Blue dog in US space station (6)
I believe the answer is:
skylab
'us space station' is the definition.
(I've seen this before)
'blue dog' is the wordplay.
'blue' becomes 'sky' (I've seen this in other clues).
'dog' becomes 'lab' (short for labrador).
'sky'+'lab'='SKYLAB'
'in' acts as a link.
(Other definitions for skylab that I've seen before include "research unit once in orbit" , "1970s' space station" , "with space to explore" , "Weather research centre that's out of this world" , "1973-79 space station" .)