Air Force Bases

NIKE - Preliminary Design Studies

The latter half of 1945 and early 1946 was spent in planning the detailed requirements of the various components and in making early design studies and tests. The DAC came into the pictice at this time and began a complete study of the aerodynamics of the missile as proposed in the initial AAGM study. Booster design was also started at this time by the AeroJet Manufacturing Company.

One of the first deliberate departures from the original system recommendations, accepted in the fall of 1945, concerned the radar tracking system. A study of the angular accuracy requirements of the tracking radars and echo fluctuation measurements on metal-painted free balloons and airplanes in flight revealed that conical lobing methods would be inadequate to yield the required smoothness and accuracy of data. Radars had been used extensively during the war, not only for surveillance and detection, but also for the pointing of antiaircraft guns. Yet none of these was sufficiently accurate for the problems posed by the guided missile. Since the standard lobing radars developed during the war were limited by rapid pulse-to-pulse fading, it was obvious that a more accurate radar would have to be developed specifically for NIKE. The smoothness of output would have to be such that target acceleration maneuvers could be promptly detected and countered without long delays necessitated by smoothing rough data. Hence, a decision was made to develop a radar system which would provide an independent measurement of angular error on each pulse (monopulse type) and thus eliminate angular perturbations caused by rapid pulse-to-pulse fading.

Two different monopulse systems were studied. One was a phase comparison system, and the other an amplitude null system, in which the rapid fading signals received from the two-lobed beams are subtracted from each other to obtain the angle error signal. The latter method was decided upon because it was simpler and more readily mechanized.

Of other radar features, attention was focused on the problem of obtaining high transmitter power with a wide range of tunability to attain maximum protection from jamming. This study resulted in the development of 250-kilowatt X-band and 1000-kilowatt S-band tunable magnetrons for the NIKE and T-33 radars,

A missile model of 0.4 scale was built in order to measure its radar reflectivity. Tests with a K-band radar illuminating the model led to the conclusion that in reflection tracking a range of between 5O,OO0 and 100,000 feet could be attained with a radar peak power of 125 kilowatts at X-band, This would barely meet the original requirement of a 60,000 foot range for the missile. Meanwhile, it was found desirable to extend missile performance to 150,000 feet and the missile tracking range a like distance. To obtain a reliable signal from the missile by reflection tracking to this range would have required techniques too far beyond the state of the art. The only alternative was to place a beacon responder in the missile to insure a clear missile signal. There were a number of other equally important factors that justified the use of the beacon responder. First, the missile had to be acquired in the launcher despite the presence of strong ground echoes; second, at the separation of booster from the missile, both parts were likely to return equally strong reflection signals so that the booster could pull the radar off the missile; third, the flame during motor burning might cause tracking interference; and finally, during the end game the missile radar would have trouble distinguishing between the missile and target as the ranges became coincident. All of these problems were successfully solved by the responder, which an echo signal considerably stronger and different in frequency from any of the interfering signals.

Next to be considered were the problems connected with the design and operation of a suitable responder of very light weight. To obtain the features of a responder, it was only necessary to add a relatively small transmitter unit to the X-band receiver which was already required on board the missile to receive the steering and burst orders. Modulator circuits of the ground-to-missile communication system were constructed and successfully tested in the laboratory for performance.

Early in the design study phase, it became apparent that the actuators for the control surfaces would require servomechanisms whose speed and torque exceeded that of any type then available. Because of the wide range of aerodynamic stiffness encountered, it was also recognized that the servos would have to be stable over a range of gain of more than fifty to one. The actuators would have to operate fins whose aerodynamic hinge moments could be of the order of 2,000 inch-pounds in the case of roll, and 700 inch-pounds in the case of steering. Full deflection of fifteen degrees would have to be attained in about 0.1 second. A study of the problem indicated that it should be possible to fulfill these requirements with a hydraulic servo system governed by an electrically controlled valve. Since no valve was available to meet these requirements, a special development program was initiated to produce a series of hydraulic valves which were eventually used in all NIKE missiles.

As to the control scheme for the servo system, it was agreed that the main feedback would have to come from a free position gyro for roll control and from transverse accelerometers for the steering orders. Gyroscopes of various makes had already been developed for other purposes and mainly required the installation of suitable potentiometer pick-ups. Accelerometer transducers, however, were not currently available in a suitable range and with appropriate damping. Consequently, a program was initiated to develop a special NIKE accelerometer transducer with magnetic damping. The hydraulic servo power system comprising actuator pistons, pressure vessels, and plumbing could be recruited with minor refinements from the contemporary aircraft hydraulic art.

In the meantime, DAC had started an intensive study to determine the aerodynamic characteristics likely to be obtained from the missile configuration assumed in the AAGM Report. The advantages of the canard arrangement and the delta shape of the cruciform rear fins were soon confirmed and retained throughout the development period. The movable fins in the forward part, however, were redesigned. They were reduced in area, moved farther ahead toward the nose for greater leverage, and their shape was altered from trapezoidal to a twenty-three-degree semi-vertex angle delta for lower drag and smaller center of pressure shift. Wind-tunnel tests were then conducted on a scale model of the new configuration at a Mach number of 1.72 in the only supersonic facility then available; viz., the Ballistics Research Laboratory at Aberdeen Proving Ground. Though scanty in many respects, the test results gave the first directly applicable data concerning the aerodynamic behavior of this type vehicle in lift, drag, and pitching moment. Moreover, they partly confirmed and partly eased the conservative assumptions or restrictions adapted in the AAGM Report.

The NIKE missile structure was to be designed to provide adequate strength and rigidity wlth the least possible weight. Since a missile is expended on each flight, non-strategic materials were to be used wherever possible wlthout sacrificing the strength-to-weight ratio needed to obtain rapid acceleration during the boost phase and high maneuverability during the guided flight phase. Other factors influencing the missile body design were aerodynamic smoothness, warhead spray pattern, component packaging, and access to installations. Surface smoothness and the minimum practical thickness compatible wlth rigidity requirements were the main design criteria for the fins.

A preliminary design study of a practical missile structure dealt with such problems as weight estimates, center of gravity due to fuel consumption, fuel flow, and ease of fabrication and assembly. For ease of fabrication, the tank structures were changed to comprise two spherical air pressure tanks and two separate cylindrical tanks for acid and aniline fuel, respectively. This simplified the fin attach structure and facilitated tank testing and accommodation of accessories in functionally-grouped sub-assemblies. The electronic guidance compartment and center warhead were interchanged to improve balance. In the area of control fins and their mechanisms, staggered shafts for pitch and yaw fins were advocated. As to the rear body, a sturdy motor mount was envisioned, with its plumbing readily accessible.

On the basis of experience just being gained with WAC CORPORAL missiles undergoing tests at White Sands Proving Ground (WSPG), design studies of cooled and uncooled motors were begun at Aerojet Corporation.

The choice of a suitable and industrially procurable booster was narrowed down to two alternatives: one comprising eight ten-inch T-1OE1 rockets, and the other a quadruple cluster of thirteen and one-half-inch Aerojet rockets. Canting the rockets or their nozzles was considered as a possible means to reduce or avoid undesirable thrust moments. The booster-to-missile attachment was studied with a view to avoiding high loads and separation difficulties.

A continuing program of warhead design and experiments was carried on between BTL and BRL. The first proposed warhead consisted of a small tapered central cylinder of high explosive which would eject a mass of shrapnel pellets in a flat expanding disk-shaped sharer, whose velocity was essentially the missile's terminal velocity. Meanwhile, new data on small high-velocity fragmentation warheads made these appear more attractive from the lethality point of view and also because they allowed for the possibility of an effective tail chase. For the next four years, an experimental program was carried on to produce an adequately wide fragment beam, to obtain uniform velocity distribution over the beam, and to provide uniform break-up into Fragments of the double-wound wrap of wire which constituted the source of the lethal particles.

The design studies and decisions just discussed were reviewed in a planning conference on 28 January 1946, and the development program for the 1946 NIKE was established.