 +_____________________________________________________________________
 ] AUTHOR:            ]                             ] DR:              ]
 ] R. MCALLISTER      ]    PASS PROGRAM NOTE        ]       35322      ]
 ]____________________]                             ]__________________]
 ] ORG/PHONE:         ] OPS NOTE ( )  USER NOTE (X) ] DATE: SEPT. 1987 ]
 ] LSIS/282-7299      ]      RELEASE NOTE( )        ] REV A: 07/12/95  ]
 ]____________________]_____________________________]__________________]
 ] OI/FLIGHT EFFECTIVITY:        ]  USER AFFECTED:                     ]
 ] REL 19 AND SUBS               ]  CREW ( )  GROUND (X)  DUMP ONLY ( )]
 ]_______________________________]_____________________________________]
 ]        MAJOR SOFTWARE AREA:       ] OPS MODES AFFECTED:             ]
 ]SSW ( )  GNC (X)  VU ( )  SM/PL ( )] G9                              ]
 ]_____________________________________________________________________]
 ] SOFTWARE SUB-AREA: IMU, GPC                                         ]
 ]_____________________________________________________________________]
 ] PRINCIPAL FUNCTIONS: V4.10                                          ]
 ]_____________________________________________________________________]
 ] TITLE:                                                              ]
 ] IMU ATT DET CAUSED LIBRARY ROUTINE ERROR                            ]
 ]_____________________________________________________________________]
 ] DESCRIPTION:                                                        ]
 ]                                                                     ]
 ] NORMALLY THE IMU'S WILL SENSE THE ACCELERATION DUE TO GRAVITY       ]
 ] DURING AN ATTITUDE DETERMINATION; THUS, THE ESTIMATED ACCELERATION  ]
 ] (THETA) AND DRIFT (ETD) VECTORS WILL BE NON-ZERO. HOWEVER, IF       ]
 ] THERE IS A HARDWARE PROBLEM SUCH THAT THE VELOCITY INPUT DATA IS    ]
 ] CONSTANT, ETD WOULD BE ZERO.                                        ]
 ]                                                                     ]
 ] IF THE IMU'S ARE ALIGNED SO THAT NEGATIVE GRAVITY IS SENSED ON THE  ]
 ] UP AXIS (I.E., SENSED VELOCITY IN NWU COORDINATES IS ALL ZERO),     ]
 ] THETA COULD ALSO BE ZERO. DURING ATTITUDE DETERMINATION, BOTH OF    ]
 ] THESE VECTORS ARE INPUTS TO THE HAL/S UNIT FUNCTION, WHICH          ]
 ] GENERATES A GPC ERROR GROUP 4 CODE 28 IF THE INPUT VECTOR IS A      ]
 ] ZERO VECTOR.                                                        ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ]USER RESPONSE:                                                       ]
 ]                                                                     ]
 ] IF GPC ERROR GROUP 4 CODE 28 IS LOGGED DURING AN ATTITUDE           ]
 ] DETERMINATION, IT WOULD BE FOR THE REASONS STATED ABOVE. BEFORE     ]
 ] CONTINUING WITH FURTHER IMU CALIBRATION, INVESTIGATE TO DETERMINE   ]
 ] CAUSE OF PROBLEM. ATTITUDE DETERMINATION MUST BE REDONE BEFORE      ]
 ] CONTINUING ANY IMU CALIBRATIONS.                                    ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]                                                                     ]
 ]_____________________________________________________________________]
 ]CONCURRENCE:                           ]APPROVAL:                    ]
 ]LSIS:  JEAN L. ZOPHY      DATE 08/15/95]                             ]
 ]     -------------------      ---------]                             ]
 ]ASD:   ERIC C. BINGHAM    DATE 08/15/95]                             ]
 ]     -------------------      ---------] DARRELL E. STAMPER 08/24/95 ]
 ]PF MGR:  OANH N. PHAM     DATE 08/21/95]------------------- -------- ]
 ]       -----------------      ---------] CHAIRMAN, SASCB      DATE   ]
 ]_______________________________________]_____________________________]
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