Source Code
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These source-code files are part of a reconstructed copy of LM131 revision 1,
the final release of the Apollo 13 Lunar Module (LM) Apollo Guidance Computer
(AGC) software.
The source reconstruction began with source code of Luminary 131 previously
transcribed from a digitized copy of that program. A dump of the flight spare
core rope memory module B5, part number 2010802-171, serial number RAY 411,
was obtained. This module is the only module different between Luminary 131
and LM131 revision 1. The dump was disassembled and all changes were incorporated
into these source files. Note that page numbers in the reconstructed code match
those on the Luminary 131 printout, although the changed code would likely have
changed page numbers for a real LM131 revision 1 listing.
Comments from the original source code are prefixed with a single '#' symbol,
whereas comments added later are prefixed by "##" or "###". Report any errors
noted by creating an
issue report at the Virtual AGC
project's GitHub repository.
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013277,000002: ## Copyright: Public domain.
013278,000003: ## Filename: LEM_GEOMETRY.agc
013279,000004: ## Purpose: A section of LM131 revision 1.
013280,000005: ## It is part of the reconstructed source code for the final
013281,000006: ## release of the flight software for the Lunar Module's (LM)
013282,000007: ## Apollo Guidance Computer (AGC) for Apollo 13. The code has
013283,000008: ## been reconstructed from a listing of Luminary 131 and a dump
013284,000009: ## of a core rope memory module B5, part number 2010802-171,
013285,000010: ## which is the only module different between LM131 revision 1
013286,000011: ## and Luminary 131. The executable generated from this source
013287,000012: ## has been verified against the module dump, so while the names,
013288,000013: ## comments, and ordering may not be exactly correct, the
013289,000014: ## resulting binary is.
013290,000015: ## Reference: pp. 322-327
013291,000016: ## Assembler: yaYUL
013292,000017: ## Contact: Ron Burkey <info@sandroid.org>.
013293,000018: ## Website: www.ibiblio.org/apollo/index.html
013294,000019: ## Mod history: 2022-10-28 MAS Created from Luminary 131.
013295,000020:
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Page 322
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013297,000022: 23,2041 BANK 23
013298,000023: 13,2000 SETLOC LEMGEOM
013299,000024: 13,2000 BANK
013300,000025:
013301,000026: 13,2070 30,2000 SBANK= LOWSUPER
013302,000027: 13,2070 E5,1642 EBANK= XSM
013303,000028:
013304,000029: # THESE TWO ROUTINES COMPUTE THE ACTUAL STATE VECTOR FOR LM,CSM BY ADDING
013305,000030: # THE CONIC R,V AND THE DEVIATIONS R,V. THE STATE VECTORS ARE CONVERTED TO
013306,000031: # METERS B-29 AND METERS/CSEC B-7 AND STORED APPROPRIATELY IN RN,VN OR
013307,000032: # R-OTHER,V-OTHER FOR DOWNLINK. THE ROUTINES NAMES ARE SWITCHED IN THE
013308,000033: # OTHER VEHICLES COMPUTER.
013309,000034:
013310,000035: # INPUT
013311,000036: # STATE VECTOR IN TEMPORARY STORAGE AREA
013312,000037: # IF STATE VECTOR IS SCALED POS B27 AND VEL B5
013313,000038: # SET X2 TO +2
013314,000039: # IF STATE VECTOR IS SCALED POS B29 AND VEL B7
013315,000040: # SET X2 TO 0
013316,000041:
013317,000042: # OUTPUT
013318,000043: # R(T) IN RN, V(T) IN VN, T IN PIPTIME
013319,000044: # OR
013320,000045: # R(T) IN R-OTHER, V(T) IN V-OTHER (T IS DEFINED BY T-OTHER)
013321,000046:
013322,000047: 13,2070 COUNT* $$/GEOM
013323,000048: 13,2070 43414 SVDWN2 BOF RVQ # SW=1=AVETOMID DOING W-MATRIX INTEG.
013324,000049: 13,2071 04756 AVEMIDSW
013325,000050: 13,2072 26073 +1
013326,000051: 13,2073 53775 VLOAD VSL*
013327,000052: 13,2074 01521 TDELTAV
013328,000053: 13,2075 57605 0 -7,2
013329,000054: 13,2076 53655 VAD VSL*
013330,000055: 13,2077 01535 RCV
013331,000056: 13,2100 57576 0,2
013332,000057: 13,2101 25220 STOVL RN
013333,000058: 13,2102 01527 TNUV
013334,000059: 13,2103 53257 VSL* VAD
013335,000060: 13,2104 57602 0 -4,2
013336,000061: 13,2105 01543 VCV
013337,000062: 13,2106 77657 VSL*
013338,000063: 13,2107 57576 0,2
013339,000064: 13,2110 15226 STODL VN
013340,000065: 13,2111 01517 TET
013341,000066: 13,2112 01234 STORE PIPTIME
013342,000067: 13,2113 77616 RVQ
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Page 323
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013344,000069: 13,2114 53775 SVDWN1 VLOAD VSL*
013345,000070: 13,2115 01521 TDELTAV
013346,000071: 13,2116 57605 0 -7,2
013347,000072: 13,2117 53655 VAD VSL*
013348,000073: 13,2120 01535 RCV
013349,000074: 13,2121 57576 0,2
013350,000075: 13,2122 25720 STOVL R-OTHER
013351,000076: 13,2123 01527 TNUV
013352,000077: 13,2124 53257 VSL* VAD
013353,000078: 13,2125 57602 0 -4,2
013354,000079: 13,2126 01543 VCV
013355,000080: 13,2127 77657 VSL*
013356,000081: 13,2130 57576 0,2
013357,000082: 13,2131 01726 STORE V-OTHER
013358,000083: 13,2132 77616 RVQ
013359,000084:
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Page 324
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013361,000086: # THE FOLLOWING ROUTINE TAKES A HALF UNIT TARGET VECTOR REFERRED TO NAV BASE COORDINATES AND FINDS BOTH
013362,000087: # GIMBAL ORIENTATIONS AT WHICH THE RR MIGHT SIGHT THE TARGET. THE GIMBAL ANGLES CORRESPONDING TO THE PRESENT MODE
013363,000088: # ARE LEFT IN MODEA AND THOSE WHICH WOULD BE USED AFTER A REMODE IN MODEB. THIS ROUTINE ASSUMES MODE 1 IS TRUNNION
013364,000089: # ANGLE LESS THAN 90 DEGS IN ABS VALUE WITH ARBITRARY SHAFT, WITH A CORRESPONDING DEFINITION FOR MODE 2. MODE
013365,000090: # SELECTION AND LIMIT CHECKING ARE DONE ELSEWHERE.
013366,000091:
013367,000092: # THE MODE 1 CONFIGURATION IS CALCULATED FROM THE VECTOR AND THEN MODE 2 IS FOUND USING THE RELATIONS
013368,000093:
013369,000094: # S(2) = 180 + S(1)
013370,000095: # T(2) = 180 - T(1)
013371,000096:
013372,000097: # THE VECTOR ARRIVES IN MPAC WHERE TRG*SMNG OR *SMNB* WILL HAVE LEFT IT.
013373,000098:
013374,000099: 13,2133 00041 RRANGLES STORE 32D
013375,000100: 13,2134 57545 DLOAD DCOMP # SINCE WE WILL FIND THE MODE 1 SHAFT
013376,000101: 13,2135 00043 34D # ANGLE LATER, WE CAN FIND THE MODE 1
013377,000102: 13,2136 67401 SETPD ASIN # TRUNNION BY SIMPLY TAKING THE ARCSIN OF
013378,000103: 13,2137 00001 0 # THE Y COMPONENT, THE ASIN GIVING AN
013379,000104: 13,2140 44206 PUSH BDSU # ANSWER WHOSE ABS VAL IS LESS THAN 90 DEG
013380,000105: 13,2141 24005 LODPHALF
013381,000106: 13,2142 14005 STODL 4 # MODE 2 TRUNNION TO 4.
013382,000107: 13,2143 24007 LO6ZEROS
013383,000108: 13,2144 24043 STOVL 34D # UNIT THE PROJECTION OF THE VECTOR
013384,000109: 13,2145 00041 32D # IN THE X-Z PLANE
013385,000110: 13,2146 41056 UNIT BOVB # IF OVERFLOW, TARGET VECTOR IS ALONG Y
013386,000111: 13,2147 52432 LUNDESCH # CALL FOR MANEUVER UNLESS ON LUNAR SURF
013387,000112: 13,2150 14041 STODL 32D # PROJECTION VECTOR.
013388,000113: 13,2151 00041 32D
013389,000114: 13,2152 44142 SR1 STQ
013390,000115: 13,2153 00051 S2
013391,000116: 13,2154 14023 STODL SINTH # USE ARCTRIG SINCE SHAFT COULD BE ARB.
013392,000117: 13,2155 00045 36D
013393,000118: 13,2156 77742 SR1
013394,000119: 13,2157 34021 STCALL COSTH
013395,000120: 13,2160 47322 ARCTRIG
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Page 325
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013397,000122: 13,2161 43206 PUSH DAD # MODE 1 SHAFT TO 2.
013398,000123: 13,2162 24005 LODPHALF
013399,000124: 13,2163 24007 STOVL 6
013400,000125: 13,2164 00005 4
013401,000126: 13,2165 77634 RTB # FIND MODE 2 CDU ANGLES.
013402,000127: 13,2166 21636 2V1STO2S
013403,000128: 13,2167 25111 STOVL MODEB
013404,000129: 13,2170 00001 0
013405,000130: 13,2171 77634 RTB # MODE 1 ANGLES TO MODE A.
013406,000131: 13,2172 21636 2V1STO2S
013407,000132: 13,2173 01107 STORE MODEA
013408,000133: 13,2174 77776 EXIT
013409,000134:
013410,000135: 13,2175 40110 CS RADMODES # SWAP MODEA AND MODEB IF RR IN MODE 2.
013411,000136: 13,2176 74740 MASK ANTENBIT
013412,000137: 13,2177 10000 CCS A
013413,000138: 13,2200 12204 TCF +4
013414,000139:
013415,000140: 13,2201 53107 DXCH MODEA
013416,000141: 13,2202 53111 DXCH MODEB
013417,000142: 13,2203 53107 DXCH MODEA
013418,000143:
013419,000144: 13,2204 06042 TC INTPRET
013420,000145: 13,2205 77650 GOTO
013421,000146: 13,2206 00051 S2
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Page 326
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013423,000148: # GIVEN RR TRUNNION AND SHAFT (T,S) IN TANGNB,+1, FIND THE ASSOCIATED
013424,000149: # LINE OF SIGHT IN NAV BASE AXES. THE HALF UNIT VECTOR, .5(SIN(S)COS(T),
013425,000150: # -SIN(T),COS(S)COS(T)) IS LEFT IN MPAC AND 32D.
013426,000151:
013427,000152: 23,2000 SETLOC INFLIGHT
013428,000153: 23,2000 BANK
013429,000154:
013430,000155: 23,2041 COUNT* $$/GEOM
013431,000156:
013432,000157: 23,2041 47135 RRNB SLOAD RTB
013433,000158: 23,2042 03753 TANGNB
013434,000159: 23,2043 21577 CDULOGIC
013435,000160: 23,2044 41401 SETPD PUSH # TRUNNION ANGLE TO 0
013436,000161: 23,2045 00001 0
013437,000162: 23,2046 57556 SIN DCOMP
013438,000163: 23,2047 14043 STODL 34D # Y COMPONENT
013439,000164:
013440,000165: 23,2050 41546 COS PUSH # .5 COS(T) TO 0
013441,000166: 23,2051 47135 SLOAD RTB
013442,000167: 23,2052 03754 TANGNB +1
013443,000168: 23,2053 21577 CDULOGIC
013444,000169: 23,2054 71406 RRNB1 PUSH COS # SHAFT ANGLE TO 2
013445,000170: 23,2055 72405 DMP SL1
013446,000171: 23,2056 00001 0
013447,000172: 23,2057 14045 STODL 36D # Z COMPONENT
013448,000173:
013449,000174: 23,2060 41356 SIN DMP
013450,000175: 23,2061 77752 SL1
013451,000176: 23,2062 24041 STOVL 32D
013452,000177: 23,2063 00041 32D
013453,000178: 23,2064 77616 RVQ
013454,000179:
013455,000180: # THIS ENTRY TO RRNB REQUIRES THE TRUNNION AND SHAFT ANGLES IN MPAC AND MPAC +1 RESPECTIVELY
013456,000181:
013457,000182: 23,2065 14025 RRNBMPAC STODL 20D # SAVE SHAFT CDU IN 21.
013458,000183: 23,2066 00155 MPAC # SET MODE TO DP. (THE PRECEEDING STORE
013459,000184: # MAY BE DP, TP OR VECTOR.)
013460,000185: 23,2067 40234 RTB SETPD
013461,000186: 23,2070 21577 CDULOGIC
013462,000187: 23,2071 00001 0
013463,000188: 23,2072 73406 PUSH SIN # TRUNNION ANGLE TO 0
013464,000189: 23,2073 77676 DCOMP
013465,000190: 23,2074 14043 STODL 34D # Y COMPONENT
013466,000191: 23,2075 41546 COS PUSH # .5COS(T) TO 0
013467,000192: 23,2076 47135 SLOAD RTB # PICK UP CDU'S.
013468,000193: 23,2077 00026 21D
013469,000194: 23,2100 21577 CDULOGIC
013470,000195: 23,2101 77650 GOTO
013471,000196: 23,2102 46054 RRNB1
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Page 327
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013474,000199:
013475,000200:
End of include-file LEM_GEOMETRY.agc. Parent file is MAIN.agc