Redstone A-6 Engine

The Udvar-Hazy Center displays a Redstone A-6 rocket engine.

The Redstone engine was the first large rocket engine manufactured by the North American Aviation Propulsion Section (which would later be become the Rocketdyne Division of North American Aviation). NAA internally named their early engines by concatenating the rated engine thrust with the nominal burn time; the Redstone engines were thus christened the "75-100" (for an engine producing 75,000 pounds of thrust for 100 seconds). Since the Redstone engine was their first large rocket engines, NAA engineers took to calling it the "A" series of engines; the sixth design iteration of this engine became the A-6.

The A-6 was the first production version of the Redstone engine. It was used in the first Redstone missiles deployed in the field, and was also used in the Redstones modified to be Jupiter-C and Juno I launch vehicles. Later Redstone missiles (and the Redstones used to launch Mercury spacecraft) used the later A-7 engine.

While I haven't found any documentation describing when the change from the A-6 to the A-7 took place, Jim Ryan of My Army Redstone Missile Days, an excellent reference for the Redstone missile and the men who fired and supported it, tells me that the Redstone Block I missiles used by the troops between 1958 and 1960 had the A-6 engine; there were only 19 Block I missiles manufactured by Chrysler (the missile contractor). In mid-1960, the switch was made to Block II missiles, which used the A-7.

Although some Redstone engines claim to be A-6 engines, this is the only A-6 engine I've actually seen. The A-6 and A-7 can be easily distinguished visibly: The A-6 has two fuel lines, located 180° apart, while the A-7 has only one fuel line. The A-7 also has a redesigned main fuel valve.

Although there were a number of external differences among the A series of engines, The History of the Redstone Missile System notes that

... [I]mprovements in the performance features and components of the NAA 75-110 engine yielded seven different engine types for use in the research and development missiles. Designated A-1 through A-7, each different type engine had the same basic operational procedures and was designed for the same performance characteristics as every other NAA 75-110 engine. Each type differed from the others only in modifications of various components. Furthermore, all seven engine types were interchangeable, as only minor tubing modifications were required for mating the engine to the missile.

This engine is Smithsonian catalog #A19910078000.