 +_____________________________________________________________________
 ] AUTHOR:            ]                             ] SMS: B27803      ]
 ] Kenneth Ayers      ]    BFS PROGRAM NOTE         ] DR:  109704      ]
 ]____________________]                             ]__________________]
 ] ORG/PHONE:         ] OPS NOTE ( )  USER NOTE (X) ] DATE: 09/24/97   ]
 ] BNA/(562) 922-3714 ]      RELEASE NOTE ( )       ]                  ]
 ]____________________]_____________________________]__________________]
 ] OI/FLIGHT EFFECTIVITY:        ]  USER AFFECTED:                     ]
 ] OI26, OI26B                   ]  CREW ( )  GROUND (X)  DUMP ONLY ( )]
 ]_______________________________]_____________________________________]
 ]           MAJOR SOFTWARE AREA:            ] OPS MODES AFFECTED:     ]
 ]BSL( ) BSS( ) GNC(X) SEQ( ) SM/SP( ) IPL( )]          1              ]
 ]_____________________________________________________________________]
 ] SOFTWARE SUB-AREA: NAV                                              ]
 ]_____________________________________________________________________]
 ] PRINCIPAL FUNCTIONS: SOD 80-0366/BFS Coding Standard A1             ]
 ]_____________________________________________________________________]
 ] TITLE: TAN(PI/2) GPC Error in AS_UPP_INIT for BFS                   ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ] DESCRIPTION:                                                        ]
 ]                                                                     ]
 ] For a due-east, rendezvous launch near T_GMTLO_REF (T_STATE less    ]
 ] than but within milliseconds of T_GMTLO_REF), a "TAN function too   ]
 ] close to singularity" error may occur in the AS_UPP_INIT calcula-   ]
 ] tion for ALP_DP.  The argument to the TAN function which may be     ]
 ] equal to PI/2 under these conditions is the following:              ]
 ]                                                                     ]
 ]     (THET - PHI_DP + AZ_DP) / 2                                     ]
 ]                                                                     ]
 ] The GPC error log will receive the following error: B1 (HAL/S sub-  ]
 ] routine error).  This error will also be visible in downlist.       ]
 ] Following the error, execution will continue at the point of inter- ]
 ] ruption with no further effects.                                    ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ] USER RESPONSE:                                                      ]
 ]                                                                     ]
 ] For due-east rendezvous missions, be aware that this error condition]
 ] exists but has no adverse affects on the software.                  ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ]CONCURRENCE:                           ]APPROVAL:                    ]
 ]BNA: <s> D. Corbin        DATE 10/20/97]                             ]
 ]    --------------------      ---------]                             ]
 ]ASD:  ERIC C. BINGHAM     DATE 11/13/97]                             ]
 ]    --------------------      ---------] DARRELL E. STAMPER 11/13/97 ]
 ]PF MGR:   M. N. MONTEZ    DATE 11/12/97]------------------- -------- ]
 ]       -----------------      ---------] CHAIRMAN, SASCB      DATE   ]
 ]_____________________________________________________________________]
 @
