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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017708,000002: ## Copyright: Public domain.
017709,000003: ## Filename: KALCMANU_STEERING.agc
017710,000004: ## Purpose: A section of Skylark revision 048.
017711,000005: ## It is part of the source code for the Apollo Guidance Computer (AGC)
017712,000006: ## for Skylab-2, Skylab-3, Skylab-4, and ASTP. No original listings of
017713,000007: ## this software are available; instead, this file was created via
017714,000008: ## disassembly of dumps of the core rope modules actually flown on
017715,000009: ## Skylab-2. Access to these modules was provided by the New Mexico
017716,000010: ## Museum of Space History.
017717,000011: ## Assembler: yaYUL
017718,000012: ## Contact: Ron Burkey <info@sandroid.org>.
017719,000013: ## Website: www.ibiblio.org/apollo/index.html
017720,000014: ## Mod history: 2023-09-04 MAS Created from Artemis 072.
017721,000015: ## 2024-03-01 MAS Updated for Skylark 48.
017722,000016:
017723,000017:
017724,000018: # GENERATION OF STEERING COMMANDS FOR DIGITAL AUTOPILOT FREE FALL MANEUVERS
017725,000019:
017726,000020: # NEW COMMANDS WILL BE GENERATED EVERY ONE SECOND DURING THE MANEUVER
017727,000021:
017728,000022: 22,2000 SETLOC KALCMON1
017729,000023: 22,2000 BANK
017730,000024:
017731,000025: 22,3104 E6,1712 EBANK= BCDU
017732,000026:
017733,000027: 22,3104 COUNT* $$/KALC
017734,000028: 22,3104 35000 NEWDELHI CAF R67BIT
017735,000029: 22,3105 70104 MASK FLAGWRD8
017736,000030: 22,3106 00006 EXTEND
017737,000031: 22,3107 13114 BZF NEWANGL -3 # NON-R67 SEQUENCE
017738,000032:
017739,000033: 22,3110 34775 CAF TRACKBIT
017740,000034: 22,3111 70075 MASK FLAGWRD1
017741,000035: 22,3112 00006 EXTEND # CHECK TRACKFLAG
017742,000036: 22,3113 13226 BZF MYSTEND # IF OFF DO MYSTEND
017743,000037:
017744,000038: 22,3114 41330 -3 CS HOLDFLAG
017745,000039: 22,3115 00006 EXTEND # CHECK HOLDFLAG
017746,000040: 22,3116 62720 BZMF NOGOM2 # IF POS, DO STOPRATE
017747,000041:
017748,000042: 22,3117 06006 NEWANGL TC INTPRET
017749,000043: 22,3120 75160 +1 AXC,1 AXC,2
017750,000044: 22,3121 02271 MIS # COMPUTE THE NEW MATRIX FROM S/C TO
017751,000045: 22,3122 03425 DEL # STABLE MEMBER AXES
017752,000046: 22,3123 77624 CALL
017753,000047: 22,3124 44304 MXM3
017754,000048: 22,3125 45575 VLOAD STADR
017755,000049: 22,3126 51471 STOVL MIS +12D # CALCULATE NEW DESIRED CDU ANGLES
017756,000050: 22,3127 77626 STADR
017757,000051: 22,3130 51477 STOVL MIS +6D
017758,000052: 22,3131 77626 STADR
017759,000053: 22,3132 75505 STORE MIS
017760,000054: 22,3133 45160 AXC,1 CALL
017761,000055: 22,3134 02271 MIS
017762,000056: 22,3135 44647 DCMTOCDU # PICK UP THE NEW CDU ANGLES FROM MATRIX
017763,000057: 22,3136 77634 RTB
017764,000058: 22,3137 45625 V1STO2S
017765,000059: 22,3140 03320 NWNGL17D STORE NCDU # NEW CDU ANGLES (TAG IS USED BY EDIT)
017766,000060: 22,3141 77414 BONCLR EXIT
017767,000061: 22,3142 01215 CALCMAN2
017768,000062: 22,3143 40064 MANUSTAT # TO START MANEUVER
017769,000063: 22,3144 35000 -1 CAF TWO # +0 OTHERWISE
017770,000064: 22,3145 55715 INCRDCDU TS KSPNDX
017771,000065: 22,3146 60000 DOUBLE
017772,000066: 22,3147 55716 TS KDPNDX
017773,000067: 22,3150 51715 INDEX KSPNDX
017774,000068: 22,3151 31717 CA NCDU # NEW DESIRED CDU ANGLES
017775,000069: 22,3152 00006 EXTEND
017776,000070: 22,3153 51715 INDEX KSPNDX
017777,000071: 22,3154 21712 MSU BCDU # INITIAL S/C ANGLE OR PREVIOUS DESIRED
017778,000072: 22,3155 00006 EXTEND # CDU ANGLES
017779,000073: 22,3156 73056 MP QUADROT
017780,000074: 22,3157 51716 INDEX KDPNDX
017781,000075: 22,3160 53627 DXCH DELCDUX # ANGLE INCREMENTS TO BE ADDED TO
017782,000076: 22,3161 51715 INDEX KSPNDX # DCDU EVERY TENTH SEC
017783,000077: 22,3162 31717 CA NCDU # BY LEM DAP
017784,000078: 22,3163 51715 INDEX KSPNDX
017785,000079: 22,3164 57712 XCH BCDU
017786,000080: 22,3165 51716 INDEX KDPNDX
017787,000081: 22,3166 55677 TS CDUXD
017788,000082: 22,3167 11715 CCS KSPNDX
017789,000083: 22,3170 13145 TCF INCRDCDU # LOOP FOR THREE AXES
017790,000084:
017791,000085: 22,3171 00003 RELINT
017792,000086:
017793,000087: # COMPARE PRESENT TIME WITH TIME TO TERMINATE MANEUVER
017794,000088:
017795,000089: 22,3172 03202 TMANUCHK TC TIMECHK
017796,000090: 22,3173 04666 TC POSTJUMP
017797,000091: 22,3174 40151 CADR CONTMANU
017798,000092:
017799,000093: 22,3175 35001 CAF ONE
017800,000094: 22,3176 05246 MANUSTAL TC WAITLIST
017801,000095: 22,3177 E6,1712 EBANK= BCDU
017802,000096: 22,3177 02257 20066 2CADR MANUSTOP
017803,000097:
017804,000098: 22,3201 15220 TCF ENDOFJOB
017805,000099:
017806,000100:
017807,000101: 22,3202 00006 TIMECHK EXTEND
017808,000102: 22,3203 40025 DCS TIME2
017809,000103: 22,3204 53724 DXCH TTEMP
017810,000104: 22,3205 00006 EXTEND
017811,000105: 22,3206 31750 DCA TM
017812,000106: 22,3207 21724 DAS TTEMP
017813,000107: 22,3210 11723 CCS TTEMP
017814,000108: 22,3211 00002 TC Q
017815,000109: 22,3212 13214 TCF +2
017816,000110: 22,3213 13224 TCF 2NDRETRN
017817,000111: 22,3214 11724 CCS TTEMP +1
017818,000112: 22,3215 00002 TC Q
017819,000113: 22,3216 13220 TCF MANUOFF
017820,000114: 22,3217 40000 COM
017821,000115: 22,3220 65030 MANUOFF AD 1SEC
017822,000116: 22,3221 00006 EXTEND
017823,000117: 22,3222 63224 BZMF 2NDRETRN
017824,000118: 22,3223 24002 INCR Q
017825,000119: 22,3224 24002 2NDRETRN INCR Q
017826,000120: 22,3225 16706 TCF Q+1
017827,000121: 22,3226 04666 MYSTEND TC POSTJUMP
017828,000122: 22,3227 74662 CADR FIXDB
017829,000123:
017830,000124: 20,2000 SETLOC MANUSTUF
017831,000125: 20,2000 BANK
017832,000126:
017833,000127: 20,2064 COUNT* $$/KALC
017834,000128: 20,2064 77776 MANUSTAT EXIT # INITIALIZATION ROUTINE FOR AUTO
017835,000129: 20,2065 35000 CAF R67BIT # MANEUVERS
017836,000130: 20,2066 70104 MASK FLAGWRD8
017837,000131: 20,2067 00006 EXTEND
017838,000132: 20,2070 12075 BZF +5
017839,000133: 20,2071 00006 EXTEND # R67 RUNNING
017840,000134: 20,2072 34761 DCA DPOSMAX
017841,000135: 20,2073 53750 DXCH TM
017842,000136: 20,2074 12104 TCF TMDON
017843,000137: 20,2075 00006 EXTEND # NON-R67 PROGRAM
017844,000138: 20,2076 30025 DCA TIME2
017845,000139: 20,2077 21750 DAS TM # TM+T0 MANEUVER COMPLETION TIME
017846,000140: 20,2100 45030 CS 1SEC
017847,000141: 20,2101 54001 TS L
017848,000142: 20,2102 45003 CS ZERO
017849,000143: 20,2103 21750 DAS TM # (TM+T0)-1
017850,000144: 20,2104 00004 TMDON INHINT
017851,000145: 20,2105 45001 CS ONE # ENABLE AUTOPILOT TO PERFORM
017852,000146: 20,2106 55330 TS HOLDFLAG # AUTOMATIC MANEUVERS
017853,000147: 20,2107 51475 INDEX WHICHDAP
017854,000148: 20,2110 12111 TCF +1
017855,000149: 20,2111 12115 TCF +4
017856,000150: 20,2112 44353 CS OCT25
017857,000151: 20,2113 55663 TS CH31TEMP
017858,000152: 20,2114 12125 TCF HIGHGAIN +3
017859,000153: 20,2115 40767 CS RATEINDX # SEE IF MANEUVERING AT HIGH RATE
017860,000154: 20,2116 66211 AD SIX
017861,000155: 20,2117 00006 EXTEND
017862,000156: 20,2120 62122 BZMF HIGHGAIN
017863,000157: 20,2121 12125 TCF +4
017864,000158: 20,2122 41530 HIGHGAIN CS RCSFLAGS # IF SO, SET HIGH RATE FLAG (BIT 15 OF
017865,000159: 20,2123 74763 MASK BIT15 # RCSFLAGS)
017866,000160: 20,2124 27530 ADS RCSFLAGS
017867,000161: 20,2125 00006 EXTEND
017868,000162: 20,2126 31742 DCA BRATE # X-AXIS MANEUVER RATE
017869,000163: 20,2127 53555 DXCH WBODY
017870,000164: 20,2130 00006 EXTEND
017871,000165: 20,2131 31744 DCA BRATE +2 # Y-AXIS MANEUVER RATE
017872,000166: 20,2132 53557 DXCH WBODY1
017873,000167: 20,2133 00006 EXTEND
017874,000168: 20,2134 31746 DCA BRATE +4 # Z-AXIS MANEUVER RATE
017875,000169: 20,2135 53561 DXCH WBODY2
017876,000170: 20,2136 31726 CA BIASTEMP +1 # INSERT ATTITUDE ERROR BIASES
017877,000171: 20,2137 55615 TS BIAS # INTO AUTOPILOT
017878,000172: 20,2140 31730 CA BIASTEMP +3
017879,000173: 20,2141 55616 TS BIAS1
017880,000174: 20,2142 31732 CA BIASTEMP +5
017881,000175: 20,2143 55617 TS BIAS2
017882,000176: 20,2144 30025 CA TIME1
017883,000177: 20,2145 65030 AD 1SEC
017884,000178: 20,2146 57722 XCH NEXTIME
017885,000179: 20,2147 04666 TC POSTJUMP
017886,000180: 20,2150 45144 CADR INCRDCDU -1
017887,000181:
017888,000182: 20,2151 00004 CONTMANU INHINT # CONTINUE WITH UPDATE PROCESS
017889,000183: 20,2152 40025 CS TIME1
017890,000184: 20,2153 61722 AD NEXTIME
017891,000185: 20,2154 10000 CCS A
017892,000186: 20,2155 65001 AD ONE
017893,000187: 20,2156 12161 TCF MANUCALL
017894,000188: 20,2157 64763 AD NEGMAX
017895,000189: 20,2160 40000 COM
017896,000190: 20,2161 05236 MANUCALL TC TWIDDLE
017897,000191: 20,2162 02167 ADRES UPDTCALL
017898,000192: 20,2163 00003 RELINT
017899,000193: 20,2164 35030 CAF 1SEC # INCREMENT TIME FOR NEXT UPDATE
017900,000194: 20,2165 27722 ADS NEXTIME
017901,000195: 20,2166 15220 TCF ENDOFJOB
017902,000196:
017903,000197: 20,2167 35000 UPDTCALL CAF R67BIT
017904,000198: 20,2170 70104 MASK FLAGWRD8
017905,000199: 20,2171 00006 EXTEND
017906,000200: 20,2172 12177 BZF +5
017907,000201:
017908,000202: 20,2173 11776 CCS R61CNTR
017909,000203: 20,2174 12176 TCF +2
017910,000204: 20,2175 12204 TCF DOREMIS
017911,000205: 20,2176 55776 TS R61CNTR
017912,000206:
017913,000207: 20,2177 37650 CAF PRIO26
017914,000208: 20,2200 05150 TC FINDVAC # OF STEERING COMMANDS
017915,000209: 20,2201 E6,1712 EBANK= BCDU
017916,000210: 20,2201 03104 44066 2CADR NEWDELHI
017917,000211:
017918,000212: 20,2203 05327 TC TASKOVER
017919,000213:
017920,000214: 20,2204 37650 DOREMIS CAF PRIO26
017921,000215: 20,2205 05150 TC FINDVAC
017922,000216: 20,2206 E6,1712 EBANK= BCDU
017923,000217: 20,2206 02640 74066 2CADR R67RSTRT # MAKE SURE MIS DOES DEGRADE
017924,000218:
017925,000219: 20,2210 05327 TC TASKOVER
017926,000220:
017927,000221: # ROUTINE FOR TERMINATING AUTOMATIC MANEUVERS
017928,000222:
017929,000223: 10,2000 SETLOC KALCMON3
017930,000224: 10,2000 BANK
017931,000225:
017932,000226: 10,2257 COUNT* $$/KALC
017933,000227: 10,2257 04513 MANUSTOP TC STOPYZ
017934,000228: 10,2260 04725 TC IBNKCALL
017935,000229: 10,2261 45232 CADR LOADYZ
017936,000230:
017937,000231: 10,2262 31277 ENDROLL CA CPHI
017938,000232: 10,2263 55677 TS CDUXD # SET CDUXD TO THE COMMANDED OUTER GIMBAL
017939,000233: 10,2264 04463 TC STOPRATE
017940,000234: 10,2265 35065 ENDMANU CAF PRIO14
017941,000235: 10,2266 05150 TC FINDVAC
017942,000236: 10,2267 E6,1776 EBANK= R61CNTR
017943,000237: 10,2267 02045 56066 2CADR ENDMANUV
017944,000238:
017945,000239: 10,2271 05327 TC TASKOVER
017946,000240:
017947,000241: 4000 SETLOC STOPRAT
017948,000242: 4000 BANK
017949,000243: 4463 COUNT* $$/KALC
017950,000244: 4463 35003 STOPRATE CAF ZERO
017951,000245: 4464 55626 TS DELCDUX
017952,000246: 4465 55627 TS DELCDUX +1 # ZERO ROLL INCREMENTAL ANGLES
017953,000247: 4466 55554 TS WBODY # RATE
017954,000248: 4467 55555 TS WBODY +1
017955,000249: 4470 55615 TS BIAS # BIAS
017956,000250:
017957,000251: 4471 44763 CS BIT15 # MAKE SURE HIGH RATE FLAG (BIT 15 OF
017958,000252: 4472 71530 MASK RCSFLAGS # RCSFLAGS) IS RESET.
017959,000253: 4473 55530 TS RCSFLAGS
017960,000254:
017961,000255: 4474 11330 CCS HOLDFLAG
017962,000256: 4475 14513 TCF STOPYZ
017963,000257: 4476 14513 TCF STOPYZ
017964,000258: 4477 55330 TS HOLDFLAG
017965,000259: 4500 31677 CA CDUXD
017966,000260: 4501 55623 TS THETADX
017967,000261: 4502 31701 CA CDUYD
017968,000262: 4503 55624 TS THETADY
017969,000263: 4504 31703 CA CDUZD
017970,000264: 4505 55625 TS THETADZ
017971,000265: 4506 51475 INDEX WHICHDAP
017972,000266: 4507 14510 TCF +1
017973,000267: 4510 14513 TCF STOPYZ
017974,000268: 4511 44353 CS OCT25
017975,000269: 4512 55663 TS CH31TEMP
017976,000270:
017977,000271: 4513 35003 STOPYZ CAF ZERO
017978,000272: 4514 55630 TS DELCDUY # ZERO PITCH, YAW
017979,000273: 4515 55631 TS DELCDUY +1 # INCREMENTAL ANGLES
017980,000274: 4516 55632 TS DELCDUZ
017981,000275: 4517 55633 TS DELCDUZ +1
017982,000276: 4520 55556 TS WBODY1 # RATES
017983,000277: 4521 55557 TS WBODY1 +1
017984,000278: 4522 55560 TS WBODY2
017985,000279: 4523 55561 TS WBODY2 +1
017986,000280: 4524 55616 TS BIAS1 # BIASES
017987,000281: 4525 55617 TS BIAS2
017988,000282: 4526 00002 TC Q
017989,000283:
017990,000284: 20,2000 SETLOC MANUSTUF
017991,000285: 20,2000 BANK
017992,000286:
017993,000287: 20,2211 COUNT* $$/KALC
017994,000288: 20,2211 30032 ZEROEROR CA CDUX # PICK UP CDU ANGLES AND STORE IN
017995,000289: 20,2212 55677 TS CDUXD # CDU DESIRED
017996,000290: 20,2213 30033 CA CDUY
017997,000291: 20,2214 55701 TS CDUYD
017998,000292: 20,2215 30034 CA CDUZ
017999,000293: 20,2216 55703 TS CDUZD
018000,000294: 20,2217 00002 TC Q
018001,000295:
018002,000296: 22,2000 SETLOC KALCMON1
018003,000297: 22,2000 BANK
018004,000298:
018005,000299: 22,3230 COUNT* $$/KALC
018006,000300: 22,3230 31277 LOADCDUD CA CPHI # STORE TERMINAL ANGLES INTO
018007,000301: 22,3231 55677 TS CDUXD # COMMAND ANGLES
018008,000302: 22,3232 31300 LOADYZ CA CTHETA
018009,000303: 22,3233 55701 TS CDUYD
018010,000304: 22,3234 31301 CA CPSI
018011,000305: 22,3235 55703 TS CDUZD
018012,000306: 22,3236 00002 TC Q
End of include-file KALCMANU_STEERING.agc. Parent file is MAIN.agc