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A scaled reconstruction of the A3 rocket being prepared for a live test firing in Kummersdorf, near Berlin. Copyright © 2008 Anatoly Zak Previous chapter: A-2 Design The successful launches of A-2 rockets shortly before Christmas 1934 became a vindication for Wernher von Braun and his rocketeers in Kummersdorf. Skeptics were shown that a liquid propellant rocket could fly far and high. Much more importantly for Von Braun's army sponsors, it was now clear that this novel technology could be used as a weapon of war, perhaps exceeding the capabilities of long-range artillery. While Germany was descending into the cesspool of nazism, the secret rocket development program discovered a financial bonanza. As Von Braun put it, the success of A-2, "gave quite a boost to rocket development, accompanied by a loosening of the official purse-strings and considerable elation among the rocketeers." (174) At the time of the A-2 launches, a much more advanced rocket, the A-3, was already in advanced stage of design. However the development of the more powerful engine for the A-3 was beset by endless problems, which repeatedly delayed the project. The rocket's aerodynamic shape also went through three re-designs from July to September 1936, as wind tunnel tests revealed potential problems with its stability. (296) Last but not least, the flight control system presented a major challenge. Instead of a crude flywheel stabilization system, which kept the A-2 on course, the A-3 would sport a three-axis gyroscopic assembly, flight control jet rudders and rudder actuators. (174) With the gyros onboard, the new rocket needed no launch support structure or guiding rails, instead it would blast off standing free on its stabilizers. (174) At the very bottom a plastic ring was connecting the stabilizers to prevent their vibration. The ring also carried a spiral antenna to receive a radio command to shut down the engine, in case of emergency. The rocket would be also equipped with a watertight instrumentation compartment containing a barograph, a thermograph and a small movie camera, designed to photograph these instruments in flight. In addition, the rocket carried sensors to record its skin temperature, the pressure in the combustion chamber, and a radio-receiver designed to shut down the engine from a radio-command, in case of emergency during the flight. If the rocket followed the prescribed trajectory, the propulsion system would be cut off when the rocket tilted to an angle of 30 degrees toward the horizon. The parachute would be released at the peak of the trajectory, as the rocket reached a horizontal position. (296, 174) The heavy nitrogen tank of the A-2 was replaced with a liquid-nitrogen pressurization system, built inside the oxidizer tank. It was equipped with an immersion heater, which activated the pressurization system. (174)(296) As nitrogen would be heated up, it would start evaporating, in turn pushing propellants into the combustion chamber. The parachute container was located right below the oxygen tank, followed by the propellant tank with the duraluminum rocket engine built inside it. The tanks were made of light alloys and designed to contain 1,000 pounds of propellant and withstand an internal pressure of 294 pounds per square inch. New pneumatically operated magnetic servo-valves controlled flow of both fuel and oxidizer, greatly reducing the possibility of explosion during ignition. (174) The rocket was topped with a conical nose carrying electric batteries. (213) Original plans called for the A-3 to break the sound barrier, but ever-increasing mass of payloads pushed that task beyond reach. (174) Test launches After ground testing in Kummersdorf, the A-3 was ready for take off in the summer of 1937. As Peenemünde, on the shore of the Baltic was still under construction, the temporary launch site for the A-3 rocket was built on the Island of Griefswalder Oie. Almost a decade earlier, the rocket pioneer, Johannes Winkler had conducted his rocket tests on the same island. (174) The launch campaign was delayed by a period of very bad weather. The first rocket to be flight-tested was partly painted with a highly hydroscopic green dye designed to color sea water at the splashdown. However during a several hours of delays, super-cold oxygen inside the rocket, caused intensive condensation of the humid sea air around the rocket. As a result, the dye started melting and trickled into the interior of the rocket via an umbilical cable interface, causing short circuits. More delays were required, as launch personnel were harassed by calls from observers waiting in a boat in the stormy sea. When the rocket finally blasted off, it flew normally for about five seconds, after which a parachute was suddenly released and immediately destroyed in the exhaust flame. The rocket itself, seemingly went out of control and tumbled into the sea. (296) According to another source it crashed just 300 meters from the launch site and exploded. (315) Eyewitnesses apparently provided contradictory accounts of the rocket behavior in flight, and no definitive explanation of the failure could be found. The second launch two days later followed a similar scenario, the rocket again turned into the wind soon after the launch and ejected a parachute. (296) It crashed five meters from the shore. Hoping that the parachute system triggered the malfunction, engineers omitted it from the next two rockets, replacing it with the flare ejector, and attempted no other modifications. However, yet again, after several foggy days, the rocket again started spinning and tumbling in flight. It ejected a flare only four seconds after a takeoff, flew almost horizontally with the wind and fell into the sea, some two kilometers from the shore. (315) After another agonizing round of discussions, it was decided to wait for a quiet day to eliminate the effect of the wind on the presumably underpowered flight control system. However, yet again, the fourth rocket failed to complete its flight. The maximum altitude achieved did not exceed 2,500 - 3,000 feet. Only after the ill-fated A-3 launch campaign was over, were the rocket's gyroscopes ultimately suspected to be culprit. As it transpired, a number of associates to Johannes Boykow, late head of the gyroscope development team, had questioned some of his solutions previously. In the end, an entire new flight control system was proposed with an estimated development cycle of 18 months. To test the new control system and other advanced features, a new A-5 rocket was proposed, while, the designation A-4 remained reserved for a much larger rocket, which had been conceived before the A-3 started flying. (174) Chronology of the A-3 project 1934: The development of the A-3 rocket starts. 1936 Spring: Static testing of the A-3 rocket is conducted at Kummersdorf. (308) 1936 July: Wind tunnel tests of the A-3 rocket reveal problems. (296) 1936 end of September: Wind tunnel tests finally confirm the stability of the fin sections of the third model of the A-3 rocket. (296) 1937 September: Static firing of the A-3 rocket is conducted. (295) 1937 end of November: The first of two pairs of A-3 rockets is delivered to Griefswalder Oie by ferryboat. (296) 1937 Dec. 4: The first A-3 is launched from Griefswalder Oie. (296) 1937 Dec. 6: The second A-3 is launched. (296, 315) 1937 Dec. 8: The third A-3 is launched. (296, 315) 1937 Dec. 11: The fourth A-3 is launched. (296, 315) A-3 technical overview:
Page author: Anatoly Zak; Last update: October 10, 2008 Page editor: Alain Chabot; Last edit: October 5, 2008 All rights reserved |
IMAGE ARCHIVE
The A-3 became the most sophisticated rocket built in Kummersdorf. However much more advanced projects -- A-4 and A-5 were conceived there, but implemented in Peenemünde. Click to enlarge. Copyright © 2008 Anatoly Zak
The internal layout of the A-3 rocket. Click to enlarge.
The A-3 rocket at the static test stand in Kummersdorf. Click to enlarge
The A-3 is being erected on the launch pad on the Island of Griefswalder Oie.
The A-3 is being prepared for launch on the Island of Griefswalder Oie, as Wernher von Braun talks to his colleagues nearby.
A rudimentary service tower was used to shield the A-3 from the stormy weather in the Baltic.
Launch personnel apparently used a narrow-gauge railway left from the construction of the lighthouse on the Island of Griefswalder Oie to deliver the propellant from the ferry to the launch pad.
The A-3 rocket blasts off from the Island of Griefswalder Oie. The island's lighthouse can be seen on the background.
Recovery team struggles with stormy sea trying to salvage pieces of the rocket. |
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