Source Code
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These source-code files are part of a reconstructed copy of Artemis 071, the
first release of the Apollo 15 through 17 Command Module (CM) Apollo Guidance
Computer (AGC) software.
The reconstruction began with source code of Artemis 072 previously transcribed
from a digitized copy of that program. The code was then updated by undoing
changes between the two versions. The reconstruction was verified by matching
memory-bank checksums to those listed in drawing 2021154-. Note that page
numbers in the reconstructed code match those on the Artemis 072 printout,
although the changed code would likely have changed page numbers for a real
Artemis 071 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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052760,000002: ## Copyright: Public domain.
052761,000003: ## Filename: LATITUDE_LONGITUDE_SUBROUTINES.agc
052762,000004: ## Purpose: A section of Artemis revision 071.
052763,000005: ## It is part of the reconstructed source code for the first
052764,000006: ## release of the flight software for the Command Module's
052765,000007: ## (CM) Apollo Guidance Computer (AGC) for Apollo 15 through
052766,000008: ## 17. The code has been recreated from a copy of Artemis 072.
052767,000009: ## It has been adapted such that the resulting bugger words
052768,000010: ## exactly match those specified for Artemis 071 in NASA
052769,000011: ## drawing 2021154-, which gives relatively high confidence
052770,000012: ## that the reconstruction is correct.
052771,000013: ## Reference: 1236
052772,000014: ## Assembler: yaYUL
052773,000015: ## Contact: Ron Burkey <info@sandroid.org>.
052774,000016: ## Website: www.ibiblio.org/apollo/index.html
052775,000017: ## Mod history: 2019-08-14 MAS Created from Artemis 072.
052776,000018:
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Page 1236
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052778,000020: # SUBROUTINE TO CONVERT RAD VECTOR AT GIVEN TIME TO LAT,LONG AND ALT
052779,000021:
052780,000022: # CALLING SEQUENCE
052781,000023:
052782,000024: # L-1 CALL
052783,000025: # L LAT-LONG
052784,000026:
052785,000027: # SUBROUTINES USED
052786,000028:
052787,000029: # R-TO-RP, ARCTAN, SETGAMMA, SETRE
052788,000030:
052789,000031: # ERASABLE INIT. REQ.
052790,000032:
052791,000033: # AXO, -AYO, AZO, TEPHEM (SET AT LAUNCH TIME)
052792,000034: # ALPHAV = POSITION VECTOR METERS B-29
052793,000035: # MPAC -- TIME (CSECS B-28)
052794,000036: # ERADFLAG =1, TO COMPUTE EARTH RADIUS, =0 FOR FIXED EARTH RADIUS
052795,000037: # LUNAFLAG=0 FOR EARTH, 1 FOR MOON
052796,000038:
052797,000039: # OUTPUT
052798,000040:
052799,000041: # LATITUDE IN LAT (REVS. B-0)
052800,000042: # LONGITUDE IN LONG (REVS. B-0)
052801,000043: # ALTITUDE IN ALT METERS B-29
052802,000044:
052803,000045: 13,2000 SETLOC LATLONG
052804,000046: 13,2000 BANK
052805,000047:
052806,000048: 13,2453 COUNT* $$/LT-LG
052807,000049: 13,2453 E4,1551 EBANK= ALPHAV
052808,000050: 13,2453 40220 LAT-LONG STQ SETPD
052809,000051: 13,2454 02241 INCORPEX
052810,000052: 13,2455 00001 0D
052811,000053: 13,2456 24007 STOVL 6D # SAVE TIME IN 6-7D FOR R-TO-RP
052812,000054: 13,2457 02152 ALPHAV
052813,000055: 13,2460 51406 PUSH ABVAL # 0-5D= R FOR R-TO-RP
052814,000056: 13,2461 16301 STODL ALPHAM # ABS. VALUE OF R FOR ALT FORMULA BELOW
052815,000057: 13,2462 11762 ZEROVEC # SET MPAC=0 FOR EARTH, NON-ZERO FOR MOON
052816,000058: 13,2463 71414 BOFF COS # USE COS(0) TO GET NON-ZERO IN MPAC
052817,000059: 13,2464 01743 LUNAFLAG # 0=EARTH,1=MOON
052818,000060: 13,2465 26466 CALLRTRP
052819,000061: 13,2466 77624 CALLRTRP CALL
052820,000062: 13,2467 55370 R-TO-RP # RP VECTOR CONVERTED FROM R B-29
052821,000063: 13,2470 77656 UNIT # UNIT RP B-1
052822,000064: 13,2471 36152 STCALL ALPHAV # U2= 1/2 SINL FOR SETRE SUBR BELOW
052823,000065: 13,2472 35766 SETGAMMA # SET GAMMA=B2/A2 FOR EARTH, =1 FOR MOON
052824,000066: 13,2473 77624 CALL # SCALED B-1
052825,000067: 13,2474 26654 SETRE # CALC RE METERS B-29
052826,000068: 13,2475 63545 DLOAD DSQ
052827,000069: 13,2476 02152 ALPHAV
052828,000070: 13,2477 63525 PDDL DSQ
052829,000071: 13,2500 02154 ALPHAV +2
052830,000072: 13,2501 75415 DAD SQRT
052831,000073: 13,2502 76405 DMP SL1R
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Page 1237
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052833,000075: 13,2503 00011 GAMRP
052834,000076: 13,2504 14021 STODL COSTH # COS(LAT) B-1
052835,000077: 13,2505 02156 ALPHAV +4
052836,000078: 13,2506 34023 STCALL SINTH # SIN(LAT) B-1
052837,000079: 13,2507 26614 ARCTAN
052838,000080: 13,2510 14747 STODL LAT # LAT B0
052839,000081: 13,2511 02152 ALPHAV
052840,000082: 13,2512 14021 STODL COSTH # COS(LONG) B-1
052841,000083: 13,2513 02154 ALPHAV +2
052842,000084: 13,2514 34023 STCALL SINTH # SIN(LONG) B-1
052843,000085: 13,2515 26614 ARCTAN
052844,000086: 13,2516 14751 STODL LONG # LONG. REVS B-0 IN RANGE -1/2 TO 1/2
052845,000087: 13,2517 02301 ALPHAM
052846,000088: 13,2520 77625 DSU # ALT= R-RE METERS B-29
052847,000089: 13,2521 02240 ERADM
052848,000090: 13,2522 34753 STCALL ALT # EXIT WITH ALT METERS B-29
052849,000091: 13,2523 02241 INCORPEX
052850,000092:
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Page 1238
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052852,000094: # SUBROUTINE TO CONVERT LAT,LONG,ALT AT GIVEN TIME TO RADIUS VECTOR
052853,000095:
052854,000096: # CALLING SEQUENCE
052855,000097:
052856,000098: # L-1 CALL
052857,000099: # L LALOTORV
052858,000100:
052859,000101: # SUBROUTINES USED
052860,000102:
052861,000103: # SETGAMMA, SETRE, RP-TO-R
052862,000104:
052863,000105: # ERASABLE INIT. REQ.
052864,000106:
052865,000107: # AXO, AYO, AZO, TEPHEM SET AT LAUNCH TIME
052866,000108: # LAT -- LATITUDE (REVS B0)
052867,000109: # LONG -- LONGITUDE (REVS B0)
052868,000110: # ALT -- ALTITUDE (METERS) B-29
052869,000111: # MPAC -- TIME (CSECS B-28)
052870,000112: # ERADFLAG =1 TO COMPUTE EARTH RADIUS, =0 FOR FIXED EARTH RADIUS
052871,000113: # LUNAFLAG=0 FOR EARTH, 1 FOR MOON
052872,000114:
052873,000115: # OUTPUT
052874,000116:
052875,000117: # R-VECTOR IN ALPHAV (METERS B-29)
052876,000118:
052877,000119: 13,2524 40220 LALOTORV STQ SETPD # LAT,LONG,ALT TO R VECTOR
052878,000120: 13,2525 02241 INCORPEX
052879,000121: 13,2526 00001 0D
052880,000122: 13,2527 34007 STCALL 6D # 6-7D = TIME FOR RP-TO-R
052881,000123: 13,2530 35766 SETGAMMA # GAMMA = B2/A2 FOR EARTH, 1 FOR MOON B-1
052882,000124: 13,2531 73545 DLOAD SIN # COS(LONG)COS(LAT) IN MPAC
052883,000125: 13,2532 00747 LAT # UNIT RP = SIN(LONG)COS(LAT) 2-3D
052884,000126: 13,2533 65275 DMPR PDDL # PD 2 GAMMA*SIN(LAT) 0-1D
052885,000127: 13,2534 00011 GAMRP
052886,000128: 13,2535 00747 LAT # 0-1D = GAMMA*SIN(LAT) B-2
052887,000129: 13,2536 65346 COS PDDL # PD4 2-3D = COS(LAT) B-1 TEMPORARILY
052888,000130: 13,2537 00751 LONG
052889,000131: 13,2540 57356 SIN DMPR # PD 2
052890,000132: 13,2541 71525 PDDL COS # PD 4 2-3D = SIN(LONG)COS(LAT) B-2
052891,000133: 13,2542 00747 LAT
052892,000134: 13,2543 71525 PDDL COS # PD 6 4-5D = COS(LAT) B-1 TEMPORARILY
052893,000135: 13,2544 00751 LONG
052894,000136: 13,2545 55475 DMPR VDEF # PD4 MPAC = COS(LONG)COS(LAT) B-2
052895,000137: 13,2546 41456 UNIT PUSH # 0-5D = UNIT RP FOR RP-TO-R SUBR.
052896,000138: 13,2547 36152 STCALL ALPHAV # ALPHAV +4= SINL FOR SETRE SUBR.
052897,000139: 13,2550 26654 SETRE # RE METERS B-29
052898,000140: 13,2551 43145 DLOAD BOFF # SET MPAC = 0 FOR EARTH, NON-ZERO FOR MOON
052899,000141: 13,2552 11762 ZEROVEC
052900,000142: 13,2553 01743 LUNAFLAG
052901,000143: 13,2554 26556 CALLRPRT
052902,000144: 13,2555 77746 COS # USE COS(0) TO GET NON-ZERO IN MPAC
052903,000145: 13,2556 77624 CALLRPRT CALL
052904,000146: 13,2557 55345 RP-TO-R # EXIT WITH UNIT R VECTOR IN MPAC
052905,000147: 13,2560 16152 STODL ALPHAV
052906,000148: 13,2561 02240 ERADM
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Page 1239
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052908,000150: 13,2562 74215 DAD VXSC # (RE + ALT)(UNIT R) METERS B-30
052909,000151: 13,2563 00753 ALT
052910,000152: 13,2564 02152 ALPHAV
052911,000153: 13,2565 77772 VSL1 # R METERS B-29
052912,000154: 13,2566 36152 STCALL ALPHAV # EXIT WITH R IN METERS B-29
052913,000155: 13,2567 02241 INCORPEX
052914,000156:
052915,000157: # SUBROUTINE TO COMPUTE EARTH RADIUS
052916,000158:
052917,000159: # INPUT
052918,000160:
052919,000161: # 1/2 SIN LAT IN ALPHAV +4
052920,000162:
052921,000163: # OUTPUT
052922,000164:
052923,000165: # EARTH RADIUS IN ERADM AND MPAC (METERS B-29)
052924,000166:
052925,000167: 13,2570 63545 GETERAD DLOAD DSQ
052926,000168: 13,2571 02156 ALPHAV +4 # SIN**2(L)
052927,000169: 13,2572 44352 SL1 BDSU
052928,000170: 13,2573 11760 DP1/2 # COS**2(L)
052929,000171: 13,2574 44275 DMPR BDSU
052930,000172: 13,2575 26611 EE
052931,000173: 13,2576 11760 DP1/2
052932,000174: 13,2577 75465 BDDV SQRT
052933,000175: 13,2600 26605 B2XSC
052934,000176: 13,2601 77622 SR4R
052935,000177: 13,2602 02240 STORE ERADM
052936,000178: 13,2603 77616 RVQ
052937,000179:
052938,000180: # THE FOLLOWING CONSTANTS WERE COMPUTED WITH A=6378166, B=6356784 METERS
052939,000181: # B2XSC = B**2 SCALED B-51
052940,000182: # B2/A2 = B**2/A**2 SCALED B-1
052941,000183: # EE = (1-B**2/A**2) SCALED B-0
052942,000184:
052943,000185: 13,2604 00446 00305 B2XSC 2DEC .0179450689 # B**2 SCALED B-51
052944,000186: 13,2606 04,3757 DP1/2 = XUNIT
052945,000187: 13,2606 17711 05254 B2/A2 2DEC .9933064884 B-1 # GAMMA= B**2/A**2 B-1
052946,000188: 13,2610 00155 25250 EE 2DEC 6.6935116 E-3 # (1-B**2/A**2) B-0
052947,000189: 13,2612 00302 17755 ERAD 2DEC 6373338 B-29 # PAD RADIUS
052948,000190:
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Page 1240
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052950,000192: # ARCTAN SUBROUTINE
052951,000193:
052952,000194: # CALLING SEQUENCE
052953,000195:
052954,000196: # SIN THETA IN SINTH B-1
052955,000197: # COS THETA IN COSTH B-1
052956,000198: # CALL ARCTAN
052957,000199:
052958,000200: # OUTPUT
052959,000201: # ARCTAN THETA IN MPAC AND THETA B-0 IN RANGE -1/2 TO +1/2
052960,000202:
052961,000203: 13,2614 77600 ARCTAN BOV
052962,000204: 13,2615 26616 CLROVFLW
052963,000205: 13,2616 63545 CLROVFLW DLOAD DSQ
052964,000206: 13,2617 00023 SINTH
052965,000207: 13,2620 63525 PDDL DSQ
052966,000208: 13,2621 00021 COSTH
052967,000209: 13,2622 77615 DAD
052968,000210: 13,2623 75454 BZE SQRT
052969,000211: 13,2624 26642 ARCTANXX # ATAN=0/0 SET THETA=0
052970,000212: 13,2625 40065 BDDV BOV
052971,000213: 13,2626 00023 SINTH
052972,000214: 13,2627 26647 ATAN=90
052973,000215: 13,2630 67542 SR1 ASIN
052974,000216: 13,2631 00025 STORE THETA
052975,000217: 13,2632 50125 PDDL BMN
052976,000218: 13,2633 00021 COSTH
052977,000219: 13,2634 26636 NEGCOS
052978,000220: 13,2635 43545 DLOAD RVQ
052979,000221: 13,2636 57545 NEGCOS DLOAD DCOMP
052980,000222: 13,2637 43244 BPL DAD
052981,000223: 13,2640 26644 NEGOUT
052982,000224: 13,2641 11760 DP1/2
052983,000225: 13,2642 00025 ARCTANXX STORE THETA
052984,000226: 13,2643 77616 RVQ
052985,000227:
052986,000228: 13,2644 52025 NEGOUT DSU GOTO
052987,000229: 13,2645 11760 DP1/2
052988,000230: 13,2646 26642 ARCTANXX
052989,000231: 13,2647 75345 ATAN=90 DLOAD SIGN
052990,000232: 13,2650 33412 LODP1/4
052991,000233: 13,2651 00023 SINTH
052992,000234: 13,2652 00025 STORE THETA
052993,000235: 13,2653 77616 RVQ
052994,000236:
052995,000237: 13,2654 04,3761 2DZERO = DPZERO
052996,000238:
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Page 1241
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052998,000240: # ..... SETGAMMA SUBROUTINE .....
052999,000241: # SUBROUTINE TO SET GAMMA FOR THE LAT-LONG AND LALOTORV SUBROUTINES
053000,000242:
053001,000243: # GAMMA = B**2/A**2 FOR EARTH (B-1)
053002,000244: # GAMMA = 1 FOR MOON (B-1)
053003,000245:
053004,000246: # CALLING SEQUENCE
053005,000247: # L CALL
053006,000248: # L+1 SETGAMMA
053007,000249:
053008,000250: # INPUT
053009,000251: # LUNAFLAG=0 FOR EARTH, =1 FOR MOON
053010,000252:
053011,000253: # OUTPUT
053012,000254: # GAMMA IN GAMRP (B-1)
053013,000255:
053014,000256: 16,2000 SETLOC LATLONG1
053015,000257: 16,2000 BANK
053016,000258: 16,3766 COUNT* $$/LT-LG
053017,000259:
053018,000260: 16,3766 43145 SETGAMMA DLOAD BOFF # BRANCH FOR EARTH
053019,000261: 16,3767 26607 B2/A2 # EARTH GAMMA
053020,000262: 16,3770 01743 LUNAFLAG
053021,000263: 16,3771 35774 SETGMEX
053022,000264: 16,3772 77735 SLOAD
053023,000265: 16,3773 11760 1B1 # MOON GAMMA
053024,000266: 16,3774 00011 SETGMEX STORE GAMRP
053025,000267: 16,3775 77616 RVQ
053026,000268: 16,3776 GAMRP = 8D
053027,000269: 13,2000 SETLOC LATLONG
053028,000270: 13,2000 BANK
053029,000271:
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Page 1242
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053031,000273: # ..... SETRE SUBROUTINE .....
053032,000274: # SUBROUTINE TO SET RE (EARTH OR MOON RADIUS)
053033,000275:
053034,000276: # RE = RM FOR MOON
053035,000277: # RE = RREF FOR FIXED EARTH RADIUS OR COMPUTED RF FOR FISCHER ELLIPSOID
053036,000278:
053037,000279: # CALLING SEQUENCE
053038,000280: # L CALL
053039,000281: # L+1 SETRE
053040,000282:
053041,000283: # SUBROUTINES USED
053042,000284: # GETERAD
053043,000285:
053044,000286: # INPUT
053045,000287: # ERADFLAG = 0 FOR FIXED RE, 1 FOR COMPUTED RE
053046,000288: # ALPHAV +4 = 1/2 SINL IF GETERAD IS CALLED
053047,000289: # LUNAFLAG = 0 FOR EARTH, =1 FOR MOON
053048,000290:
053049,000291: # OUTPUT
053050,000292: # ERADM = 504RM FOR MOON (METERS B-29)
053051,000293: # ERADM = ERAD OR COMPUTED RF FOR EARTH (METERS B-29)
053052,000294:
053053,000295: 13,2654 71220 SETRE STQ DLOAD
053054,000296: 13,2655 00051 SETREX
053055,000297: 13,2656 26701 504RM
053056,000298: 13,2657 71214 BON DLOAD # BRANCH FOR MOON
053057,000299: 13,2660 01703 LUNAFLAG
053058,000300: 13,2661 26671 TSTRLSRM
053059,000301: 13,2662 26613 ERAD
053060,000302: 13,2663 45014 BOFF CALL # ERADFLAG=0 FOR FIXED RE, 1 FOR COMPUTED
053061,000303: 13,2664 00742 ERADFLAG
053062,000304: 13,2665 26667 SETRXX
053063,000305: 13,2666 26570 GETERAD
053064,000306: 13,2667 36240 SETRXX STCALL ERADM # EXIT WITH RE OR RM METERS B-29
053065,000307: 13,2670 00051 SETREX
053066,000308: 13,2671 77214 TSTRLSRM BON VLOAD # ERADFLAG=0, SET R0=RLS
053067,000309: 13,2672 00702 ERADFLAG # =1 R0=RM
053068,000310: 13,2673 26667 SETRXX
053069,000311: 13,2674 02026 RLS
053070,000312: 13,2675 64446 ABVAL SR2R # SCALE FROM B-27 TO B-29
053071,000313: 13,2676 77650 GOTO
053072,000314: 13,2677 26667 SETRXX
053073,000315: 13,2700 0000051 SETREX = S2
053074,000316: 13,2700 00065 01265 504RM 2DEC 1738090 B-29 # METERS B-29 (MOON RADIUS)
End of include-file LATITUDE_LONGITUDE_SUBROUTINES.agc. Parent file is MAIN.agc