Radio set especially designed for a space traveller (8)
I believe the answer is:
Here is my best explanation:
'a space traveller' is the definition.
(I've seen this before)
'radio set especially designed' is the wordplay.
'especially designed' indicates an anagram (letters re-designed in a particular way).
'radioset' anagrammed gives 'ASTEROID'.
'for' acts as a link.
(Other definitions for asteroid that I've seen before include "Small celestial body composed of rock and metal", "Piece of rock that moves around the heavens", "Rocky object", "Celestial body", "way-out rock", "Small body orbiting sun", "Small planet orbiting the Sun", "A minor planet", "Heavenly body" and "Bit of rock that moves around the heavens".)