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.

013393,000002:                                                                                                  ## Copyright:   Public domain.
013394,000003:                                                                                                  ## Filename:    LEM_GEOMETRY.agc
013395,000004:                                                                                                  ## Purpose:     A section of Luminary 1C, revision 131.
013396,000005:                                                                                                  ##              It is part of the source code for the Lunar Module's (LM)
013397,000006:                                                                                                  ##              Apollo Guidance Computer (AGC) for Apollo 13.
013398,000007:                                                                                                  ##              This file is intended to be a faithful transcription, except
013399,000008:                                                                                                  ##              that the code format has been changed to conform to the
013400,000009:                                                                                                  ##              requirements of the yaYUL assembler rather than the 
013401,000010:                                                                                                  ##              original YUL assembler.
013402,000011:                                                                                                  ## Reference:   pp. 322-327
013403,000012:                                                                                                  ## Contact:     Ron Burkey <info@sandroid.org>.
013404,000013:                                                                                                  ## Website:     www.ibiblio.org/apollo/index.html
013405,000014:                                                                                                  ## Mod history: 05/10/03 RSB.   Began transcribing.
013406,000015:                                                                                                  ##              05/14/05 RSB    Corrected website reference above.
013407,000016:                                                                                                  ##              2010-08-24 JL   Fixed page 330 number.
013408,000017:                                                                                                  ##              2017-01-06 RSB  Page numbers now agree with those on the
013409,000018:                                                                                                  ##                              original harcopy, as opposed to the PDF page
013410,000019:                                                                                                  ##                              numbers in 1701.pdf.
013411,000020:                                                                                                  ##              2017-02-23 RSB  Proofed comment text using octopus/ProoferComments.
013412,000021:                                                                                                  ##              2017-03-07 RSB  Fixed comment-text error noted while proofing
013413,000022:                                                                                                  ##                              Luminary 116.
013414,000023: 

Page 322

013416,000025: 23,2041                                           BANK     23                                    
013417,000026: 13,2000                                           SETLOC   LEMGEOM                               
013418,000027: 13,2000                                           BANK                                           
013419,000028: 
013420,000029: 13,2070  30,2000                                  SBANK=   LOWSUPER                              
013421,000030: 13,2070  E5,1642                                  EBANK=   XSM                                   
013422,000031: 
013423,000032:                                                                                                  #  THESE TWO ROUTINES COMPUTE THE ACTUAL STATE VECTOR FOR LM,CSM BY ADDING
013424,000033:                                                                                                  #  THE CONIC R,V AND THE DEVIATIONS R,V.  THE STATE VECTORS ARE CONVERTED TO
013425,000034:                                                                                                  #  METERS B-29 AND METERS/CSEC B-7 AND STORED APPROPRIATELY IN RN,VN OR
013426,000035:                                                                                                  #  R-OTHER,V-OTHER FOR DOWNLINK.  THE ROUTINES NAMES ARE SWITCHED IN THE
013427,000036:                                                                                                  #  OTHER VEHICLES COMPUTER.
013428,000037: 
013429,000038:                                                                                                  #  INPUT
013430,000039:                                                                                                  #        STATE VECTOR IN TEMPORARY STORAGE AREA
013431,000040:                                                                                                  #        IF STATE VECTOR IS SCALED POS B27 AND VEL B5
013432,000041:                                                                                                  #                SET X2 TO +2
013433,000042:                                                                                                  #        IF STATE VECTOR IS SCALED POS B29 AND VEL B7
013434,000043:                                                                                                  #                SET X2 TO 0
013435,000044: 
013436,000045:                                                                                                  #  OUTPUT
013437,000046:                                                                                                  #        R(T) IN RN, V(T) IN VN, T IN PIPTIME
013438,000047:                                                                                                  #  OR
013439,000048:                                                                                                  #        R(T) IN R-OTHER, V(T) IN V-OTHER        (T IS DEFINED BY T-OTHER)
013440,000049: 
013441,000050: 13,2070                                           COUNT*   $$/GEOM                               
013442,000051: 13,2070           43414        SVDWN2             BOF      RVQ                                   #  SW=1=AVETOMID DOING W-MATRIX INTEG.
013443,000052: 13,2071           04756                                    AVEMIDSW                              
013444,000053: 13,2072           26073                                    +1                                    
013445,000054: 13,2073           53775                           VLOAD    VSL*                                  
013446,000055: 13,2074           01521                                    TDELTAV                               
013447,000056: 13,2075           57605                                    0          -7,2                       
013448,000057: 13,2076           53655                           VAD      VSL*                                  
013449,000058: 13,2077           01535                                    RCV                                   
013450,000059: 13,2100           57576                                    0,2                                   
013451,000060: 13,2101           25220                           STOVL    RN                                    
013452,000061: 13,2102           01527                                    TNUV                                  
013453,000062: 13,2103           53257                           VSL*     VAD                                   
013454,000063: 13,2104           57602                                    0          -4,2                       
013455,000064: 13,2105           01543                                    VCV                                   
013456,000065: 13,2106           77657                           VSL*                                           
013457,000066: 13,2107           57576                                    0,2                                   
013458,000067: 13,2110           15226                           STODL    VN                                    
013459,000068: 13,2111           01517                                    TET                                   
013460,000069: 13,2112           01234                           STORE    PIPTIME                               
013461,000070: 13,2113           77616                           RVQ                                            

Page 323

013463,000072: 13,2114           53775        SVDWN1             VLOAD    VSL*                                  
013464,000073: 13,2115           01521                                    TDELTAV                               
013465,000074: 13,2116           57605                                    0          -7,2                       
013466,000075: 13,2117           53655                           VAD      VSL*                                  
013467,000076: 13,2120           01535                                    RCV                                   
013468,000077: 13,2121           57576                                    0,2                                   
013469,000078: 13,2122           25720                           STOVL    R-OTHER                               
013470,000079: 13,2123           01527                                    TNUV                                  
013471,000080: 13,2124           53257                           VSL*     VAD                                   
013472,000081: 13,2125           57602                                    0          -4,2                       
013473,000082: 13,2126           01543                                    VCV                                   
013474,000083: 13,2127           77657                           VSL*                                           
013475,000084: 13,2130           57576                                    0,2                                   
013476,000085: 13,2131           01726                           STORE    V-OTHER                               
013477,000086: 13,2132           77616                           RVQ                                            
013478,000087: 

Page 324

013480,000089:                                                                                                  #  THE FOLLOWING ROUTINE TAKES A HALF UNIT TARGET VECTOR REFERRED TO NAV BASE COORDINATES AND FINDS BOTH
013481,000090:                                                                                                  #  GIMBAL ORIENTATIONS AT WHICH THE RR MIGHT SIGHT THE TARGET.  THE GIMBAL ANGLES CORRESPONDING TO THE PRESENT MODE
013482,000091:                                                                                                  #  ARE LEFT IN MODEA AND THOSE WHICH WOULD BE USED AFTER A REMODE IN MODEB.  THIS ROUTINE ASSUMES MODE 1 IS TRUNNION
013483,000092:                                                                                                  #  ANGLE LESS THAN 90 DEGS IN ABS VALUE WITH ARBITRARY SHAFT, WITH A CORRESPONDING DEFINITION FOR MODE 2.  MODE
013484,000093:                                                                                                  #  SELECTION AND LIMIT CHECKING ARE DONE ELSEWHERE.
013485,000094: 
013486,000095:                                                                                                  #  THE MODE 1 CONFIGURATION IS CALCULATED FROM THE VECTOR AND THEN MODE 2 IS FOUND USING THE RELATIONS
013487,000096: 
013488,000097:                                                                                                  #        S(2) = 180 + S(1)
013489,000098:                                                                                                  #        T(2) = 180 - T(1)
013490,000099: 
013491,000100:                                                                                                  #  THE VECTOR ARRIVES IN MPAC WHERE TRG*SMNG OR *SMNB* WILL HAVE LEFT IT.
013492,000101: 
013493,000102: 13,2133           00041        RRANGLES           STORE    32D                                   
013494,000103: 13,2134           57545                           DLOAD    DCOMP                                 #  SINCE WE WILL FIND THE MODE 1 SHAFT
013495,000104: 13,2135           00043                                    34D                                   #  ANGLE LATER, WE CAN FIND THE MODE 1
013496,000105: 13,2136           67401                           SETPD    ASIN                                  #  TRUNNION BY SIMPLY TAKING THE ARCSIN OF
013497,000106: 13,2137           00001                                    0                                     #  THE Y COMPONENT, THE ASIN GIVING AN
013498,000107: 13,2140           44206                           PUSH     BDSU                                  #  ANSWER WHOSE ABS VAL IS LESS THAN 90 DEG
013499,000108: 13,2141           24005                                    LODPHALF                              
013500,000109: 13,2142           14005                           STODL    4                                     #  MODE 2 TRUNNION TO 4.
013501,000110: 13,2143           24007                                    LO6ZEROS                              
013502,000111: 13,2144           24043                           STOVL    34D                                   #  UNIT THE PROJECTION OF THE VECTOR
013503,000112: 13,2145           00041                                    32D                                   #        IN THE X-Z PLANE
013504,000113: 13,2146           41056                           UNIT     BOVB                                  #  IF OVERFLOW, TARGET VECTOR IS ALONG Y
013505,000114: 13,2147           52432                                    LUNDESCH                              #  CALL FOR MANEUVER UNLESS ON LUNAR SURF
013506,000115: 13,2150           14041                           STODL    32D                                   #  PROJECTION VECTOR.
013507,000116: 13,2151           00041                                    32D                                   
013508,000117: 13,2152           44142                           SR1      STQ                                   
013509,000118: 13,2153           00051                                    S2                                    
013510,000119: 13,2154           14023                           STODL    SINTH                                 #  USE ARCTRIG SINCE SHAFT COULD BE ARB.
013511,000120: 13,2155           00045                                    36D                                   
013512,000121: 13,2156           77742                           SR1                                            
013513,000122: 13,2157           34021                           STCALL   COSTH                                 
013514,000123: 13,2160           47322                                    ARCTRIG                               

Page 325

013516,000125: 13,2161           43206                           PUSH     DAD                                   #  MODE 1 SHAFT TO 2.
013517,000126: 13,2162           24005                                    LODPHALF                              
013518,000127: 13,2163           24007                           STOVL    6                                     
013519,000128: 13,2164           00005                                    4                                     
013520,000129: 13,2165           77634                           RTB                                            #  FIND MODE 2 CDU ANGLES.
013521,000130: 13,2166           21636                                    2V1STO2S                              
013522,000131: 13,2167           25111                           STOVL    MODEB                                 
013523,000132: 13,2170           00001                                    0                                     
013524,000133: 13,2171           77634                           RTB                                            #  MODE 1 ANGLES TO MODE A.
013525,000134: 13,2172           21636                                    2V1STO2S                              
013526,000135: 13,2173           01107                           STORE    MODEA                                 
013527,000136: 13,2174           77776                           EXIT                                           
013528,000137: 
013529,000138: 13,2175           40110                           CS       RADMODES                              #  SWAP MODEA AND MODEB IF RR IN MODE 2.
013530,000139: 13,2176           74740                           MASK     ANTENBIT                              
013531,000140: 13,2177           10000                           CCS      A                                     
013532,000141: 13,2200           12204                           TCF      +4                                    
013533,000142: 
013534,000143: 13,2201           53107                           DXCH     MODEA                                 
013535,000144: 13,2202           53111                           DXCH     MODEB                                 
013536,000145: 13,2203           53107                           DXCH     MODEA                                 
013537,000146: 
013538,000147: 13,2204           06042                           TC       INTPRET                               
013539,000148: 13,2205           77650                           GOTO                                           
013540,000149: 13,2206           00051                                    S2                                    

Page 326

013542,000151:                                                                                                  #  GIVEN RR TRUNNION AND SHAFT (T,S) IN TANGNB,+1, FIND THE ASSOCIATED
013543,000152:                                                                                                  #  LINE OF SIGHT IN NAV BASE AXES.  THE HALF UNIT VECTOR, .5(SIN(S)COS(T),
013544,000153:                                                                                                  #  -SIN(T),COS(S)COS(T)) IS LEFT IN MPAC AND 32D.
013545,000154: 
013546,000155: 23,2000                                           SETLOC   INFLIGHT                              
013547,000156: 23,2000                                           BANK                                           
013548,000157: 
013549,000158: 23,2041                                           COUNT*   $$/GEOM                               
013550,000159: 
013551,000160: 23,2041           47135        RRNB               SLOAD    RTB                                   
013552,000161: 23,2042           03753                                    TANGNB                                
013553,000162: 23,2043           21577                                    CDULOGIC                              
013554,000163: 23,2044           41401                           SETPD    PUSH                                  #  TRUNNION ANGLE TO 0
013555,000164: 23,2045           00001                                    0                                     
013556,000165: 23,2046           57556                           SIN      DCOMP                                 
013557,000166: 23,2047           14043                           STODL    34D                                   #  Y COMPONENT
013558,000167: 
013559,000168: 23,2050           41546                           COS      PUSH                                  #  .5 COS(T) TO 0
013560,000169: 23,2051           47135                           SLOAD    RTB                                   
013561,000170: 23,2052           03754                                    TANGNB     +1                         
013562,000171: 23,2053           21577                                    CDULOGIC                              
013563,000172: 23,2054           71406        RRNB1              PUSH     COS                                   #  SHAFT ANGLE TO 2
013564,000173: 23,2055           72405                           DMP      SL1                                   
013565,000174: 23,2056           00001                                    0                                     
013566,000175: 23,2057           14045                           STODL    36D                                   #  Z COMPONENT
013567,000176: 
013568,000177: 23,2060           41356                           SIN      DMP                                   
013569,000178: 23,2061           77752                           SL1                                            
013570,000179: 23,2062           24041                           STOVL    32D                                   
013571,000180: 23,2063           00041                                    32D                                   
013572,000181: 23,2064           77616                           RVQ                                            
013573,000182: 
013574,000183:                                                                                                  #  THIS ENTRY TO RRNB REQUIRES THE TRUNNION AND SHAFT ANGLES IN MPAC AND MPAC +1 RESPECTIVELY
013575,000184: 
013576,000185: 23,2065           14025        RRNBMPAC           STODL    20D                                   #  SAVE SHAFT CDU IN 21.
013577,000186: 23,2066           00155                                    MPAC                                  #  SET MODE TO DP.  (THE PRECEEDING STORE
013578,000187:                                                                                                  #  MAY BE DP, TP OR VECTOR.)
013579,000188: 23,2067           40234                           RTB      SETPD                                 
013580,000189: 23,2070           21577                                    CDULOGIC                              
013581,000190: 23,2071           00001                                    0                                     
013582,000191: 23,2072           73406                           PUSH     SIN                                   #  TRUNNION ANGLE TO 0
013583,000192: 23,2073           77676                           DCOMP                                          
013584,000193: 23,2074           14043                           STODL    34D                                   #  Y COMPONENT
013585,000194: 23,2075           41546                           COS      PUSH                                  #  .5COS(T) TO 0
013586,000195: 23,2076           47135                           SLOAD    RTB                                   #  PICK UP CDU'S.
013587,000196: 23,2077           00026                                    21D                                   
013588,000197: 23,2100           21577                                    CDULOGIC                              
013589,000198: 23,2101           77650                           GOTO                                           
013590,000199: 23,2102           46054                                    RRNB1                                 

Page 327
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013593,000202: 
013594,000203: 

End of include-file LEM_GEOMETRY.agc.  Parent file is MAIN.agc