 +_____________________________________________________________________
 ] AUTHOR:            ]                             ] DR:              ]
 ] J. ZOPHY           ]    PASS PROGRAM NOTE        ]      42640       ]
 ]____________________]                             ]__________________]
 ] ORG/PHONE:         ] OPS NOTE ( )  USER NOTE (X) ] DATE: SEPT. 1987 ]
 ] IBM/282-8409       ]      RELEASE NOTE( )        ] REV A: 09/27/90  ]
 ]____________________]_____________________________]__________________]
 ] OI/FLIGHT EFFECTIVITY:        ]  USER AFFECTED:                     ]
 ] OI20 AND SUBS                 ]  CREW (X)  GROUND ( )  DUMP ONLY ( )]
 ]_______________________________]_____________________________________]
 ]    MAJOR SOFTWARE AREA:           ] OPS MODES AFFECTED:             ]
 ]SSW ( )  GNC (X)  VU ( )  SM/PL ( )] G2, G8                          ]
 ]_____________________________________________________________________]
 ] SOFTWARE SUB-AREA:  ORBIT, DAP, IMU                                 ]
 ]_____________________________________________________________________]
 ] PRINCIPAL FUNCTIONS: 4.35                                           ]
 ]_____________________________________________________________________]
 ] TITLE:                                                              ]
 ] ORBIT DAP CONFIGURATION DURING AND AFTER IMU FAIL OR OPS MODE       ]
 ] RECALL                                                              ]
 ]_____________________________________________________________________]
 ] DESCRIPTION:                                                        ]
 ] THE ORBIT DAP AUTOMATICALLY RECONFIGURES TO WHAT IS CALLED THE IMU  ]
 ] FAIL MODE WHENEVER THE ATTITUDE DATA GOOD FLAG IS SENSED TO BE IN   ]
 ] THE OFF STATE FOR AT LEAST 960 MSEC. THIS CONFIGURATION CONSISTS OF ]
 ] THE FOLLOWING: MANUAL FREE DRIFT CONTROL MODE (PULSE ROTATIONAL     ]
 ] SUBMODE) AND PULSE TRANSLATION SUBMODE.  AS LONG AS THE IMU FAIL    ]
 ] MODE IS IN EFFECT, SELECTION OF AUTO MODE, DISCRETE RATE ROTATIONAL ]
 ] SUBMODE, MANUAL INRTL OR MANUAL LVLH MODE IS PREVENTED. WHEN IMU    ]
 ] DATA IS RESTORED, THE DAP REMAINS IN THE FREE/PULSE/PULSE MODE      ]
 ] UNTIL ANOTHER MODE IS SELECTED VIA PBI.                             ]
 ]                                                                     ]
 ] NOTE: THE ATTITUDE DATA GOOD FLAG (ATT_DG) WILL BE SET TO OFF WHEN  ]
 ] ALL THREE IMU'S ARE DESELECTED BY IMU RM; OR, IN THE TWO IMU CASE,  ]
 ] WHENEVER THE ATTITUDE ERROR BETWEEN IMU'S IS OUT OF TOLERANCE       ]
 ] (I-LOAD). RM DESELECTION OF ALL IMU'S CAN OCCUR FOR COMBINATIONS    ]
 ] OF MANUAL DESELECTION, HARDWARE FAILURES, OR COMMFAULTS WHICH COULD ]
 ] BE CAUSED BY OTHER LRU FAILURES.                                    ]
 ]                                                                     ]
 ] IT SHOULD BE NOTED THAT IT IS NOT UNCOMMON FOR THE ATTITUDE DATA    ]
 ] GOOD FLAG TO BE OFF FOR AT LEAST 160 MSEC AFTER AN OPS TRANSITION   ]
 ] (OR OPS MODE RECALL WITH GPC TARGET CHANGE), DUE TO COMMFAULTS.     ]
 ]_____________________________________________________________________]
 ] USER RESPONSE:                                                      ]
 ] BE AWARE OF THE DESCRIBED AUTOMATIC MODING ASSOCIATED WITH IMU      ]
 ] FAILURES IN OPS 2 AND 8.                                            ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ]CONCURRENCE:                           ]APPROVAL:                    ]
 ]IBM: PATTI A. THORNTON    DATE 10/16/90]                             ]
 ]    --------------------      ---------]                             ]
 ]FDSD:   SAM ANKNEY        DATE 10/18/90]                             ]
 ]     -------------------      ---------] DARRELL E. STAMPER 10/31/90 ]
 ]PF MGR:  K. L. LINDSAY    DATE 10/30/90]------------------- -------- ]
 ]       -----------------      ---------] CHAIRMAN, SASCB      DATE   ]
 ]_______________________________________]_____________________________]
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