8-25] STABILIZATION REQUIREMENTS 439 



can sometimes be quite severe and in such cases their effects should be 

 studied as part of the systems design. 



8-25 STABILIZATION REQUIREMENTS 



The stabilization requirements vary for the search and track modes. 

 In search, a lack of space stabilization would allow the search pattern to 

 move with the interceptor from its preassigned space sector, and the desired 

 target might not be found. 



Deviations from true space stabilization in search are produced mainly by 



(a) Aircraft angular motions^^ 



(i) Dynamic antenna control loop errors 



(c) Incorrect commands to the control loops 



(d) Inaccuracies in the vertical reference 



The total deviation from true space stabilization that can be allowed is 

 related to the loss in target detection probability that it produces. ^^ Usually 

 0.25° to 1.5° deviation from the ideal space stabilized pattern can be 

 permitted. However, the deviation varies as a function of the search angle 

 with respect to the aircraft. 



In the tracking mode, antenna space stabilization is needed for several 

 reasons: 



(a) To prevent the course computer from operating on inaccurate 

 antenna motions due to interceptor space motion rather than target sight- 

 line motion in space. ^^ 



(^) To prevent the antenna beam from drifting off the target because of 

 aircraft motion during short periods when the radar signal fades. 



(<:) To prevent system instability caused by coupling of the interceptor 

 motion with its commands through resulting antenna space motions. This 

 is a form of positive feedback, because as the interceptor moves the antenna 

 in space, the antenna motion produces signals used by the computer to 

 direct the interceptor farther in the same direction. To prevent instability 

 in this positive feedback loop, it is necessary to have the loop gain ^^ always 

 less than unity. This is most important in systems using an autopilot. The 

 problems involved in providing the necessary isolation in the search and 

 track modes are discussed in the paragraphs that follow. 



"Another source of error may be produced, especially in some missile systems, from control 

 loop disturbance torques created by an unbalanced antenna undergoing large rotational space 

 accelerations. However, a detailed discussion of this is beyond the scope of the text. 



i^Detection probability is discussed in Paragraphs 3-9 to 3-14. 



i^Another source of error may be produced, especially in some missile systems, from control 

 loop disturbance torques created by an unbalanced antenna undergoing large linear or rota- 

 tional space accelerations. However, a detailed discussion of this is beyond the scope of the 

 text. 



2fThis includes antenna motion detectors, filters, computer, pilot or autopilot, aircraft 

 transfer functions, and the isolation factor provided by the closed, space stabilized antenna 

 control loops (See Paragraph 8-32). 



