Source Code
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This source code is very close to the Apollo Guidance Computer software for the
Apollo 13 Lunar module. This revision of the Luminary 131 program is from December
of 1969, whereas there was a later revision in January of 1970, and still another
revision in February, which is the code that flew on the mission.
As far as this transcription is concerned, it was originally from a copy made in 1991 of
a printout from the collection of AGC developer Don Eyles for collector David Craig.
It was subsequently scanned by Gary Neff, reprocessed for online
presentation at the now-discontinued History of Recent Science and Technology (HRST) website
of MIT's Dibner Institute (the full-quality scans being discarded in the process),
and finally transcribed by Ron Burkey for the Virtual AGC Project. Although a
high-quality replacement scan for a completely illegible page was later provided by Gary
Neff, the reduced legibility of the reprocessed HRST posting nevertheless caused many
errors to be introduced into the transcription. Accordingly, a second scan of the same physical
printout was made in 2017 for the Virtual AGC Project's collection at the Internet Archive,
and used to correct the transcription errors. All of the scanned materials mentioned,
as well as other Luminary 131 related material, are available online.
Don Eyles apprently made additional hand-written notes in printout between 1991 and 2017,
so the two scans are not identical in that respect. The page-headings in the printout read, in part:GAP: ASSEMBLE REVISION 131 OF AGC PROGRAM LUMINARY BY NASA 2021112-091 17:53 DEC. 19, 1969Note that the date is the date the printout was made, not the date on which the program revision was released, although these happen to be very close together. |
041850,000002: ## Copyright: Public domain.
041851,000003: ## Filename: LUNAR_AND_SOLAR_EPHEMERIDES_SUBROUTINES.agc
041852,000004: ## Purpose: A section of Luminary 1C, revision 131.
041853,000005: ## It is part of the source code for the Lunar Module's (LM)
041854,000006: ## Apollo Guidance Computer (AGC) for Apollo 13.
041855,000007: ## This file is intended to be a faithful transcription, except
041856,000008: ## that the code format has been changed to conform to the
041857,000009: ## requirements of the yaYUL assembler rather than the
041858,000010: ## original YUL assembler.
041859,000011: ## Reference: pp. 978-981
041860,000012: ## Contact: Ron Burkey <info@sandroid.org>.
041861,000013: ## Website: www.ibiblio.org/apollo/index.html
041862,000014: ## Mod history: 05/29/03 RSB. Began transcribing.
041863,000015: ## 05/14/05 RSB Corrected website reference above.
041864,000016: ## 2017-01-06 RSB Page numbers now agree with those on the
041865,000017: ## original hardcopy, as opposed to the PDF page
041866,000018: ## numbers in 1701.pdf.
041867,000019: ## 2017-02-26 RSB Proofed comment text using octopus/ProoferComments.
041868,000020: ## 2017-03-13 RSB Comment-text fixes noted in proofing Luminary 116.
041869,000021:
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Page 978 |
041871,000023: # NAME - LSPOS - LOCATE SUN AND MOON DATE - 25 OCT 67
041872,000024: # MOD NO.1
041873,000025: # MOD BY NEVILLE ASSEMBLY SUNDANCE
041874,000026:
041875,000027: # FUNCTIONAL DESCRIPTION
041876,000028:
041877,000029: # COMPUTES UNIT POSITION VECTOR OF THE SUN AND MOON IN THE BASIC REFERENCE SYSTEM. THE SUN VECTOR S IS
041878,000030: # LOCATED VIA TWO ANGLES. THE FIRST ANGLE (OBLIQUITY) IS THE ANGLE BETWEEN THE EARTH EQUATOR AND THE ECLIPTIC. THE
041879,000031: # SECOND ANGLE IS THE LONGITUDE OF THE SUN MEASURED IN THE ECLIPTIC.
041880,000032: # THE POSITION VECTOR OF THE SUN IS
041881,000033: # -
041882,000034: # S = (COS(LOS), COS(OBL)*SIN(LOS), SIN(OBL)*SIN(LOS)), WHERE
041883,000035:
041884,000036: # LOS = LOS +LOS *T-(C *SIN(2PI*T)/365.24 +C *COS(2PI*T)/365.24)
041885,000037: # 0 R 0 1
041886,000038: # LOS (RAD) IS THE LONGITUDE OF THE SUN FOR MIDNIGHT JUNE 30TH OF THE PARTICULAR YEAR.
041887,000039: # 0
041888,000040: # LOS (RAD/DAY) IS THE MEAN RATE FOR THE PARTICULAR YEAR.
041889,000041: # R
041890,000042:
041891,000043: # LOS AND LOS ARE STORED AS LOSC AND LOSR IN RATESP.
041892,000044: # 0 R
041893,000045: # COS(OBL) AND SIN(OBL) ARE STORED IN THE MATRIX KONMAT.
041894,000046:
041895,000047: # T, TIME MEASURED IN DAYS (24 HOURS), IS STORED IN TIMEP.
041896,000048:
041897,000049: # C AND C ARE FUDGE FACTORS TO MINIMIZE THE DEVIATION. THEY ARE STORED AS ONE CONSTANT (CMOD), SINCE
041898,000050: # 0 1 2 2 1/2
041899,000051: # C *SIN(X)+C *COS(X) CAN BE WRITTEN AS (C +C ) *SIN(X+PHI), WHERE PHI=ARCTAN(C /C ).
041900,000052: # 0 1 0 1 1 0
041901,000053:
041902,000054: # THE MOON IS LOCATED VIA FOUR ANGLES, THE FIRST IS THE OBLIQUITY. THE SECOND IS THE MEAN LONGITUDE OF THE MOON,
041903,000055: # MEASURED IN THE ECLIPTIC FROM THE MEAN EQUINOX TO THE MEAN ASCENDING NODE OF THE LUNAR ORBIT, AND THEN ALONG THE
041904,000056: # ORBIT. THE THIRD ANGLE IS THE ANGLE BETWEEN THE ECLIPTIC AND THE LUNAR ORBIT. THE FOURTH ANGLE IS THE LONGITUDE
041905,000057: # OF THE NODE OF THE MOON, MEASURED IN THE LUNAR ORBIT. LET THESE ANGLES BE OBL,LOM,IM, AND LON RESPECTIVELY.
041906,000058:
041907,000059: # THE SIMPLIFIED POSITION VECTOR OF THE MOON IS
041908,000060: # -
041909,000061: # M=(COS(LOM), COS(OBL)*SIN(LOM)-SIN(OBL)*SIN(IM)*SIN(LOM-LON), SIN(OBL)*SIN(LOM)+COS(OBL)*SIN(IM)*SIN(LOM-LON))
041910,000062:
041911,000063: # WHERE
041912,000064: # LOM=LOM +LOM *T-(A *SIN 2PI*T/27.5545+A *COS(2PI*T/27.5545)+B *SIN 2PI*T/32+B *COS(2PI*T/32)), AND
041913,000065: # 0 R 0 1 0 1
041914,000066: # LON=LON +LON
041915,000067: # 0 R
041916,000068: # A , A , B AND B ARE STORED AS AMOD AND BMOD (SEE DESCRIPTION OF CMOD, ABOVE). COS(OBL), SIN(OBL)*SIN(IM),
041917,000069: # 0 1 0 1
041918,000070: # SIN(OBL), AND COS(OBL)*SIN(IM) ARE STORED IN KONMAT AS K1, K2, K3 AND K4, RESPECTIVELY. LOM , LOM , LON , LON
041919,000071: # ARE STORED AS LOM0, LOMR, LON0, AND LONR IN RATESP. 0 R 0 R
041920,000072:
041921,000073: # THE THREE PHIS ARE STORED AS AARG, BARG, AND CARG(SUN). ALL CONSTANTS ARE UPDATED BY YEAR.
041922,000074:
041923,000075: # CALLING SEQUENCE
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Page 979 |
041925,000077: # CALL LSPOS. RETURN IS VIA CPRET.
041926,000078:
041927,000079: # ALARMS OR ABORTS
041928,000080: # NONE
041929,000081:
041930,000082: # ERASABLE INITIALIZATION REQUIRED
041931,000083: # TEPHEM - TIME FROM MIDNIGHT 1 JULY PRECEDING THE LAUNCH TO THE TIME OF THE LAUNCH (WHEN THE AGC CLOCK WENT
041932,000084: # TO ZERO). TEPHEM IS TP WITH UNITS OF CENTI-SECONDS.
041933,000085:
041934,000086: # TIME2 AND TIME1 ARE IN MPAC AND MPAC +1 WHEN PROGRAM IS CALLED.
041935,000087:
041936,000088: # OUTPUT
041937,000089: # UNIT POSITIONAL VECTOR OF SUN IN VSUN. (SCALED B-1)
041938,000090: # UNIT POSITIONAL VECTOR OF MOON IN VMOON. (SCALED B-1)
041939,000091:
041940,000092: # SUBROUTINES USED
041941,000093: # NONE
041942,000094:
041943,000095: # DEBRIS
041944,000096: # CURRENT CORE SET, WORK AREA AND FREEFLAG
041945,000097:
041946,000098: 04,2773 BANK 04
041947,000099: 15,2000 SETLOC EPHEM
041948,000100: 15,2000 BANK
041949,000101:
041950,000102: 15,3647 E5,1714 EBANK= VSUN
041951,000103: 15,3647 COUNT* $$/EPHEM
041952,000104: 15,3647 15,3647 LUNPOS EQUALS LSPOS
041953,000105:
041954,000106: 15,3647 54201 LSPOS SETPD SR
041955,000107: 15,3650 00001 0
041956,000108: 15,3651 20617 14D # TP
041957,000109: 15,3652 56371 TAD DDV
041958,000110: 15,3653 01707 TEPHEM # TIME OF LAUNCH
041959,000111: 15,3654 12024 CSTODAY # 24 HOURS-8640000 CENTI-SECS/DAY B-33
041960,000112: 15,3655 00031 STORE TIMEP # T IN DAYS
041961,000113: 15,3656 77170 AXT,1 AXT,2
041962,000114: 15,3657 00000 0
041963,000115: 15,3660 00000 0
041964,000116: 15,3661 77614 CLEAR
041965,000117: 15,3662 00274 FREEFLAG # SWITCH BIT
041966,000118: 15,3663 77745 POSITA DLOAD
041967,000119: 15,3664 12004 KONMAT +2 # ZEROS
041968,000120: 15,3665 00027 STORE GTMP
041969,000121: 15,3666 40745 POSITB DLOAD DMP*
041970,000122: 15,3667 00031 TIMEP # T
041971,000123: 15,3670 12050 VAL67 +4,1 # 1/27 OR 1/32 OR 1/365
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Page 980 |
041973,000125: 15,3671 42661 SL DAD*
041974,000126: 15,3672 20211 8D
041975,000127: 15,3673 12046 VAL67 +2,1 # AARG
041976,000128: 15,3674 40756 SIN DMP* # SIN(T/27+PHI) OR T/32 OR T/365
041977,000129: 15,3675 12044 VAL67,1 # (A0**2+A1**2)**1/2 SIN(X+PHIA)
041978,000130: 15,3676 62015 DAD INCR,1 # PLUS
041979,000131: 15,3677 00027 GTMP # (B0**2+B1**2)**1/2 SIN(X+PHIB)
041980,000132: 15,3700 77771 DEC -6 B-14
041981,000133: 15,3701 00027 STORE GTMP # OR (C0**2+C1**2)**1/2 SIN(X+PHIC)
041982,000134: 15,3702 77614 BOFSET
041983,000135: 15,3703 00054 FREEFLAG
041984,000136: 15,3704 33666 POSITB
041985,000137: 15,3705 40745 POSITD DLOAD DMP*
041986,000138: 15,3706 00031 TIMEP # T
041987,000139: 15,3707 65747 RATESP,2 # LOMR,LOSR,LONR
041988,000140: 15,3710 42661 SL DAD*
041989,000141: 15,3711 20206 5D
041990,000142: 15,3712 65741 RATESP +6,2 # LOMO,LOSO,LONO
041991,000143: 15,3713 77625 DSU
041992,000144: 15,3714 00027 GTMP
041993,000145: 15,3715 10021 STORE STMP,2 # LOM,LOS,LON
041994,000146: 15,3716 63135 SLOAD INCR,2
041995,000147: 15,3717 00050 X2
041996,000148: 15,3720 77775 DEC -2 B-14
041997,000149: 15,3721 53015 DAD BZE
041998,000150: 15,3722 12026 RCB-13 # PLUS 2
041999,000151: 15,3723 33753 POSITE # 2ND
042000,000152: 15,3724 77644 BPL
042001,000153: 15,3725 33663 POSITA # 1ST
042002,000154: 15,3726 45345 POSITF DLOAD DSU # 3RD
042003,000155: 15,3727 00021 STMP # LOM
042004,000156: 15,3730 00025 STMP +4 # LON
042005,000157: 15,3731 65356 SIN PDDL # SIN(LOM-LON)
042006,000158: 15,3732 00021 STMP
042007,000159: 15,3733 65356 SIN PDDL # SIN LOM
042008,000160: 15,3734 00021 STMP
042009,000161: 15,3735 55546 COS VDEF # COS LOM
042010,000162: 15,3736 53521 MXV UNIT
042011,000163: 15,3737 12002 KONMAT # K1,K2,K3,K4,
042012,000164: 15,3740 02723 STORE VMOON
042013,000165: 15,3741 65345 DLOAD PDDL
042014,000166: 15,3742 12004 KONMAT +2 # ZERO
042015,000167: 15,3743 00023 STMP +2
042016,000168: 15,3744 65356 SIN PDDL # SIN LOS
042017,000169: 15,3745 00023 STMP +2
042018,000170: 15,3746 55546 COS VDEF # COS LOS
042019,000171: 15,3747 53521 MXV UNIT
042020,000172: 15,3750 12002 KONMAT
042021,000173: 15,3751 02715 STORE VSUN
042022,000174: 15,3752 77616 RVQ
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Page 981 |
042024,000176: 15,3753 77745 POSITE DLOAD
042025,000177: 15,3754 12004 KONMAT +2 # ZEROS
042026,000178: 15,3755 00027 STORE GTMP
042027,000179: 15,3756 77650 GOTO
042028,000180: 15,3757 33705 POSITD
042029,000181: 05,2000 SETLOC EPHEM1
042030,000182: 05,2000 BANK
042031,000183:
042032,000184: 05,3505 COUNT* $$/EPHEM
042033,000185: 05,3505 STMP EQUALS 16D
042034,000186: 05,3505 GTMP EQUALS 22D
042035,000187: 05,3505 TIMEP EQUALS 24D
042036,000188:
End of include-file LUNAR_AND_SOLAR_EPHEMERIDES_SUBROUTINES.agc. Parent file is MAIN.agc