While access to additional university and corporate laboratories was essential to the project, the massive buildup of in-house research and development capability was a critical factor in Peenemünde’s success. It was not enough to attract highly talented engineers who could produce fundamentally new ideas, nor did it suffice to have those individuals led by excellent managers like von Braun and Dornberger. Only the possession of a lavishly funded and staffed organization allowed the rocket group to create working technology in a very short time. Dornberger’s in-house or “everything-under-one-roof” philosophy made a further contribution by fostering internal communication and increasing efficiency. In combination, these assets and strengths gave Peenemünde mastery, in only five years, of the three technologies key to the A-4’s success: large liquid-fuel rocket engines, supersonic aerodynamics, and guidance and control.
THIEL AND THE BIG ENGINE
Walter Thiel’s transfer to the rocket section toward the end of 1936 was a milestone on the road to the ballistic missile. Within months his analytical and scientific approach would result in a reconsideration of the entire direction in which engine design had been proceeding under Walter Riedel and Wernher von Braun. Their 1,500-kg-thrust motor, the one that powered the A-3 and the A-5, was a big step forward in size and efficiency, but it was taking the Ordnance group down a deadend road. Based on practical experience and the limited theoretical calculations in von Braun’s 1934 dissertation, Kummersdorf’s engines had become longer and longer. That had been done to give fuel and oxidizer droplets enough time to evaporate, mix, and burn properly. But the 25-ton engine threatened to become completely unwieldy, and the efficiency of combustion in the 1,500-kg motor still left something to be desired. It was significantly below the target performance—an exhaust velocity of about 2,000 m/sec—that would be needed to get the most out of the chosen combination of alcohol and liquid oxygen at a combustion chamber pressure of 10 atmospheres.2
Thiel, a pale, dark-haired, intense individual in horn-rimmed glasses, fitted one of the stereotypes of the German scientist of the Nazi period. He was loyal to the regime but too focused on his work to be very political. As far as is known, he never joined the Party. In the style of the German university professor, he could be authoritarian and arrogant to his subordinates. He was also high-strung and subject to episodes of depression when under stress; Dornberger and von Braun had to smooth over many conflicts. But Thiel brought to the rocket group a doctorate in chemical engineering, keen theoretical insight, tremendous ambition, and an imaginative mind. As Wahmke’s replacement in the research section, he had been a consultant to Hellmuth Walter, had experimented with hydrogen peroxide engines in the laboratory himself, and had supervised a graduate student working on the fundamental processes of combustion in a Heylandt 20-kg-thrust motor.3
Thiel’s initial program in early 1937 continued to focus on basic research into all areas of rocket propulsion, including exotic propellants like liquid hydrogen. He also outlined ambitious plans for cooperation with academic institutes in developing more heat-resistant metal alloys, a better theory of combustion, and more thorough temperature and composition measurements of burning exhaust jets. Thiel was forced, however, to depend on Ordnance’s own resources at Kummersdorf and Peenemünde. Although von Braun’s group had been working with two or three academic institutes in aerodynamics and measuring techniques since 1935–36, the Army’s obsession with security kept contacts with research institutions to a minimum before the outbreak of World War II.4 Ordnance’s goal was to develop and produce a ballistic missile in the deepest secrecy and then to use it without warning during a war. For any hint of the German rocket program to reach the outside world not only would ruin the effect of surprise but might also encourage other powers to pursue the technology more intensely. Virtually all proposals for contracting research outside Ordnance were therefore rejected to minimize the danger of security leaks.
Despite that handicap, in 1937–38 Thiel came quickly to four of the innovations that would make an efficient 25-ton-thrust motor possible. The first was an injection system that greatly improved the atomization and mixing of the two propellants. The 1,500-kg engine had used a modification of the old Heylandt system, with a mushroom-shaped injector extending down from the top of the motor, spraying watered alcohol upward toward the liquid-oxygen injectors. Dornberger claims the credit for having suggested small “centrifugal” nozzles that tended to atomize propellant droplets more completely, while spraying them outward in a rotational motion that produced better mixing. Thiel promptly began working with the Schlick firm, which produced the nozzles. By July 1937 he had demonstrated that fitting an injector with centrifugal nozzle holes to a 1,500-kg motor produced an immediate increase in exhaust velocity from 1,700 to 1,900 m/sec. A higher exhaust velocity meant a more efficient use of propellants and also improved the steering forces of the jet vanes by up to 20 percent.5
A further improvement in performance was promised by mid-1937 experiments with the “pre-chamber system.” This second innovation placed the injector holes for both fuel and oxidizer in their own small chamber on top of the combustion chamber, producing better mixing before burning. Moreover, it helped to prevent heat damage and burnthroughs by keeping the flame front farther from the nozzles. Figure 3.1 shows the later configuration of the A-4 25-ton motor with eighteen of these small injection chambers.6
Two other Thiel innovations fundamental to the success of the A-4 took longer to emerge but can be glimpsed in the thorough and scientific research program that he laid out in the summer of 1937. The first was shortening the combustion chamber. Throughout 1937 Thiel and his assistants at Kummersdorf carried out a number of experiments of the most varied types. They included designing a small 100-kg motor for basic research and using gasoline and compressed air for ease of handling in repetitive testing. He quickly came to the conclusion that the volume of the combustion chamber was crucial to efficient burning, not the length. Further experiments in 1937–38 proved that it would be possible to reduce the length of motors by enlarging their cross-section. Better injection systems also contributed to more complete combustion, lessening the need to give the propellant droplets a relatively long time to remain in the chamber. As shown in experiments on a new 1,500-kg motor, it was therefore possible to reduce the volume of the combustion chamber to a fraction of that of the old engine. A short chamber with a nearly spherical shape also lessened other problems inherent in long engines, including pressure fluctuations and poor mixing. The 25-ton engine, Thiel decided by August 1938, could be dramatically shorter than earlier planned, thus making it much easier to manufacture and incorporate into the rocket.7
