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The R-2 ballistic missile was the first Russian departure from German rocket technology inherited by the USSR at the end of World War II.
R-1 tech dossier:
In the autumn of 1946, Marshal Zhigarev, the Commander-in-Chief of the Soviet Air Force, reportedly, told to Soviet Air Force scientist G. Tokady, "We must admit that our A-4-type rockets do not satisfy our long-term needs; they were good to frighten England, but should there be an American-Soviet war, they would be useless; what we really need are long-range, reliable rockets capable of hitting target areas on the American continent."(9)
By mid-1946, during his stay in Germany, Sergei Korolev, the leader of the Soviet post-war rocket research, had already started to draft Russian successor to the A-4, later designated as R-2 (from Russian PAKETA-2 or P-2). It was to be equipped with propellant tanks streched about three meters off the length of its German original and with more powerful engine -- 32 tons comparing to 25 tons in A-4 engine. As a result, the rocket could reach up to 600 km range, i.e. twice as much as that of the A-4. The higher engine trust required unacceptably high flow rates in the existing A-4's turbo pump. To solve the problem, Germans working for the Soviets proposed to boost the pump by directing exhaust gases from the combustion chamber back into the pump. Korolev probably saw this idea as too complicated. Instead, he simply decided to install a second pump.
In the summer of 1946, Gröttrup was asked to propose modifications for the A-4, in addition to redrawing A-4's blueprints and getting ready pilot production line for the rocket. Deadline was set at mid-September.
Gröttrup and his team come up with about 150 possible improvements, many of them born yet in Peenemunde. About half of them was accepted right away and the rest was asked to be resubmitted in more detailed form. Accepted proposals included pressurized propellant tanks, flight control systems moved down under the propellant tanks and propellant turbo pumps driven by gases taken out of the engine's exhaust stream.
Additionally, in the autumn of 1946, the Soviets asked Gröttrup team to sketch a missile capable of reaching a 1,500 miles range. No payload capacity or accuracy requirements were given. In several days, Gröttrup produced a drawing based on the A9/A10 project, a two-stage, comikadze-piloted rocket conceived in Peenemunde for the attacks on the continental United States and Soviet military factories in Urals.
In NII-88, Professor Umpefenbach filled Gröttrup's place as a chief German scientist in 1948. Like his predeccesor, he was unhappy with the role Russians assigned to his group, as well as he didn't see any professional challenge in the projects like R-2. "...I proved him (Korolev) ages ago that his plan of simply building a longer A-4 and providing it with a more powerful thrust won't materially increase the range," recalled Umpefenbach.(10) Nevertheless, it was the R-2 which was actually built as a first Soviet successor to the A-4 on the NII-88 experimental plant. Despite Umpefenbach skeptitism, R-2 did feature significant improvements, comparing with the A-4. Unlike R-10*, a rocket designed by the Germans as a successor to A-4, the upper position fuel tank was the only one made as a part of external structure of the rocket (monocoque type), while the lower oxidizer reservuar was still wrapped inside of the protective rocket skin. The problems of thermal isolation of liquid oxygen as well as structural strength of the tank made this decision necessary. (3)
As it was proposed yet in Germany, the instrumental section was moved from the top of the rocket into position between oxygen tank and tail section. A 1.5-ton warhead was separable. The rocket was 17.65 meters tall and the same diameter as the A-4 and R-1. A take off weight has reached 20,416 kg (i.e. 7 tons plus to the A-4/R-1); including 4,528 kg of the structure. The engine for the R-2 was again developed by Glushko's bureau under designation RD-101. Its performance was improved by the implementation of the fuel of higher concentration than that used in RD-100. Amount of water mixed with the alhocol pumped in R-2 tanks was reduced to 8%, comparing with 15% added in the R-1's fuel.
The experimental version of the rocket designated R-2E (from Russian P-2 Experimental'naya -Experimental) was launched for the first time from Kapustin Yar on September 21, 1949.(4) The vehicle had minor structural differences from the standard R-2 design, what made R-2E 9 centimeters shorter then the final configuration. A series of intensive flight testing of the standard R-2 were started on October 26, 1950.
The article by Anatoly Zak; Last update: April 18, 2013
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The R-2 missile on the launch pad in Kapustin Yar. Credit: TsNIIMash
The R-2E missile on the transporter. Credit: TsNIIMash
The R-2 missiles in storage. Credit: TsNIIMash
Shown to the scale, left to right: R-2, R-5 and R-1 ballistic missiles. Copyright © 2001 Anatoly Zak
The RD-101 engine, which powered the R-2 missile. Copyright © 2002 Anatoly Zak
A scale model of the R-2A rocket. Copyright © 2011 Anatoly Zak