Space Race competitor, for short (4)
I believe the answer is:
ussr
'space race competitor for short' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ussr that I've seen before include "Country established in 1922 and dissolved in 1991, in short" , "Former federation of Russial and other states" , "Country established in1922 and dissolved in 1991, in short" , "The Beatles? song 'Back in the . . . .'" , "In brief, former Soviet federation" .)