Redstone Propulsion

When the von Braun group, relocated to Redstone Arsenal, began de­veloping the Redstone missile, it chose North American Aviation’s XLR43-NA-1 liquid-propellant rocket engine, developed for the

air force’s Navaho missile, as the basis for the Redstone propul­sion unit. A letter contract with NAA on March 27, 1951, provided 120 days of research and development to make that engine comply with the ordnance corps’ specifications and to deliver a mockup and two prototypes of the engine (then to be designated NAA 75-110, referring to 75,000 pounds of thrust operating for 110 seconds). Sup­plemental contracts in 1952 and 1953 increased the number of en­gines to be delivered and called for their improvement. These con­tracts included 19 engines, with subsequent powerplants purchased by the prime contractor, Chrysler, through subcontracts.25

The story of how North American Aviation had initially devel­oped the XLR43-NA-1 illustrates much about the ways launch – vehicle technology developed in the United States. NAA came into existence in 1928 as a holding company for a variety of avia­tion-related firms. It suffered during the Depression after 1929, and General Motors acquired it in 1934, hiring James H. Kindelberger, nicknamed “Dutch," as its president—a pilot in World War I and an engineer who had worked for Donald Douglas before moving to NAA. Described as “a hard-driving bear of a man with a gruff, earthy sense of humor—mostly scatological—[who] ran the kind of flexible operation that smart people loved to work for," he re­organized NAA into a manufacturing firm that built thousands of P-51 Mustangs for the army air forces in World War II, the B-25 Mitchell bomber, and the T-6 Texas trainer. With the more cautious but also visionary John Leland Atwood as his chief engineer, Dutch made NAA one of the principal manufacturers of military aircraft during the conflict, its workforce rising to 90,000 at the height of wartime production before it fell to 5,000 after the end of the war. Atwood became president in 1948, when Dutch rose to chairman of the board and General Motors sold its share of the company. The two managers continued to service the military aircraft market in the much less lucrative postwar climate, when many competitors shifted to commercial airliners.26

Despite the drop in business, NAA had money from wartime production, and Kindelberger hired a top-notch individual to head a research laboratory filled with quality engineers in the fields of elec­tronics, automatic control with gyroscopes, jet propulsion, and mis­siles. He selected William Bollay, a former von Karman student. Fol­lowing receipt of his Ph. D. in aeronautical engineering at Caltech, Bollay had joined the navy in 1941 and been assigned to Annapolis where the Bureau of Aeronautics (BuAer) was working on experimen­tal engines, including the JATOs Robert Truax was developing. At war’s end, Bollay was chief of the Power Plant Development Branch

for BuAer. As such, he was responsible for turbojet engines, and at the time, NAA was developing the FJ-1 Fury, destined to become one of the navy’s first jet fighters. Bollay came to work for NAA during the fall of 1945 in a building near the Los Angeles airport, where he would create what became the Aerophysics Laboratory.27

On October 31, 1945, the army air forces’ Air Technical Service Command released an invitation for leading aircraft firms to bid on studies of guided missiles. NAA proposed a surface-to-surface rocket with a range of 175-500 miles that it designated Navaho (for North American vehicle alcohol [plus] hydrogen peroxide and oxygen). The proposal resulted in a contract on March 29, 1946, for MX-770, the designation of the experimental missile. Other con­tracts for the missile followed. The Navaho ultimately evolved into a complicated project before its cancellation in 1958. It included a rocket booster and ramjet engines with a lot of legacies passed on to aerospace technology, but for the Redstone, only the rocket engine that evolved to become NAA 75-10 is relevant.28

NAA did not originally intend to manufacture the engine. As an early employee of the firm recalled, the company was “forced into the engine business—we had the prime contract for Navaho and couldn’t find a subcontractor who would tackle the engine for it, so we decided to build it for ourselves." NAA’s plans for developing the engine began with the German V-2 as a model but soon led to “an en­tirely new design rated at 75,000 pounds thrust" (as compared with about 56,000 for the V-2). In the spring of 1946, Bollay and his as­sociates had visited Fort Bliss to conduct numerous interviews with many of the Germans who had worked on the V-2, including von Braun, Walter Riedel, and Konrad Dannenberg. By the middle of June 118 1946, Bollay’s team began redesigning the V-2 engine with the aid of

Chapter 3 drawings and other documents obtained from the Peenemunde files. In September, the firm secured the loan of a complete V-2.29

The NAA engineers also conferred with JPL, GE, Bell Aircraft Corp., the National Advisory Committee for Aeronautics’ labora­tory in Cleveland (later Lewis Research Center), the Naval Ord­nance Test Station at Inyokern, and Aerojet about various aspects of rocket technology.30 Thus, the heritage of the Redstone engine went well beyond what NAA had learned from the V-2.

By October 1947, the Astrophysics Laboratory had grown to more than 500 people. This necessitated a move to a plant in nearby Downey in July 1948. By the following fall, the engineers had taken apart and reconditioned the V-2 engine, examining all of its parts carefully. The team had also built the XLR41-NA-1, a rocket engine like the V-2 but using U. S. manufacturing techniques and design

standards, some improved materials, and various replacements of small components. Then, by early 1950, the team had redesigned the engine to a cylindrical shape, replacing the spherical contour of the V-2, which produced efficient propulsion but was hard to form and weld. Bollay’s people kept the propellants for the V-2 (75 per­cent alcohol and liquid oxygen). But in place of the 18-pot design of the V-2, which had avoided combustion instability, NAA engineers developed two types of flat injectors—a doublet version in which the alcohol and liquid oxygen impinged on one another to achieve mixing, and a triplet, wherein two streams of alcohol met one of liquid oxygen. They tested subscale versions of these injectors in small engines fired in the parking lot. Their methodology was purely empirical, showing the undeveloped state of analytical capabilities in this period. They, too, encountered combustion instability. But they found that the triplet type of injector provided slightly higher performance due to improved mixing of the propellants.31

Meanwhile, NAA searched for a place where it could test larger engines. It found one in the Santa Susana Mountains northwest of Los Angeles in Ventura County, California. The firm obtained a permit in November 1947 for engine testing there. It leased the land and built rocket-testing facilities in the rugged area where Tom Mix had starred in western movies, using company funds for about a third of the initial costs and air force funding for the rest. By early 1950, the first full-scale static test on XLR43-NA-1 took place.32

Full-scale engine tests with the triplet injector revealed severe combustion instability, so engineers reverted to the doublet injec­tor that partly relieved the problem. Although the reduced combus­tion instability came at a cost of lower performance, the XLR43- NA-1 still outperformed the V-2, enabling use of the simpler and less bulky cylindrical combustion chamber that looked a bit like a farmer’s milk container with a bottom that flared out at the nozzle. The engine delivered 75,000 pounds of thrust at a specific impulse 8 percent better than that of the V-2. Further enhancing perfor­mance was a 40 percent reduction in weight. The new engine re­tained the double-wall construction of the V-2 with regenerative and film cooling. Tinkering with the placement of the igniter plus injection of liquid oxygen ahead of the fuel solved the problem with combustion instability. The engine used hydrogen peroxide – powered turbopumps like those on the V-2 except that they were smaller and lighter. It also provided higher combustion pressures.

Like the V-2, the XLR43-NA-1 began ignition with a preliminary stage in which the propellants flowed at only some 10 to 15 percent of full combustion rates. If observation suggested that the engine

was burning satisfactorily, technicians allowed it to transition to so-called main stage combustion. To enable the engineers to ob­serve ignition and early combustion, von Braun, who was working with the NAA engineers by this time, suggested rolling a small, surplus army tank to the rear of the nozzle. By looking at the com­bustion process from inside the tank, engineers could see what was happening while protected from the hot exhaust, enabling them to reduce problems with rough starts by changing sequencing and im­proving purges of the system in a trial-and-error process. Through such methods, the XLR43-NA-1 became the basis for the Redstone missile’s NAA 75-110.33

Having supervised the development of this engine and the ex­pansion of the Aerophysics Laboratory to about 2,400 people on staff, Bollay left North American in 1951 to set up his own com­pany, which built army battlefield missiles. In 1949, he had hired Samuel K. Hoffman, who had served as a design engineer for Fair­child Aircraft Company, Lycoming Manufacturing Company, and the Allison Division of General Motors. He then worked his way up from project engineer with the Lycoming Division of the Aviation Corporation to become its chief engineer, responsible for the design, development, and production of aircraft engines. In 1945 he became a professor of aeronautical engineering at his alma mater, Penn State University, the position he left in 1949 to head the Propulsion Sec­tion of what became NAA’s Aerophysics Laboratory.

As Hoffman later recalled, Bollay had hired him for his practi­cal experience building engines, something the many brilliant but young engineers working in the laboratory did not possess. Hoffman succeeded Bollay in 1951. Meanwhile, he and Bollay had overseen 120 the development of a significantly new rocket engine. Although it Chapter 3 had used the V-2 as a starting point and bore considerable resem­blance to the cylindrical engine developed at Peenemunde before the end of the war, it had advanced substantially beyond the Ger­man technology and provided greater thrust with a smaller weight penalty. Also, it marked the beginnings of another rocket-engine manufacturing organization that went on to become the Rocket- dyne Division of NAA in 1955, destined to become the foremost producer of rocket engines in the country.34

Development of the NAA 75-110 engine for the Redstone mis­sile did not stop in 1951. Improvements continued through seven engine types, designated A-1 through A-7. Each of these engines had fundamentally the same operational features, designed for identical performance parameters. The engines were interchangeable, requir­ing only minor modifications in their tubing for them to be installed

in the Redstone missile. All of them except A-5 flew on Redstone tests between August 20, 1953, and November 5, 1958, with A-1 be­ing the prototype and A-2, for example, having an inducer added to the liquid-oxygen pump to prevent cavitation (bubbles forming in the oxidizer, causing lower performance of the turbopump and even damage to hardware as the bubbles imploded).35

During the course of these improvements, the Chrysler Corpo­ration had become the prime contractor for the Redstone missile, receiving a letter contract in October 1952 and a more formal one on June 19, 1953. Thereafter, it and NAA had undertaken a product – improvement program to increase engine reliability and reproduc­ibility. A comparison of the numbers of components in the pneu­matic control system for the A-1 and A-7 engines, used respectively in 1953 and 1958, illustrates the results (see table 3.1).36

Obviously, the fewer components needed to operate a complex system like the engine for a large missile, the fewer things there are that can go wrong in its launching and flight. Thus, this threefold reduction in components on a single system for the engine must have contributed significantly to the reliability of its operation. This was especially true since Rocketdyne engineers (as they be­came after 1955) tested each new component design both in the lab­oratory and in static firings before qualifying it for production. They also simulated operating conditions at extreme temperatures, levels of humidity, dust, and the like, because the Redstone was scheduled for deployment and use by the army in the field. Static engine tests showed reliability higher than 96 percent for the engines.

This was a remarkably high figure, considering that Rocketdyne purchased about half of Redstone engine components (or parts thereof) from outside suppliers; but the parts had to be built to a higher standard than those used in conventional aircraft. The rea­son was that the stresses of an operating rocket engine were greater than those for an airplane. All welds for stressed components had to undergo radiographic inspection to ensure reliability. The army then required a minimum of four static engine tests to prove each new model worked satisfactorily before the service would accept the system. Two of these tests had to last for 15 seconds each, and a third was for the full rated duration. This, presumably, was 110 sec­onds, but according to Chrysler’s publication on the Redstone, the engine ultimately produced 78,000 pounds of thrust for a duration of 117 seconds.37