V-2 rocket
The V-2 rocket, with the development name Aggregat-4, was the world's first practical, modern ballistic missile. The missile, powered by a liquid-propellant rocket engine, was developed during the Second World War in Nazi Germany as a "vengeance weapon" and assigned to attack Allied cities as retaliation for the Allied bombings of German cities. After an altitude of 100km was selected to define the edge of space, the rocket also became retroactively the first artificial object to travel into space with the vertical launch of MW 18014 on 20 June 1944.
Research of military use of long-range rockets began when the graduate studies of Wernher von Braun were noticed by the German Army. A series of prototypes culminated in the A4, which went to war as the. Beginning in September 1944, more than 3,000 were launched by the Wehrmacht against Allied targets, first London and later Antwerp and Liège. According to a 2011 BBC documentary, the attacks from resulted in the deaths of an estimated 9,000 civilians and military personnel, while a further 12,000 laborers and concentration camp prisoners died as a result of their forced participation in the production of the weapons.
The rockets traveled at supersonic speeds, impacted without audible warning, and proved unstoppable. No countermeasures existed except for misdirection and attacks on launch sites and manufacturing facilities. However, postwar and historical assessments found they had little material or strategic impact on the war, despite the great cost of the program.
Teams from the Allied forces—the United States, the United Kingdom, France and the Soviet Union—raced to procure the Germans' missile technology. Though Operation Paperclip, captured hardware and manufacturing facilities, the V-2 was very influential on later ballistic missile and spaceflight development.
Development history
During the late 1920s, a young Wernher von Braun bought a copy of Hermann Oberth's book, Die Rakete zu den Planetenräumen. In 1928 a Raketenrummel or "Rocket Rumble" fad in the popular media was initiated by Fritz von Opel and Max Valier, a collaborator of Oberth, by experimenting with rockets, including public demonstrations of manned rocket cars and rocket planes. The “Rocket Rumble” was highly influential on von Braun as a teenage space enthusiast. He was so enthusiastic after seeing one of the public Opel-RAK rocket car demonstrations, that he constructed and launched his own homemade toy rocket car on a crowded sidewalk and was later taken in for questioning by the local police, until released to his father for disciplinary action.Starting in 1930, von Braun attended the Technische Hochschule in Charlottenburg, where he assisted Oberth in liquid-fueled rocket motor tests. Von Braun was working on his doctorate when the Nazi Party gained power in Germany. An artillery captain, Walter Dornberger, arranged an Ordnance Department research grant for von Braun, who from then on worked next to Dornberger's existing solid-fuel rocket test site at Kummersdorf. Von Braun's thesis, Construction, Theoretical, and Experimental Solution to the Problem of the Liquid Propellant Rocket, was kept classified by the German Army and was not published until 1960. By the end of 1934 his group had launched multiple rockets, two of which reached heights of, respectively.
At the time, many Germans were interested in American physicist Robert H. Goddard's research. Before 1939, German engineers and scientists occasionally contacted Goddard directly with technical questions. Von Braun used Goddard's plans from various journals and incorporated them into the building of the Aggregate series of rockets, named for the German word for mechanism or mechanical system.
After successes at Kummersdorf with the first two Aggregate series rockets, Braun and Walter Riedel began thinking of a much larger rocket in the summer of 1936, based on a projected thrust engine. In addition, Dornberger specified the military requirements needed to include a 1-ton payload, a range of 172 miles with a dispersion of 2 or 3 miles, and transportable using road vehicles.
After the A-4 project was postponed due to unfavorable aerodynamic stability testing of the A-3 in July 1936, Braun specified the A-4 performance in 1937, and, after an "extensive" series of test firings of the A-5 scale test model, using a motor redesigned from the troublesome A-3 by Walter Thiel, A-4 design and construction was ordered 1938–39. When in 1939, Adolf Hitler was shown tests of rocket motors, he was not particularly impressed.
Nevertheless, in 28–30 September 1939, Der Tag der Weisheit conference met at Peenemünde to initiate the funding of university research to solve rocket problems. By late 1941, the Army Research Center at Peenemünde possessed the technologies essential to the success of the A-4. The four main technologies for the A-4 were large liquid-fuel rocket engines, supersonic aerodynamics, gyroscopic guidance and rudders in jet control.
During early September 1943, Braun promised the Long-Range Bombardment Commission that the A-4 development was "practically complete/concluded", but even by the middle of 1944, a complete A-4 parts list was still unavailable. Hitler was sufficiently impressed by the enthusiasm of its developers, and needed a "wonder weapon" to maintain German morale, so he authorized its deployment in large numbers.
The V-2s were constructed at the Mittelwerk site by prisoners from Mittelbau-Dora, a concentration camp where 20,000 prisoners died.
In 1943, an Austrian resistance group led by Heinrich Maier managed to send exact drawings of the V-2 rocket to the American Office of Strategic Services. Location sketches of V-rocket manufacturing facilities, such as those in Peenemünde, were also sent to the Allied general staff in order to enable Allied bombers to perform airstrikes. This information was particularly important for Operation Crossbow and Operation Hydra, both preliminary missions for Operation Overlord. The group was gradually captured by the Gestapo and most of the members were executed.
Technical details
The A4 used a 75% ethanol/25% water mixture for fuel and liquid oxygen for oxidizer. The water reduced the flame temperature, acted as a coolant by turning to steam, augmented thrust, tended to produce a smoother burn, and reduced thermal stress.Rudolf Hermann's supersonic wind tunnel was used to measure the A4's aerodynamic characteristics and center of pressure, using a model of the A4 within a 40 square centimeter chamber. Measurements were made using a Mach 1.86 blowdown nozzle on 8 August 1940. Tests at Mach numbers 1.56 and 2.5 were made after 24 September 1940.
At launch the A4 propelled itself for up to 65 seconds on its own power, and a program motor held the inclination at the specified angle until engine shutdown, after which the rocket continued on a ballistic free-fall trajectory. The rocket reached a height of or 264,000 ft after shutting off the engine.
The fuel and oxidizer pumps were driven by a steam turbine, fueled by decomposition of concentrated hydrogen peroxide facilitated by a sodium permanganate catalyst. Both the alcohol and oxygen tanks were an aluminum-magnesium alloy.
The turbopump, rotating at 4,000 rpm, forced the fuel mixture and oxygen into the combustion chamber at 125 liters per second, where they were ignited by a spinning electrical igniter. The engine produced 8 tons of thrust during the preliminary stage whilst the fuel was gravity-fed, before increasing to 25 tons as the turbopump pressurised the fuel, lifting the 13.5 ton rocket. Combustion gases exited the chamber at, and a speed of per second. The oxygen to fuel mixture was 1.0:0.85 at 25 tons of thrust; as ambient pressure decreased with flight altitude, thrust increased to 29 tons. The turbopump assembly contained two centrifugal pumps, one for the fuel mixture, and one for the oxygen. The turbine was connected directly by a shaft to the alcohol pump and through a flexible joint and shaft to the oxygen pump. The turbopump delivered of alcohol and of liquid oxygen per second to a combustion chamber at.
Dr. Thiel's 25 ton rocket motor design relied on pump feeding, as opposed to earlier pressure-fed designs. The motor used centrifugal injection, and used both regenerative cooling and film cooling. Film cooling admitted alcohol into the combustion chamber and exhaust nozzle under slight pressure through four rings of small perforations. The mushroom-shaped injection head was removed from the combustion chamber to a mixing chamber, the combustion chamber was made more spherical while being shortened from 6 to 1-foot in length, and the connection to the nozzle was made cone shaped. The resultant 1.5 ton chamber operated at a combustion pressure of. Thiel's 1.5 ton chamber was then scaled up to a 4.5 ton motor by arranging three injection heads above the combustion chamber. By 1939, eighteen injection heads in two concentric circles at the head of the thick sheet-steel chamber, were used to make the 25 ton motor.
The warhead was a source of trouble. The explosive used was amatol 60/40 detonated by an electric contact fuze. Amatol had the advantage of stability, and the warhead was protected by a thick layer of glass wool, but even so it could still explode during the re-entry phase. The warhead weighed and contained of explosive. The warhead's explosive percentage by weight was 93%, a very high portion compared to other types of munitions.
A protective layer of glass wool was also used for the fuel tanks to prevent the A-4 from forming ice, a problem which plagued other early ballistic missiles such as the balloon tank-design SM-65 Atlas which entered US service in 1959. The tanks held of ethyl alcohol and of oxygen.
The V-2 was guided by four external rudders on the tail fins, and four internal graphite vanes in the jet stream at the exit of the motor. These 8 control surfaces were controlled by Helmut Hölzer's analog computer, the Mischgerät, via electrical-hydraulic servomotors, based on electrical signals from the gyros. The Siemens Vertikant LEV-3 guidance system consisted of two free gyroscopes for lateral stabilization, coupled with a PIGA accelerometer, or the Walter Wolman radio control system, to control engine cutoff at a specified velocity. Other gyroscopic systems used in the A-4 included Kreiselgeräte's SG-66 and SG-70. The V-2 was launched from a pre-surveyed location, so the distance and azimuth to the target were known. Fin 1 of the missile was aligned to the target azimuth.
Some later V-2s used "guide beams", radio signals transmitted from the ground, as an added input to the Mischgerät analog computer to keep the missile on course in azimuth. The flying distance was controlled by the timing of the engine cut-off, Brennschluss, ground-controlled by a Doppler system or by different types of on-board integrating accelerometers. Thus, range was a function of engine burn time, which ended when a specific velocity was achieved. Just before engine cutoff, thrust was reduced to eight tons, in an effort to avoid any water hammer problems a rapid cutoff could cause.
Dr. Friedrich Kirchstein of Siemens of Berlin developed the V-2 radio control for motor cutoff. For velocity measurement, Professor Wolman of Dresden created an alternative of his Doppler tracking system in 1940–41, which used a ground signal transponded by the A-4 to measure the velocity of the missile. By 9 February 1942, Peenemünde engineer Gerd had documented the radio interference area of a V-2 as around the "Firing Point", and the first successful A-4 flight on 3 October 1942 used radio control to command motor cutoff. Although Hitler commented on 22 September 1943 that "It is a great load off our minds that we have dispensed with the radio guiding-beam; now no opening remains for the British to interfere technically with the missile in flight", about 20% of the operational V-2 launches were beam-guided. The Operation Pinguin V-2 offensive began on 8 September 1944, when Lehr- und Versuchsbatterie No. 444 launched a single rocket guided by a radio beam directed at Paris. Wreckage of combat V-2s occasionally contained the transponder for velocity and fuel cutoff.
The painting of the operational V-2s was mostly a ragged-edged pattern with several variations, but at the end of the war a plain olive green rocket was also used. During tests the rocket was painted in a characteristic black-and-white chessboard pattern, which aided in determining if the rocket was spinning around its longitudinal axis.
The original German designation of the rocket was "V2", unhyphenated – exactly as used for any Third Reich-era "second prototype" example of an RLM-registered German aircraft design – but U.S. publications such as Life magazine were using the hyphenated form "V-2" as early as December 1944.