Complex sentence: Kvant-1 did not have any propulsion systems of its own and to reach Mir, Kvant-1 was mated with a Functional Service Module (FSM)--carrying propulsion and electrical systems--to act as a space tug.
Split into simpler sentences: Kvant-1 did not have any propulsion systems of its own. To reach Mir, Kvant-1 was mated with a Functional Service Module (FSM)--carrying propulsion and electrical systems--to act as a space tug.