94 THE DEVELOPMENT OF WEAPONS SYSTEM REQUIREMENTS 



and transmit this information to CIC for decision and target assignment. 

 Since there are 20 targets, a maximum time of 6 seconds per target is 

 permissible. During this phase, it is sufficient to know whether the targets 

 are high, medium, or low altitude. 



Requirements Dictated by Vectoring. During vectoring, inter- 

 ceptors are vectored to the measured altitudes of the assigned targets (for 

 the assumed system logic of the hypothetical example). A height-finding 

 error can limit system performance in the following ways. 



1. It can cause the interceptor to fly at an unnecessarily high altitude, 

 thereby degrading speed and maneuvering capability. 



2. It can cause the interceptor to approach the target with an altitude 

 differential which its weapon (assumed to be a guided missile) 

 cannot overcome. 



3. It increases the zone of probable target positions which must be 

 searched by the AI radar. 



The first limitation can be attenuated somewhat by the use of tactical 

 doctrine based on a prior knowledge of threat characteristics. For example, 

 if the probable threats are known to have a performance ceiling of 50,000 ft, 

 there would be little point in directing the interceptor to fly at 60,000 ft 

 even though the height finder indicated such an altitude. 



The second limitation must be related to weapon characteristics and 

 aircraft and fire-control system characteristics. An inspection of the missile 

 performance (Fig. 2-6) shows that the weapon can itself correct substantial 

 altitude errors by its maneuvering capability. For a weapon traVel of 3.2 

 n.mi. or more, altitude errors to 2 n.mi. can be corrected if the weapon is 

 fired horizontally. A further attenuation of the effects of altitude can be 

 obtained from the fire-control system. Following AI radar lock-on, the 

 pilot obtains a reasonably precise measurement of relative target elevation. 

 This may be used by the fire-control system to point the aircraft up or 

 down as required to eliminate an elevation error. Of course, the required 

 climb or dive angle must be compatible with aircraft performance character- 

 istics. 



The third limitation — the required AI radar search zone needed to 

 encompass the height-finding inaccuracies — is also most important. As will 

 be demonstrated later, the range performance of a radar system is strongly 

 influenced by the volume it must search. 



On the basis of these considerations, a height-finding error of approxi- 

 mately 0,5 n.mi. (3000 ft) standard deviation at a range of 75 n.mi. 

 represents a reasonable first approximation to the height-finding accuracy 

 requirement. This corresponds to a maximum error of about 1.5 n.mi. — 

 a value which is still within the guided missile performance capabilities. 



