Sivb Aft Skirt Environmental Control
FORWARD SKI RT THERMOCONDITIONING
The electrical/electronic equipment in the S-IVB forward skirt area is thermally conditioned by a heat transfer subsystem using a circulating coolant for the medium. Principal components of the system, located in the S-IVB stage forward skirt area, are a fluid distribution subsystem and cold plates. The coolant is supplied to the S-IVB by the IU thermoconditioning system starting when electrical power is applied to the vehicle and continuing throughout the mission. For a description of this system refer to Section VII.
FORWARD SKI RT AREA PURGE
The forward skirt area is purged with GN2 to minimize the danger of fire and explosion while propellants are being loaded or stored in the stage, or during other hazardous conditions. The purge is supplied by the IU purge system which purges the entire forward skirt/IU/adapter area. The total flow rate into this area is approximately 3500 scfm.
PROPULSION
This stage provides vehicle propulsion twice during this mission. The first burn occurs immediately after S-II/S-IVB separation and lasts long enough to insert the vehicle into earth orbit. The second burn injects the spacecraft into a high apogee elliptical orbit.
At J-2 engine first burn cutoff, the auxiliary propulsion system (APS) ullage engines are ignited and burn until T5 + 1 minute and 28 seconds, providing stabilization and settling of the propellants. At APS engine ignition, the APS yaw and pitch control modes are enabled (roll already active) for the required attitude control of the stage payload during coast. LH2 continuous venting is activated at T5 + 59.0 seconds and continues until the oxygen/hydrogen (O2/H2) burner second start.
Prior to second burn, the systems are again readied for an engine start. Approximately 4 minutes before restart, the chilldown systems are reactivated to condition the lines by removing gases collected in the propellant supply system. The 02/H2 burner is started approximately 9 minutes prior to second burn to pressurize the propellant tanks ullage space and to provide thrust to settle the propellants.
LH2 continuous venting is terminated immediately after the O2/H2 burner start. Approximately one minute before engine start, the APS ullage engines are fired and the O2/H2 burner is shut down. The recirculation system is deactivated and engine restart is initiated. With this, the APS ullage engines are shut off, and the APS yaw and pitch control modes are deenergized. The roll control mode remains active throughout the second burn.
At the end of J-2 engine second burn the APS pitch and yaw modes are again enabled to provide attitude control of the stage and payload during terminal coast. In addition, the lox and LH2 pressures are vented through the stage nonpropulsive vents.
The J-2 rocket engine (figure 5-9) is a high performance, multiple restart engine utilizing liquid oxygen and liquid hydrogen as propellants. The engine attains a thrust of
203,000 pounds during first burn and 203,000 pounds during second burn. The only substances used in the engine are the propellants and helium gas. The extremely low operating temperature of the engine prohibits the use of lubricants or -other fluids. The engine features a single, tubular-walled, ( bell-shaped thrust chamber and two independently driven direct drive turbopumps for liquid oxygen and liquid hydrogen. Both turbopumps are powered in series by a single gas generator, which utilizes the same propellants as the thrust chamber. The main hydraulic pump is driven by the oxidizer turbopump turbine. The ratio of fuel to oxidizer is controlled by bypassing liquid oxygen from the discharge side of the oxidizer turbopump to the inlet side through a servovalve.
The engine valves are controlled by a pneumatic system powered by gaseous helium which is stored in a sphere inside the start bottle. An electrical control system, which uses solid state logic elements, is used to sequence the start and shutdown operations of the engine. Electrical power is supplied from aft battery No. 1.
During the burn periods, the lox tank is pressurized by flowing cold helium through the heat exchanger in the oxidizer turbine exhaust duct. The heat exchanger heats the cold helium, causing it to expand. The LH2 tank is pressurized during burn periods by GH2 from the thrust chamber fuel manifold.
During burn periods in the pitch and yaw planes, thrust vector control is achieved by gimbaling the main engine. Hydraulic pressure for gimbal actuation is provided by the main hydraulic pump. During coast mode the APS engines give the pitch and yaw thrust vector control. Roll control during both the burn periods and the coast modes is achieved # by firing the APS engines. (v
Start Preparations
Preparations for an engine start include ascertaining the positions and status of various engine and stage systems and components. The J-2 engine electrical control system controls engine operation by means of electrical signals. The heart of the engine electrical control system is the electrical control package (17. figure 5-9). It sequences and times the functions required during engine start or cutoff.
Each cutoff automatically causes the electrical control package circuitry to reset itself, ready for restart, providing that all reset conditions are met. The LVDC issues an engine ready bypass signal just prior to each engine start attempt. This bypass signal acts in the same manner as a cutoff would act. The reset signals engine ready and this allows the LVDC to send its start command. Receipt of the start command initiates the. engine start sequence. "
ENGINE START SEQUENCE
When engine start is initiated (3, figure 6-3), the spark exciters in the electrical control package provide energy for the gas generator (GG) and augmented spark igniter (ASI) spark plugs (4). The helium control and ignition phase control valves, in the pneumatic control package (1), are simultaneously energized, allowing helium from the helium tank (2) to flow through the pneumatic regulator to the pneumatic control system. The helium is routed through the / internal check valve in the pneumatic control package (1) to ^
S-IVB ENGINE START
SEQUENCE
EVENT
TIME IN SECONDS
S-IVB 1ST BURN S-IVB 2ND BURN
PRE-IGNITION
NOTE
ALL PNEUMATIC VALVES ARE CONTROLLED BY THE PNEUMATIC CONTROL PACKAGE WHICH IS
LOCATED ON THE ENGINE. HELIUM FOR THE PNEUMATIC SYSTEM IS SUPPI IED BY THE CONTROL SPHERE INSIDE THE GH2 START TANK
I rit U
Start Command -;
Engine Ready
LEGEND S-IVB 1ST BURN
Start Command -;
Engine Ready
- Engine Start Sequence
Augumented Spark Igniter (ASI) Spark Plugs and gas generator (GG) spark plugs fire.
Bleed valves stop return flow to propel 1 ant' tanks.
Oxidizer dome and gas generator oxidizer injector are purged.
Main fuel valve allows LH2 to flow into engine thrust chamber and into ASI.
ASI oxidizer valve allows lox flow to ASI.
Sparks ignite the propellants in the ASI.
Fuel injection temperature OK signal received causing the
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