The high pressure pumps inject the fuel and oxidizer into the main combustion chamber, where the second stage of combustion occurs. The expansion of the hot gases through the chamber and the nozzle produces thrust. Temperatures inside the main combustion chamber reach 6,000 degrees Fahrenheit, hot enough to melt steel. Meanwhile, liquid hydrogen circulates through miles of tubing at -423 degrees to cool the engines. Turbomachinery in the pumps rotate at up to 37,000 revolutions per minute.
Cutaway diagram shows the arrangement of the pumps around a main engine powerhead.
Each SSME is controlled by its own computer, which checks the health of the engines 50 times per second during countdown and ascent. The controller can shut an engine down if it detects a problem. The SSME's are built by Rocketdyne at Canoga Park, California. Acceptance testing takes place at Stennis Space Center, Mississippi. Rocketdyne technicians ready an SSME for shipment.