Original sentence: In addition to the crew and payload the reusable orbiter carries most of the main propulsion system, but the propellant for its three main engines is fed from a  external tank, and two reusable solid rocket boosters help propel both the orbiter and the external tank during the first two minutes of ascent
Edited sentence: In addition to the crew and payload the reusable orbiter carries most of the main propulsion system, but the propellant for its three main engines is fed from an external tank, and two reusable solid rocket boosters help propel both the orbiter and the external tank during the first two minutes of ascent