Main Propulsion System

Overview
The main propulsion system includes three main engines, controllers and supporting equipment.

Orbiter Main Propulsion System Helium Subsystem
Helium is used to purge tanks and actuate valves.

Main Propulsion System Propellant Management Subsystem
Liquid hydrogen and liquid oxygen are fuels used by the system.

External Tank
The external tank feeds fuel to the main propulsion system.

Space Shuttle Main Engines
The main engines are reusable, high-performance, liquid-propellant rocket engines with variable thrust.

Pogo Suppression System
A pogo suppression system prevents engine thrust oscillation.

Space Shuttle Main Engine Controllers
Each controller operates in conjunction with other components to provide a self-contained system for engine control, checkout and monitoring.

Malfunction Detection
There are three separate means of detecting malfunctions within the main propulsion system.

Orbiter Hydraulic Systems
Three hydraulic systems supply pressure to the main propulsion system, providing thrust vector control and actuating engine valves on each SSME.

Thrust Vector Control
Ascent thrust vector control directs thrust of the main engines and SRBs to control attitude and trajectory from liftoff through second-stage ascent.

Helium, Oxidizer and Fuel Flow Sequence The complete sequence begins several hours before launch and ends after main engine cutoff.