R-7 / 8K71, 8K74 - SS-6 SAPWOOD
The Korolev design bureau's R-7/SS-6 Sapwood was the world's first intercontinental. Though R-7s were never widely deployed, the launch systems became the basis for the most successful satellite launch booster in the world. Flight tests of the R-7 missile began in May of 1957 and the first twelve tests were completed by late January 1958. During these initial tests, the Soviet Union launched the Sputnik satellite in October 1957 followed by Sputnik II in November of the same year. The Sputnik launched revealed to the US the strength of the Soviet rocket program.
In 1947, Mikhail Tikhonravov established a group for conducting systematic research projects at the Research Institute of Artillery Sciences. Members of this group were instructed to study the possibility of developing composite (multi-stage) ballistic missiles. After analyzing the groupís findings, Korolev decided to create a rough sketch of a powerful composite missile. The parameters of the R-7 were first outlined in a Soviet governmental order from February 13, 1953 that called for the development of a two-stage ballistic missile with a range of 8000 km with a payload carry of 3,000 kg and a gross liftoff weight of 170 tons. However, the design specifications where changed to incorporate the thermonuclear warheads, which were found to weigh approximately 6,000 kg. The resulting increase in payload weight reduced the missiles ranged to only 5,500 km. As a result, to preserve the previous range specifications, it was necessary to redesign the missile. In the end, weight saving measures where incorporated into all facets of the program allowing for the payload increase and preserving the necessary range.
Instead of using stacked stages typical of U.S. systems the R-7 (and subsequent Soyuz rockets) arranged its boosters laterally around a single core rocket. The R-7 rocket consisted of five parts, a core stage surrounded by four strap-on boosters. The strap-on boosters, utilizing the RD-107 rocket, formed the first stage of the system. The RD-107 had four main nozzles with two steering vernier engines which gimbaled on one axis. The core stage utilized a RD-108 rocket (which is essentially a RD-107 with four steering verniers (flight control), became the second stage. All stages are fueled by liquid oxygen and kerosene.
The R-7 differed completely from all previously developed missiles in terms of its layout, frame configuration, dimensions, weight, rated engine power, the number of systems and their designation, and more. The R-7 missileís layout featured two stages with parallel separation and was, in fact, a multiple booster assembly. Its first stage comprised four strap-on boosters measuring 19 meters (62 feet) long each and with a maximum diameter of three meters (10 feet). They were attached symmetrically to the missileís central section (second stage).
Strap-on boosters and the central section were similar to single-stage missiles with front-mounted oxidizer tanks. The fuel tanks of all sections served as load-bearing structures. During launch, the propulsion units of all five sections were activated simultaneously. This layout made it possible to activate all engines on the ground, rather than during flight (in the vacuum of space). Each section was equipped with a four-chamber and open-layout liquid-propellant sustainer engine firing liquid oxygen and kerosene. Hydrogen peroxide and liquid nitrogen were used to operate turbo-pump units of rocket engines and for supercharging fuel tanks, respectively.
The R-7 missile was 31.4 meters (103 feet) long and had a diameter of 11.2 meters (36.7 feet). It had a liftoff weight of 283 metric tons, including 250 metric tons of fuel, a range of 8,000 kilometers (4,971 miles) and a payload of 5.4 metric tons. It could carry a nuclear warhead with a yield of three to five megatons. The nuclear warhead was attached to the instrument compartment of the central section using three ejection explosive charges. Using it, it was possible to destroy a large area through an air or ground burst.
The R-7 missile was equipped with a combined guidance system, the autonomous subsystem of which ensured angular stabilization and stabilization of the center of mass during the active trajectory leg. A radio-technical subsystem adjusted the sideways movement of the center of mass at the end of the active trajectory leg and shut off the engines for greater targeting accuracy. Reversible steering-engine chambers and rudders executed various commands of the guidance system.
The missile had a combined command structure consisting of both an independent autonomous system and a radio command system. The independent autonomous system provided attitude control for the missile with respect to the vehicle's center of mass and motion on the planned trajectory. It also controlled the synchronous draining of the propellant tanks in all units of the first stage. The system of radio control carried out in-flight trajectory corrections and provided for an increase of delivery accuracy.
On May 20, 1954, the Soviet Government issued a resolution instructing the OKB-1 to develop an intercontinental and thermonuclear-capable missile. Special Design Bureau No. 456 headed by Valentin Glushko developed powerful new engines for the R-7 missile. The R-7ís guidance system was designed by Nikolai Pilyugin and Boris Petrov, and Vladimir Barmin designed the launch facility. Several other organizations were also involved in this project.
At the same time, the decision was made to establish a new ICBM testing site. In February 1955, the Council of Ministers of the USSR (Soviet Government) adopted a resolution on starting the construction of a testing site called the Fifth Research and Testing Site of the Soviet Defense Ministry (NIIP-5). The decision was made to build the testing site near the village of Baikonur and the Tyura-Tam double-track railway section in Kazakhstan. This space center was considered a top-secret facility, and the R-7 launch facility was completed in April 1957.
The design of the R-7 missile was completed in July 1954, and the Soviet Government approved its creation on November 20, 1954. The missile was ready for testing in early 1957. Starting mid-May 1957, the first tests of the missile were conducted, revealing major drawbacks in its design. The first missile lifted off on May 15, 1957. Visual observations showed the flight pattern to be normal, but changes in the composition of missile engine gases were subsequently detected in its tail section. An assessment of telemetry data showed that the missile had become unstable, after one of side sections fell off. The accident was caused by a ruptured fuel pipeline.
The next launch was scheduled for June 11, 1957, but it never took place due to defective engines in the missileís central section. The missile lifted off once again on July 12, 1957, but lost its in-flight stability in the 33rd second of flight and started deviating from its preset trajectory. This particular malfunction was caused by a short-circuited integrator responsible for the missileís revolution.
The fourth R-7 launch (August 21, 1957) finally proved successful, and the missile hit a preset target area for the first time. This missile, also known as Item No. 8K718, with an M1-9 warhead, lifted off from the Baikonur space center (Tyura-Tam testing site), completed its active trajectory leg and released its warhead, which then hit a preset area of the Kamchatka Peninsula. But this launch had one major drawback: the warhead disintegrated during reentry.
On August 27, 1957, Soviet newspapers reported the successful test of a multi-stage missile with an enhanced range in the USSR. Positive results of R-7 flights along the active trajectory leg made it possible to use the missile for launching the first two man-made satellites, on October 4 and November 3, 1957. Conceived as an ICBM, the R-7 possessed a sufficient thrust-to-weight ratio for sending a rather heavy payload into orbit, and this factor was used to full advantage during the launching of these two satellites.
After assessing the results of six R-7 launches, experts upgraded the missile warhead (they installed a new one). They also upgraded the warhead-separation systems and installed slot-type antennas (also called slot arrays) of the telemetry system. The first fully successful R-7 launch took place on March 29, 1958, and its warhead reached the target area intact. Subsequent flight tests were conducted in 1958-1959, making it possible to upgrade the R-7 design still further.
The first R-7 missiles were manufactured at Plant No. 88, a pilot production facility of the OKB-1, in Kaliningrad, now Korolyov, near Moscow. Due to the pilot plantís limited capacity, Dmitry Kozlov, the leading designer of the R-7 missile, was sent on a business trip to Kuibyshev, now Samara, in February 1958, with instructions to launch commercial production of these missiles at Aviation Plant No. 1, now the Progress State Research and Production Rocket Space Center, which manufactured bombers in the past. The first production missiles came off the assembly line already in December 1958.
Joint R-7 flight tests were conducted from December 1958 until November 1959. A total of 16 missiles were launched during these tests, including eight production versions. The tests made it possible to decide whether the Soviet Armed Forces could adopt the R-7 missile.
Design and failure analysis of the first R-7 flights led to a modification of the nose cone and its mode of separation. Between late March and early July 1958 the new design with a modified nose cone was successfully tested. On 02 July 1958, a ministerial decree called for the development of an improved ICBM based on the R-7 design. The new R-7A (8K74) included a modernized lighter warhead, more powerful engines and an increased propellant volume. Thus maximum range was increased from 8000 up to 12000 km. Newly developed inertial navigation systems replaced previous radio control systems greatly improving accuracy.
The Soviets conducted 16 flight tests to ensure the reliability of the new control design. Following the tests in December 1959, the first of the R-7 launch complexes were put on an alert and deployment of the rockets began in January 1960. In January 1960 the Soviets successfully delivered a nose cone into the pacific ocean. Eight missile launches were carried out of which seven were successful.
In 1958, the decision was made to build a combat launch station, called the Angara facility, near the town of Plesetsk in Russiaís Arkhangelsk Region. This facility was completed on January 1, 1960, and it successfully launched two test missiles on July 16, 1960, for the first time in the history of the Soviet Armed Forces. Prior to launch, the missile was delivered from a technical position aboard a railway train with a transporter/erector, and placed on a massive launch facility. Pre-launch operations lasted over two hours.
Apart from the R-7, Soviet experts continued to develop the R-7A missile system with an even longer range of 12,000 kilometers (7,450 miles), an upgraded guidance system, more reliable engines and a lighter warhead. The R-7A missile featured more powerful engines and a somewhat larger fuel load, made possible by reducing the free volume of its fuel tanks. The R-7A ICBM was officially adopted for service on September 12, 1960.
The entire missile system proved to be cumbersome, vulnerable, expensive and hard to operate. A refueled missile could remain on the launch pad for no more than 30 days. An entire factory was needed to generate and replenish the required oxygen reserves for refueling deployed missiles. The targeting accuracy of these missiles was not very impressive either. It became obvious that only a few R-7 missiles and their modified versions could be placed on combat duty. A total of four launch pads were built, and both missile versions were discarded from service by late 1968.
The R-7 was never deployed in significant numbers. The missile took too long to fuel, its above ground launch facilities were large and vulnerable to attack. Finally, the system could only be only be held on standby for 24 hours before the propellant seals began to fail. Fewer than ten were believed to be nuclear deployed, wth only one dedicated ICBM pad was built at Baikonur, and six to eight in the Angara complex at Plesetsk.
As a nuclear weapons platform, the R-7 was quickly became obsolete do to rapid technical improvements. Among these improvements was the development of zero warning rockets, utilizing storable propellants and smaller warheads. By mid-1968 the SS-6 ICBM had been phased out of the operational inventory. Use of the SS-6 is now restricted to space applications.
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