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Aviation History
1962
1962 - 0095.PDF
1GHT International, 18 January 1962 From this point on we are talking about a series of variations ,iund a basic design designated Atlas A. The A series was from .; start a research and development project; because, despite the timism of both manufacturer and customer, the ICBM was still from maturity. The enormity of the problems facing the <igners was not exaggerated by the Von Neumann committee, J accordingly their recommendations were followed. Convair came the prime contractor, with the responsibility for building e structure of the missile and for the assembly and test of com- . -ted missiles under the technical management direction provided the AF Ballistic Missile Division and Ramo-Wooldridge. The ; dance problem had been studied for some time at the Masssa- msetts Institute of Technology under a group directed by Dr L narles Draper. Production of the first airborne guidance system arid ground transmitters passed to the General Electric Company, ar.d the computer section was made by the Burroughs Corporation. On this page a description is given of the manner in which the huge tank is fabricated from special steel strip. The strips are first bent into rings, which are "stove piped" and welded as shown in a detail in the cutaway drawing on pages 90-91 Later all-inertial guidance went to the American Bosch Arma Corporation. General Electric produced the first nosecones— technically "re-entry vehicles"—joined later by Avco. This left the engine development to Rocketdyne, who got the largest single share of the money after Convair. The breakdown of money passed to the "associate contractors" up to mid-1959 was: Convair 22 per cent, Rocketdyne 17 per cent, GE guidance 11 per cent, GE re-entry vehicle 11 per cent, American Bosch Arma 6 per cent, Burroughs 3 per cent. The thousands of sub-contractors backing up the project collected 30 per cent, a massive sum giving some indication of the number of contractors involved. Structure As noted previously, the main structure is a pure monocoque cylinder divided into two tanks, the upper for liquid oxygen and the lower for RP-1 kerosine. Tests on aluminium riveted skins were disappointing, in that no sealant could prevent leakage at the joints. Convair turned to a specially developed cold- rolled austenitic steel (AISI grade 301), with a minimum tensile strength of 200,0001b/sq in. The ability of this material to be welded satisfactorily, its high strength: weight ratio, toughness, and resistance to temperature extremes made it eminently suitable for a balloon structure. The stainless-steel sheets are rolled to very 'ose tolerances at the factory, and delivered to Convair in long I; ;>ils 36in wide. After inspection, strips about 10ft long are J tt-welded together and reinforced with a backup strip spot- ' elded on both sides of the butt joint. The circular bands formed in s way are held in hoop fixtures and lap-welded together, starting ™ the nose, until the 23-section balloon is completed. Gauge 95 thickness starts at O.OlOin at the nose, increasing to 0.020in at the first bend. In the constant-section part there are further increases, but no gauge exceeds 0.040in. Tooling for the tanks is relatively simple, although the welding fixtures employed are elaborate. The forward bulkhead is of unstiffened butt-welded petal construction, while the aft closure is made up from bands similar to the tank sides, stiffened externally to take the loads from the sustainer engine. The tanks are then held at slightly less than lOlb/sq in, which straightens out all the wrinkles and dents. After the fabrication hoops are removed the tanks are ready for static-pressure tests. The entire tank is erected in a tower and partially filled with water. The volume above the fluid is pressurized to "well in excess of flight pressure" (601b/sq in RP-1, 261b/sq in lox) to detect leaks. From this point on, the pressure is never allowed to drop below 61b/sq in. This same basic structure is used on all models of Atlas, except for different nose- skin thickness on the space boosters. According to Convair, a comparable structure of chemical-milled, butt-jointed 2014 alumini um alloy would be more expensive to produce and repair. The forward adapter for the re-entry vehicle varies from series to series to accommodate the different types of nosecone. The boost section, which slides off on rails beneath the tanks, is of conventional semi-monocoque construction stiffened by external stringers. It encloses the whole of the propulsion system, and other systems are housed in long lateral fairings on either side of the lower (RP-1) tank. Propulsion Development and production in the US of large liquid rocket engines stemmed from a 1947 contract awarded to North American Aviation for the XB-64 (later SM-64) Navaho. The missile was to be a long-range, wing-supported ramjet boosted to supersonic operating speed and altitude by a large liquid-propel- lant rocket. This challenge led to the founding of a new North American division called Rocketdyne. The original Navaho booster used alcohol and lox and produced 75,0001b thrust. In principle it borrowed heavily from the V-2, with a double- walled thrust chamber and a hydrogen-peroxide steam generator for driving the propellant turbopump. But in detail the engine incorporated several departures from German technique. The thrust chamber was provided with improved cooling for the higher heat-transfer rate, a single injector replaced the 18 used on the V-2, and turbopump performance was considerably improved. Reliability compared very favourably with V-2, giving some measure of the advances made in design: V-2 engines tested at the White Sands proving ground showed a life expectancy of 10 to 15 short firings; but an early Navaho unit made 115 firings. Navaho II followed, and this specification required a cluster of two uprated versions of the earlier engines developing 120,0001b thrust. This was the key development link to the engines used today. Basically the new engine was lighter, performance was increased, and it was much simpler. The geared-turbopump performance exceeded anything achieved before in mechanical design for the type used, with a suction specific speed of 18,000 and a propellant-pump operating speed of 5,500 r.p.m. Turbcpump power had previously been supplied by burning a third propellant in a gas generator, but the third propellant was now replaced by fuel bled back from the pressure side of the turbopump. This marked the beginning of "bootstrapping," popular in most later engines, where the high fuel pressures substitute for the auxiliary high-pressure source used for actuating valves in the system. It was also at this point that the first tubular-walled, regeneratively cooled thrust chamber was introduced. Navaho III, a still later and larger version, demanded a cluster of three 135,0001b engines, developing a total of 405,0001b thrust in one vast booster package. In this design thrust-chamber pressure was raised from 300 to 5001b/sq in. A switch was made from alcohol/water and lox, to kerosine and lox, showing an improve ment in specific impulse from 267 to 286 expressed at optimum sea-level expansion from a 1,0001b/sq in chamber. The power requirement for the turbopump rose to 2,400 s.h.p., a big jump from the 835 h.p. of Navaho I. Combustion temperature in the regeneratively cooled chamber increased to nearly 6,000°F. Other advances were the hinged thrust chambers for vehicle thrust-vector and roll control (on Atlas the complete engine gimbals) and a whole host of parallel advances in theory, materials and in such equipment as the large, flexible high-pressure propellant lines and thrust-chamber actuators. None of this became operational, since Navaho was cancelled in 1957; but it was a foundation upon which the propulsion
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