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  AUTHOR:                                          SMS: B08064      
  G. MARINELLI           BFS PROGRAM NOTE                           
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  ORG/PHONE:          OPS NOTE ( )  USER NOTE (X)  DATE: 06/01/81   
  382-510     5528         RELEASE NOTE ( )        REV:  09/27/89   
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  OI/FLIGHT EFFECTIVITY:          USER AFFECTED:                     
  STS-2 & SUBS                    CREW (X)  GROUND ( )  DUMP ONLY ( )
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            MAJOR SOFTWARE AREA:             OPS MODES AFFECTED:     
 BSL( ) BSS(X) GNC( ) SEQ( ) SM/SP( ) IPL( ) 1, 3, 6                 
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  SOFTWARE SUB-AREA: BUS, RM                                          
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  PRINCIPAL FUNCTIONS: MG038101/3.1.9.1                               
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  TITLE: TWO ON TWO SPLIT SET OF FLIGHT CRITICAL STRINGS              
                                                                      
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  DESCRIPTION:                                                        
                                                                      
   TRACKING PASS IS BASED ON THE STATUS OF 4 FLIGHT CRITICAL          
   STRINGS.  BFS MAKES NO ASSOCIATION BETWEEN FC STRINGS AND          
   PASS GPC'S.  DURING OPS 1, 3, AND 6, 25 HZ TRANSFER DATA           
   IS TRANSMITTED ONCE PER MINOR CYCLE BY PASS ON FC 5-8,             
   CORRESPONDING TO STRINGS 1-4.  THE DATA FROM ALL ENABLED           
   STRINGS IS COMPARED FOLLOWING INPUT.  BFS CONTINUES TO             
   LISTEN ON THOSE STRINGS WHOSE TRANSFER DATA AGREES.  IF            
   TWO INDEPENDENT SETS OF AGREEING STRINGS ARE DETERMINED            
   THROUGH COMPARISON OF THE TRANSFER DATA, BFS SUSTAINS              
   TRACKING ON STRING 1 AND ITS SET PARTNER.                          
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 USER RESPONSE:                                                       
                                                                      
   FROM THE BFS TRACKING STANDPOINT, IT IS PREFERABLE TO              
   ASSIGN STRINGS 3 AND 4 OR 2 AND 4 TO THE SAME GPC IF IT            
   BECOMES NECESSARY TO ESTABLISH A 2_OR                              
   3_PRIMARY_GPC_REDUNDANT_SET.                                       
   FOR THE 3 GPC REDUNDANT SET, THIS PREVENTS BFS FROM                
   FOLLOWING A SINGLE GPC WHICH HAS FALLEN OUT OF THE RS.             
   FOR THE 2 GPC REDUNDANT SET, BFS WOULD TRACK STRINGS 1 AND         
   2 OR 1 AND 3.                                                      
   THE ABOVE RECOMMENDATION DOES NOT TAKE INTO                        
   CONSIDERATION OTHER EXISTING SYSTEM FAILURES.                      
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 CONCURRENCE:                           APPROVAL:                    
 RI:<S> C. PURTELL         DATE 09/27/89                             
  --------------------         ---------                             
 SSD: SAM ANKNEY           DATE 11/02/89                             
  --------------------         --------- M.C. GREMILLION    11/09/89 
 PF MGR:DAVID STEPHENSON   DATE 11/02/89------------------- -------- 
        -----------------      --------- CHAIRMAN, SASCB      DATE   
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