2-15] ACCURACY OF THE PROVISIONAL AEW SYSTEM 83 



measurements be referenced to a fixed angular coordinate reference system. 

 Errors may be induced in the azimuth measurements by aircraft motions 

 if the AEW radar is not space stabilized. Therefore, the preliminary design 

 must consider how AEW aircraft motions affect the AEW radar system 

 measurements. If the effects are substantial, means must be provided for 

 correcting the errors thus introduced. For the purpose of this analysis it 

 will be initially assumed that stabilization errors do not degrade the angular 

 accuracy by more than 10 per cent. The effect of this assumption may be 

 examined in more detail when the operation of the system has been more 

 completely analyzed and understood. 



Time Delay Errors. A possible source of additional position error on 

 a moving target is the fact that time may elapse between the measurement 

 of target position by the AEW radar and the registration and use of this 

 information in the CIC. If the time delay is td, the amount of position 

 error is simply 



e = Vtd n.mi. 



where V = velocity of object being tracked. 



Since the data-handling system must process information at least as fast 

 as it is coming into the system, the maximum possible value of the time 

 delay would be approximately equal to the time, tsc, for the AEW fan beam 

 to make a 360° scan. For example, if the scan time were 6 seconds, the 

 maximum error against an 800 fps target caused by time delay would be 

 approximately 0.8 n.mi. For 1200 fps interceptors, this error would be 

 50 per cent larger or about 1.2 n.mi. 



Three courses of action are open to the designer with respect to this error. 

 (1) The error may be tolerated if it does not appreciably affect system 

 performance. (2) Scan speed and data processing speed may be increased 

 to reduce the error magnitude to an acceptable level. (3) The position 

 information may be up-dated by using estimates of velocity and heading 

 of the object being tracked along with a knowledge of the time delay, to 

 produce a term which cancels the time-delay error. 



For preliminary design of the overall AEW system, it will be assumed 

 that time-delay error does not increase the total position error by more than 

 10 per cent. The effects of this assumption upon system operation and the 

 detailed requirements of AEW radar can be examined when more is under- 

 stood about the interrelationships among various parameters of the air 

 defense system. At that time a decision can be made about the course of 

 action to be taken to correct the time-delay error. 



Summary of Assumed Accuracy Characteristics. For purposes of 

 analysis, the AEW^ radar is assumed to have the following characteristics: 



