While von Braun was grappling with those problems at Kummersdorf, the parallel Heylandt program continued. The clear intent of the autumn 1932 contract for a 20-kg-thrust engine had been to produce a laboratory instrument, since its thrust was only one-eighth of that of the 1931 Heylandt rocket-car. The small engine’s weight in comparison to its thrust was such that the ballistics and munitions section had to fend off a serious challenge from an unnamed leader of Ordnance. He declared liquid-fuel rocket technology worthless, because obviously this engine could never lift itself off the ground!64
Although it was clear that engines of higher performance characteristics could be built by Heylandt, Ordnance did not energetically pursue that option, presumably because of the Kummersdorf work. Von Horstig inquired about a 200-kg-thrust engine in December 1932, but six months later Ordnance submitted an order only for a 60-kg engine that Heylandt had proposed. The primary motivation appears to have been to prevent the layoff of Heylandt’s rocket group. That engine was successfully tested on company grounds in September 1933. When the company offered in November to build an engine with up to 400 kg of thrust, however, Section 1 turned it down, and told Heylandt to expect no further contracts.65
Satisfied that the technology developed at Kummersdorf was superior, Ordnance further consolidated liquid-fuel rocket development in January 1934 by hiring Walter Riedel, the key engineer in Heylandt’s group. Riedel, ten years older than the precocious doctoral student, provided the practical design experience von Braun lacked, plus the experience of having worked on rocket engines ever since Valier’s original liquid-fuel experiments. It is indicative of how young the rocket group would be that he became known as “Papa” Riedel. As chief of the design office at Peenemünde when it opened in 1937, he was all of thirty-five years old.66
Notwithstanding the Heylandt work and the small spinoff contract to Pietsch and Rudolph, the main line of development had always been von Braun’s. Starting from Raketenflugplatz designs, he built the alcohol/liquid-oxygen “1W” series (W for water-cooled), with a thrust of about 130 kg. Dornberger’s memoirs give a picturesque description of the explosion that supposedly destroyed much of the test stand at the first test on December 21, 1932. That recollection is inconsistent with von Braun’s own memory of the first test being a success in January 1933. In any case, explosions, leaks, and burnthroughs did follow. The redesign process was tedious and largely empirical, involving endless variants. Eventually von Braun was able to go to regenerative cooling with the “1B” series (B for Brennstoff or fuel) and then the “2B” series with 300 kg of thrust in the autumn of 1933 or thereabouts.67
Von Braun’s program in 1933 had three main objectives. The first was development of engines based on aluminum alloys. Raketenflugplatz had begun using aluminum for the obvious purpose of saving weight and thus increasing the performance of launched vehicles. In the spring of 1933, troubled by the number of engine failures, von Braun went searching for expertise. “Solidly in Nebel’s footsteps, I grabbed the telephone directory and got in touch with welding experts, instrumentation firms, valve factories, and pyrotechnical laboratories.” He had learned something from the entrepreneurial methods of his former mentor.68
Soon engine parts manufacturing was farmed out to various firms, and von Braun and his superiors made contact in April 1933 with a firm that specialized in aluminum anodizing (Eloxieren: surface hardening through the electrolytic formation of an oxidization layer). This proved a crucial breakthrough in increasing the durability of engines. The firm had been working with Nebel, but Ordnance insisted that it cut off all contact with him. In turn that firm led von Braun and his superiors to a small manufacturer who would be the primary contractor for engine and alcohol-tank construction for three years: Zarges, in the southwest German city of Stuttgart. At first it would be a mutually agreeable relationship, but eventually the distance, secrecy considerations, and a desire for greater control over quality would result in a decision to manufacture in-house at Peenemünde.69
Von Braun’s second objective was the fully automatic operation of ignition and tank pressurization. Proper ignition was a serious problem; if too much fuel or oxidizer reached the engine first and ignition was delayed, an explosion usually resulted. By the end of 1933 the problem was reasonably in hand, but it was never completely solved. Many experiments were also conducted to solve the old problem of how to pressurize the tanks. The weight-saving method of increasing liquid oxygen evaporation with small burning cartridges was tried, but putting gaseous oxygen in the fuel tank led to explosions. It became necessary to use compressed nitrogen or evaporated liquid nitrogen in the alcohol tank, although that meant a separate tank and system. Both forms of nitrogen were tried, but all the problems of tank pressurization remained. As the fuel drained from the tank, the gas would expand and the pressure would drop, resulting in a drop in the rate and pressure of propellant delivery to the engine over time. That meant a slow drop in thrust. Since the pressure of the burning gases in the rocket engine’s combustion chamber was about ten atmospheres in the engines of that time, it was necessary to force the propellants into the chamber with a pressure of a few atmospheres higher. That meant the fuel and oxidizer tanks had to withstand at least fifteen atmospheres of pressure (in practice even more), which made them heavy. As rockets got larger, the structural weight problem was magnified exponentially. The limits on tank pressure also limited combustion chamber pressure, which limited performance, because higher-pressure engines are more efficient. It was already clear that complicated turbopumps would have to be developed for larger missiles to get around those problems, a solution already discussed in the works of Oberth and the other pioneers.70
Von Braun’s third objective was the design and construction of the rocket itself. By June 1933 the drawings were in hand for the first vehicle, the Aggregat-1 (“Aggregate” or “Assembly”), better known as the A-1. It was based on the 300-kg-thrust engine, and its unique feature was its method of stabilization, which derived directly from its origins in an artillery establishment. A liquid-fuel rocket cannot be spun on its axis like an artillery shell or a solid rocket because of the disturbing forces on the propellants in the tanks and lines. As a crude interim solution, Dornberger proposed that only part of the vehicle be spun. Thus the nose of the A-1 was a large gyroscope that stabilized it by brute force. (A gyroscope’s axis, like that of a top, will tend to remain fixed in space. If perturbed by an external force it will move or “precess” at a right angle to the force exerted. A gyroscope’s resistance to precession is directly dependent on its angular momentum, a product of its mass and rate of rotation.) Before launch, the gyroscope would be spun up to 9,000 rpm by an electric motor on the ground, then left to run solely on its momentum during the rocket’s brief flight.71
But the A-1 was never to fly. “It took us exactly one half year to build…—and exactly one-half second to blow it up,” says von Braun, a bit hyperbolically. The late 1933 or early 1934 explosion was due to persistent difficulties with the fuel and oxygen valves, leading to delayed or hard ignition. Eventually the third A-1 was successfully started on the ground, but it was destroyed by the mechanical failure of the liquid-oxygen tank. Ordnance decided on a major redesign, entitled the A-2 (see Figure 1.1). Von Braun’s group separated the tanks and placed the gyro rotor between them. Moving the gyro to the middle had the advantage of bringing the center of gravity backward, thus shortening the moment arm of any deviations of thrust away from the rocket’s axis. That increased the stability of the rocket in the early part of the flight, when aerodynamic forces were weakest because of the rocket’s low velocity, although stability was actually decreased in the later part of the flight because the rocket’s center of gravity was closer to its center of aerodynamic pressure. Separating the tanks also stopped the problem of leakage into the fuel tank caused by vibration-induced cracking of the oxygen tank.72