Source Code
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These source-code files are part of a reconstructed copy of Skylark 048, the
Block II Command Module (CM) Apollo Guidance Computer (AGC) software for the
Skylab-2, Skylab-3, Skylab-4, and Apollo-Soyuz Test Project missions.
They have been created via disassembly of binary dumps of the original core rope
memory modules actually flown on Skylab-2, part numbers 2010802-541, 2010802-551,
2010802-561, 2010802-571, 2010802-581, and 2010802-591. Access to these modules
was provided by the New Mexico Museum of Space History, who we are much indebted to.
The source code for the Apollo 15, 16, and 17 software, Artemis 072, was used as
a starting point. Heavy use was made of TRW 4900.5-244, Programmed Guidance Equations
for Skylark Command Module Earth Orbital Program, dated 14 February 1972. This document
contains pseudocode of essentially all of Skylark, using original program labels which
have been copied for this source reconstruction.
Since only binary dumps (rather than listings) of Skylark are available as source material,
all comments and labels are approximate.
They have been taken from the Programmed Guidance Equations or other AGC programs where
possible, or, in some places, written from scratch to match what we believe would have
been in the original listing.
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033313,000002: ## Copyright: Public domain.
033314,000003: ## Filename: LUNAR_AND_SOLAR_EPHEMERIDES_SUBROUTINES.agc
033315,000004: ## Purpose: A section of Skylark revision 048.
033316,000005: ## It is part of the source code for the Apollo Guidance Computer (AGC)
033317,000006: ## for Skylab-2, Skylab-3, Skylab-4, and ASTP. No original listings of
033318,000007: ## this software are available; instead, this file was created via
033319,000008: ## disassembly of dumps of the core rope modules actually flown on
033320,000009: ## Skylab-2. Access to these modules was provided by the New Mexico
033321,000010: ## Museum of Space History.
033322,000011: ## Assembler: yaYUL
033323,000012: ## Contact: Ron Burkey <info@sandroid.org>.
033324,000013: ## Website: www.ibiblio.org/apollo/index.html
033325,000014: ## Mod history: 2024-02-19 MAS Created from Luminary 131.
033326,000015: ## 2024-03-04 MAS Updated for Skylark 48.
033327,000016:
033328,000017: # NAME - LSPOS - LOCATE SUN AND MOON DATE - 25 OCT 67
033329,000018: # MOD NO.1
033330,000019: # MOD BY NEVILLE ASSEMBLY SUNDANCE
033331,000020:
033332,000021: # FUNCTIONAL DESCRIPTION
033333,000022:
033334,000023: # COMPUTES UNIT POSITION VECTOR OF THE SUN AND MOON IN THE BASIC REFERENCE SYSTEM. THE SUN VECTOR S IS
033335,000024: # LOCATED VIA TWO ANGLES. THE FIRST ANGLE (OBLIQUITY) IS THE ANGLE BETWEEN THE EARTH EQUATOR AND THE ECLIPTIC. THE
033336,000025: # SECOND ANGLE IS THE LONGITUDE OF THE SUN MEASURED IN THE ECLIPTIC.
033337,000026: # THE POSITION VECTOR OF THE SUN IS
033338,000027: # -
033339,000028: # S = (COS(LOS), COS(OBL)*SIN(LOS), SIN(OBL)*SIN(LOS)), WHERE
033340,000029:
033341,000030: # LOS = LOS +LOS *T-(C *SIN(2PI*T)/365.24 +C *COS(2PI*T)/365.24)
033342,000031: # 0 R 0 1
033343,000032: # LOS (RAD) IS THE LONGITUDE OF THE SUN FOR MIDNIGHT JUNE 30TH OF THE PARTICULAR YEAR.
033344,000033: # 0
033345,000034: # LOS (RAD/DAY) IS THE MEAN RATE FOR THE PARTICULAR YEAR.
033346,000035: # R
033347,000036:
033348,000037: # LOS AND LOS ARE STORED AS LOSC AND LOSR IN RATESP.
033349,000038: # 0 R
033350,000039: # COS(OBL) AND SIN(OBL) ARE STORED IN THE MATRIX KONMAT.
033351,000040:
033352,000041: # T, TIME MEASURED IN DAYS (24 HOURS), IS STORED IN TIMEP.
033353,000042:
033354,000043: # C AND C ARE FUDGE FACTORS TO MINIMIZE THE DEVIATION. THEY ARE STORED AS ONE CONSTANT (CMOD), SINCE
033355,000044: # 0 1 2 2 1/2
033356,000045: # C *SIN(X)+C *COS(X) CAN BE WRITTEN AS (C +C ) *SIN(X+PHI), WHERE PHI=ARCTAN(C /C ).
033357,000046: # 0 1 0 1 1 0
033358,000047:
033359,000048: # THE MOON IS LOCATED VIA FOUR ANGLES. THE FIRST IS THE OBLIQUITY. THE SECOND IS THE MEAN LONGITUDE OF THE MOON,
033360,000049: # MEASURED IN THE ECLIPTIC FROM THE MEAN EQUINOX TO THE MEAN ASCENDING NODE OF THE LUNAR ORBIT, AND THEN ALONG THE
033361,000050: # ORBIT. THE THIRD ANGLE IS THE ANGLE BETWEEN THE ECLIPTIC AND THE LUNAR ORBIT. THE FOURTH ANGLE IS THE LONGITUDE
033362,000051: # OF THE NODE OF THE MOON, MEASURED IN THE LUNAR ORBIT. LET THESE ANGLES BE OBL,LOM,IM, AND LON RESPECTIVELY.
033363,000052:
033364,000053: # THE SIMPLIFIED POSITION VECTOR OF THE MOON IS
033365,000054: # -
033366,000055: # 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))
033367,000056:
033368,000057: # WHERE
033369,000058: # 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
033370,000059: # 0 R 0 1 0 1
033371,000060: # LON=LON +LON
033372,000061: # 0 R
033373,000062: # A , A , B AND B ARE STORED AS AMOD AND BMOD (SEE DESCRIPTION OF CMOD, ABOVE). COS(OBL), SIN(OBL)*SIN(IM),
033374,000063: # 0 1 0 1
033375,000064: # SIN(OBL), AND COS(OBL)*SIN(IM) ARE STORED IN KONMAT AS K1, K2, K3 AND K4, RESPECTIVELY. LOM , LOM , LON , LON
033376,000065: # ARE STORED AS LOMO, LOMR, LONO, AND LONR IN RATESP. 0 R 0 R
033377,000066:
033378,000067: # THE THREE PHIS ARE STORED AS AARG, BARG, AND CARG(SUN). ALL CONSTANTS ARE UPDATED BY YEAR.
033379,000068:
033380,000069: # CALLING SEQUENCE
033381,000070: # CALL LSPOS. RETURN IS VIA CPRET.
033382,000071:
033383,000072: # ALARMS OR ABORTS
033384,000073: # NONE
033385,000074:
033386,000075: # ERASABLE INITIALIZATION REQUIRED
033387,000076: # TEPHEM - TIME FROM MIDNIGHT 1 JULY PRECEDING THE LAUNCH TO THE TIME OF THE LAUNCH (WHEN THE AGC CLOCK WENT
033388,000077: # TO ZERO). TEPHEM IS TP WITH UNITS OF CENTI-SECONDS.
033389,000078:
033390,000079: # TIME2 AND TIME1 ARE IN MPAC AND MPAC +1 WHEN PROGRAM IS CALLED.
033391,000080:
033392,000081: # OUTPUT
033393,000082: # UNIT POSITIONAL VECTOR OF SUN IN VSUN. (SCALED B-1)
033394,000083: # UNIT POSITIONAL VECTOR OF MOON IN VMOON. (SCALED B-1)
033395,000084:
033396,000085: # SUBROUTINES USED
033397,000086: # NONE
033398,000087:
033399,000088: # DEBRIS
033400,000089: # CURRENT CORE SET, WORK AREA AND FREEFLAG
033401,000090:
033402,000091: 04,3206 BANK 04
033403,000092: 26,2000 SETLOC EPHEM
033404,000093: 26,2000 BANK
033405,000094:
033406,000095: 26,2034 E5,1724 EBANK= VSUN
033407,000096: 26,2034 COUNT* $$/EPHEM
033408,000097:
033409,000098: 26,2034 54201 LSPOS SETPD SR
033410,000099: 26,2035 00001 0
033411,000100: 26,2036 20617 14D # TP
033412,000101: 26,2037 56371 TAD DDV
033413,000102: 26,2040 01701 TEPHEM # TIME OF LAUNCH
033414,000103: 26,2041 14076 CSTODAY # 24 HOURS-8640000 CENTI-SECS/DAY B-33
033415,000104: 26,2042 41206 PUSH DMP # T IN DAYS
033416,000105: 26,2043 14074 KOMEGAC
033417,000106: 26,2044 43261 SL DAD
033418,000107: 26,2045 20212 9D
033419,000108: 26,2046 02013 CARG
033420,000109: 26,2047 41356 SIN DMP
033421,000110: 26,2050 02011 CMOD
033422,000111: 26,2051 77725 PDDL
033423,000112: 26,2052 54205 DMP SL
033424,000113: 26,2053 14072 LOSR
033425,000114: 26,2054 20207 6
033426,000115: 26,2055 45215 DAD DSU
033427,000116: 26,2056 02007 LOSO
033428,000117: 26,2057 73406 PUSH SIN
033429,000118: 26,2060 41206 PUSH DMP
033430,000119: 26,2061 14102 KONMAT3
033431,000120: 26,2062 65352 SL1 PDDL
033432,000121: 26,2063 72405 DMP SL1
033433,000122: 26,2064 14100 KONMAT1
033434,000123: 26,2065 71525 PDDL COS
033435,000124: 26,2066 00001 0
033436,000125: 26,2067 53466 VDEF UNIT
033437,000126: 26,2070 43406 PUSH RVQ
033438,000127:
033439,000128: 26,2071 01315 26267 LOSR 2DEC* .00273780317 B+4*
033440,000129: 26,2073 00131 26612 KOMEGAC 2DEC* .00273777859 B+1*
033441,000130: 26,2075 00040 36540 CSTODAY 2DEC 8640000 B-32
033442,000131: 26,2077 16533 32024 KONMAT1 2DEC* .91745773 B-1*
033443,000132: 26,2101 06273 01466 KONMAT3 2DEC* .397833274 B-1*
End of include-file LUNAR_AND_SOLAR_EPHEMERIDES_SUBROUTINES.agc. Parent file is MAIN.agc