Get real lament chasing traveller in space (4,4)
I believe the answer is:
come true
'get real' is the definition.
(I know this)
'lament chasing traveller in space' is the wordplay.
'lament' becomes 'rue' (I've seen this before).
'chasing' means one lot of letters go next to another (some letters chase after others).
'traveller in space' becomes 'comet' (comets travel through space).
'rue' after 'comet' is 'COME TRUE'.
(Other definitions for come true that I've seen before include "Turn out to be accurate" , "Happen in the way that was hoped or forecast" , "Happen in reality, as dreams may (4, 4)" , "More cute (anag)" , "Materialise" .)