120 THE DEVELOPMENT OF WEAPONS SYSTEM REQUIREMENTS 



at launch. The results of such a process as applied to our 

 fictitious problem are shown in Fig. 2-42. 



This analysis shows that the allowable launching tolerance varies quite 

 widely, depending upon the launching range. The tolerances on heading at 

 launch are quite tight for very large or very small ranges. They are 

 comparatively liberal for intermediate ranges. For example, if missile firing 

 occurs from 20,000 ft range at 90° off the target's nose, an error of 12° is 

 permitted. The missile time of flight for this instance is 12 seconds. 



The usable minimum missile launching range is determined by the 

 requirement that the interceptor not pass closer than 1000 ft to either the 

 impact point or the target in order to preclude self-destruction. Using the 

 defined maneuvering capabilities of the interceptor, the minimum launching 

 range or breakaway barrier dictated by this requirement may be calculated 

 by graphical techniques similar to those used for the latmChing tolerance 

 determination. The result of such an analysis (for a nonmaneuvering 

 target) is shown superimposed on the missile launch zone diagram (Fig. 

 2-42). 



Thus the allowable missile launching ranges and angular aiming errors — 

 as limited by the characteristics of the target, interceptor, and guided 

 missile and the target avoidance problem — are determined for each angle 

 off the target. Note that the allowable angular launching tolerances are 

 appreciably smaller than an inspection of only the missile performance 

 diagram would indicate — 5° to 10° compared with 10° to 30° for the missile 

 itself (Fig. 2-6). This is a typical result of a study which examines the 

 guided missile performance in its expected tactical environment. It can 

 be seen that the allowable launching tolerances determine the required 

 accuracy of the AI radar and fire-control system. This is why the AI radar 

 designer must be certain the missile performance is defined for operation 

 in the expected tactical environment. 



Fire-Control System Parameters — Attack Doctrine. All the 



basic information needed for fire-control system specification is now 

 available. 



The fire-control system must be compatible with five requirements or 

 limitations: (1) minimum average penetration distance; (2) "around-the- 

 clock" launching capability; (3) collision vectoring; (4) missile launching 

 tolerances; and (5) interceptor maneuver limits. 



A modified form of collision guidance — known as lead collision — 

 provides a reasonable answer. For any tactical situation this guidance 

 system attempts to direct the interceptor on a straight-line course to a point 

 where the missiles may be fired with high kill probability. The straight-line 

 characteristic reduces penetration, reduces intc-ceptor maneuver require- 

 ments, and allows missile launching to take place at any angle off the 



