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LEM_GEOMETRY.s
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LEM_GEOMETRY.s
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# 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 <[email protected]>.
# 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 [email protected]
# 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 2021112-61
# 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 DEVIATIONS R,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 VEHICLE'S 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*SMNG 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
# (This page has nothing on it.)