Liquid Rocket Systems ArrangementSecondary propulsion systems (as contrasted to the primary propulsion systems of the launch vehicle) are installed in the reentry module and the adapter module to provide capability for separation from the launch vehicle either under normal conditions or in emergency conditions; for translational maneuvering in six basic directions: up, down, left, right, forward and rearward and for attitude control about the pitch, roll and yaw axes. One system, the retrograde rocket system, provides the necessary velocity decrement to initiate reentry.
Propulsive thrust to perform these functions is generated by three individual systems: the orbit attitude and maneuver system (OAMS), the reentry cortrol systems (RCS), and the retrograde rocket system (RRS). The orbit attitude and maneuver system is installed in the equipment and retrograde sections of the adapter module. The reentry control systems are located in the reentry module. The retrograde rocket system is clustered in the center of the retrograde section, just aft of the reentry module heat shield.
ORBIT ATTITUDE AND MANEUVER SYSTEM (OAMS)
The OAMS is a liquid bipropellant rocket engine propulsion system constructed on a modular basis consisting of thrust chamber assemblies; pressure storage tanks; pressure regulators; propellant tanks; propellant shut-off valves; propellant and pressurant lines; propellant line cutter-sealer assemblies; and five component packages which provide means of ground testing, pressurant and propellant tank filling, burst diaphragms, relief valves and instrumentation. The components are divided according to function into a thrust chamber assembly group, an oxidizer/fuel group and a pressurizing group.
The OAMS thrust chamber assembly group consists of 16 engines, each mounted in a fixed position and operated at a fixed thrust level. (The amount of force desired from each. engine for maneuvering is obtained by varying the time it is operated at the fixed thrust level.) Eight of the engines develop about 25 pounds; two produce about 85 pounds and six develop approximately 100 pounds of thrust.
The engines provide attitude and maneuver control from spacecraft separation from the launch vehicle until the adapter equipment section is jettisoned. The OAMS engines are operated by signals from the orbit attitude and maneuver electronics system. Pitch, roll and yaw torques are obtained by firing the 25 pounds thrust engines in pairs. Maneuvering is accomplished by firing the 100 pounds thrust engines for lateral, vertical and forward movement. Two of these fire to the aft to provide thrust for spacecraft separation from the launch vehicle. The two 85 pounds thrust engines fire forward to provide rearward motion. Engines for lateral and vertical maneuvering installed in GT-3 are inoperative dummy engines. These maneuvers are not necessary for the GT-3 mission.
Each engine assembly consists of two propellant valves with calibrated orifices and filters, a fuel and oxidizer injection system, a combustion chamber, and an expansion nozzle. The propellant valves are quick acting and are normally closed and operated by solenoid action; that is, the valves open upon application of an appropriate electrical signal to permit the flow of fuel and/or oxidizer to the injector to which they are fitted. In the event of electrical malfunction of any kind. no signal is transmitted and therefore the solenoid valves remain closed. Valve construction is such that the parts in contact with the fuel and oxidizer are not adversely affected by the corrosive nature of the propellants.
The combustion chamber and the expansion nozzle are lined with an ablative material which maintains internal geometry and protects the external wall from temperature damage.
The engines operate on storable hypergolic propellants. The oxidizer is nitrogen tetroxide; the fuel is monomethylhydrazine. Fuel quantities vary according to mission requirements.
The oxidizer and fuel propellant tanks are all-welded titanium spherical structures. Propellant tank volume and arrangement will vary in accordance with mission requirements. Two propellant shut-off valves permit isolation of the propellants from the engine chamber assemblies in the event of engine malfunction. One valve is m the oxidizer feed system and the other valve is in the fuel feed system. The oxidizer/fuel group valves are electric motor operated.
Since the OAMS functions under a weightless condition during much of its operational lifetime, it is necessary to use a pressurization system to expel propellants on demand.
To achieve positive expulsion of propellants, both the oxidizer and the fuel are in bladder containers inside storage tanks. Gas is induced between the tank wall and the bladder to provide a "squeezing" pressure that forces propellant to the engines.
The pressurant which forces the oxidizer and fuel to the engine is helium. The pressurization system includes a storage tank, component packages and pressure regulation group.
The pressurant tanks also are all-welded titanium spheres each with a volume of 1700 cubic inches. The pressure in the propellant tanks is regulated at 295 pounds per square inch. The number of tanks installed will vary with mission requirements.
REENTRY CONTROL SYSTEMS (RCS)
The reentry control systems are completely independent of the orbit attitude and maneuver system and are installed in the reentry module just forward of the pressurized cabin. There are two completely independent reentry control systems Each is a liquid bipropellant rocket engine propulsion system constructed on a modular basis. Both are identical and provide redundancy in the event of a malfunction of one system.
There are eight fixed-thrust-level, fixed mounted engines in each of the two systems. As in the OAMS, they operate on storable hyperbolic propellants supplied by a cold gas, pressurized, positive expulsion feed system. The oxidizer and fuel flow in the thrust chamber assembly is controlled by electrically operated valves. The basic operation of each RCS is identical to that of the orbit attitude and maneuver system. The reentry control systems respond to electrical signals from the orbit attitude and maneuver electronics system, the same unit which operates to provide input to the orbit attitude and maneuver engines.
In the event of a malfunction of one system, the remaining RCS has sufficient total impulse capacity and thrust to assure attitude control during retrograde, stabilization for a safe reentry, and thrust as necessary to steer the reentering spacecraft to the desired landing point.
Attitude is controlled through the attitude control and maneuvering electronics from inputs of the astronaut's hand controller. Pitch, roll and yaw torques are obtained by selective firing of pairs of engines. Each has a nominal rocket engine thrust output rated at about 25 pounds.
The fluids involved in the operation of the RCS are identical to those in the OAMS except for the pressurant which is nitrogen in the case of the RCS. The pressurizing group and the fuel packages are contained in the non-pressurized section of the reentry module. The pressurant tank has a fluid volume of 185 cubic inches. The pressure regulator maintains a 295 pounds per square inch to the propellant tanks.
The propellant tanks, one oxidizer and one fuel, are all-welded titanium cylindrical structures. The oxidizer tank has a fluid volume capacity of 439 cubic inches; the fuel tank has a fluid volume capacity of 546 inches. The engines of the reentry control systems have characteristics similar to those of the orbit attitude and maneuvering system 25 pounds thrust engines.
RETROGRADE ROCKET SYSTEM (RRS)
The Thiokol RRS, an independent system, consists of four solid propellant rocket motors mounted in the retrograde section of the adapter and located symmetrically about the longitudinal axis of the spacecraft.
The retrograde rockets, each with approximately 2500 pounds of thrust, provide an impulse to the reentry module resulting in a sufficient velocity decrement to initiate reentry into the Earth's atmosphere. The retrograde rockets are fired automatically by an electrical signal from an onboard electronic timer. There is also a manual backup initiation capability. The rockets fire sequentially at a nominal 5.5-second interval.
The spent retrograde rockets are jettisoned with the retrograde section of the adapter approximately 45 seconds after rocket firing initiation. In the event of an abort before orbital altitude and velocities are achieved, the retrograde rockets may be salvo fired by the flight crew to aid in separation of the spacecraft from the launch vehicle.
Each rocket consists of a motor case, a partially submerged contour nozzle, and dual pyrogenic igniters with removable pressure cartridge initiators. The motor case is an all-welded titanium alloy sphere slightly greater than one foot in diameter. The nozzles include an expansion cone a throat insert and a nozzle bulkhead. The pyrogenic igniter is a small rocket of short burn duration which fires into the charge of the retrorocket thus igniting it.
Copyright 1997-2005 by John
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