definitions for voyager that I've seen before include "Sea or space traveller" , "Traveller to a distant land" , "One on a long journey" , "Traveler to a distant land" , "Person making a journey on water or in space" .)

I've seen this clue in The Mirror.

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