Nike System Component Development Jan 1946 - Jan 1947
The period essentially covering the year 1946 was deliberately devoted to the independent development of major system components, which was pushed forward on many technical fronts. It included laboratory simulator work and culminated in the first real experimental missile firings on the test range.
The 1946 NIKE was to be designed and fabricated for uncontrolled vertical flight tests to provide information on launching methods, booster propulsion, separation, motor performance, and flight stability. While the preliminary design studies were being reduced to practical application in the form of the 1946 NIKE missile, work was continued on the development of ground guidance components for installation and test in later missiles.Radar
To gain experience with monopulse tracking in the X-band region, an SCR-545 radar was converted to this new type of operation. In making this conversion, the antenna system was replaced by a monopulse rapid-fading (RF) system with a lens antenna. The performance of the SCR-545 mount for the monopulse system was improved by the addition of tachometer feedback in the angle servos.
As originally envisioned in the AAGM Report, the target and missile tracking radars were to be combined into a single mount with two separate lens antennas mounted on a rotatable beam structure on top of a common radar van. The azimuth of the target radar beam was to be adjusted by moving the entire beam structure, and the difference between the target azimuth and the missile azimuth was to be adjusted by moving the missile radar antenna with respect to the beam structure. This original plan was dropped mainly because of the excessive power requirements to meet the slewing rates and because of the problem of one antenna assembly shadowing the other when mounted in such close proximity.
Consideration was then given to the idea of having both antennas rotate in azimuth with respect to the beam structure and making the beam structure rotate only as required to prevent shadowing. Further study of this dual mount, however, revealed serious drawbacks, such as severe requirements of the mechanical rigidity of the top-heavy rotating super-structure, bending of the beam assembly due to solar heat, and the problem of placement of a common vehicle so that radar visibility is obtained to all launchers without jeopardy of best target coverage of the defense zone.
To avoid these difficulties, it was finally decided to abandon the dual mount structure and accept completely separate mounts as a more attractive solution. With each track antenna assembly mounted on a separate low-slung flat bed trailer, both mounts must be accurately leveled and an adjustable parallax correction provided in the computer.
The basic power supply for the radar was standardized at 400 cycles per second rather than the usual sixty cycles per second because of saving in weight and size for power equipment. Experimental studies of the acquisition radar resulted in the choice of S-band and in the raising of the power requirement of the tunable magnetron tube to 1,000 kilowatts.Computer
In a system such as NIKE, the characteristics of the guidance computer are of critical importance during the last few seconds before intercept. It was recognized that one of the terminal accuracy problems centered around the possibility of filtering out the tracking noise without unduly delaying the recognition of a true target maneuver. Some thought was given to determining the optimum steering function by hand computations; however, it was soon realized that the enormous number of sample computations required would make such a procedure virtually impossible.
Consequently, early in 1946, an analog device called the Computer-Analyzer was built specifically to analyze the end game. This apparatus solved the guidance equations in two dimensions so that lateral miss could be studied under wide variations in the steering order equations, the noise level, the smoothing and stability parameters, and the magnitude, nature, and timing of target evasion. Over 7,000 runs, comprising nearly 700 distinct situations, were made and analyzed. From these runs emerged optimum smoothing, prediction, and order-shaping techniques, in addition to a large body of knowledge concerning the effects of various kinds of target maneuvers. The circuits of the R&D computer were based on this analysis.
By the end of 1946, the computer design had advanced to a block diagram stage from which the detail design could be made. The computer philosophy adopted was quite different from that conceived in the original AAGM Report, but most of the basic plans were retained in modified form. To simplify the prediction process, the coordinate system of the computer was changed fram the polar radar form to Cartesian earthbound axes, oriented according to the pre-launch axis bearing of the missile gyro. This presentation was more adapted to overcome the parallax problems inherent to the two separate antenna stations for missile and target radars, and the considerable separation required by the radar and launching sites. It also afforded greater flexibility in choosing the most advantageous trajectory shape, as well as easing the resolution of steering orders into their pitch and yaw ccmrponents. These changes also necessitated the introduction of a new method of trajectory shaping to approach the most efficient flight path.
Detail design studies were started on the subjects of steering order computer, pre-launch computer, burst computer, sequence of operation, component accuracies, voltage regulation, standardized feedback amplifiers, radar-to-computer data transmission system, and visual means for displaying the attack.NIKE-46 Missile
At the beginning of the 1946 development period, a decision had been made to proceed with the manufacture of fourteen experimental missiles for flight test at WSPG in the fall of the same year. The first four of these were to be ballasted wooden dummies simulating a missile in shape and inherent dynamic properties only. In addition to furnishing much needed drag information, they were destined to prove booster propulsion and separation or to show what unexpected problems might arise. The other ten were to be real missiles in the sense that they would be equipped with a self-sustaining power plant. No attempt was yet to be made at roll stabilization. Neither would these missiles be controlled in pitch or yaw; their fins were to be fixed. The purpose of the latter ten rounds was to study power plant operation and flight stability under power.
Wind-tunnel tests of the 7.5 per cent model of the NIKE missile were continued at APG to cover an intermediate speed (Mach number 1.28), in addition to the higher one (Mach number 1.72) previously explored. These experiments were supplemented by subsonic tests on other scaled models in the ten-foot wind tunnel at the California Institute of Technology. Lift, drag, and stability, as well as aileron and control-fin hinge moments, were determined and found to be generally satisfactory.
The design of the first test missile was frozen by the middle of February, 1946. This design embodied a cruciform delta wing canard configuration, the details of which have already been discussed. Though basic requirements of the concept were maintained during the engineering and fabrication of the 1946 missile, certain revisions were made in the light of actual design development and in the adaption of the missile to its uncontrolled test program functions.Booster Assembly
Among the principal changes was the use of four parallel Aerojet solid fuel (Paraplex) rockets with uncanted nozzles, designed to deliver a thrust of 22,000 pounds each for two seconds and impel the 1946 type of test missile to supersonic velocity. The early designs-based on the grouping of eight T10E1 11,000-pound thrust rocket units-were discarded at the end of March 1946, when the development of the larger Aeroject units had sufficiently progressed for incorporation in the 1946 program. Development of the 22,000-pound-thrust booster rocket for for the NIKE-46 was initiated at the Aerojet Engineering Corporation in April 1946, under a subcontract from DAC. AeroJet was to furnish 56 boosters, to be assembled in clusters of four each by DAC. Preliminary development of the booster assembly was completed in July 1946 and static proof firings were started in the following month. Out of a total of 68 full-scale firings, eight failures were experienced, two of which occurred at WSPG. One additional failure occurred near the end of boost in a WSPG launching, when the nozzle of one unit was burned through. Although the test results indicated a need for further improvement in reliability and reproducibility, booster performance gave promise of ultimate fulfillment of the desired degree of reproducibility.
The propellant finally selected for the booster rocket consisted of a single perforated grain Paraplex-base fuel and potassium perchlorate oxidizer. The particular formulation of constituents used for this application was designated as AK-6 propellant (formerly called PF-6), having the following composition by weight: Potassium Perchlorate, 73%; Paraplex P-10, 26.85%; and Tertiary-Butyl Hydrogen Peroxide, 0.15%. The ignition element consisted of granular black blasting powder contained in a plastic capsule, together with two ordinary electric blasting squibs which served as initiators.Power Plant
The power plant for NIKE-46 missiles comprised a bi-propellant, regeneratively cooled, liquid rocket motor. Developed and manufactured by AeroJet as Model X21AL-2600, the 40-pound motor was designed to produce a sea level thrust of 2,600 pounds for 21 seconds. A fuel mixture containing about 65% aniline and 35% furfuryl alcohol was oxidized by red fuming nitric acid. The liquid load consisted of 220 pounds of oxidizer and 80 pounds of fuel. The propellant tanks were constructed as integral structural parts of the missile fuselage.
Development of the rocket engine for the 1946 NIKE was initiated at AeroJet late in 1945, under a subcontract from DAC. AeroJet was to furnish rocket motors, control valves, and pressure regulators (for pressure feed system) for ten missiles. Other components of the power plant, including tanks, lines, and starting valve, were designed and fabricated by DAC. The development tests were completed by the end of April 1946.
The design of the prototype assemblies was predicated on the final version of the respective experimental assemblies. The prototype motor and control valve were successfully fire-tested on the thrust stand during May. Final proof fire tests were made in a mockup of the actual NIKE installation, using the field firing sequence. Test results were equal to specification requirements and the design was declared adequate. The complete power plant was then subjected to a full-scale static test at WSPG. Acceptance tests on the tenth motor were completed in September 1946.Structural Arrangements
In the structural arrangements, the delta shape was selected for both the control fins and main fins to improve the lift-to-drag ratio, and the control fins were moved farther forward along the missile body than was suggested in the basic plan. The design studies revealed that considerable advantage could be gained in the use of two spherical tanks for the high-pressure gas storage, mounted between separate tanks for the oxidizer and the Fuel. With this arrangement, the space around the spheres could be used for Improved wing-attach structure and power plant components, and the aft section could be removed as a unit for easy access to the motor installation. The wing structure was designed, in conjunction with the booster assembly, to reduce the moment arm of the applied thrust of individual booster cylinders.
After allocations had been made for missile components, the length of the missile was increased from the proposed 19 feet to 19 1/2 feet in order to provide additional warhead space. The proposed warhead was first divided into two units, one to be located in the nose section and the other in the aft section. On the basis of fragmentation tests, it was later decided to divide the warheads into three sections-one located in the nose section, another in the middle section forward of the oxidizer tank, and the third in the afterbody of the vehicle forward of the motor installation. Space intended for the warheads, control mechanisms, and radio equipment of the final missile was used for instrumentation and beacon radio installations in the NIKE-46.Instrumentation
All experimental missiles were instrumented in an effort to gain as much quantitative performance information as feasible from each and every flight. The R&D design philosophy was governed by a decision that missiles were never to be fired as mere test vehicles but as steps in the evolution of the eventual weapon. Consequently, instrumentation had to be accommodated where space could be found. During the early stages of the test program when no control equipment or warheads were carried in the missile, there was sufficient room for internal instrumentation. However, as development progressed and more control mechanisms were carried in test flights, less space remained for instrumentation. In the final version, which included warheads, no internal space was left and external instrumentation had to suffice.
The original program called for simple missile-borne instrumentation to record linear accelerations and rolling motion in flight of the powered test missiles. Telemetry was expected to emerge eventually as the ultimate solution for future missile-flight test-recording work; however, none of the missile telemetry development programs then being pursued had progressed far enough to produce a reliable apparatus that would fit into the NIKE test rounds at the time the NIKE-46 program was crystallized. Therefore, a conventional photographic system of recording instruments was used in the hope that a legible film might be recovered from the impact wreckage. No recording instruments were carried by the three dummy rounds. Each powered missile was equipped with a radar beacon to serve as a tracking aid.Launcher Equipment
The basic launcher arrangement, as taken from the AAGM Report, consisted of four vertical guide rails spaced at 90 degrees about the missile, but passing within the booster structure. As the booster cylinders-- originally eight T10E1 units-were supported outside the guide rails, the members had to be cantilevered from a rigid base. In later design development of the booster, when the T1OE1 rockets were replaced by four Aerojet 22,000-pound thrust motors, Further restrictions were placed on the size and location of the guide rails which could be accommodated within the booster structure. The length and cross-section of the rails were determined by calculating the cantilever length feasible for the moment of inertia of the members and consideration of the booster velocity and stability which would be obtained in the launcher at take-off.
The design of the mechanism for raising and lowering the rails was dictated by the availability of component equipment. This problem eliminated hydraulic mechanisms, and to a large degree restricted the kind of electric actuators which would be considered. A one horsepower electric motor was selected to drive a cable drum through a worm gear reducer.
The first such mechanical launcher, from which the 1946 series of test missiles were to be launched at WSPG, was built in the form of an assembly of four parallel steel rails of hollow rectangular cross-section welded to a pivoted root frame on which it could be tilted to a horizontal position for loading and raised for (nearly) vertical launching. During the launching operation, the missile would slide upward between the rails, guided by pins, while the boosters rode outside the rail quadrant spaces. Although the launcher proved adequate, it was subject to appreciable vibrations which were difficult to measure. The vibration problem was later eliminated in several steps of redesign of the launcher, all aimed at making it sturdier and simpler.