 +_____________________________________________________________________
  AUTHOR:                                          SMS: B21015      
   R. MENARD             BFS PROGRAM NOTE          DR:  108583      
 ____________________                             __________________
  ORG/PHONE:          OPS NOTE (X)  USER NOTE ( )  DATE:            
   (310) 922-1692          RELEASE NOTE ( )           6/17/93       
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  OI/FLIGHT EFFECTIVITY:          USER AFFECTED:                     
           OI-21, 22              CREW ( )  GROUND (X)  DUMP ONLY ( )
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            MAJOR SOFTWARE AREA:             OPS MODES AFFECTED:     
 BSL( ) BSS( ) GNC( ) SEQ( ) SM/SP(X) IPL( )       OPS 3             
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  SOFTWARE SUB-AREA: S-BAND ANTENNA MANAGEMENT                        
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  PRINCIPAL FUNCTIONS: MG038119/3.2.1.2.5.2                           
                       MG038106/3.3.6-1A                              
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  TITLE:                                                              
          POSSIBLE LOSS OF COMMUNICATIONS ON 301 TRANSITION           
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  DESCRIPTION:                                                        
 WHEN THE BFS TRANSITIONS TO MAJOR MODE 301 FROM OPS 0, IT IS POSSIBLE
 TO LOSE COMMUNICATIONS FOR UP TO 2 SECONDS.  COMMUNICATION LOSS      
 OCCURS BECAUSE THE SBANDAM MODULE CALCULATES THE LINE OF SIGHT VECTOR
 TO THE TDRS AND SELECTS THE APPROPRIATE ANTENNA BASED ON STALE       
 NAVIGATION DATA LEFT OVER FROM MAJOR MODE 106 OR FROM A PREVIOUS     
 MAJOR MODE 301 TO OPS 0 TRANSITION.  LOSS OF COMMUNICATION WILL      
 CORRECT ITSELF AFTER 2 SECONDS WHEN THE NAVIGATION MODULE UPDATES THE
 SHUTTLE COORDINATES FOR USE BY THE SBANDAM MODULE.  THE SBANDAM      
 MODULE WILL THEN CORRECTLY DETERMINE THE APPROPRIATE ANTENNA AND     
 RESTORE COMMUNICATIONS.                                              
                                                                      
                                                                      
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  USER RESPONSE:                                                      
                                                                      
   USERS SHOULD BE AWARE OF A POSSIBLE LOSS OF COMMUNICATIONS WHICH   
   WILL BE RESTORED IN 2 SECONDS.                                     
                                                                      
                                                                      
                                                                      
                                                                      
                                                                      
                                                                      
                                                                      
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 CONCURRENCE:                           APPROVAL:                    
 RI: <S> J. AGRES          DATE 06/23/93                             
     --------------------      ---------                             
 FDSD:   W. R. PRUETT      DATE 07/30/93                             
      -------------------      --------- DARRELL E. STAMPER 08/03/93 
 PF MGR:  JAMES BAGWELL    DATE 07/30/93------------------- -------- 
         MOISES N. MONTEZ       07/30/93 CHAIRMAN, SASCB      DATE   
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