Propellant Tanks Pressurization And Venting
LH 2
-PROPULSIVE VENTS
LH2 PROPULSIVE VENTS _
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AMBIENT HELIUM ÇTORAGF
LH 2
-PROPULSIVE VENTS
AMBIENT HELIUM ÇTORAGF
FROM GSE
VENT & RELIEF VALVE 41.0-45.0 PSIA
LATCH OPEN NPV VALVE 41.0-44.0PSIA
— GASEOUS HYDROGEN
LIQUID HYDROGEN niMiiiiiri LIQUID OXYGEN GASEOUS OXYGEN SENSE LINE
FROM GSE
I il
VENT & RELIEF VALVE 41.0-45.0 PSIA
LATCH OPEN NPV VALVE 41.0-44.0PSIA
LOX PROPULSIVE
VENT
SUSSE
LOX NON-PROPULSIVE VENTS
— GASEOUS HYDROGEN
LIQUID HYDROGEN niMiiiiiri LIQUID OXYGEN GASEOUS OXYGEN SENSE LINE
pressure through operation of solenoid valves in the lox tank pressure control module (5). In this manner, lox tank pressurization is maintained during all engine burn periods. An S-IVB lox tank pressure reading becomes available in the command module (CM) at S-II/S-IVB separation. This pressure is sensed by the pressure transducer (12) and is relayed to the S-II FUEL/S-IVB OXID gauges (13) in the CM and, via telemetry, to the ground.
Repressurization
The normal repressurization procedure is initiated at Tg + 48.1 seconds. It uses cold helium from the cold helium storage spheres (2, figure 6-9). The cold helium pressure is reduced to approximately 385 psia as it flows through the lox tank pressure control module (5). It next flows through the lox tank repressurization control (10), and into the O2/H2 burner (11). Should the regulator in the lox tank pressure control module (5) fail, the backup pressure switch (9) will maintain a pressure of 350-465 psia at the O2/H2 burner. The backup pressure switch controls the pressure by opening or closing valves in the lox tank repressurization module (10). As the cold helium is heated in the O2/H2 burner it expands and is routed to the lox tank. Pressure in the lox tank increases and is sensed by the flight control pressure switch (4) and the pressure transducer (12). The pressure switch (4) maintains lox tank pressure between 38-41 psia by opening and closing solenoid shutoff valves in the lox tank repressurization control module (10). The pressure transducer (12) transmits a continuous pressure reading to telemetry and to the LV TANK PRESS gauges (13) in the CM. At Tg + 496.6 seconds, cryogenic repressurization is switched off. Ambient repressurization is turned on at Tg + 497.6 seconds. Ambient helium from the ambient helium storage spheres (3) flows through the lox tank ambient helium repressurization control module (14) to the lox tank. Here the pressure is sensed by the flight control pressure switches (4). The pressure switches (4) control lox tank pressure by opening or closing the control valves in the lox tank ambient helium, repressurization control module (14). Just before the engines second burn, ambient repressurization is terminated (Tg + 520.0 seconds)
NOTE
The ambient repressurization portion of the repressurization procedure is in reality a backup procedure. Should the O2/H2 burner fail, ambient repressurization ensures lox tank pressure for engine start requirements.
Lox Venting
The lox tank vent subsystem provides for controlled lox tank venting during normal stage operation and for pressure relief venting when tank overpressures occur. The lox tank venting subsystem operates through a ground controlled combination vent and relief valve. This valve is pneumatically operated upon receipt of the ground command. Prior to loading, the vent and relief valve is placed in the open position and the boiloff of lox during loading is directed through one propulsive vent in the aft skirt of the stage (figure 6-8). When LOX tank prepressurization commfences, the valve is closed and placed in the relief position. Over-pressures from the lox tank will then be vented as necessary.
A ground command non-propulsive function is available in the lox tank vent subsystem. The lox vent and relief valve is commanded to the open position permitting non-propulsive venting through two non-propulsive vents placed 180 degrees apart. See figures 2-1 and 6-5 for the sequence of operation.
LH2SYSTEM
The LH2 is stored in an insulated tank at less than -423°F. Total volume of the tank is approximately 10,500 cubic feet with an ullage volume of approximately 300 cubic feet. The LH2 tank is prepressurized to 28 psia minimum and 31 psia maximum.
LH2 Low Pressure Fuel Duct
LH2 from the tank is supplied to the J-2 engine turbopump through a vacuum jacketed low pressure 10-inch duct. This duct is capable of flowing 80-pounds per second at -423°F and at a transfer pressure of 28 psia. The duct is located in the aft tank side wall above the common bulkhead joint. Bellows in this duct compensate for engine gimbaling, manufacturing tolerances, and thermal motion.
LH2 Fill and Drain
Prior to loading, the LH2 tank is purged with helium gas. At the initiation of loading, the ground controlled combination vent and relief valve is opened, and the directional control valve is positioned to route GH2 overboard to the burn pond.
Loading begins with precool at a flow of 500 gpm. When the 5% load level is reached fast fill is initiated at a flow of 3000 gpm. At the 98% load level, fast fill stops and a slow fill at 500 gpm begins. A fast fill emergency cutoff sensor has been provided to compensate for a primary control cutoff failure. Slow fill is terminated at the 100% load level, and this level is then maintained by a replenish flowrate of 0 to 300 gpm, as required. The replenish flow is maintained through the LH2 tank prepressurization operation.
Liquid level during fill is monitored by means of the LH2 mass probes. A backup overfill sensor is provided to terminate flow in the event of a 100% load cutoff failure.
An LH2 vent system provides command venting of the LH2 tank plus overpressure relief capability. Pressure sensing switches are provided to control tank pressure during fill and flight.
LH2 TANK PRESSURIZATION
LH2 tank pressurization is divided into "three basic procedures.. These procedures are called prepressurization, pressurization, and repressurization. The term prepressurization is used for that portion of the pressurization performed on the ground prior to liftoff. The term pressurization is used to indicate pressurization during engine burn periods, and lastly, repressurization indicates pressurization just before the second burn period.
The pressurants used during the three LH2 tank pressurization procedures are gaseous hydrogen (GH2) gaseous helium. Cold helium from a ground source (25, figure 6-9) is used during the prepressurization period. The cold helium storage spheres (2), located in the LH2 tank, supply cold helium for use during the repressurization period. The five ambient helium storage spheres (15), filled by ground support equipment (16), supply an alternate source of helium for use during the repressurization period.
The LH2 tank pressure is controlled by the flight control pressure switches (17) (dual redundant) regardless of the pressurization procedure used. These switches control solenoid shutoff valves in each of the supply subsystems.
Prepressurization
At Tj —97 seconds, the LH2 tank is prepressurized (figure 6-9) by ground support equipment. Cold helium (25) flows through the LH2 tank pressurization module (18) and into the LH2 tank. When the LH2 tank pressure increases to 31 psia (Ti-43 seconds), the flight control pressure switch (17) shuts off the ground supply of cold helium (25) to complete prepressurization.
Pressurization
Pressurization is controlled by the flight control pressure switches (17, figure 6-9) which open or close solenoid valves in the LH2 tank pressurization module (18). Gaseous hydrogen (19) bled from the J-2 engine flows through the LH2 tank pressurization module (18) to the LH2 tank. As pressure in the LH2 tank increases to 31 psia, the flight control pressure switches (17) close valves in the LH2 tank pressurization module to maintain tank pressure at 28-31 psia. This pressure is sensed by the pressure transducer (20) and is relayed to the S-IVB fuel gauges (21) in the CM and, via telemetry, to the ground. In this manner, LH2 tank pressurization is maintained during engine burn periods.
Repressurization
The normal repressurization procedure is initiated at 'l(, + 48.1 seconds. It uses cold helium from the cold helium storage spheres (2, figure 6-9). The cold helium pressure is reduced to approximately 385 psia as it flows through the lox tank pressure control module (5). The cold helium next flows through the LH2 tank repressurization control (22), and into the O2/H2 burner (11). Should the regulator in the lox tank pressure control module (5) fail, the backup pressure switch (23) will maintain a pressure of 350-465 psia at the O2/H2 burner. The backup pressure switch controls the pressure by opening or closing valves in the LH2 tank repressurization module (22). As the cold helium is heated in the O2/H2 burner (11), it expands and is routed to the LH2 tank. Pressure in the LH2 tank increases and is sensed by the flight control pressure switch (17) and the pressure transducer (20). The pressure switch (17) maintains LH2 tank pressure between 28-31 psia by opening and closing solenoid shutoff valves in the LH2 tank repressurization control module (22). The pressure transducer (20) transmits a continuous pressure reading to telemetry and to the LV TANK PRESS gauges (21) in the CM. At T6 + 496.6 seconds, cryogenic repressurization is switched off. Ambient repressurization is turned on at T6 + 497.6 seconds. Ambient helium from the ambient helium storage spheres (15) flows through the LH2 tank ambient helium repressurization control module (24) to the LH2 tank. Here the pressure is sensed by the flight control pressure switches (17). The pressure switches (17) control LH2 tank pressure by opening or closing, the control valves in the LH2 tank ambient helium repressurization control module (24). Just before the engines second burn, ambient repressurization is terminated (T6 + 520.0 seconds).
NOTE
The ambient repressurization portion of the repressurization procedure is in reality a backup procedure. Should the O2/H2 burner fail, ambient repressurization ensures LH2 tank pressure for engine start requirements.
LH2 Venting
The LH2 tank vent subsystem (figure 6-9) is equipped to perform either a propulsive or non-propulsive venting function. The non-propulsive venting is the normal mode used.
The non-propulsive function is performed through the use of a ground controlled combination vent and relief valve which permits the option of routing the GH2 through either the ground vent lines or through non-propulsive relief venting. The valve is in the ground vent line open position until T-40 seconds at which time it is positioned to the in-flight non-propulsive relief function. The non-propulsive vents are located 180 degrees to each other so as to cancel any thrust effect.
The propulsive venting function is a command function which operates through two control valves upstream of the non-propulsive directional control valve. This mode vents the GH2 through two propulsive vents located axial to the stage. Propulsive venting provides a small additional thrust, prior to second J-2 engine burn, for propellant settling. Figure 2-1 and figure 6-5 illustrate the sequential operation of the venting subsystems.
PNEUMATIC CONTROL
The pneumatic control system (figure 6-10) provides pressure for all pneumatically operated valves on the stage and for the engine start tank vent valve on the J-2 engine. The pneumatic control system is filled with gaseous helium from ground support equipment to 3200 ± 100 psig. The onboard pneumatic control system consists of the helium fill module, an ambient helium bottle and a pneumatic power control module.
The helium fill module regulates and reduces the incoming supply to 490 ±25 psia for operation of control valves during preflight activities. The ambient helium storage bottle is initially pressurized to 750 psia, and is capable of supplying operating pressure to stage control valves at that pressure. After propellant loading has begun, and the cold helium bottles are chilled down, the pressure is raised to 3100 psia and both the ambient and cold helium bottles are then completely pressurized to their flight pressure of 3100 psia by the time the LH2 tank reaches a 92% load level.
The pneumatic power control module is set at 475 psig which is equivalent to 490 psia on the ground and 475 psia in orbit. These pressure levels are essential to the operation of the LH2 directional control valve, the propulsion vent shutoff valve, the lox and LH2 fill and drain valves, the lox and LH2 turbopump turbine purge module, the lox chilldown pump purge control, the lox and LH2 prevalves and chilldown and shutoff valves, the lox tank vent/relief valves, the LH2 propulsive vent valve, and the J-2 engine GH2 start system vent/relief valve. Each pneumatically operated component is attached to a separate actuation control module containing dual solenoids, which provide on-off control.
DISCONNECT AMBIENT HE FILL 3100 PSIG 70° F
TO J-2 ENGINE START TANK VENT & RELIEF VALVE
CONTROL
HELIUM
SPHERE
FILL
HELIUM MODULE
AMBIENT
HELIUM
SPHERE
PLENUM
PNEUMATIC POWER CONTROL MODULE
LH2 VENT & RELIEF VALVE
^LH2 CONTINUOUS VENT REGULATOR MODULATOR
LOX FILL & DRAIN VALVE
^DIRECTIONAL ' CONTROL VALVE LH2
LH2 FILL & DRAIN VALVE
r"
LOX VENT & RELIEF VALVE
Zf LH2 CHILLDOWN SHUTOFF VALVE LOX CHILLDOWN SHUTOFF VALVE
=T LH2 PREVALVE I
I LOX PREVALVE
LATCH OPEN LOX VENT & RELIEF VALVE (LOX NPV)
IvOl-
-f ENGINE PURGE PUMP
CHILLDOWN PUMP PURGE
(02/H2 BURNER) LOX PROPELLANT VALVE
LOX SHUTDOWN ! VALVE
LH2 PROPELLANT VALVE
Figure 6-10
The pneumatic control system is protected from over-pressure by a normally open, pressure switch controlled, solenoid valve. This switch maintains system pressure between 490 - 600 psia.
flight control
The flight control system incorporates two systems for flight and attitude control. During powered flight, thrust vector steering is accomplished by gimbaling the J-2 engine for pitch and yaw control, and by operating the APS engines for roll control. Steering during coast flight is by use of the APS engines alone. (See Auxiliary Propulsion Systems subsection for coast flight steering.)
ENGINE GIMBALING
During the boost and separation phase, the J-2 engine is commanded to the null position to prevent damage by shifting. The engine is also nulled before engine restart to minimize the possibility of contact between the engine bell and the interstage at S-II/S-IVB separation, and-to minimize inertial effects at ignition. The engine is gimbaled (figure 6-11) in a 7.0 degrees square pattern by a closed loop hydraulic system. Mechanical feedback from the actuator to the servovalve completes the closed engine position loop.
When a steering command is received from the flight control computer, a torque motor in the servovalve shifts a control flapper to direct the fluid flow through one of two nozzles. The direction of the flapper is dependent upon signal polarity.
Two actuators are used to translate the steering signals into
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