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1993-02-04
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"6_2_15_2.TXT" (1366 bytes) was created on 11-02-87
SHUTTLE PROPULSION SYSTEM OVERVIEW
NASA's Space Shuttle opened a new era of space transportation
when it was launched for the first time in 1981. Essentially a
reusable space vehicle, the Shuttle permits greater participation
in space by the world-wide scientific community than ever
before.
The Shuttle is composed of an orbiter -- a winged spacecraft
-- and a propulsion system. The Shuttle propulsion system,
consisting of three main engines, an external tank, and two solid
rocket boosters, is one of the most advanced propulsion systems
currently in existence. The external tank is the only major
component that is used only once.
The two solid rocket boosters and three main engines mounted
on the orbiter provide the initial ascent thrust to lift the
Shuttle and its payload off the launch pad. During a normal
mission, the boosters provide thrust for approximately 2 minutes
after lift-off, then are separated from the vehicle. The engines
provide thrust for a total of 8 minutes after lift-off. The
Marshall Space Flight Center in Huntsville, Ala., is responsible
for management of the Shuttle propulsion elements.
"6_2_15_3.TXT" (3800 bytes) was created on 11-02-87
SPACE SHUTTLE MAIN ENGINES
The Space Shuttle main engine is the most advanced liquid-
fueled rocket engine ever built. Its main features are variable
thrust, high performance, reusability, total redundancy, and a
fully integrated controller. The performance of the engine is the
highest thrust for its weight of any engine yet developed.
Three main engines are mounted on the orbiter aft fuselage
in a triangular pattern. The engines are spaced so that they are
moveable during flight and, in conjunction with the two solid
rocket boosters, are used to steer the Shuttle vehicle during
flights as well as provide thrust for launch.
Fuel for the engines, liquid hydrogen and liquid oxygen, is
contained in the external tank, the largest element of the
Shuttle. Fuel is supplied from the tank at a rate of about
178,000 liters (47,000 gallons) per minute of hydrogen and 64,000
liters (17,000 gallons) per minute of oxygen.
The main engines use a staged combustion cycle in which all
propellants entering the engines are used to produce thrust more
efficiently than any rocket engine developed previously. In the
staged combustion cycle, propellants are burned partially at high
pressure and relatively low temperature, and then burned
completely at high temperature and high pressure in the main
combustion chamber. The rapid mixing of the propellants under
these conditions is so complete that a combustion efficiency of
about 99 percent is attainable.
Each engine has three primary levels of thrust or power --
minimum, rated and full power. Engine thrust, however, can be
varied throughout the range from minimum to full power level
depending on mission needs. Shuttle payloads will be sized to be
compatible with launch-to-orbit at a maximum of 104 percent of
rated power level, with each engine developing 2,174,286 Newtons
(488,000 pounds) of thrust, 1,734,803 Newtons (390,000 pounds) at
sea level. Full power level (109 percent of rated power) will be
available for use in emergency situations. During the latter part
of ascent, engine thrust will be reduced to insure that an
acceleration force of no more than three times that of Earth's
gravity is reached. This acceleration level, permitted by the
throttleable Shuttle engines, is about one-third the acceleration
experienced on previous manned space flights and is well under
the physical stress limits of non-astronaut scientists who fly
aboard the Shuttle. The lowest thrust throttle setting --
minimum power level -- equals 65 percent of rated power.
The Shuttle main engine is the first rocket engine to use a
built-in electronic digital controller. The controller will
accept commands from the orbiter for engine start, shutdown and
change in throttle setting, and also will monitor engine
operation. In the event of a failure, the controller takes action
automatically to correct the problem or shutdown the engine
safely.
Shuttle main engines are thoroughly inspected and tested
between flights to assure acceptable operation during subsequent
flights. The design goal is to operate for 7.5 accumulated
hours.
Main Engine
Length 4.25 meters (14 feet)
Diameter 2.4 meters (7.8 feet)
(Nozzle Exit)