Complex sentence: Each engine was capable of 300 kg of thrust, although these engines could not be used after April, 1987 with the arrival of the Kvant-1 module at the station's aft port.
Split into simpler sentences: Each engine was capable of 300 kg of thrust. Both of the engines could not be used after April, 1987 with the arrival of the Kvant-1 module at the station's aft port.