Source Code

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, 1969
Note 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: 

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

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

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                                            

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