The main propulsion system includes three main engines, controllers
and supporting equipment.
Main Propulsion System Helium Subsystem
Helium is used to purge tanks and actuate valves.
Propulsion System Propellant Management Subsystem
Liquid hydrogen and liquid oxygen are fuels used by the system.
The external tank feeds fuel to the main propulsion system.
Shuttle Main Engines
The main engines are reusable, high-performance, liquid-propellant
rocket engines with variable thrust.
A pogo suppression system prevents engine thrust oscillation.
Shuttle Main Engine Controllers
Each controller operates in conjunction with other components
to provide a self-contained system for engine control, checkout
There are three separate means of detecting malfunctions within
the main propulsion system.
Three hydraulic systems supply pressure to the main propulsion
system, providing thrust vector control and actuating engine valves
on each SSME.
Ascent thrust vector control directs thrust of the main engines
and SRBs to control attitude and trajectory from liftoff through
Oxidizer and Fuel Flow Sequence The complete sequence begins
several hours before launch and ends after main engine cutoff.