Source Code
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These source-code files are part of a reconstructed copy of Comanche 44, the
initial release (though not the final mission release) of the Apollo 10
Command Module (CM) Apollo Guidance Computer (AGC) software. Subsequent releases
were Comanche 45 and Comanche 45/2 (the flown release on Apollo 10). The reconstruction
is believed to be exactly accurate, but in the absence of an actual Apollo-era
listing of Comanche 44, some explanation of the reconstruction process is needed
to insure confidence in that accuracy.
The starting point was the source code of Comanche 51
(separately previously reconstructed from an Apollo-era listing of Comanche 55,
flown on Apollo 11). Comanche 51 source code was then modified
by undoing changes known to have been made between revisions 44 and 51. The now-reconstructed
Comanche 44 source code was verified by assembling it and checking that the assembled code had
the expected known-correct memory-bank checksums.
Note that page numbers in the reconstructed code match those on the Comanche 55 printout,
although the source code would likely have different page numbers in a contemporary
Comanche 44 listing.
Annotations that were not present in the contemporary source code have been added to the reconstructed
code to justify each change relative to Comanche 51. Here's a guide to the Apollo documentation referenced
in those annotations:
In most cases, only the titles (rather than the full texts) of PCRs are known. In addition to the
explanatory annotations, there is also
a step-by-step commentary about the reconstruction process.
Comments expected to have been present in 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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053027,000002: ## Copyright: Public domain.
053028,000003: ## Filename: LATITUDE_LONGITUDE_SUBROUTINES.agc
053029,000004: ## Purpose: A section of Comanche revision 044.
053030,000005: ## It is part of the reconstructed source code for the
053031,000006: ## original release of the flight software for the Command
053032,000007: ## Module's (CM) Apollo Guidance Computer (AGC) for Apollo 10.
053033,000008: ## The code has been recreated from a copy of Comanche 055. It
053034,000009: ## has been adapted such that the resulting bugger words
053035,000010: ## exactly match those specified for Comanche 44 in NASA drawing
053036,000011: ## 2021153D, which gives relatively high confidence that the
053037,000012: ## reconstruction is correct.
053038,000013: ## Assembler: yaYUL
053039,000014: ## Contact: Ron Burkey <info@sandroid.org>.
053040,000015: ## Website: www.ibiblio.org/apollo/index.html
053041,000016: ## Mod history: 2020-12-03 MAS Created from Comanche 51.
053042,000017:
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Page 1236
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053044,000019: # SUBROUTINE TO CONVERT RAD VECTOR AT GIVEN TIME TO LAT,LONG AND ALT
053045,000020:
053046,000021: # CALLING SEQUENCE
053047,000022: # L-1 CALL
053048,000023: # L LAT-LONG
053049,000024:
053050,000025: # SUBROUTINES USED
053051,000026: # R-TO-RP, ARCTAN, SETGAMMA, SETRE
053052,000027:
053053,000028: # ERASABLE INIT. REQ.
053054,000029: # AXO, -AYO, AZO, TEPHEM (SET AT LAUNCH TIME)
053055,000030: # ALPHAV = POSITION VECTOR METERS B-29
053056,000031: # MPAC -- TIME (CSECS B-28)
053057,000032: # ERADFLAG =1, TO COMPUTE EARTH RADIUS, =0 FOR FIXED EARTH RADIUS
053058,000033: # LUNAFLAG=0 FOR EARTH, 1 FOR MOON
053059,000034:
053060,000035: # OUTPUT
053061,000036: # LATITUDE IN LAT (REVS. B-0)
053062,000037: # LONGITUDE IN LONG (REVS. B-0)
053063,000038: # ALTITUDE IN ALT METERS B-29
053064,000039:
053065,000040: 30,3750 BANK 30
053066,000041: 13,2000 SETLOC LATLONG
053067,000042: 13,2000 BANK
053068,000043:
053069,000044: 13,2370 COUNT 13/LT-LG
053070,000045:
053071,000046: 13,2370 E4,1551 EBANK= ALPHAV
053072,000047: 13,2370 40220 LAT-LONG STQ SETPD
053073,000048: 13,2371 02242 INCORPEX
053074,000049: 13,2372 00001 0D
053075,000050: 13,2373 24007 STOVL 6D # SAVE TIME IN 6-7D FOR R-TO-RP
053076,000051: 13,2374 02152 ALPHAV
053077,000052: 13,2375 51406 PUSH ABVAL # 0-5D= R FOR R-TO-RP
053078,000053: 13,2376 16310 STODL ALPHAM # ABS. VALUE OF R FOR ALT FORMULA BELOW
053079,000054: 13,2377 11563 ZEROVEC # SET MPAC=0 FOR EARTH, NON-ZERO FOR MOON
053080,000055: 13,2400 71414 BOFF COS # USE COS(0) TO GET NON-ZERO IN MPAC
053081,000056: 13,2401 01743 LUNAFLAG # 0=EARTH, 1=MOON
053082,000057: 13,2402 26403 CALLRTRP
053083,000058: 13,2403 77624 CALLRTRP CALL
053084,000059: 13,2404 55371 R-TO-RP # RP VECTOR CONVERTED FROM R B-29
053085,000060: 13,2405 77656 UNIT # UNIT RP B-1
053086,000061: 13,2406 36152 STCALL ALPHAV # U2= 1/2 SINL FOR SETRE SUBR BELOW
053087,000062: 13,2407 26571 SETGAMMA # SET GAMMA=B2/A2 FOR EARTH, =1 FOR MOON
053088,000063: 13,2410 77624 CALL # SCALED B-1
053089,000064: 13,2411 26601 SETRE # CALC RE METERS B-29
053090,000065: 13,2412 63545 DLOAD DSQ
053091,000066: 13,2413 02152 ALPHAV
053092,000067: 13,2414 63525 PDDL DSQ
053093,000068: 13,2415 02154 ALPHAV +2
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Page 1237
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053095,000070: 13,2416 75415 DAD SQRT
053096,000071: 13,2417 76405 DMP SL1R
053097,000072: 13,2420 00011 GAMRP
053098,000073: 13,2421 14021 STODL COSTH # COS(LAT) B-1
053099,000074: 13,2422 02156 ALPHAV +4
053100,000075: 13,2423 34023 STCALL SINTH # SIN(LAT) B-1
053101,000076: 13,2424 26531 ARCTAN
053102,000077: 13,2425 15104 STODL LAT # LAT B0
053103,000078: 13,2426 02152 ALPHAV
053104,000079: 13,2427 14021 STODL COSTH # COS(LONG) B-1
053105,000080: 13,2430 02154 ALPHAV +2
053106,000081: 13,2431 34023 STCALL SINTH # SIN(LONG) B-1
053107,000082: 13,2432 26531 ARCTAN
053108,000083: 13,2433 15106 STODL LONG # LONG. REVS B-0 IN RANGE -1/2 TO 1/2
053109,000084: 13,2434 02310 ALPHAM
053110,000085: 13,2435 77625 DSU # ALT= R-RE METERS B-29
053111,000086: 13,2436 02241 ERADM
053112,000087: 13,2437 35110 STCALL ALT # EXIT WITH ALT METERS B-29
053113,000088: 13,2440 02242 INCORPEX
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Page 1238
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053115,000090: # SUBROUTINE TO CONVERT LAT,LONG,ALT AT GIVEN TIME TO RADIUS VECTOR
053116,000091:
053117,000092: # CALLING SEQUENCE
053118,000093: # L-1 CALL
053119,000094: # L LALOTORV
053120,000095:
053121,000096: # SUBROUTINES USED
053122,000097: # SETGAMMA, SETRE, RP-TO-R
053123,000098:
053124,000099: # ERASABLE INIT. REQ.
053125,000100: # AXO, AYO, AZO, TEPHEM SET AT LAUNCH TIME
053126,000101: # LAT -- LATITUDE (REVS B0)
053127,000102: # LONG -- LONGITUDE (REVS B0)
053128,000103: # ALT -- ALTITUDE (METERS) B-29
053129,000104: # MPAC -- TIME (CSECS B-28)
053130,000105: # ERADFLAG =1 TO COMPUTE EARTH RADIUS, =0 FOR FIXED EARTH RADIUS
053131,000106: # LUNAFLAG=0 FOR EARTH, 1 FOR MOON
053132,000107:
053133,000108: # OUTPUT
053134,000109: # R-VECTOR IN ALPHAV (METERS B-29)
053135,000110:
053136,000111: 13,2441 40220 LALOTORV STQ SETPD # LAT,LONG,ALT TO R VECTOR
053137,000112: 13,2442 02242 INCORPEX
053138,000113: 13,2443 00001 0D
053139,000114: 13,2444 34007 STCALL 6D # 6-7D = TIME FOR RP-TO-R
053140,000115: 13,2445 26571 SETGAMMA # GAMMA = B2/A2 FOR EARTH, 1 FOR MOON B-1
053141,000116: 13,2446 73545 DLOAD SIN # COS(LONG)COS(LAT) IN MPAC
053142,000117: 13,2447 01104 LAT # UNIT RP = SIN(LONG)COS(LAT) 2-3D
053143,000118: 13,2450 65275 DMPR PDDL # PD 2 GAMMA*SIN(LAT) 0-1D
053144,000119: 13,2451 00011 GAMRP
053145,000120: 13,2452 01104 LAT # 0-1D = GAMMA*SIN(LAT) B-2
053146,000121: 13,2453 65346 COS PDDL # PD4 2-3D= COS(LAT) B-1 TEMPORARILY
053147,000122: 13,2454 01106 LONG
053148,000123: 13,2455 57356 SIN DMPR # PD 2
053149,000124: 13,2456 71525 PDDL COS # PD 4 2-3D= SIN(LONG)COS(LAT) B-2
053150,000125: 13,2457 01104 LAT
053151,000126: 13,2460 71525 PDDL COS # PD 6 4-5D= COS(LAT) B-1 TEMPORARILY
053152,000127: 13,2461 01106 LONG
053153,000128: 13,2462 55475 DMPR VDEF # PD4 MPAC = COS(LONG)COS(LAT) B-2
053154,000129: 13,2463 41456 UNIT PUSH # 0-5D = UNIT RP FOR RP-TO-R SUBR.
053155,000130: 13,2464 36152 STCALL ALPHAV # ALPHAV +4= SINL FOR SETRE SUBR.
053156,000131: 13,2465 26601 SETRE # RE METERS B-29
053157,000132: 13,2466 43145 DLOAD BOFF # SET MPAC = 0 FOR EARTH, NON-ZERO FOR MOON
053158,000133: 13,2467 11563 ZEROVEC
053159,000134: 13,2470 01743 LUNAFLAG
053160,000135: 13,2471 26473 CALLRPRT
053161,000136: 13,2472 77746 COS # USE COS(0) TO GET NON-ZERO IN MPAC
053162,000137: 13,2473 77624 CALLRPRT CALL
053163,000138: 13,2474 55344 RP-TO-R # EXIT WITH UNIT R VECTOR IN MPAC
053164,000139: 13,2475 16152 STODL ALPHAV
053165,000140: 13,2476 02241 ERADM
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Page 1239
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053167,000142: 13,2477 74215 DAD VXSC # (RE + ALT)(UNIT R) METERS B-30
053168,000143: 13,2500 01110 ALT
053169,000144: 13,2501 02152 ALPHAV
053170,000145: 13,2502 77772 VSL1 # R METERS B-29
053171,000146: 13,2503 36152 STCALL ALPHAV # EXIT WITH R IN METERS B-29
053172,000147: 13,2504 02242 INCORPEX
053173,000148:
053174,000149: # SUBROUTINE TO COMPUTE EARTH RADIUS
053175,000150:
053176,000151: # INPUT
053177,000152: # 1/2 SIN LAT IN ALPHAV +4
053178,000153:
053179,000154: # OUTPUT
053180,000155: # EARTH RADIUS IN ERADM AND MPAC (METERS B-29)
053181,000156:
053182,000157: 13,2505 63545 GETERAD DLOAD DSQ
053183,000158: 13,2506 02156 ALPHAV +4 # SIN**2(L)
053184,000159: 13,2507 44352 SL1 BDSU
053185,000160: 13,2510 11561 DP1/2 # COS**2(L)
053186,000161: 13,2511 44275 DMPR BDSU
053187,000162: 13,2512 26526 EE
053188,000163: 13,2513 11561 DP1/2
053189,000164: 13,2514 75465 BDDV SQRT
053190,000165: 13,2515 26522 B2XSC
053191,000166: 13,2516 77622 SR4R
053192,000167: 13,2517 02241 STORE ERADM
053193,000168: 13,2520 77616 RVQ
053194,000169:
053195,000170: # THE FOLLOWING CONSTANTS WERE COMPUTED WITH A=6378166, B=6356784 METERS
053196,000171: # B2XSC = B**2 SCALED B-51
053197,000172: # B2/A2 = B**2/A**2 SCALED B-1
053198,000173: # EE = (1-B**2/A**2) SCALED B-0
053199,000174:
053200,000175: 13,2521 00446 00305 B2XSC 2DEC .0179450689 # B**2 SCALED B-51
053201,000176:
053202,000177: 13,2523 04,3560 DP1/2 = XUNIT
053203,000178: 13,2523 17711 05254 B2/A2 2DEC .9933064884 B-1 # GAMMA= B**2/A**2 B-1
053204,000179:
053205,000180: 13,2525 00155 25250 EE 2DEC 6.6935116 E-3 # (1-B**2/A**2) B-0
053206,000181:
053207,000182: 13,2527 00302 17755 ERAD 2DEC 6373338 B-29 # PAD RADIUS
053208,000183:
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Page 1240
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053210,000185: # ARCTAN SUBROUTINE
053211,000186:
053212,000187: # CALLING SEQUENCE
053213,000188: # SIN THETA IN SINTH B-1
053214,000189: # COS THETA IN COSTH B-1
053215,000190: # CALL ARCTAN
053216,000191:
053217,000192: # OUTPUT
053218,000193: # ARCTAN THETA IN MPAC AND THETA B-0 IN RANGE -1/2 TO +1/2
053219,000194:
053220,000195: 13,2531 77600 ARCTAN BOV
053221,000196: 13,2532 26533 CLROVFLW
053222,000197: 13,2533 63545 CLROVFLW DLOAD DSQ
053223,000198: 13,2534 00023 SINTH
053224,000199: 13,2535 63525 PDDL DSQ
053225,000200: 13,2536 00021 COSTH
053226,000201: 13,2537 77615 DAD
053227,000202: 13,2540 75454 BZE SQRT
053228,000203: 13,2541 26557 ARCTANXX # ATAN=0/0 SET THETA=0
053229,000204: 13,2542 40065 BDDV BOV
053230,000205: 13,2543 00023 SINTH
053231,000206: 13,2544 26564 ATAN=90
053232,000207: 13,2545 67542 SR1 ASIN
053233,000208: 13,2546 00025 STORE THETA
053234,000209: 13,2547 50125 PDDL BMN
053235,000210: 13,2550 00021 COSTH
053236,000211: 13,2551 26553 NEGCOS
053237,000212: 13,2552 43545 DLOAD RVQ
053238,000213: 13,2553 57545 NEGCOS DLOAD DCOMP
053239,000214: 13,2554 43244 BPL DAD
053240,000215: 13,2555 26561 NEGOUT
053241,000216: 13,2556 11561 DP1/2
053242,000217: 13,2557 00025 ARCTANXX STORE THETA
053243,000218: 13,2560 77616 RVQ
053244,000219:
053245,000220: 13,2561 52025 NEGOUT DSU GOTO
053246,000221: 13,2562 11561 DP1/2
053247,000222: 13,2563 26557 ARCTANXX
053248,000223: 13,2564 75345 ATAN=90 DLOAD SIGN
053249,000224: 13,2565 11607 LODP1/4
053250,000225: 13,2566 00023 SINTH
053251,000226: 13,2567 00025 STORE THETA
053252,000227: 13,2570 77616 RVQ
053253,000228:
053254,000229: 13,2571 04,3562 2DZERO = DPZERO
053255,000230:
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Page 1241
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053257,000232: # ..... SETGAMMA SUBROUTINE .....
053258,000233: # SUBROUTINE TO SET GAMMA FOR THE LAT-LONG AND LALOTORV SUBROUTINES
053259,000234:
053260,000235: # GAMMA = B**2/A**2 FOR EARTH (B-1)
053261,000236: # GAMMA = 1 FOR MOON (B-1)
053262,000237:
053263,000238: # CALLING SEQUENCE
053264,000239: # L CALL
053265,000240: # L+1 SETGAMMA
053266,000241:
053267,000242: # INPUT
053268,000243: # LUNAFLAG=0 FOR EARTH, =1 FOR MOON
053269,000244:
053270,000245: # OUTPUT
053271,000246: # GAMMA IN GAMRP (B-1)
053272,000247:
053273,000248: 13,2571 43145 SETGAMMA DLOAD BOFF # BRANCH FOR EARTH
053274,000249: 13,2572 26524 B2/A2 # EARTH GAMMA
053275,000250: 13,2573 01743 LUNAFLAG
053276,000251: 13,2574 26577 SETGMEX
053277,000252: 13,2575 77735 SLOAD
053278,000253: 13,2576 11561 1B1 # MOON GAMMA
053279,000254: 13,2577 00011 SETGMEX STORE GAMRP
053280,000255: 13,2600 77616 RVQ
053281,000256: 13,2601 GAMRP = 8D
053282,000257:
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Page 1242
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053284,000259: # ..... SETRE SUBROUTINE .....
053285,000260: # SUBROUTINE TO SET RE (EARTH OR MOON RADIUS)
053286,000261:
053287,000262: # RE = RM FOR MOON
053288,000263: # RE = RREF FOR FIXED EARTH RADIUS OR COMPUTED RF FOR FISCHER ELLIPSOID
053289,000264:
053290,000265: # CALLING SEQUENCE
053291,000266: # L CALL
053292,000267: # L+1 SETRE
053293,000268:
053294,000269: # SUBROUTINES USED
053295,000270: # GETERAD
053296,000271:
053297,000272: # INPUT
053298,000273: # ERADFLAG = 0 FOR FIXED RE, 1 FOR COMPUTED RE
053299,000274: # ALPHAV +4 = 1/2 SINL IF GETERAD IS CALLED
053300,000275: # LUNAFLAG = 0 FOR EARTH, =1 FOR MOON
053301,000276:
053302,000277: # OUTPUT
053303,000278: # ERADM = 504RM FOR MOON (METERS B-29)
053304,000279: # ERADM = ERAD OR COMPUTED RF FOR EARTH (METERS B-29)
053305,000280:
053306,000281: 13,2601 71220 SETRE STQ DLOAD
053307,000282: 13,2602 00051 SETREX
053308,000283: 13,2603 26626 504RM
053309,000284: 13,2604 71214 BON DLOAD # BRANCH FOR MOON
053310,000285: 13,2605 01703 LUNAFLAG
053311,000286: 13,2606 26616 TSTRLSRM
053312,000287: 13,2607 26530 ERAD
053313,000288: 13,2610 45014 BOFF CALL # ERADFLAG=0 FOR FIXED RE, 1 FOR COMPUTED
053314,000289: 13,2611 00742 ERADFLAG
053315,000290: 13,2612 26614 SETRXX
053316,000291: 13,2613 26505 GETERAD
053317,000292: 13,2614 36241 SETRXX STCALL ERADM # EXIT WITH RE OR RM METERS B-29
053318,000293: 13,2615 00051 SETREX
053319,000294: 13,2616 77214 TSTRLSRM BON VLOAD # ERADFLAG=0, SET R0=RLS
053320,000295: 13,2617 00702 ERADFLAG # =1 R0=RM
053321,000296: 13,2620 26614 SETRXX
053322,000297: 13,2621 02026 RLS
053323,000298: 13,2622 64446 ABVAL SR2R # SCALE FROM B-27 TO B-29
053324,000299: 13,2623 77650 GOTO
053325,000300: 13,2624 26614 SETRXX
053326,000301: 13,2625 0000051 SETREX = S2
053327,000302: 13,2625 00065 01265 504RM 2DEC 1738090 B-29 # METERS B-29 (MOON RADIUS)
053328,000303:
053329,000304:
053330,000305:
053331,000306:
End of include-file LATITUDE_LONGITUDE_SUBROUTINES.agc. Parent file is MAIN.agc