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.
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 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.
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.
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 early 1960 theR-7A missile was put on active alert.
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.
The public display of a Soviet SS-6 rocket at the Paris Air Show in 1967 jolted the US scientific astronautics intelligence community into awareness of many weaknesses in its evaluative processes. These revelations were of much greater intelligence significance than the factual information gleaned from inspection of the missile itself. As a result it became possible to identify many shortcomings in the analytical phase of the intelligence cycle.
In retrospect, it was clear that the principal shortcomings of the US analytical cycle did not result from mistakes in the interpretation of the available data, nor from deficiencies in the quality or quantity of the data. Instead, error most frequently arose from attempts to relate Soviet technology directly to that of the United States. Rather than believe direct telemetry evidence, the community erroneously relied too heavily on US design precepts.
It was now evident that this approach involved a dangerous assumption, and that Soviet technological approaches in the field of astronautics often differed significantly from those of the United States. Erroneous judgments reached by ignoring available intelligence because it gave answers seemingly inconsistent with "our way of doing things" have unfortunately been common in the scientific intelligence field. The Soviet approach to rocket engine design could be radically different from that of the US, and a direct comparison could be dangerously misleading.
The most surprising feature of the SS-6, the use of multi-chambered engines, was not recognized. This was due to an adverse influence of US design practice on the thinking of intelligence analysts. Although the number of combustion chambers was incorrectly derived, the presence of four engines in the first stage and one engine in the sustainer stage was correctly derived.
A combination of high specific impulse and thrust level of the SS-6 engine, given the 1957 time frame when it was being initially flown, however, should have alerted US analysts to the fact that something was amiss with their interpretation. The strategic system which preceded the SS-6 in research and development flight testing, the SS-4, as well as systems which followed it, such as the SS-5 and SS-7, all used multi-chambered engines. Analysts within the community were reluctant to accept the multi-chambered engine configurations of both the SS-4 and SS-5, even in the light of evidence that such was the case.
In particular, the specific propellant combination employed by the system was incorrectly determined because the volumetric ration of the bi-liquid was derived from a telemetry interpretation which assumed the sustainer tanks were of the same diameter. There was some support for the view that the SS-6 employed a kerosene-base fuel, but the majority view that the oxidizer was liquid oxygen turned out to be correct. It was immediately obvious upon seeing the vehicle in Paris that the propellant combination would logically be kerosene for fuel and liquid oxygen as the oxidizer, consistent with the Soviet announcements at the time.
The specific impulse of the first stage of the system, and the overall energy capability of the stage, were incorrectly derived; both because of the assumption that the area ratio of the first stage engines should be related to the area ratio of the sustainer engine in about the same manner as in engines of US design of the same type. Many intelligence officers within the US intelligence community were correct in their assessment of the specific combination employed, but unfortunately their adversaries, guided by the "divine righteousness of domestic design concepts," overruled their superior technical judgments.
The detailed configuration of the four boosters was improperly interpreted, principally because of the erroneous assumption that liquid propellant tanks for large rocket vehicles would logically be formed from right circular cylinders. Additionally, the general configuration (parallel, or partial), was misinterpreted by many. This argument, incidentally, grew into one of the major intelligence controversies of the decade. Those who turned out to be wrong on this issue based their decisions upon "domestic logic" rather than objectively interpreting available intelligence information such as intercepted radio telemetry. The basic Soviet philosophy of building and handling large rocket vehicles was therefore misunderstood because of the foregoing errors.
|Historical Review - Western Estimates|
|First system flight test||January 30, 1958|
|Operational training flights began||October 1959|
|Initial operational capability||Early 1960|
|Deployed missiles retrofitted with 9000 lb reentry vehicle Late||1960-Early 1961|
|Maximum operational deployment (four missiles) reached||1962|
|Last missile test firing||1966|
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