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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047128,000002: ## Copyright: Public domain.
047129,000003: ## Filename: LATITUDE_LONGITUDE_SUBROUTINES.agc
047130,000004: ## Purpose: A section of LM131 revision 1.
047131,000005: ## It is part of the reconstructed source code for the final
047132,000006: ## release of the flight software for the Lunar Module's (LM)
047133,000007: ## Apollo Guidance Computer (AGC) for Apollo 13. The code has
047134,000008: ## been reconstructed from a listing of Luminary 131 and a dump
047135,000009: ## of a core rope memory module B5, part number 2010802-171,
047136,000010: ## which is the only module different between LM131 revision 1
047137,000011: ## and Luminary 131. The executable generated from this source
047138,000012: ## has been verified against the module dump, so while the names,
047139,000013: ## comments, and ordering may not be exactly correct, the
047140,000014: ## resulting binary is.
047141,000015: ## Reference: pp. 1127-1133
047142,000016: ## Assembler: yaYUL
047143,000017: ## Contact: Ron Burkey <info@sandroid.org>.
047144,000018: ## Website: www.ibiblio.org/apollo/index.html
047145,000019: ## Mod history: 2022-10-28 MAS Created from Luminary 131.
047146,000020:
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Page 1127
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047148,000022: # SUBROUTINE TO CONVERT RAD VECTOR AT GIVEN TIME TO LAT,LONG AND ALT
047149,000023:
047150,000024: # CALLING SEQUENCE
047151,000025: # L-1 CALL
047152,000026: # L LAT-LONG
047153,000027:
047154,000028: # SUBROUTINES USED
047155,000029: # R-TO-RP, ARCTAN, SETGAMMA, SETRE
047156,000030:
047157,000031: # ERASABLE INIT. REQ.
047158,000032: # AXO, -AYO, AZO, TEPHEM (SET AT LAUNCH TIME)
047159,000033: # ALPHAV = POSITION VECTOR METERS B-29
047160,000034: # MPAC -- TIME (CSECS B-28)
047161,000035: # ERADFLAG =1, TO COMPUTE EARTH RADIUS, =0 FOR FIXED EARTH RADIUS
047162,000036: # LUNAFLAG=0 FOR EARTH, 1 FOR MOON
047163,000037:
047164,000038: # OUTPUT
047165,000039: # LATITUDE IN LAT (REVS. B-0)
047166,000040: # LONGITUDE IN LONG (REVS. B-0)
047167,000041: # ALTITUDE IN ALT METERS B-29
047168,000042:
047169,000043: 30,3766 BANK 30
047170,000044: 13,2000 SETLOC LATLONG
047171,000045: 13,2000 BANK
047172,000046:
047173,000047: 13,2347 COUNT* $$/LT-LG
047174,000048: 13,2347 E4,1431 EBANK= ALPHAV
047175,000049: 13,2347 40220 LAT-LONG STQ SETPD
047176,000050: 13,2350 03674 INCORPEX
047177,000051: 13,2351 00001 0D
047178,000052: 13,2352 24007 STOVL 6D # SAVE TIME IN 6-7D FOR R-TO-RP
047179,000053: 13,2353 02032 ALPHAV
047180,000054: 13,2354 51406 PUSH ABVAL # 0-5D= R FOR R-TO-RP
047181,000055: 13,2355 16070 STODL ALPHAM # ABS. VALUE OF R FOR ALT FORMULA BELOW
047182,000056: 13,2356 24007 ZEROVEC # SET MPAC=0 FOR EARTH, NON-ZERO FOR MOON
047183,000057: 13,2357 71414 BOFF COS # USE COS(0) TO GET NON-ZERO IN MPAC
047184,000058: 13,2360 01743 LUNAFLAG # 0=EARTH, 1=MOON
047185,000059: 13,2361 26362 CALLRTRP
047186,000060: 13,2362 77624 CALLRTRP CALL
047187,000061: 13,2363 51700 R-TO-RP # RP VECTOR CONVERTED FROM R B-29
047188,000062: 13,2364 77656 UNIT # UNIT RP B-1
047189,000063: 13,2365 36032 STCALL ALPHAV # U2= 1/2 SINL FOR SETRE SUBR BELOW
047190,000064: 13,2366 26546 SETGAMMA # SET GAMMA=B2/A2 FOR EARTH, =1 FOR MOON
047191,000065: 13,2367 77624 CALL # SCALED B-1
047192,000066: 13,2370 26556 SETRE # CALC RE METERS B-29
047193,000067: 13,2371 63545 DLOAD DSQ
047194,000068: 13,2372 02032 ALPHAV
047195,000069: 13,2373 63525 PDDL DSQ
047196,000070: 13,2374 02034 ALPHAV +2
047197,000071: 13,2375 75415 DAD SQRT
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Page 1128
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047199,000073: 13,2376 76405 DMP SL1R
047200,000074: 13,2377 00011 GAMRP
047201,000075: 13,2400 14021 STODL COSTH # COS(LAT) B-1
047202,000076: 13,2401 02036 ALPHAV +4
047203,000077: 13,2402 34023 STCALL SINTH # SIN(LAT) B-1
047204,000078: 13,2403 26506 ARCTAN
047205,000079: 13,2404 15120 STODL LAT # LAT B0
047206,000080: 13,2405 02032 ALPHAV
047207,000081: 13,2406 14021 STODL COSTH # COS(LONG) B-1
047208,000082: 13,2407 02034 ALPHAV +2
047209,000083: 13,2410 34023 STCALL SINTH # SIN(LONG) B-1
047210,000084: 13,2411 26506 ARCTAN
047211,000085: 13,2412 15122 STODL LONG # LONG. REVS B-0 IN RANGE -1/2 TO 1/2
047212,000086: 13,2413 02070 ALPHAM
047213,000087: 13,2414 77625 DSU # ALT= R-RE METERS B-29
047214,000088: 13,2415 03673 ERADM
047215,000089: 13,2416 35124 STCALL ALT # EXIT WITH ALT METERS B-29
047216,000090: 13,2417 03674 INCORPEX
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Page 1129
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047218,000092: # SUBROUTINE TO CONVERT LAT,LONG,ALT AT GIVEN TIME TO RADIUS VECTOR
047219,000093:
047220,000094: # CALLING SEQUENCE
047221,000095: # L-1 CALL
047222,000096: # L LALOTORV
047223,000097:
047224,000098: # SUBROUTINES USED
047225,000099: # SETGAMMA, SETRE, RP-TO-R
047226,000100:
047227,000101: # ERASABLE INIT. REQ.
047228,000102: # AXO, AYO, AZO, TEPHEM SET AT LAUNCH TIME
047229,000103: # LAT -- LATITUDE (REVS B0)
047230,000104: # LONG -- LONGITUDE (REVS B0)
047231,000105: # ALT -- ALTITUDE (METERS) B-29
047232,000106: # MPAC -- TIME (CSECS B-28)
047233,000107: # ERADFLAG =1 TO COMPUTE EARTH RADIUS, =0 FOR FIXED EARTH RADIUS
047234,000108: # LUNAFLAG=0 FOR EARTH, 1 FOR MOON
047235,000109:
047236,000110: # OUTPUT
047237,000111: # R-VECTOR IN ALPHAV (METERS B-29)
047238,000112:
047239,000113: 13,2420 40220 LALOTORV STQ SETPD # LAT,LONG,ALT TO R VECTOR
047240,000114: 13,2421 03674 INCORPEX
047241,000115: 13,2422 00001 0D
047242,000116: 13,2423 34007 STCALL 6D # 6-7D= TIME FOR RP-TO-R
047243,000117: 13,2424 26546 SETGAMMA # GAMMA=B2/A2 FOR EARTH, 1 FOR MOON B-1
047244,000118: 13,2425 73545 DLOAD SIN # COS(LONG)COS(LAT) IN MPAC
047245,000119: 13,2426 01120 LAT # UNIT RP = SIN(LONG)COS(LAT) 2-3D
047246,000120: 13,2427 65275 DMPR PDDL # PD 2 GAMMA*SIN(LAT) 0-1D
047247,000121: 13,2430 00011 GAMRP
047248,000122: 13,2431 01120 LAT # 0-1D= GAMMA*SIN(LAT) B-2
047249,000123: 13,2432 65346 COS PDDL # PD4 2-3D= COS(LAT) B-1 TEMPORARILY
047250,000124: 13,2433 01122 LONG
047251,000125: 13,2434 57356 SIN DMPR # PD 2
047252,000126: 13,2435 71525 PDDL COS # PD 4 2-3D = SIN(LONG)COS(LAT) B-2
047253,000127: 13,2436 01120 LAT
047254,000128: 13,2437 71525 PDDL COS # PD 6 4-5D = COS(LAT) B-1 TEMPORARILY
047255,000129: 13,2440 01122 LONG
047256,000130: 13,2441 55475 DMPR VDEF # PD4 MPAC= COS(LONG)COS(LAT) B-2
047257,000131: 13,2442 41456 UNIT PUSH # 0-5D= UNIT RP FOR RP-TO-R SUBR.
047258,000132: 13,2443 36032 STCALL ALPHAV # ALPHAV +4= SINL FOR SETRE SUBR.
047259,000133: 13,2444 26556 SETRE # RE METERS B-29
047260,000134: 13,2445 43145 DLOAD BOFF # SET MPAC=0 FOR EARTH, NON-ZERO FOR MOON
047261,000135: 13,2446 24007 ZEROVEC
047262,000136: 13,2447 01743 LUNAFLAG
047263,000137: 13,2450 26452 CALLRPRT
047264,000138: 13,2451 77746 COS # USE COS(0) TO GET NON-ZERO IN MPAC
047265,000139: 13,2452 77624 CALLRPRT CALL
047266,000140: 13,2453 55716 RP-TO-R # EXIT WITH UNIT R VECTOR IN MPAC
047267,000141: 13,2454 16032 STODL ALPHAV
047268,000142: 13,2455 03673 ERADM
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Page 1130
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047270,000144: 13,2456 74215 DAD VXSC # (RE + ALT)(UNIT R) METERS B-30
047271,000145: 13,2457 01124 ALT
047272,000146: 13,2460 02032 ALPHAV
047273,000147: 13,2461 77772 VSL1 # R METERS B-29
047274,000148: 13,2462 36032 STCALL ALPHAV # EXIT WITH R IN METERS B-29
047275,000149: 13,2463 03674 INCORPEX
047276,000150:
047277,000151: # SUBROUTINE TO COMPUTE EARTH RADIUS
047278,000152:
047279,000153: # INPUT
047280,000154: # 1/2 SIN LAT IN ALPHAV +4
047281,000155:
047282,000156: # OUTPUT
047283,000157: # EARTH RADIUS IN ERADM AND MPAC (METERS B-29)
047284,000158:
047285,000159: 13,2464 63545 GETERAD DLOAD DSQ
047286,000160: 13,2465 02036 ALPHAV +4 # SIN**2(L)
047287,000161: 13,2466 44352 SL1 BDSU
047288,000162: 13,2467 24005 DP1/2 # COS**2(L)
047289,000163: 13,2470 44275 DMPR BDSU
047290,000164: 13,2471 26505 EE
047291,000165: 13,2472 24005 DP1/2
047292,000166: 13,2473 75465 BDDV SQRT
047293,000167: 13,2474 26501 B2XSC
047294,000168: 13,2475 77622 SR4R
047295,000169: 13,2476 03673 STORE ERADM
047296,000170: 13,2477 77616 RVQ
047297,000171:
047298,000172: # THE FOLLOWING CONSTANTS WERE COMPUTED WITH A=6378166, B=6356784 METERS
047299,000173: # B2XSC = B**2 SCALED B-51
047300,000174: # B2/A2 = B**2/A**2 SCALED B-1
047301,000175: # EE = (1-B**2/A**2) SCALED B-0
047302,000176:
047303,000177: 13,2500 00446 00305 B2XSC 2DEC .0179450689 # B**2 SCALED B-51
047304,000178: 13,2502 12,2004 DP1/2 = XUNIT
047305,000179: 13,2502 17711 05254 B2/A2 2DEC .9933064884 B-1 # GAMMA= B**2/A**2 B-1
047306,000180: 13,2504 00155 25250 EE 2DEC 6.6935116 E-3 # (1-B**2/A**2) B-0
047307,000181:
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Page 1131
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047309,000183: # ARCTAN SUBROUTINE
047310,000184:
047311,000185: # CALLING SEQUENCE
047312,000186: # SIN THETA IN SINTH B-1
047313,000187: # COS THETA IN COSTH B-1
047314,000188: # CALL ARCTAN
047315,000189:
047316,000190: # OUTPUT
047317,000191: # ARCTAN THETA IN MPAC AND THETA B-0 IN RANGE -1/2 TO +1/2
047318,000192:
047319,000193: 13,2506 77600 ARCTAN BOV
047320,000194: 13,2507 26510 CLROVFLW
047321,000195: 13,2510 63545 CLROVFLW DLOAD DSQ
047322,000196: 13,2511 00023 SINTH
047323,000197: 13,2512 63525 PDDL DSQ
047324,000198: 13,2513 00021 COSTH
047325,000199: 13,2514 77615 DAD
047326,000200: 13,2515 75454 BZE SQRT
047327,000201: 13,2516 26534 ARCTANXX # ATAN=0/0 SET THETA=0
047328,000202: 13,2517 40065 BDDV BOV
047329,000203: 13,2520 00023 SINTH
047330,000204: 13,2521 26541 ATAN=90
047331,000205: 13,2522 67542 SR1 ASIN
047332,000206: 13,2523 00025 STORE THETA
047333,000207: 13,2524 50125 PDDL BMN
047334,000208: 13,2525 00021 COSTH
047335,000209: 13,2526 26530 NEGCOS
047336,000210: 13,2527 43545 DLOAD RVQ
047337,000211: 13,2530 57545 NEGCOS DLOAD DCOMP
047338,000212: 13,2531 43244 BPL DAD
047339,000213: 13,2532 26536 NEGOUT
047340,000214: 13,2533 24005 DP1/2
047341,000215: 13,2534 00025 ARCTANXX STORE THETA
047342,000216: 13,2535 77616 RVQ
047343,000217:
047344,000218: 13,2536 52025 NEGOUT DSU GOTO
047345,000219: 13,2537 24005 DP1/2
047346,000220: 13,2540 26534 ARCTANXX
047347,000221: 13,2541 75345 ATAN=90 DLOAD SIGN
047348,000222: 13,2542 11003 LODP1/4
047349,000223: 13,2543 00023 SINTH
047350,000224: 13,2544 00025 STORE THETA
047351,000225: 13,2545 77616 RVQ
047352,000226:
047353,000227: 13,2546 12,2006 2DZERO = DPZERO
047354,000228:
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Page 1132
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047356,000230: # ..... SETGAMMA SUBROUTINE .....
047357,000231: # SUBROUTINE TO SET GAMMA FOR THE LAT-LONG AND LALOTORV SUBROUTINES
047358,000232:
047359,000233: # GAMMA = B**2/A**2 FOR EARTH (B-1)
047360,000234: # GAMMA = 1 FOR MOON (B-1)
047361,000235:
047362,000236: # CALLING SEQUENCE
047363,000237: # L CALL
047364,000238: # L+1 SETGAMMA
047365,000239:
047366,000240: # INPUT
047367,000241: # LUNAFLAG=0 FOR EARTH, =1 FOR MOON
047368,000242:
047369,000243: # OUTPUT
047370,000244: # GAMMA IN GAMRP (B-1)
047371,000245:
047372,000246: 13,2546 43145 SETGAMMA DLOAD BOFF # BRANCH FOR EARTH
047373,000247: 13,2547 26503 B2/A2 # EARTH GAMMA
047374,000248: 13,2550 01743 LUNAFLAG
047375,000249: 13,2551 26554 SETGMEX
047376,000250: 13,2552 77735 SLOAD
047377,000251: 13,2553 24005 1B1 # MOON GAMMA
047378,000252: 13,2554 00011 SETGMEX STORE GAMRP
047379,000253: 13,2555 77616 RVQ
047380,000254: 13,2556 GAMRP = 8D
047381,000255:
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Page 1133
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047383,000257: # ..... SETRE SUBROUTINE .....
047384,000258: # SUBROUTINE TO SET RE (EARTH OR MOON RADIUS)
047385,000259:
047386,000260: # RE = RM FOR MOON
047387,000261: # RE = RREF FOR FIXED EARTH RADIUS OR COMPUTED RF FOR FISCHER ELLIPSOID
047388,000262:
047389,000263: # CALLING SEQUENCE
047390,000264: # L CALL
047391,000265: # L+1 SETRE
047392,000266:
047393,000267: # SUBROUTINES USED
047394,000268: # GETERAD
047395,000269:
047396,000270: # INPUT
047397,000271: # ERADFLAG = 0 FOR FIXED RE, 1 FOR COMPUTED RE
047398,000272: # ALPHAV +4 = 1/2 SINL IF GETERAD IS CALLED
047399,000273: # LUNAFLAG = 0 FOR EARTH, =1 FOR MOON
047400,000274:
047401,000275: # OUTPUT
047402,000276: # ERADM = 504RM FOR MOON (METERS B-29)
047403,000277: # ERADM = ERAD OR COMPUTED RF FOR EARTH (METERS B-29)
047404,000278:
047405,000279: 13,2556 71220 SETRE STQ DLOAD
047406,000280: 13,2557 00051 SETREX
047407,000281: 13,2560 10003 504RM
047408,000282: 13,2561 71214 BON DLOAD # BRANCH FOR MOON
047409,000283: 13,2562 01703 LUNAFLAG
047410,000284: 13,2563 26573 TSTRLSRM
047411,000285: 13,2564 10001 ERAD
047412,000286: 13,2565 45014 BOFF CALL # ERADFLAG=0 FOR FIXED RE, 1 FOR COMPUTED
047413,000287: 13,2566 00742 ERADFLAG
047414,000288: 13,2567 26571 SETRXX
047415,000289: 13,2570 26464 GETERAD
047416,000290: 13,2571 37673 SETRXX STCALL ERADM # EXIT WITH RE OR RM METERS B-29
047417,000291: 13,2572 00051 SETREX
047418,000292: 13,2573 77214 TSTRLSRM BON VLOAD # ERADFLAG=0, SET R0=RLS
047419,000293: 13,2574 00702 ERADFLAG # =1 R0=RM
047420,000294: 13,2575 26571 SETRXX
047421,000295: 13,2576 02023 RLS
047422,000296: 13,2577 64446 ABVAL SR2R # SCALE FROM B-27 TO B-29
047423,000297: 13,2600 77650 GOTO
047424,000298: 13,2601 26571 SETRXX
047425,000299: 13,2602 0000051 SETREX = S2
047426,000300:
047427,000301:
End of include-file LATITUDE_LONGITUDE_SUBROUTINES.agc. Parent file is MAIN.agc