 +_____________________________________________________________________
  AUTHOR:                                          DR:              
  TALBERT                PASS PROGRAM NOTE            46510         
 ____________________                             __________________
  ORG/PHONE:          OPS NOTE ( )  USER NOTE (X)  DATE: SEPT. 1987 
  ENG/282-8453             RELEASE NOTE( )         REV A: 06/14/89  
 ___________________________________________________________________
  OI/FLIGHT EFFECTIVITY:          USER AFFECTED:                     
  REL 19 AND SUBS                 CREW (X)  GROUND ( )  DUMP ONLY ( )
 ____________________________________________________________________
         MAJOR SOFTWARE AREA:        OPS MODES AFFECTED:             
 SSW ( )  GNC (X)  VU ( )  SM/PL ( ) G3                              
 _____________________________________________________________________
  SOFTWARE SUB-AREA:  GUID                                            
 _____________________________________________________________________
  PRINCIPAL FUNCTIONS: 4.209, 4.211                                   
 _____________________________________________________________________
  TITLE:                                                              
  TARGET MISS RELATED TO TIG IN THE PAST                              
 _____________________________________________________________________
  DESCRIPTION:                                                        
                                                                      
  THE FOLLOWING TWO REQUIREMENT ISSUES ARE ASSOCIATED WITH TIG IN THE 
  PAST.                                                               
                                                                      
  A. IF A TARGET LOAD IS DONE WITH TIME OF IGNITION (TIG) IN THE PAST 
     IN MM 301 AND A TRANSITION IS MADE TO MM 302, GUIDANCE WILL      
     PROPAGATE THE STATE VECTOR FROM THE TIME OF THE LOAD TO THE      
     STATE VECTOR TIME AT THE TRANSITION TO MM 302. THIS PROPAGATION  
     MAY BE INACCURATE DUE TO: 1) THE LARGE INITIAL STEP IT MAY TAKE  
     (THE INCREMENT OF TIME "DELTA T" WILL BE THE ELAPSED TIME BETWEEN
     THE TIME OF THE LOAD AND THE TIME OF THE MM 302 TRANSITION)      
     AND 2) THE FACT THAT NO J2 EFFECTS ARE TAKEN INTO ACCOUNT.       
     THIS PROPAGATION WAS DESIGNED FOR DELTA T'S EQUAL TO             
     APPROXIMATELY 1 SECOND.                                          
                                                                      
     THE ERROR IN THE PROPAGATION IS PROPORTIONAL TO THE MAGNITUDE    
     OF THE DELTA T DESCRIBED ABOVE. (OBSERVED TO BE APPROXIMATELY 13 
     NAUTICAL MILES IN RANGE FROM ENTRY INTERFACE TO THE LANDING SITE 
     AND A FLIGHT PATH ANGLE MISS OF .00037 DEGREES PER MINUTE OF     
     DELTA T.                                                         
                                                                      
     NOTE THAT THIS IS A REQUIREMENTS PROBLEM AND PROCEDURALLY TARGET 
     LOADS WITH TIG IN THE PAST IN MM 301 SHOULD NOT BE ALLOWED.      
     CR 39785 AND DR 44754 FIXED TIG IN THE PAST PROBLEMS ON STS-3    
     AND STS-4 FLIGHT SOFTWARE, BUT REQUIREMENTS DO NOT COVER THIS    
     ABNORMAL CASE.                                                   
                                                                      
  B. IF A LOAD IS DONE IN MM 301 PRIOR TO SCHEDULED TIG AND A PRO TO  
     MM 302 IS DONE AFTER SCHEDULED TIG, GUIDANCE WILL MISS THE TAR-  
     GET RANGE FROM ENTRY INTERFACE TO LANDING SITE (REI) AND FLIGHT  
     PATH ANGLE (GAMMA).  THE MAGNITUDE OF THE MISS INCREASES IN PRO- 
     PORTION TO THE DELTA T BETWEEN THE SCHEDULED TIG AND THE MM 302  
     PRO.  (DELTA REI APPROXIMATELY 19 MILES AND DELTA GAMMA OF       
 _____________________________________________________________________
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 +_____________________________________________________________________
                        SUPPLEMENTAL SHEET                            
                                                                      
 _____________________________________________________________________
  AUTHOR:                                          DR:              
  TALBERT                PASS PROGRAM NOTE            46510         
 ____________________                             __________________
  ORG/PHONE:          OPS NOTE ( )  USER NOTE (X)  DATE: SEPT. 1987 
  ENG/282-8453             RELEASE NOTE( )         REV A: 06/14/89  
 ___________________________________________________________________
  TITLE:                                                              
  TARGET MISS RELATED TO TIG IN THE PAST                              
 _____________________________________________________________________
  DESCRIPTION:                                                        
                                                                      
     APPROXIMATELY .0200885 DEGREES FOR A DELTA T = 4 MINUTES WAS     
     OBSERVED IN THE SDL).                                            
                                                                      
     NOTE THAT THE CR 39785 (LATE PRO TO 302) FIX MADE THE FLIGHT PATH
     ANGLE MISS MARGINALLY ACCEPTABLE. (FURTHER ANALYSIS IS BEING     
     DONE TO RESOLVE THE REQUIREMENT ISSUE.)                          
                                                                      
                                                                      
                                                                      
                                                                      
                                                                      
                                                                      
                                                                      
 _____________________________________________________________________
  USER RESPONSE:                                                      
                                                                      
  A. DO NOT PERFORM A TARGET LOAD WITH TIG IN THE PAST ON MM 301.     
                                                                      
     IF TIG IS IN THE PAST AND A TARGET LOAD IS NECESSARY, PRO TO MM  
     302 AND PERFORM THE LOAD.                                        
                                                                      
     IF THE TARGET LOAD IS DONE WITH TIG IN THE PAST IN MM 301, AFTER 
     THE PRO TO MM 302, RE-EXECUTE THE LOAD (ITEM 22 ON MNVR DISPLAY) 
     IN MM 302. ( THE LOAD WILL BE REJECTED IF TIG IS OVER 5 MINUTES  
     IN THE PAST.)                                                    
                                                                      
  B. IF THE PRO TO MM 302 IS DELAYED CONSIDERABLE AMOUNT OF TIME,     
     EXECUTE THE LOAD (ITEM 22 ON MNVR DISP) IN MM 302. (THE LOAD     
     WILL BE REJECTED IF TIG IS OVER 5 MINUTES IN THE PAST.)          
                                                                      
 _____________________________________________________________________
 CONCURRENCE:                           APPROVAL:                    
 IBM: WYATT COOPER         DATE 07/13/89                             
     --------------------      ---------                             
 SSD: SAM ANKNEY           DATE 07/14/89                             
     --------------------      --------- M.C. GREMILLION    08/20/89 
 PF MGR: MOISES N. MONTEZ  DATE 07/31/89------------------- -------- 
        -----------------      --------- CHAIRMAN, SASCB      DATE   
 ____________________________________________________________________
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