The Space Shuttle Orbiter vehicle employs two earth storable bipropellant propulsion subsystems to provide orbit maneuvering and vehicle attitude control. Respectively, these are the Orbit Maneuvering Subsystem (OMS) and the Reaction Control Subsystem (RCS).
The OMS provides the velocity increments necessary to achieve final insertion of the vehicle into earth orbit, to perform orbital changes, and to de-orbit the vehicle. The OMS is made up of two normally independent propulsion subsystems in removable pods. Each contains a 6000 lb. thrust rocket engine, propellant tankage, and necessary feed and control componentry. The propellant capacity of 24,721 lbs. for both pods provide a nominal 1000 ft/sec velocity increment. In addition, a supplementary propellant supply, the cargo bay kit, boosts the all-up delta V capability to 2500 ft/sec.
The Reaction Control Subsystem provides the orbiter with the necessary stabilization, maneuvering, and translation capability while in earth orbit and during re-entry. The current RCS concept has evolved as the result of detailed trade-offs between several competing options. The most recent trade study has resulted in a change from monopropellant to bipropellant to provide lower operational program costs.
The RCS is composed of two aft modules containing twelve primary thrusters each and a single forward module containing sixteen primary thrusters and six vernier thrusters. The primary thrusters and the vernier thrusts provide 900 lbs. and 15 to 25 lbs. thrust, respectively. Like the OMS, the RCS modules are totally self-contained propulsion subsystems.