A drug gets one travelling through space? (8)
I believe the answer is:
asteroid
'one travelling through space?' is the definition.
(asteroids travel through space)
'a drug' is the wordplay.
'drug' becomes 'steroid' (type of drug).
'a'+'steroid'='ASTEROID'
'gets' acts as a link.
(Other definitions for asteroid that I've seen before include "Rocky body in orbit" , "Any of the small planets revolving around the sun" , "way-out rock" , "Bits of rock that move around the heavens" , "Small planet orbiting the Sun" .)