The Origin of the Soviet ICBM ProgrammeIn the middle of 1947 a concept of unitised ballistic missiles was proposed by M.K. Tikhonravov  who was one of the Soviet Union's rocketry pioneers. After WWII he worked at Nll-4 of the Defence Department of the USSR (Nil m Russian stands for p;cu,ch;-c i:;s;sdovatci5i,y Sr.stitut or in English for Scientific Research Institute). The institute which was designated "military command 25840"  was in the Academy of Ordnance Sciences at that time. Tikhonravov's "rocket packet", as he called it, was conceived as a cluster of identical rockets which would be jettisoned during the ascent when their propellants had been used up. S.P Korolyov acquainted with this suggestion. During 1949-1951 the Mathematical Institute of the Academy of Sciences (MIAN is its Russian acronym) of the USSR conducted feasibility studies on various schemes for viable multi-stage ICBM configurations under Korolyov's orders. Many versions of the "rocket packets" were examined, namely: "nourishable" (feeding) packets with propellants pouring from tank into tank, those consisting of separate integral tanks without pouring, those of three, five or seven identical rockets and those of rocket units of different sizes and loaded fuel weight [j]. In December 1950 Korolyov's OKB-1 (OKB in Russian stands for Osoboye Konstruktorskoye Buro or in Engiish for Special Design Bureau) began work on determining the performance characteristics of missiles with long range capability in the quest for an optimal design of ICBM . In 1952 common NII-4/MIAN/OKB-1 efforts went into the design of a five-unit packet missile consisting of a central sustainer (Block A in Russian terms) and attached to it four strap-on boosters (Blocks B, V, G, D in Russian alphabetical order). All propulsion units would be ignited simultaneously on the ground at lift-off with the four boosters (as the first stage) dropping off later and a core unit (as the second stage) taking over to continue the ascent. The initial project envisaged the development of an ICBM of nearly 200 tonnes and capable of delivering a warhead of 3 tonnes at a distance of 8500 km. In 1952 V.P. Glushko's OKB-456 (known under the name GDL-OKB) started work on the single-chamber engines RD-105 and RD-106 using a combination of liquid oxygen (LOX) and kerosene. The RD-105 was to have produced 55 tonnes of thrust and was intended as a strap-on booster. The RD-106 was for a central sustainer and was to have provided a lift-off thrust of 53 tonnes (or 65.8 tonnes in vacuum). But development of these poverful one-chamber LOX-kerosene motors came to grief due to serious problems with burning stability in the chamber.
8K71 The First ICBMThe R-7 would have been capable of transporting a warhead weighing nearly 5.4 tonnes across a distance of 8600 km. The loaded weight of the missile was to be 283 tonnes  and its propulsion units were to have produced nearly 400 tonnes of thrust at lift-off. in 1953 OKB-456 worked out an outline design for the more powerful engines RD-107 and RD-108 and early in 1954 development and construction of the new motors began. Work on the RD-105/106 engines was then cancelled. The RD-107 engine would have provided a lift off thrust of 83 tonnes  and would be attached to the bottom of each of the four strap-on boosters B, V, G and D. The RD-107 was designated "izdeliye" 8D74" during development and manufacturing stages. ''Izdeliye" in English means "product". This name is given to any military and space production in Russia (and in the Soviet Union too). So Soviet/ Russian designers, engineers, military men, managers and so on call missiles, rocket motors, launch vehicles and spacecraft by the same word - "izdeliye". The RD-108 ("izdeliye 8D75") which delivered a lift-off thrust of 75 tonnes  (95.5 tonnes in vacuum) was a propulsion unit for the core unit A. Both LOX-kerosene motors were simiFar four-chamber clusters. On account of the identical multi-chamber design, the process of construction, R&D testing and bringing to operational status could be simplified and hastened, although the core engine was to be a single-chamber one according to the original Korolyov requirements. On 20 May 1954 the Soviet government came to a decision on the creation of an ICBM . OKB-1 was given the go-ahead to begin development and con- struction of the R-7 parts of the missile. In July 1954 the R-7's outline design had been prepared in 15 volumes  and the first drawings had appeared of the missile components. The R-7 was given the development/manufacture designation "product 8K71". In the middle of 1955 static firing tests with RD-107/108 experimental single combustion chambers were held. Then two chambers were clustered and in December 1955 static tests with a dual chamber assembly were accomplished. The four-chamber motor was static fired in January 1956 for the first time. By the summer of 1956 the entire rocket unit was assembled (without boosters) - it included the central sus-tainer (Block A unit) - and in August 1956 was static fired for the first time at the huge test bench near Zagorsk (now Sergiyev-Posad) not far from Moscow . Then the single booster was tested and finally all rocket units were put together and the total ICBM packet was tested in the winter of 1956-1957.
8K71PS The First Sputnik LauncherRight from the start of R-7 development Korolyov with utmost clarity visualised it as a feasible and powerful space launch vehicle. In plans sent to the Soviet leadership on 29 August 1955 Korolyov recommended the launching of artificial satellites, probes toward the Moon and manned spacecraft . On 30 January 1956 the Soviet Government passed a resolution for the development of a heavy artificial satellite called Object D and a special version of the R-7 for its launch into orbit (Objects A, B, V and G - in Russian alphabetical order - were designated versions of ICBM warheads ). But Object D proceeded slower than work on the R-7 programme progressed and in December 1956 Korolyov took the decision to first put into orbit "the simplest possible satellite" named PS (v/hich in Russian stands for Prosteisnyi Sputnik). Object D later became Sputnik-3. After the 8K71 suborbital flight of 7 September 1957  (the author takes the liberty of making the supposition that it was an unsuccessful attempt to orbit the first Soviet Sputnik!), the satellite PS-1 opened the Space Age on 4 October 1957. The first two Soviet satellites PS-1 and PS-2 were launched by basically the same R&D test version of the R-7 ICBM but somewhat modified and designated 8K71PS. The dummy warhead had been removed of course. Moreover the radiopackage which weighed 300 kg was removed from the top of the central sustainer  since there was no need for high pointing accuracy of the payload. This unit was replaced by a conical adapter for attachment of the PS object to the core unit A . Test The sequence of the core engine's cut-off was simplified. The modified engine RD-108 designated 8D75PS cut itself off upon propellant burn-out without a final thrust stage. At T+100 seconds (T-0 is the moment of lift-off) the strap-on booster engines 8D74PS went over to the first intermediate thrust stage (60.2 tonnes of thrust) in order to push the procedure for dropping off the strap-on boosters up to a higher altitude and decrease dynamic forces on the lightened central sustainer during separation . The 8D74/75 motors of the R&D test version of the 8K71 and respectively the corresponding 8D74PS/75PS engines were still in the early stage of their development and manufacture. They had performance characteristics that were somewhat lower than their original specification. Bit by bit during flight and static tests, numerous changes and improvements were introduced into the engines' design. For the first time the 8D75PS engine's turbopump used hydrogen peroxide with a strength of 82 per cent to drive it instead of 80 per cent as with the earlier R&D engines 8D74/75. As well as the warhead and radiopackage, the system of vibration measurement RTS-5 (Radio Telemetry System - 5) was removed from the central sustainer  of the launch vehicle 87K71PS. The weight of propellant was somewhat decreased and the total weight of the 8K71PS became less than that of the 8K71 ICBM (see Table 1.1).
8A91 The Sputniks LauncherDuring 1956 and 1957, the R-7 ICBM-based two-stage launch vehicle 8A91 was designed by OKB-1 expressly for orbiting satellite Object D. The 8A91 launcher was fired twice - on 27 April 1958 and on 15 May 1958. The first attempt ended in failure when the launch vehicle broke up at T+88 seconds after blast-off. 8A91 was powered by the next versions of the RD-107/108 motors designated 8D76 and 8D77 respectively. Also these engines were at an early stage of their development. But after tests and revisions of the R&D engines 8D74/75, some further changes were made to them, an important innovation being that the fuel consumption for feeding the chamber cooling jacket was decreased. As a result the specific impulse increased. The design of the chamber's injector heads was changed. The central sustainer engine 8D77 produced 15 per cent less thrust than the operational motor 8D75. After T+85s of the ascent the strap-on booster engines 8D76 went over to the first intermediate thrust stage for the same reason as those of 8K71PS. The sustainer tank's operational pressure was reduced and nitrogen consumption for pressurisation of the core tanks fell about 15 per cent. Upon examination of the results of the first trial launches, the operational pressure in the strap-on tanks was reduced too and nitrogen consumption for booster tank pressurisation was 10 per cent less than in the test version 8K71 ICBM and the 8K71PS launch vehicle. The radiopackage was again absent on the top of the central sustainer. The core engine 8D77 shut down when its propellants were used up without a final thrust stage. After the two launches of 1958, the 8A91 vehicle was not used again. The next R-7 based space carrier vehicle became the three-stage Moon rocket 8K72, which is the subject of Part 2 of 'Soviet Rocketry that Conquered Space' and is due to appear in a forthcoming issue.