LEM_GEOMETRY.agc
### FILE="Main.annotation"
## Copyright: Public domain.
## Filename: LEM_GEOMETRY.agc
## Purpose: A section of Luminary revision 116.
## It is part of the source code for the Lunar Module's (LM)
## Apollo Guidance Computer (AGC) for Apollo 12.
## This file is intended to be a faithful transcription, except
## that the code format has been changed to conform to the
## requirements of the yaYUL assembler rather than the
## original YUL assembler.
## Reference: pp. 321-326
## Assembler: yaYUL
## Contact: Ron Burkey <info@sandroid.org>.
## Website: www.ibiblio.org/apollo/index.html
## Mod history: 2017-01-22 MAS Created from Luminary 99.
## 2017-03-07 RSB Transcribed, and then proofed comment-text using
## 3-way diff vs Luminary 99 and Luminary 131.
## (Admittedly, the former is more for detecting errors
## in Luminary 99 than the other way around.)
## Page 321
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 322
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 323
# 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 GIVING 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 324
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 325
# 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 326
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