GROUND SUPPORT

Ground support operations play an important part in getting the second stage ready for operation. Among the vital operations in this area are check­out (performed mostly with complex electronic equipment and computerized routines which stimu­late stage systems and analyze responses), leak detection and insulation purge, and engine com­partment conditioning.

Leak Detection and Insulation Purge

The purpose of this system is to detect hydrogen, oxygen, or air leaks; to dilute and remove leaking gases; and to prevent air from liquifying during tanking operations.

Any operation involving liquid hydrogen can be. extremely hazardous; liquid hydrogen in the pres­ence of oxygen can explode or create a fire. The low-temperature atmosphere of liquid hydrogen causes air to liquify and solidify against the hy­drogen tank wall if there is any leak in the tank insulation. The organic portion of the insulation will become impact-sensitive when drenched in liquid air or oxygen; insulation saturated with cryopumped air will add weight to the stage and
could cause damage during draining because of a pressure buildup created by the liquified air re­turning to a gas. For these reasons, detection, con­trol, and elimination of any hydrogen leaks from the stage and ground equipment are of great importance. The leak detection system checks out the liquid hydrogen tank, tank insulation, and the common bulkhead. The areas to be checked are divided (tank wall, forward bulkhead, and common bulk­head), each with inlet and outlet taps. A gas ana­lyzer determines the concentration of hydrogen in the purge gas (helium) after it has been forced through the insulation, and thus indicates any leak­age.

From the start of hydrogen loading until launch, the insulation and core of the common bulkhead are continuously purged of hazardous gases. Vacuum equipment is used for evacuation to pre­vent pressure buildup in the insulation and bulk­heads by removing trapped gases. The insulation purge prevents air from entering the insulation in the event of damage during cryogenic operations.

Engine Compartment Conditioning

The purpose of this system is to purge the engine and interstage areas of explosive mixtures and to maintain proper temperature in critical regions of the aft compartment of the second stage. The com­partment is purged before tanking and while the propellants are loaded.

The system consists of a 13-inch diameter feed line, manifold, ducts, and a series of vents surrounding the engine compartment and skirt area. The system provides temperature control for the hydraulic systems and certain components on the J-2 engines. The purge gas is forced through orifices in the mani­fold to the following areas requiring warming: the area between the thrust structure and the liquid oxygen tank, the bottom of the thrust structure including the lower surface of the thrust cone, the aft skirt and interstage, and the top surface of the heat shield.

The vent holes are located under the supporting hat sections on the outside of the aft skirt; this prevents wind, rain, and dust from entering the engine com­partment. The vents are located so that the flow pattern provides good thermal control and expels hazardous gases.

The aft skirt and interstage are purged with warm (80 to 250 degrees) nitrogen. The nitrogen is sent through the feed line into the manifold, and then through ducts to the temperature-sensitive areas. By maintaining a 98 per cent nitrogen atmosphere in the engine compartment, desired temperatures are maintained and the danger of fire or explosion resulting from propellant leaks are minimized.

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j SATURN V NEWS REFERENCE

THIRD STAGE FACT SHEET

FORWARD SKIRT

LH? TANK

HELIUM SPHERES

APS MODULE AFT SKIRT

AMBIENT HELIUM SPHERES RETROROCKET

J 2 ENGINE AFT INTERSTAGE

DAC-13067

WEIGHT: 34,000 lb. (dry) including 7,700-lb. aft interstage

262,0 lb. (loaded)

DIAMETER: 21 ft. 8 in.

HEIGHT: 58 ft. 7 in.

BURN TIME: 1st burn—2.75 min. (approx.)

2nd burn….. 5.2 min. (approx.)

VELOCITY: 1st burn—17,500 miles per hour at burnout (approx.)

2nd burn—24,500 miles per hour (approx, typical lunar mission escape velocity)

ALTITUDE AT BURNOUT: 115 miles after 1st burn and into a translunar injection on 2nd burn MAJOR STRUCTURAL COMPONENTS

AFT INTERSTAGE THRUST STRUCTURE COMMON BULKHEAD

AFT SKIRT PROPELLANT TANK FORWARD SKIRT

MAJOR SYSTEMS

PROPULSION: One bipropellant J-2 engine Total Thrust: 225,000 lb. (maximum)

Propellants: LH2—63,000 gal. (37,000 lb.)

LOX—20,000 gal. (191,000 lb.)

HYDRAULIC: Power for gimbaling J-2 engine

ELECTRICAL: One 56 VDC and three 28 VDC batteries, providing basic power for all electrical functions

TELEMETRY AND INSTRUMENTATION: Five modulation subsystems, providing transmission of flight data to ground stations ENVIRONMENTAL CONTROL: Provides temperature-controlled environment for components in aft skirt, aft interstage, and forward skirt ORDNANCE: Provides explosive power for stage separation, retrorocket ignition, ullage rocket ignition and jettison, and range safety requirements FLIGHT CONTROL: Provides stage attitude control and propellant ullage control