LEM GEOMETRY

Scanned pages: 320-325

LEM_GEOMETRY.agc

# Copyright:  Public domain.
# Filename:  LEM_GEOMETRY.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:  320-325
# Mod history:  2009-05-16 RSB  Adapted from the corresponding
#        Luminary131 file, using page
#        images from Luminary 1A.
#
# 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 320
    BANK  23
    SETLOC  LEMGEOM
    BANK

    SBANK=  LOWSUPER
    EBANK=  XSM

# THESE TWO ROUTINES COMPUTE THE ACTUAL STATE VECTOR FOR LM,CSM BY ADDING
# THE CONIC R,V AND THE DEVIATIONSR,V. THE STATE VECTORS ARE CONVERTED TO
# METERS B-29 AND METERS/CSEC B-7 AND STORED APPROPRIATELY IN RN,VN OR
# R-OTHER , V-OTHER FOR DOWNLINK. THE ROUTINES NAMES ARE SWITCHED IN THE
# OTHER VEHICLES COMPUTER.
#
# INPUT
#   STATE VECTOR IN TEMPORARY STORAGE AREA
#   IF STATE VECTOR IS SCALED POS B27 AND VEL B5
#      SET X2 TO +2
#   IF STATE VECTOR IS SCALED POS B29 AND VEL B7
#      SET X2 TO 0
#
# OUTPUT
#   R(T) IN RN, V(T) IN VN, T IN PIPTIME
# OR
#   R(T) IN R-OTHER, V(T) IN V-OTHER   (T IS DEFINED BY T-OTHER)

    COUNT*  $$/GEOM
SVDWN2    BOF  RVQ    # SW=1=AVETOMID DOING W-MATRIX INTEG.
      AVEMIDSW
      +1
    VLOAD  VSL*
      TDELTAV
      0 -7,2
    VAD  VSL*
      RCV
      0,2
    STOVL  RN
      TNUV
    VSL*  VAD
      0 -4,2
      VCV
    VSL*
      0,2
    STODL  VN
      TET
    STORE  PIPTIME
    RVQ
# Page 321
SVDWN1    VLOAD  VSL*
      TDELTAV
      0 -7,2
    VAD  VSL*
      RCV
      0,2
    STOVL  R-OTHER
      TNUV
    VSL*  VAD
      0 -4,2
      VCV
    VSL*
      0,2
    STORE  V-OTHER
    RVQ

# Page 322
#     THE FOLLOWING ROUTINE TAKES A HALF UNIT TARGET VECTOR REFERRED TO NAV BASE COORDINATES AND FINDS BOTH
# GIMBAL ORIENTATIONS AT WHICH THE RR MIGHT SIGHT THE TARGET. THE GIMBAL ANGLES CORRESPONDING TO THE PRESENT MODE
# ARE LEFT IN MODEA AND THOSE WHICH WOULD BE USED AFTER A REMODE IN MODEB. THIS ROUTINE ASSUMES MODE 1 IS TRUNNION
# ANGLE LESS THAN 90 DEGS IN ABS VALUE WITH ARBITRARY SHAFT, WITH A CORRESPONDING DEFINITION FOR MODE 2. MODE
# SELECTION AND LIMIT CHECKING ARE DONE ELSEWHERE.
#
#     THE MODE 1 CONFIGURATION IS CALCULATED FROM THE VECTOR AND THEN MODE 2 IS FOUND USING THE RELATIONS
#
#     S(2) = 180 + S(1)
#     T(2) = 180 - T(1)
#
#     THE VECTOR ARRIVES IN MPAC WHERE TRG*SMNB OR *SMNB* WILL HAVE LEFT IT.

RRANGLES  STORE  32D
    DLOAD  DCOMP    # SINCE WE WILL FIND THE MODE 1 SHAFT
      34D    # ANGLE LATER, WE CAN FIND THE MODE 1
    SETPD  ASIN    # TRUNNION BY SIMPLY TAKING THE ARCSIN OF
      0    # THE Y COMPONENT, THE ASIN GIVIN AN
    PUSH  BDSU    # ANSWER WHOSE ABS VAL IS LESS THAN 90 DEG
      LODPHALF
    STODL  4    # MODE 2 TRUNNION TO 4.

      LO6ZEROS
    STOVL  34D    # UNIT THE PROJECTION OF THE VECTOR
      32D    #   IN THE X-Z PLANE
    UNIT  BOVB    # IF OVERFLOW,TARGET VECTOR IS ALONG Y
      LUNDESCH  # CALL FOR MANEUVER UNLESS ON LUNAR SURF
    STODL  32D    # PROJECTION VECTOR.
      32D
    SR1  STQ
      S2
    STODL  SINTH    # USE ARCTRIG SINCE SHAFT COULD BE ARB.
      36D
    SR1
    STCALL  COSTH
      ARCTRIG
# Page 323
    PUSH  DAD    # MODE 1 SHAFT TO 2.
      LODPHALF
    STOVL  6
      4
    RTB      # FIND MODE 2 CDU ANGLES.
      2V1STO2S
    STOVL  MODEB
      0
    RTB      # MODE 1 ANGLES TO MODE A.
      2V1STO2S
    STORE  MODEA
    EXIT

    CS  RADMODES  # SWAP MODEA AND MODEB IF RR IN MODE 2.
    MASK  ANTENBIT
    CCS  A
    TCF  +4

    DXCH  MODEA
    DXCH  MODEB
    DXCH  MODEA

    TC  INTPRET
    GOTO
      S2
# Page 324
# GIVEN RR TRUNNION AND SHAFT (T,S) IN TANGNB,+1,FIND THE ASSOCIATED
# LINE OF SIGHT IN NAV BASE AXES.  THE HALF UNIT VECTOR, .5(SIN(S)COS(T),
# -SIN(T),COS(S)COS(T)) IS LEFT IN MPAC AND 32D.

    SETLOC  INFLIGHT
    BANK

    COUNT*  $$/GEOM

RRNB    SLOAD  RTB
      TANGNB
      CDULOGIC
    SETPD  PUSH    # TRUNNION ANGLE TO 0
      0
    SIN  DCOMP
    STODL  34D    # Y COMPONENT

    COS  PUSH    # .5 COS(T) TO 0
    SLOAD  RTB
      TANGNB +1
      CDULOGIC
RRNB1    PUSH  COS    # SHAFT ANGLE TO 2
    DMP  SL1
      0
    STODL  36D    # Z COMPONENT

    SIN  DMP
    SL1
    STOVL  32D
      32D
    RVQ

# THIS ENTRY TO RRNB REQUIRES THE TRUNNION AND SHAFT ANGLES IN MPAC AND MPAC +1 RESPECTIVELY

RRNBMPAC  STODL  20D    # SAVE SHAFT CDU IN 21.
      MPAC    # SET MODE TO DP.  (THE PRECEEDING STORE
          # MAY BE DP. TP OR VECTOR.)
    RTB  SETPD
      CDULOGIC
      0
    PUSH  SIN    # TRUNNION ANGLE TO 0
    DCOMP
    STODL  34D    # Y COMPONENT
    COS  PUSH    # .5COS(T) TO 0
    SLOAD  RTB    # PICK UP CDU'S.
      21D
      CDULOGIC
    GOTO
      RRNB1
# Page 325 (empty page)