Satellite's second leg (4)
I believe the answer is:
moon
'satellite's' is the definition.
(moon is a kind of satellite)
'second leg' is the wordplay.
'second' becomes 'mo' (both are short periods of time).
'leg' becomes 'on' (cricket term, fielding positions).
'mo'+'on'='MOON'
(Other definitions for moon that I've seen before include "Orbiting body" , "High light" , "Expose one's buttocks" , "who headed a religious 29 [CULT]" , "down one's pants" .)