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Aviation History
1960
1960 - 1119.PDF
PLIGHT, 22 July 1960 117 sion. The resulting viscous mixture is then cast into its chamberand cured to a hard rubbery solid. In the current missile a polyurethane propellant is employed, to which powdered metal isadded to increase the density and specific impulse and improve tensile, elongation and stress-relaxation properties. At present thedivergent nozzles are lined with graphite or molybdenum, but other refractories will be required for the propellants of higherspecific impulse which will be used in the more advanced Polaris. Thrust/weight ratio, and consequent launch acceleration, arehigher than those for previous ballistic missiles. In order to minimize length, and provide control about the roll axis, bothstages have four nozzles. Although it would increase the actuation forces required, work is in hand on a first stage with gimballednozzles; but control is at present exercised by vectoring the jet from each nozzle by means of a jetevator (a concave shroud lyingalongside the nozzle exit). In the neutral position the jetevators lie clear of the jet and produce no drag, but when the trajectorymust be corrected one or more shrouds may be hydraulically positioned to provide the required deflection for the correct time.Altogether the system has worked excellently, and its installed weight is quite low. With regard to guidance, it is no exaggeration to say that theFBM system poses exceptional problems. It is a sine qua non that the exact launching position of each missile must be known.In fact, its precise position must be plotted from the moment the submarine slips her moorings at her home base until the cut-offof second-stage propulsion and the start of ballistic flight. Since these two events may be separated by several weeks, it is clear thata simple inertial system would introduce unacceptable errors. There are accordingly three distinct systems, all integrated toenable the missile to know precisely where it is at all times. Navigation of the submarine is effected by SINS (ship's inertialnavigation system) by the Sperry Gyroscope Co, in consultation with MIT; also participating in submarine navigation is theAutonetics Division of North American Aviation, whose pure- inertial equipment has been used by earlier nuclear submarinesduring prolonged submerged passages. Owing to the long periods FBM SUBMARINES SSB (N) 598 599 600 601 602 608 609 610 611 Name George Washington Patrick Henry Theodore Roosevelt Robert E. Lee Abraham Lincoln Ethan Allen Sam Houston Thos. A. Edison John Marshall Displacement (tons) Sur- faced 5.400 5,400 5.400 5,400 5,400 6,900 6,900 6.900 6,900 Sub- merged 6.700 6,700 6,700 6,700 6,700 8,600 8,600 8,600 8,600 Length (ft) 380 380 380 380 380 410 410 410 410 Launched 9.6.59 22.9.59 3.10.59 18.12.59 15.5.60 1960 1960 Comm'd 30.12.59 2.5.60 mid-60 autumn 60 early 61 1961 1961 15 Heat exchanger 16 Circulation pumps 17 Propulsion turbines 18 Reversing gear External 19 Retractable bollards in ten positions 20 "Sail" 21 Stabilizer 22 Control position (ship surfaced) 23 Hatch to deck 24 Missile hatches 25 Reactor installation hatch 26 Radar scanners (?) 27 Control surfaces 28 Multi-blade propeller Note: In addition to the above, three ships are funded, three more authorizedand six planned. of time involved, the inertial position has to be refined periodicallyby external references. One of these involves the'tracking of celestial bodies, the accuracy of which will be improved when allthe Transit satellites are in orbit. It is reasonable to assume that some form of ground radio system, such as Decca, could also beemployed in certain parts of the world. These checks of the inertial position might require a bit of the submarine to projectabove the surface, but one can imagine submerged beacon systems which would not. Precise ship position, speed and direction, and target data, arefed to the fire-control system, developed by GE's ordnance depart- ment. The system is fully transistorized and includes both analogueand digital computers which verify and transfer complex data with microsecond delay. As well as providing the link between naviga-tion of the parent vessel and that of the missile, the fire-control establishes true north, local vertical, allowance necessary for"geographic anomalies" and final corrections up to the point of firing (Polaris would ideally be launched from a stationary sub-marine). Final data are passed through an umbilical cable, dis- connected during the launch sequence. Structural deflection ofthe submarine's hull has to be allowed for in the alignment between critical elements of the fire-control with the launch tube concerned.In any case the two are placed as close together as possible (see cutaway drawing of ship). MIT developed the airborne part of the guidance system,assisted by GE who, together with a team headed by Hughes Aircraft and including Minneapolis-Honeywell, make productionsystems. American publications have suggested its weight is approximately 2001b>—under one-quarter that of Thor. This slash-ing reduction in payload is backed up by the fully tested, radical warhead, of 0.5 MT (500kT) yield. Although this is rather lower r Iliffe & Sons Ltd 1960 #•*'"•
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