GIMBAL LOCK AVOIDANCE

Scanned pages: 364
# Copyright:  Public domain.
# Filename:  GIMBAL_LOCK_AVOIDANCE.agc
# Purpose:   Part of the source code for Luminary 1A build 099.
#    It is part of the source code for the Lunar Module's (LM)
#    Apollo Guidance Computer (AGC), for Apollo 11.
# Assembler:  yaYUL
# Contact:  Ron Burkey <info@sandroid.org>.
# Website:  www.ibiblio.org/apollo.
# Pages:  364
# Mod history:  2009-05-17 RSB  Adapted from the corresponding
#        Luminary131 file, using page
#        images from Luminary 1A.
#    2010-12-31 JL  Fixed page number comment.
#
# This source code has been transcribed or otherwise adapted from
# digitized images of a hardcopy from the MIT Museum.  The digitization
# was performed by Paul Fjeld, and arranged for by Deborah Douglas of
# the Museum.  Many thanks to both.  The images (with suitable reduction
# in storage size and consequent reduction in image quality as well) are
# available online at www.ibiblio.org/apollo.  If for some reason you
# find that the images are illegible, contact me at info@sandroid.org
# about getting access to the (much) higher-quality images which Paul
# actually created.
#
# Notations on the hardcopy document read, in part:
#
#  Assemble revision 001 of AGC program LMY99 by NASA 2021112-061
#  16:27 JULY 14, 1969

# Page 364
    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  # = 1008-19 FUDGE FACTOR TO CONVERT
          # MANEUVER ANGLE TO MANEUVER TIME