Space
Shuttle Basics
Space
Shuttle Main Engines
The three main
engines of the space shuttle, in conjunction with the solid rocket
boosters, provide the thrust to lift the orbiter off the ground
for the initial ascent. The main engines continue to operate for
8.5 minutes after launch, the duration of the shuttle's powered
flight.
After the solid
rockets are jettisoned, the main engines provide thrust which accelerates
the shuttle from 4,828 kilometers per hour (3,000 mph) to over 27,358
kilometers per hour (17,000 mph) in just six minutes to reach orbit.
They create a combined maximum thrust of more than 1.2 million pounds.
As the shuttle
accelerates, the main engines burn a half-million gallons of liquid
propellant provided by the large, orange external fuel tank. The
main engines burn liquid hydrogen -- the second coldest liquid on
Earth at minus 423 degrees Fahrenheit (minus 252.8 degrees Celsius)
-- and liquid oxygen.
The engines'
exhaust is primarily water vapor as the hydrogen and oxygen combine.
As they push the Shuttle toward orbit, the engines consume liquid
fuel at a rate that would drain an average family swimming pool
in under 25 seconds generating over 37 million horsepower. Their
turbines spin almost 13 times as fast as an automobile engine spins
when it is running at highway speed.
The main engines
develop thrust by using high-energy propellants in a staged combustion
cycle. The propellants are partially combusted in dual preburners
to produce high-pressure hot gas to drive the turbopumps. Combustion
is completed in the main combustion chamber. Temperatures in the
main engine combustion chamber can reach as high as 6,000 degrees
Fahrenheit (3,315.6 degrees Celsius).
Each space
shuttle main engine operates at a liquid oxygen/liquid hydrogen
mixture ratio of 6 to 1 to produce a sea level thrust of 179,097
kilograms (375,000 pounds) and a vacuum thrust of 213,188 (470,000
pounds). The engines can be throttled over a thrust range of 65
percent to 109 percent, which provides for a high thrust level during
liftoff and the initial ascent phase but allows thrust to be reduced
to limit acceleration to 3 g's during the final ascent phase. The
engines are gimbaled to provide pitch, yaw and roll control during
the ascent. | 
