### FILE="Main.annotation"
## Copyright:   Public domain.
## Filename:    GIMBAL_LOCK_AVOIDANCE.agc
## Purpose:     A section of Luminary revision 173.
##              It is part of the reconstructed source code for the second
##              (unflown) release of the flight software for the Lunar
##              Module's (LM) Apollo Guidance Computer (AGC) for Apollo 14.
##              The code has been recreated from a reconstructed copy of
##              Luminary 178, as well as Luminary memo 167 (revision 1).
##              It has been adapted such that the resulting bugger words
##              exactly match those specified for Luminary 173 in NASA
##              drawing 2021152N, which gives relatively high confidence
##              that the reconstruction is correct.
## Reference:   p.  369
## Assembler:   yaYUL
## Contact:     Ron Burkey <info@sandroid.org>.
## Website:     www.ibiblio.org/apollo/index.html
## Mod history: 2019-09-18 MAS  Created from Luminary 178.

## Page 369
                BANK            15

                SETLOC          KALCMON1
                BANK


# DETECTING GIMBAL LOCK
LOCSKIRT        EQUALS          NOGIMLOC

NOGIMLOC        SET
                                CALCMAN3
WCALC           LXC,1           DLOAD*
                                RATEINDX                # CHOOSE THE DESIRED MANEUVER RATE
                                ARATE,1                 # FROM A LIST OF FOUR
                SR4             CALL                    # COMPUTE THE INCREMENTAL ROTATION MATRIX
                                DELCOMP                 # DEL CORRESPONDING TO A 1 SEC ROTATION
                                                        # ABOUT COF
                DLOAD*          VXSC
                                ARATE,1
                                COF
                STODL           BRATE                   # COMPONENT MANEUVER RATES 45 DEG/SEC
                                AM
                DMP             DDV*
                                ANGLTIME
                                ARATE,1
                SR
                                5
                STORE           TM                      # MANEUVER EXECUTION TIME SCALED AS T2
                SETGO
                                CALCMAN2                # 0(OFF) = CONTINUE MANEUVER
                                NEWANGL         +1      # 1(ON) = START MANEUVER
#          THE FOUR SELECTABLE FREE FALL MANEUVER RATES SELECTED BY
#          LOADING RATEINDX WITH 0,2,4,6, RESPECTIVELY


ARATE           2DEC            .0088888888             # = 0.2 DEG/SEC       $ 22.5 DEG/SEC
                2DEC            .0222222222             # = 0.5 DEG/SEC       $ 22.5 DEG/SEC
                2DEC            .0888888888             # = 2.0 DEG/SEC       $ 22.5 DEG/SEC
                2DEC            .4444444444             # = 10.0 DEG/SEC      $ 22.5 DEG/SEC

ANGLTIME        2DEC            .0001907349             # = 100B-19     FUDGE FACTOR TO CONVERT
                                                        # MANEUVER ANGLE TO MANEUVER TIME