Obstruction set back lead communications satellite (7)
I believe the answer is:
telstar
'communications satellite' is the definition.
(I've seen this in another clue)
'obstruction set back lead' is the wordplay.
'obstruction' becomes 'let' (let can mean a hindrance).
'set back' says the letters should be written in reverse.
'lead' becomes 'star' (synonyms).
'let' back-to-front is 'tel'.
'tel'+'star'='TELSTAR'
(Other definitions for telstar that I've seen before include "Distant transmitter" , "Early sixties satellite" , "Old satellite" , "Communications satellite" , "Communication satellite" .)