### FILE="Main.annotation"
## Copyright:   Public domain.
## Filename:    LEM_GEOMETRY.agc
## Purpose:     A section of Luminary revision 173.
##              It is part of the reconstructed source code for the second
##              (unflown) release of the flight software for the Lunar
##              Module's (LM) Apollo Guidance Computer (AGC) for Apollo 14.
##              The code has been recreated from a reconstructed copy of
##              Luminary 178, as well as Luminary memo 167 (revision 1).
##              It has been adapted such that the resulting bugger words
##              exactly match those specified for Luminary 173 in NASA
##              drawing 2021152N, which gives relatively high confidence
##              that the reconstruction is correct.
## Reference:   pp. 325-330
## Assembler:   yaYUL
## Contact:     Ron Burkey <info@sandroid.org>.
## Website:     www.ibiblio.org/apollo/index.html
## Mod history: 2019-09-18 MAS  Created from Luminary 178.

## Page 332
                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 326
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 327
#          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 328
                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 329
# 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 330
## Note: This page is empty in the printout of the assembly listing.