Michael Neufeld - The Rocket and the Reich

The joint character of Peenemünde had thus collapsed in less than a year, although daily cooperation and coordination were still a necessity. While the separation was neither a direct product of interservice rivalry nor of a Luftwaffe policy to assert its independence, the net effect was to loosen the rocket alliance further. It is symbolically appropriate that Peenemünde-West eventually put up a fence around its perimeter.

The momentous events of the years after 1935—the rise and decline of the Luftwaffe alliance, the experiments with rocket aircraft, the founding of Peenemünde, and the birth of the A-4—tend to overshadow the primary job of the engineers at Kummersdorf and Peenemünde, which was to carry forward the development of the Ordnance rocket series and its associated technologies. Following the A-2 success in December 1934, the Army planned an ambitious new step. Not only would the A-3 be much bigger, necessitating greatly increased thrust, but above all it would require an active guidance system to replace the crude stopgap measure of a single massive gyroscope.

Developing the new “3B” series of 1,500-kg-thrust engines was the most straightforward part of the job. The basic concept of the A-2 engine was just scaled up: Welded inside the alcohol tank was a long cylindrical combustion chamber. The length of the chamber was intended to give the propellants more time to burn completely. A double wall allowed regenerative cooling by the circulation of the watered alcohol before injection. The injection system was, however, changed under Walter Riedel’s influence to one similar to the Heylandt systems. Whereas the “2B” engines, derived from Raketenflugplatz designs, had only fuel and oxidizer jets pointed at each other, the “3B” engines had a mushroom-shaped injector sticking down from the top of the engine. From the underside of the cap, alchohol jets sprayed upward against liquid oxygen jets coming down from a number of small injectors at the top of the combustion chamber. This innovation increased exhaust velocity from 1,600 m/sec to more than 1,700 because of more efficient combustion, with a resulting increase in performance. But this necessarily worsened the cooling problem because of the increase in the temperature of the burning gases. 49

The solution was an endless series of experiments with different aluminum alloys and variations on the basic engine concept. After successfully testing a steel configuration of the 1,500-kg engine in the summer and fall of 1935, the Kummersdorf group went on to test aluminum alloy engines and tankage built by Zarges in Stuttgart and a few other firms that had been let in on the secret. Secrecy was such an obsession that in early 1935 manufacturers were asked to send shipments to a shadow firm under Rudolph’s name in a town next to Kummersdorf, rather than use a military address. The inconvenience of shipping the highly secret components across the country to Kummersdorf and, not infrequently, back to the firms for repairs was a factor in the decision to concentrate manufacturing capability in Rudolph’s workshops when Peenemünde was planned and built. Another factor was growing dissatisfaction with the work of the primary contractor, Zarges, whose small company was based in Stuttgart. Zarges lacked the highly skilled welders necessary to carry out precision work on difficult alloys, and it was not easy to find manufacturing capacity elsewhere. Those experiences reinforced the Ordnance group’s preference for an Army-run facility with “everything under one roof.” 50

By contrast, designing and building a three-axis, gyroscopic guidance and control system for a flying rocket was beyond the capability of Army Ordnance. In this case, contracting the whole problem to a company was unavoidable. In 1933 or early 1934 the Navy recommended that the rocket group contact Aerogeodetic, a firm primarily based in Berlin. The Navy had surreptitously bought the Dutch company in 1926 and had used it as a cover for secret work, mostly in heavy ship-based gyroscopic navigation and fire-control systems. A year or two after the Nazi seizure of power the company changed its name to Kreiselgeräte GmbH (Gyro Devices, Ltd.) and gave up the headquarters in the Netherlands that served as a front. 51

The heart and soul of Kreiselgeräte was its technical director, Johannes Maria Boykow (1879–1935). Von Braun gives a striking description of the man:

Boykow was one of the strangest and most charming characters I have ever met. A former naval officer of the Imperial Austrian Navy, he had seen the whole world and knew how to spin a yarn. Before the First World War, he had quit the services to become a dramatic actor. Drafted back when the war broke out, he became a destroyer captain, a naval aviator and finally got in touch with torpedo development. And it was here that he ran into the problems of the gyroscope which were to concern him for the rest of his life. He acquired hundreds of patents and gradually became the [German] Navy’s No. 1 expert in gyro compasses and… fire control equipment. He was a true genius, but… he did not bother much about the mundane engineering phases of his inventions. His company’s design office often found it necessary to deviate considerably from his original ideas, and therefore the end products but vaguely resembled his initial proposals. Unfortunately, I found this out only after severe setbacks. When I first met Boykow, I was left spellbound by his analytic sharpness and imagination and, being a novice in the gyro field myself, I took everything he said for granted.

By October 1934 Boykow had begun designing what would become the A-3 guidance and control system. For the task he could draw on experiments with aircraft autopilots he had made independently of Kreiselgeräte. But he died not much more than a year later, leaving it to the company to complete. 52

After preliminary laboratory experiments with stabilization in one axis, Kreiselgeräte assembled the first version of what it called the “Sg 33” in mid-1936. Its final form for the A-3 is illustrated in Figure 2.1. The Sg 33 had the function of simply holding the rocket to a vertical course, yet it was, in the end, too complicated for the technology of the time. Two gyros were to hold a stabilized platform horizontal. When the rocket tipped in pitch (nose backward or forward) or yaw (side to side) the corresponding gyro wheel, spinning at 20,000 rpm, would move (“precess”) at right angles, as the laws of physics dictate. This movement was sensed by electrical contacts, which in turn released nitrogen gas through small nozzles to push the platform back into place. (Unlike succeeding systems, the platform gyros had no direct influence on the attitude of the rocket.) Located on top of the platform were two devices to measure the movement of the rocket in a horizontal direction away from the initial vertical trajectory. The primitive accelerometers used little wagons on tracks to convert horizontal acceleration into a measurement of horizontal speed, which was then sent to the control system of the rocket. Under the platform were three “rate gyros.” Their function was to measure the rate at which the rocket was turning away from its specified direction, whether in pitch, yaw, or roll (turning around the longitudinal axis). The signals from the rate gyros were used to push the rocket back into its initial vertical attitude. 53

The control forces commanded by the wagons and rate gyros were sent to “jet vanes” in the rocket exhaust, which deflected the direction of thrust—an idea anticipated by Oberth and other pioneers. (Goddard had already experimented in New Mexico with jet vanes and a less ambitious gyro system as early as 1932.) But it was no easy task finding materials that would withstand the fiery temperatures and erosion of a rocket exhaust. The Kummersdorf group were finally able to develop, in conjunction with a contractor, molybdenum and tungsten vanes that were at least adequate to the task, but only after hundreds of test failures. Those vanes were rotated by rods that came down from electrical servomotors in the guidance system at the top of the A-3. 54