Aggregate (rocket family)

The ''Aggregat'' series (German for "Aggregate") was a set of ballistic missile designs developed in 1933–1945 by a research program of Nazi Germany's Army ( ''Heer''). Its greatest success was the A4, more commonly known as the V2.

A1 (1933)

The A1 was the first rocket design in the ''Aggregat'' series. It was designed in 1933 by Wernher von Braun at the German Army research program at Kummersdorf headed by Colonel Dr Walter Dornberger. The A1 was the grandfather of most modern rockets. The rocket was long, in diameter, and had a takeoff weight of . The engine, designed by Arthur Rudolph, used a pressure-fed rocket propellant system burning ethanol and liquid oxygen, and produced 2.9 kN (660 lbf) of thrust for 16 seconds. The LOX tank was located within the fuel tank and insulated with a fiberglass material. The rocket was stabilized by a 3 axes gyroscope system in the nose, supplied by Kreiselgeräte GmbH. The rocket could not be rotated for stability as with a ballistic shell, as centrifugal force would force the liquid fuel to rise up along the walls of their tanks, which made feeding propellants to the combustion chamber difficult. Although the engine had been successfully test fired, the first flight attempt blew up on the launching pad on 21 December 1933, half a second after ignition. The cause was a buildup up of propellants before ignition of its engine. Since the design was thought to be unstable, no further attempts were made, and efforts moved to the A2 design. The A1 was too nose-heavy, and to compensate, the gyroscope system was moved to the middle of the A2, between the oxygen and ethanol tanks.

A2 (1934)

Static tests and assembly were completed by 1 October 1934. Two A2s were built for a full-out test, and were named after a Wilhelm Busch cartoon, ''Max and Moritz''. On 19 and 20 December 1934, they were launched in front of senior Army officers on Borkum island in the North Sea. They reached altitudes of and . The A2s had the same dimensions as the A1, and the same engine, but separate propellant tanks. The cylindrical regeneratively cooled combustion chamber was welded inside the ethanol tank. The mushroom-shaped injector system consisted of fuel and oxidizer jets pointing at one another. Propellants were pressurized from a nitrogen tank, a system which was also used for the A3 and A5.

A3 (1935–1937)

Development of the A3 can be traced at least to February 1935 when Major Ernst Ritter von Horstig sent General der Artillerie Karl Becker a budget of almost half a million marks for the construction of two new test stands at Kummersdorf. Included were mobile test rigs, small locomotives, and office and storage space. The A3 plans called for a rocket with an inertial guidance system and a thrust engine.

In March 1936, Generaloberst Werner von Fritsch witnessed a static firing of an A3 engine at Kummersdorf, and was sufficiently impressed to lend his support to the rocket program. Like the earlier A1 and A2 rockets, the A3 used a pressure-fed propellant system, and the same liquid oxygen and 75% ethanol mixture as the earlier designs. It generated its for 45 seconds. It used a three-gyroscope system to deflect tungsten alloy jet vanes. The design was finished in early 1936 and further modifications that made the rocket stable at supersonic velocities were finalized later that year.

The shape of the rocket was based on the 8-mm rifle bullet, in anticipation of supersonic flight. The rocket was in length, feet in diameter, and weighed when fueled. Fins were included, for "arrow stability", structurally anchored by an antenna ring. The stabilized platform used a pitch gyro and a yaw gyro, connected to pneumatic servos, which stabilized the platform along the pitch and yaw axes. Electrical carriages on the platform acted as integrating accelerometers. These signals were mixed with those from the SG-33 system, to drive the molybdenum-tungsten jet vane control servomotors. The SG-33 was fixed to the rocket, not the stabilized platform, and used three rate gyros to sense roll, pitch and yaw deviations. Two of the jet vanes rotated in the same direction for pitch and yaw control, and in opposite directions for roll control. The guidance and control system was designed by Fritz Mueller, based on Johannes Maria Boykow's ideas, the technical director of Kreiselgeräte GmbH ("Gyro Instruments Limited").

The A3 engine was a scaled-up version of the A2, but with a mushroom-shaped injector at the top of the combustion chamber, based on a design by Walter Riedel. Ethanol was sprayed upwards to mix with the oxygen sprayed downward from jets at the top of the chamber. This increased efficiency and generated higher temperatures.

This was the first of the ''Aggregat'' rockets to be launched from the Peenemünde area. As part of Operation Lighthouse the first A3 was launched on 4 December 1937, but suffered problems with premature parachute deployment and engine failure, and crashed close to the takeoff point. The second launch on 6 December 1937 suffered similar problems. The parachute was disabled in the third and fourth rockets launched on 8 and 11 December 1937, but these, too, experienced engine failures, though the lack of parachute drag allowed them to crash further from the launch site. They reached altitudes between , before falling into the sea.

According to another source, one A3 reached a maximum downrange of and maximum altitude of .

With each launch a failure, von Braun and Dornberger looked for the cause. At first there was some thought of an electrostatic charge that prematurely set off the parachute, but this was largely disproved. Ultimately, the failures were attributed to the inadequate design of the rocket's experimental inertial guidance system and minor instabilities in the body and fin design. The control system was found to be unable to keep the rocket from turning with a wind greater than . The stable platform gyros were limited to a 30 degree range of motion, and when the platform tumbled, the parachutes deployed. The jet vanes needed to move faster, and have a larger control force, to stop the rolling. The fins were redesigned in the A5, when it was realized an expanding jet plume as the rocket gained altitude, would have destroyed the A3 fin stabilizing antenna ring.

After this unsuccessful series of launches, the A3 was abandoned and A4 work postponed, while work on the A5 commenced.

According to Dornberger, the A3 "...had not been equipped to take any payload. It was a purely experimental missile." Similarly, the A5 was to be "for research purposes only."

Specifications

:Length:
:Diameter:
:Finspan:
:Launch mass:
:Fuel: Ethanol and liquid oxygen
:Liftoff thrust: 14.7 kN

A5 (1938–1942)

The A5 played a vital role in testing the aerodynamics and technology of the A4. Its rocket motor was identical to the A-3, but with a new control system provided by Siemens, was long, with a diameter of and a takeoff weight of . The A5 was fitted with a Brennschluss receiving set, a parachute recovery system, could stay afloat in water for up to two hours, and was painted yellow and red, aiding recovery. New tail surfaces were tested in the Zeppelin Aircraft Works subsonic tunnel and the supersonic tunnel in Aachen. The internal vanes were now made of graphite instead of molybdenum. Uncontrolled A5s were launched from Griefswalder Oie in late 1938. Models that were long and in diameter were dropped from Heinkel He 111s starting in September 1938, testing supersonic speeds in the absence of a supersonic wind tunnel. Hellmuth Walter also made models of the A5m which included a hydrogen peroxide motor, with potassium permanganate as a catalyst, and were test launched in March 1939. The final fin configuration was wider, curved outward to accommodate the expanding exhaust gases, included external air vanes, but no ring antenna.

The A-5, like the A-3, was fueled with ethanol with liquid oxygen as an oxidant. The first successful guided flights were made in October 1939, with three of the first four flights using a Kreiselgeräte complete guidance and control system called SG-52. This used a 3-gyro stabilized platform for attitude control and a tilt program, whose signals were mixed with rate gyros, and fed to a control system connected to the jet vanes by aluminium rods. The Siemens ''Vertikant'' control system first flew on 24 April 1940. The Siemens system used three gyros, particularly 3 rate gyros providing stabilization, and hydraulic servomotors to move the jet vanes to correct pitch and yaw, and control roll. The Möller Askania, or Rechlin system, first flew on 30 April 1940, and used position gyros, a mixing system and a servo system. A-5 testing included a guide plane system for lateral control, and a radio system for propulsion cutoff at a preselected speed, after which the rocket followed a ballistic trajectory. The A-5s reached a height of and a range of . Up to 80 launches by October 1943 developed an understanding of the rocket's aerodynamics, and tests of a better guidance system. The aerodynamic data resulted in a fin and rudder design that was basically the same one used for the A-4.

At the conclusion of the A-5 testing, Dornberger stated, "I now knew that we should succeed in creating a weapon with far greater range than any artillery. What we had successfully done with the A-5 must be equally valid, in improved form, for the A-4."

A4/V-2 rocket (1942–1945)

In the late 1920s, Karl Becker realised that a loophole in the Treaty of Versailles allowed Germany to develop rocket weapons. General Becker was very influential during the development of the A4 until he committed suicide on 8 April 1940 following criticism from Adolf Hitler.

The A4 was a full-sized design with a range of about 322 kilometers (200 mi), an initial peak altitude of 89 kilometers (55 mi) and a payload of about a tonne. Versions of the A4 were used in warfare. They included the first ballistic missile and the first projectile to reach outer space.

The propellants of choice continued to be liquid oxygen, with a 75% ethanol and 25% water mixture. The water reduced the flame temperature, acted as a coolant, and reduced thermal stress.

This increase in capability came from a redesign of the A3 engine, now known as the A5, by Walter Thiel. It became clearer that von Braun's designs were turning into useful weapons, and Dornberger moved the team from the artillery testing grounds at Kummersdorf (near Berlin) to Peenemünde, on the island of Usedom on Germany's Baltic coast, to provide more room for testing and greater secrecy. This version was reliable, and by 1941 the team had fired about 70 A5 rockets. The first A4 flew in March 1942, flying about 1.6 kilometers (1 mi) and crashing into the water. The second launch reached an altitude of 11 kilometers (7 mi) before exploding. The third rocket, launched on 3 October 1942, followed its trajectory perfectly. It landed 193 kilometers (120 mi) away, and reached a height of 83 kilometers (52 mi). The highest altitude reached during the war was on 20 June 1944.

Production started in 1943 on the rocket. The missile testing ground at Blizna was quickly located by the Polish resistance movement, the Home Army (''Armia Krajowa''), thanks to reports from local farmers. Armia Krajowa field agents managed to obtain pieces of the fired rockets by arriving on the scene before German patrols. In early March 1944, British Intelligence Headquarters received a report of an ''Armia Krajowa'' agent (code name: ''"Makary"'') who had covertly surveyed the Blizna railway line and observed a freight car heavily guarded by SS troops containing ''"''an object which, though covered by a tarpaulin, bore every resemblance to a monstrous torpedo''"''. Subsequently, a plan was formed to make an attempt to capture a complete unexploded V-2 rocket and transport it to Britain. Around 20 May 1944, a relatively undamaged V-2 rocket fell on the swampy bank of the Bug River

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