Pictured here is one of the four Rocket Engine Modules mounted on the Propulsion Module. Each module consists of a large thruster and three smaller thrusters. The large thruster can generate a force of 22 newtons, while each of the smaller thrusters develop only 1 newton. By firing thrusters in different combinations and for varying lengths of time, the Navigation Team can change the orientation and orbit of the spacecraft. Note how the two stern-facing thrusters are slightly canted; they are aligned with the pre-launch center of mass of the spacecraft to minimize unwanted spin when fired. The thrusters are mono-propellant units which operate by expanding and expelling hydrazine from the main and auxiliary propellant tanks.
