Combustion chamber: silica fiber cloth, phenolic-bonded asbestos, filament-wound glas roving; body stainless steel, graphite liner; throat silica carbide
Rocketdyne SE 7-1 Rocket Engine developed for application as the Saturn-IVB (Third Stage) Auxiliary Propulsion System (APS) Ullage Engine. (Ullage is the free space within a tank above the liquid propellant. Derived from the term 'ullage' in winemaking, where it refers to the space above the liquid in a container such as a barrel or wine bottle - within the weightless environment of space during intervals when the Saturn Third stage J-2 main engine is not active, liquid propellant hydrogen and oxygen (LH2/LOX) may float around in the empty tank volume and inadvertently get sucked into the main engine resulting in the undesired effect of cavitation. The ignition of the Ullage engine prior to main engine restart induced propellant settling within the tank to inhibit this cavitation). Two of these engines, rated for a specific impulse of 274 Seconds (Vacuum) / 72 pounds thrust each, were installed on the S-IVB to support stage restart capability. The ablatively cooled, pressure fed thrust chamber ran hypergolic propellants Monomethylhydrazine (MMH) as fuel/Nitrogen Tetroxide (NTO) as oxidizer and has a total burn life of 425 seconds.
The APS Ullage engines were used to facilitate propellant settling after completion of the first J-2 burn on the Saturn third stage and during restart chill-down immediately prior to the second J-2 burn which placed the Apollo CSM/LM in Translunar Injection. They were also used on several Apollo missions for ground commanded, guided lunar impact trajectory burns of the S-IVB/IU spent stage after separation from the Command Service Module and extraction of the Lunar Module (S-IVB lunar surface impact was desired to generate seismic data in conjunction with an experiment supporting compositional analysis of the Moon's interior. Data was collected via seismometers left by earlier Apollo crews).
This SE 7-1 is a direct derivative of the (SE 7) 100 pound thrust engine used on the Gemini Orbital Attitude and Maneuver System (OAMS). Differences between the Gemini engine and the APS SE 7-1 include a reduction in operating chamber pressure (from 150 to 100 psia); rated thrust (from 95 to 72 lbs); and the propellant inlet fittings (from tube stub to dual redundant right angle fittings for adaptation of the engine to the Saturn APS).
The thrust chamber body is made in two segments; the combustion zone segment and the nozzle segment. The combustion zone segment is fabricated from a 6-degree oriented (referenced to engine centerline), resin-impregnated, high-silica fiber cloth. In addition, the thrust chamber body is wrapped with a layer of phenolic-bonded asbestos fiber to provide increased heat resistance and sealing capabilities. The bond line between the combustion chamber segment and the nozzle segment is located in a low-pressure, low-stress area aft of the throat insert. Structural support for the thrust chamber body assembly is provided by alternate layers of high-temperature high-strength glass cloth and filament-wound glass roving, bonded by phenolic resin. Additional layers of glass roving provide added strength in the injector attached and throat areas. The thrust chamber body is encased in a stainless steel shell to provide a positive seal between the thrust chamber and the launch vehicle. The engine combustion chamber contains a one-piece JTA graphite liner. A throat insert of solid silica carbide is used to resist the erosive effects of the combustion gases.
The thrust chamber injector is fabricated from stainless steel. It consists of 16 pieces of unlike doublets which impinge on a splash plate providing propellant mixing for high combustion efficiency.
Engine operation is controlled by two fast-acting electrically-operated solenoid propellant valves. These are attached to a mounting bracket which in turn is attached to the injector plate. The basic propellant valve design embodies a hermetically sealed solenoid. Valve sealing is accomplished through the use of a precision ground ball, attached to the armature, which rests on a Teflon seat in the closed position. A metal stop below the Teflon seat is incorporated to limit the armature stroke. Closing is accomplished through the use of a spring, and sealing force is obtained from the spring and pressure of propellant acting on the ball.