"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)