130 THE DEVELOPMENT OF WEAPONS SYSTEM REQUIREMENTS 



2-28 



LOCK-ON RANGE AND LOOK-ANGLE REQUIREMENTS 

 DICTATED BY THE CONVERSION PROBLEM 



The establishment of the weapon firing range as a function of target 

 aspect angle completes the information needed to calculate lock-on range 

 requirements for the conversion probability of 0.825. Fig. 2-47 displays 



Distribution of 

 Vectoring Headings 



Perfect 



-Lead Collision 



Course 



f, Contours 



10 sec 

 800 fps 

 1200 fps 



RANGE (n. mi.) 

 Fig. 2-47 Interceptor System Model for Conversion Problem. 



the essential elements of the problem. If lock-on occurs at {R, d) the 

 heading error that must be corrected has two components: (1) the vectoring 

 uncertainty and (2) the difference between the correct collision-course lead 

 angle at {R, d) and the correct lead collision-course lead angle at {R, d). 

 We shall assume that the distribution of vectoring errors is centered about 

 the correct collision lead angle for point (i?, d). The error which is present 

 at lock-on must be reduced below the allowable 2° pilot bias error prior to 

 reaching the missile firing range at 10 seconds time-to-go. We shall assume 

 that the time available for reduction of the steering error at lock-on is equal 

 to the time available to an interceptor passing through the point {R, 6) on 

 a lead collision course prior to reaching the missile launch range. Fig. 2-47 

 illustrates the situation. Contours indicating the time from {R, d) to missile 

 release are shown, as well as a typical heading distribution at {R, d) which 

 will arise at lock-on. (The distribution of aircraft headings relative to a 

 perfect collision vectoring course is defined in Fig. 2-32.) 



The lead collision-course lead angle is a function of both time-to-go and 

 aspect angle. Fig. 2-48 illustrates the variation in lead-collision lead angle 

 as a function of time-to-go and aspect angle. For a given {R, d) value, the 

 lead collision-course lead angle always is less than the correct collision- 

 course lead angle. 



The time required to reduce an initial steering error is shown in Fig. 2-49 

 for various initial values of steering error. The primary factor contributing 



