Michael Neufeld - The Rocket and the Reich

Also guiding the rocket were the long, narrow fins that gave it longitudinal stability or, to use the more picturesque German term, “arrow stability.” They ensured that, when the vehicle pitched or yawed around its center of gravity, the lift forces generated by the fins would tend to force the vehicle back to its original position—nose-on into the airflow—so it would have an inherent aerodynamic stability like an arrow. (In technical terms, the fins ensured that the rocket’s center of pressure was behind its center of gravity.) Finding the appropriate shape for the fins was another difficult task. The Luftwaffe alliance was helpful here, because in late 1935 the Technical Office was able to introduce von Braun to one of the handful of supersonic wind tunnel groups in the country, at the Technical University in Aachen, near the Dutch and Belgian borders. An assistant professor there, Dr. Rudolf Hermann, made the preliminary drag measurements that allowed a calculation of the performance of the rocket. He then worked on the fin form so that stability through the whole range from zero velocity to supersonic was assured. 55

At the beginning of December 1937, a year later than von Braun’s 1935 estimate, four A-3s were finally ready for launch. They were not small: 6.5 m (22 ft) long and 0.7 m (2.3 ft) in diameter, with a fueled weight of 750 kg (1,650 lb). Each rocket carried registering instruments to measure either the heating of the skin through friction or atmospheric temperature and pressure during a parachute descent from a peak altitude of 20 km. The launch site was the Greifswalder Oie, the small island with high cliffs a few kilometers offshore from Peenemünde. Ironically, it was the same location Oberth had requested for the launching of his Frau im Mond rocket in 1929, only to be refused by the Prussian authorities because he might endanger the lighthouse there. In the Third Reich, however, a request from the military was not likely to be turned down. 56

Converting the island proved to be a major task and expense for the Army, because about the only thing on the island, except for the lighthouse, was the combination farmhouse-guesthouse run by the island’s lessee. It was fortunate that a small-gauge railway had been left in place from the erection of the lighthouse, because there were no roads. When a liquid oxygen tanker truck was brought over to the island, the launch crew spent hours trying to pull it out of the mud. The Army New Construction Office built a dock, a launch bunker, a generator building, and temporary barracks. Telephone lines were strung to link the buildings. A large tent was put up in a wooded area for workspace. An ancient ferry was leased to haul the equipment from the mainland. 57

Toward the end of November a select crew of about 120 individuals from Peenemünde and Berlin, headed by Dornberger, Zanssen, and von Braun, assembled on the island for “Operation Beacon.” Most were new to the launch business, as the rocket program had grown so much since the A-2s. Enthusiasm ran high, which was fortunate, because conditions were trying. The weather became miserable: It rained for days, which delayed the launches, and then it was bitterly cold. The wind threatened to tear the tent pegs right out of the ground. An “extraordinary plague of mice and rats” emerged to gnaw on the tar paper of the bunkers, so that constant tearing sounds could be heard, and rain seeped through after ten days. More ominously, the field mice showed a taste for cable insulation, causing short circuits. Technical delays in the launching tried the patience of the many high-level visitors and caused problems with the launch organization, because so much was on loan from other organizations—airplanes from the Luftwaffe, boats from the Navy, photo and measuring equipment from other branches of Ordnance. 58

Finally, about 10 A.M. on December 4 the crew managed to launch the first A-3, patriotically named “Deutschland.” For the first three seconds the rocket ascended vertically, then suddenly the parachute popped out of the side, trailed behind the still accelerating vehicle, and was incinerated. The rocket turned into the wind, and the engine shut off automatically when it tipped over too far. After about twenty seconds it crashed back onto the island only about 300 meters from the launch site, exploding violently on impact. According to Dornberger: “Eyewitness accounts were wildly contradictory. Everyone claimed to have seen something different. We decided to venture on a second launching.” When the second A-3 was sent on its way two days later, virtually the same thing happened, with the vehicle crashing only 5 meters offshore. Now that it was clear that the parachute had been deployed, it was only natural to blame the powder charge that pushed it out. The parachute was omitted for the third launch on December 8, and a signal flare was put in its place. The wind was stronger than on earlier attempts, and the rocket turned quickly into it, ejecting the flare after four seconds. Again the engine cut out automatically and the rocket crashed 2 kilometers out to sea. The last attempt on December 11 was almost identical. 59

Those results were shocking and discouraging, but already during the many interminable delays on the Oie, Dornberger, von Braun, and the chief engineers threw themselves energetically into explaining the failures. Attention focused initially on the possibility of a static electricity buildup on the skin of the rocket, setting off the parachute charge. But ground tests conducted later in December indicated that that was definitely not the case. The fact that the A-3 tended to turn into the wind rather than stay on a vertical course also implied that the control system was too weak. The rocket appeared to be excessively stable; the fins had apparently moved the center of pressure so far back that the jet vanes lacked the power to fight back against the aerodynamic forces. The servomotors that moved the vanes also seemed to lack sufficient power, a consequence of the undeveloped state of this technology. 60

While it was in fact true that the control system was too weak and the rocket too stable, those problems did not explain the ejection of the parachute or flare every time. Only after review of the launch films, repeated ground tests, and meetings with Kreiselgeräte did it become clear in January 1938 what had gone wrong. The Achilles heel of the Sg 33 guidance and control system was its inability to stop a rapid rolling of the A-3. For reasons of simplification, the stable platform had no ability to turn around the vertical axis and no roll gyro to sense whether the rocket was moving in that axis. If the vehicle rolled at a rate of more than six degrees per second, the forces acting on the platform gyros would quickly overwhelm their ability to compensate for the precession induced by the rolling. When one of the gyros hit the end of its allowed range of motion (30 degrees), it would lurch back, and the platform would tumble over, losing its ability to control the vehicle. The circuitry for letting out the parachute had been linked to the platform on the assumption that at the peak of the trajectory the rocket would turn over, upsetting the platform. But the fundamental flaw was that the control forces exerted by the jet vanes, on command of the rate gyro for the roll axis, were far too weak. Assymmetries in the fins, in conjunction with wind, would be enough to start a roll that overpowered the control system. In every case this had happened so fast that the platform toppled in the first three or four seconds. 61

Because of a lack of experience, no one in Ordnance or Kreiselgeräte had seen this coming. Kreiselgeräte specialized in heavy naval systems, and the engineers in Army Ordnance had been completely dependent on the company and on Boykow’s original design. Thus von Braun came to rue his uncritical enthusiasm for the late inventor. It was clear that much more effort and resources had to be put into guidance and control and that competing companies had to be pulled into the program. Dornberger and his subordinates saw as well that it was a mistake after the A-2s to conclude that frequent launches were unnecessary. A new vehicle, called the A-5 (since the A-4 designation had already been assigned), would have to be built to test guidance systems systematically in the air, rather than only with the burning rocket on a test stand, as had been done at Kummersdorf. The excessive stability of the A-3 also confirmed earlier impressions that the wind tunnel testing at Aachen had been far too limited to give an adequate understanding of the forces acting on a flying rocket. Only the engine system of the A-3 had worked without a hitch. But the 25-ton-thrust A-4 engine was a huge step that required a massive infusion of resources and more systematic work. That at least had begun with Thiel’s transfer from Schumann’s research section and the construction of Peenemünde. 62