Molybdenum Disilicide, L-605 (Cobalt base) alloy, Stainless Steel, Copper, plastic insulator coating
A Marquardt R-4D rocket engine developed for use on the Apollo Service Module, Lunar Module for attitude control and velocity change maneuvers. The engine was also used as the main propulsion thruster on the Lunar Orbiter, for auxiliary propulsion on the Agena upperstage (the engine designation for this application was the SE 5-5) and continues to see use in a variety of earth orbital and deep space robotic payloads. It was also qualified for use on the Air Force Manned Orbiting Laboratory (MOL) until that program was terminated. In order to support project Apollo, Marquardt initiated engine development in February 1962, and qualification was achieved December 1965.
The R-4D engine consists of two high-response integral solenoid operated valves, an injector head assembly, two piece thrust chamber, and associated clamps and seals. The injector head assembly performs two functions: propellant mixing, and combustion chamber and preigniter cooling. In addition, this assembly provides a support for the oxidizer and fuel valve assemblies, the mounting flange for the combustion chamber seal and combustion chamber, the attach holes for mounting the rocket engine, and contains the fuel and oxidizer passages.
The injector head assembly contains four concentric rings of equally space holes on the face of the assembly and preigniter. These are arrayed to facilitate chamber wall cooling (outer ring),primary fuel orifices (first intermediate ring), preigniter fuel cooling holes for film cooling of preigniter (second intermediate ring) and primary oxidizer orifices (innermost ring). The preigniter chamber is a tubular chamber extending from the face of the injector head assembly and contains two propellant injection orifices. It is designed to mix and ignite a small quantity of propellants prior to ignition of the main combustion chamber, thereby minimizing ignition delays of the main propellant streams and provide smooth main chamber pressure buildup.
Propellant valving is provided by two normally closed, twin coil, solenoid actuated, coaxial flow, poppet-type valves, with integral propellant flow regulation orifices and inlets. The integral fixed orifices are incorporated into each valve to provide the correct propellant pressure drops at the design inlet pressure to required thrust level. Inlet screens provide protection against large particle contamination which might be generated during assembly of the engine to the system.
The combustion chamber is fuel film cooled molybdenum with molybdenum disilicide coating which allows it to reliably operate at sustained temperatures of 2000 Degrees F. The 40:1 area ratio expansion bell is ribbed L-605 (cobalt base alloy).