GIMBAL LOCK AVOIDANCE

# Copyright:  Public domain.
# Filename:  GIMBAL_LOCK_AVOIDANCE.agc
# Purpose:  Part of the source code for Comanche, build 055.
#    It is part of the source code for the Command Module's (CM)
#    Apollo Guidance Computer (AGC), Apollo 11.
# Assembler:  yaYUL
# Reference:  pp. 412-413
# Contact:  Onno Hommes <ohommes@cmu.edu>.
# Website:  www.ibiblio.org/apollo.
# Mod history:  05/07/09 OH  Transcription Batch 1 Assignment
#
# The contents of the "Comanche055" files, in general, are transcribed
# from scanned documents.
#
#  Assemble revision 055 of AGC program Comanche by NASA
#  2021113-051.  April 1, 1969.
#
#  This AGC program shall also be referred to as Colossus 2A
#
#  Prepared by
#      Massachusetts Institute of Technology
#      75 Cambridge Parkway
#      Cambridge, Massachusetts
#
#  under NASA contract NAS 9-4065.
#
# Refer directly to the online document mentioned above for further information.
# Please report any errors to info@sandroid.org.

# Page 412
    BANK  15
    SETLOC  KALCMON1
    BANK

    EBANK=  BCDU
# DETECTING GIMBAL LOCK
LOCSKIRT  EQUALS  WCALC
WCALC    LXC,1  DLOAD*
      RATEINDX
      ARATE,1
    SR4  CALL    # COMPUTE THE INCREMENTAL ROTATION MATRIX
      DELCOMP    # DEL CORRESPONDING TO A 1 SEC ROTATION
          # ABOUT COF
    DLOAD*  VXSC
      ARATE,1
      COF
    MXV
      QUADROT
    STODL  BRATE
      AM
    DMP  DDV*
      ANGLTIME
      ARATE,1
    SR
      5
    STOVL  TM
      BRATE
    VXSC
      BIASCALE
    STORE  BIASTEMP  # ATTITUDE ERROR BIAS TO PREVENT OVERSHOOT
          # IN SYSTEM
    SETGO      # STATE SWITCH CALCMAN2 (43D)
      CALCMAN2  # 0(OFF) = BYPASS STARTING PROCEDURE
      NEWANGL +1  # 1(ON) = START MANEUVER


ARATE    2DEC  .0022222222  # = .05 DEG/SEC

    2DEC  .0088888889  # = .2 DEG/SEC

    2DEC  .0222222222  # = .5 DEG/SEC

    2DEC  .0888888889  # = 2 DEG/SEC                $22.5 DEG/SEC

ANGLTIME  2DEC  .000190735  # = 100B - 19

          # MANEUVER ANGLE TO MANEUVER TIME

QUADROT    2DEC  .1    # ROTATION MATRIX FROM S/C AXES TO CONTROL

# Page 413
    2DEC  0    # AXES  (X ROT = -7.25 DEG)

    2DEC  0

    2DEC  0

    2DEC  .099200    # =(.1)COS7.25

    2DEC  -.012620  # =-(.1)SIN7.25

    2DEC  0

    2DEC  .012620    # (.1)SIN7.25

    2DEC  .099200    # (.1)COS7.25

BIASCALE  2DEC  .0002543132  # = (450/180)(1/0.6)(1/16384)