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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025022,000002: ## Copyright: Public domain.
025023,000003: ## Filename: P30,P38.agc
025024,000004: ## Purpose: A section of Skylark revision 048.
025025,000005: ## It is part of the source code for the Apollo Guidance Computer (AGC)
025026,000006: ## for Skylab-2, Skylab-3, Skylab-4, and ASTP. No original listings of
025027,000007: ## this software are available; instead, this file was created via
025028,000008: ## disassembly of dumps of the core rope modules actually flown on
025029,000009: ## Skylab-2. Access to these modules was provided by the New Mexico
025030,000010: ## Museum of Space History.
025031,000011: ## Assembler: yaYUL
025032,000012: ## Contact: Ron Burkey <info@sandroid.org>.
025033,000013: ## Website: www.ibiblio.org/apollo/index.html
025034,000014: ## Mod history: 2023-09-04 MAS Created from Artemis 072.
025035,000015: ## 2024-03-05 MAS Updated for Skylark 48.
025036,000016:
025037,000017: # PROGRAM DESCRIPTION P30 DATE 5-1-69
025038,000018:
025039,000019: # MOD.I BY S. ZELDIN- TO ADD P31 AND ADAPT P30 FOR P31 USE. 22DEC67
025040,000020: # MOD.II BY P.WOLFF TO REDUCE CODING AND DELETE RESTART PROTECTION 4-30-69
025041,000021: # MOD.III BY C.BEALS TO DELETE P31 1NOV69
025042,000022:
025043,000023: # FUNCTIONAL DESCRIPTION
025044,000024: # P30 (EXTERNAL DELTA-V TARGETTING PROGRAM)
025045,000025: # ACCEPTS ASTRONAUT INPUTS OF TIG,DELV(LV) AND COMPUTES, FOR DISPLAY,
025046,000026: # APOGEE, PERIGEE, DELV(MAG), MGA ASSOCIATED WITH DESIRED MANEUVER
025047,000027:
025048,000028: # THE FOLLOWING SUBROUTINES ARE USED IN P30
025049,000029: # S30/31.1 COMPUTES APOGEE AND PERIGEE ALTITUDE
025050,000030: # P30/P31 - DISPLAYS TIG
025051,000031: # CNTUP30 - DISPLAYS DELV(LV)
025052,000032: # COMPTGO CLOCKTASK COMPUTE TTOGO
025053,000033: # LOMAT COMPUTE X,Y,Z IN LV COORDS
025054,000034: # PARAM30 - DISPLAYS APOGEE, PERIGEE, DELV(MAG), MGA, TIME FROM TIG,
025055,000035: # MARKS SINCE LAST THRUSTING MANEUVER
025056,000036:
025057,000037: # CALLING SEQUENCE VIA JOB FROM V37
025058,000038:
025059,000039: # EXIT VIA V37 CALL OR GOTOPOOH
025060,000040:
025061,000041: # OUTPUT FOR POWERED FLIGHT
025062,000042: # VTIG X
025063,000043: # RTIG
025064,000044: # DELVSIN X
025065,000045:
025066,000046: # P30 CALCULATIONS
025067,000047:
025068,000048: # P30 CALC BASED ON STORED TARGET PARAMETERS (R OF IGNITION (RTIG), V OF
025069,000049: # IGNITION (VTIG), TIME OF IGNITION (TIG), DELV(LV), COMPUTE PERIGEE ALTITUDE
025070,000050: # APOGEE ALTITUDE AND DELTA-V REQUIRED IN REF. COORDS. (DELVSIN)
025071,000051: #
025072,000052: # ERASABLE INITIALIZATION REQUIRED
025073,000053: # TIG TIME OF IGNITION DP B28CS
025074,000054: # DELVSLV SPECIFIED DELTA-V IN LOCAL VERT.
025075,000055: # COORDS. OF ACTIVE VEHICLE AT
025076,000056: # TIME OF IGNITION VCT. B+7M/CS
025077,000057:
025078,000058: # SUBROUTINES CALLED
025079,000059: # THISPREC
025080,000060:
025081,000061: # OUTPUT
025082,000062: # RTIG POSITION AT TIG VCT. B+29M
025083,000063: # VTIG VELOCITY AT TIG VCT. B+7M
025084,000064: # DELVSIN DELVSLV IN REF COORDS VCT. B+7M/CS
025085,000065:
025086,000066: # DEBRIS QTEMP TEMP. ERASABLE
025087,000067: # QPRET, MPAC
025088,000068: # PUSHLIST
025089,000069:
025090,000070: 35,2000 SETLOC P30S1
025091,000071: 35,2000 BANK
025092,000072:
025093,000073: 35,2250 E7,1603 EBANK= +MGA
025094,000074:
025095,000075: 35,2250 COUNT* $$/P30
025096,000076: 35,2250 07710 P30 TC UPFLAG
025097,000077: 35,2251 00027 ADRES UPDATFLG # SET UPDATFLG
025098,000078: 35,2252 07710 TC UPFLAG
025099,000079: 35,2253 00031 ADRES TRACKFLG # SET TRACKFLG
025100,000080: 35,2254 35041 DSP0633 CAF V06N33 # DISPLAY TIME OF IGNITION
025101,000081: 35,2255 05550 TC VNFLASH
025102,000082: 35,2256 34603 CAF V06N81
025103,000083: 35,2257 05550 TC VNFLASH
025104,000084: 35,2260 07710 TC UPFLAG
025105,000085: 35,2261 00045 ADRES XDELVFLG # BIT 8 FLAG 2
025106,000086: 35,2262 06006 TC INTPRET
025107,000087: 35,2263 71214 CLEAR DLOAD
025108,000088: 35,2264 00670 UPDATFLG # RESET UPDATFLG
025109,000089: 35,2265 03413 TIG # TIME IGNITION SCALED AT 2(+28)CS
025110,000090: 35,2266 34041 STCALL TDEC1
025111,000091: 35,2267 11400 THISPREC # ENCKE ROUTINE FOR
025112,000092:
025113,000093: 35,2270 77775 VLOAD
025114,000094: 35,2271 00007 VATT
025115,000095: 35,2272 27616 STOVL VTIG
025116,000096: 35,2273 00001 RATT
025117,000097: 35,2274 03610 STORE RTIG
025118,000098: 35,2275 03516 STORE RACT3
025119,000099: 35,2276 53435 VXV UNIT
025120,000100: 35,2277 03616 VTIG
025121,000101: 35,2300 36543 STCALL UNRM
025122,000102: 35,2301 73333 LOMAT
025123,000103: 35,2302 61375 VLOAD VXM
025124,000104: 35,2303 03405 DELVSLV
025125,000105: 35,2304 00001 0
025126,000106: 35,2305 77772 VSL1
025127,000107: 35,2306 03624 STORE DELVSIN
025128,000108: 35,2307 77646 ABVAL
025129,000109: 35,2310 27764 STOVL VGDISP # MAG DELV
025130,000110: 35,2311 03610 RTIG
025131,000111: 35,2312 53315 PDVL VAD
025132,000112: 35,2313 03624 DELVSIN
025133,000113: 35,2314 03616 VTIG
025134,000114: 35,2315 77624 CALL
025135,000115: 35,2316 54021 S30/31.1
025136,000116: 35,2317 77776 EXIT
025137,000117: 35,2320 32366 PARAM30 CAF V06N42 # DISPLAY HAPO, HPER, DELTAV
025138,000118: 35,2321 05550 TC VNFLASH
025139,000119: 35,2322 06006 REFTEST TC INTPRET
025140,000120: 35,2323 77214 BOFF VLOAD
025141,000121: 35,2324 01742 REFSMFLG # TEST FOR REFSMFLAG ON
025142,000122: 35,2325 72357 NOTSET
025143,000123: 35,2326 03624 DELVSIN
025144,000124: 35,2327 45006 PUSH CALL
025145,000125: 35,2330 56734 GET+MGA
025146,000126: 35,2331 77776 EXIT
025147,000127: 35,2332 02340 DISPMGA TC COMPTGO
025148,000128:
025149,000129: 35,2333 34604 DISP45 CAF V16N45 # DISPLAY MARK CNT, TFI, +MGA
025150,000130: 35,2334 05550 TC VNFLASH
025151,000131: 35,2335 07722 TC DOWNFLAG
025152,000132: 35,2336 00155 ADRES TIMRFLAG # RESET TIMRFLAG
025153,000133: 35,2337 14103 TCF GOTOPOOH
025154,000134:
025155,000135: 35,2340 00006 COMPTGO EXTEND
025156,000136: 35,2341 23262 QXCH PHSPRDT6
025157,000137:
025158,000138: 35,2342 07710 TC UPFLAG # SET TIMRFLAG
025159,000139: 35,2343 00155 ADRES TIMRFLAG
025160,000140: 35,2344 35003 CAF ZERO
025161,000141: 35,2345 54772 TS NVWORD1
025162,000142:
025163,000143: 35,2346 35001 CAF ONE
025164,000144: 35,2347 05246 TC WAITLIST
025165,000145: 35,2350 E7,1412 EBANK= TIG
025166,000146: 35,2350 03071 50067 2CADR CLOKTASK
025167,000147:
025168,000148: 35,2352 05375 TC 2PHSCHNG
025169,000149: 35,2353 40036 OCT 40036 # 6.3SPOT FOR CLOKTASK
025170,000150: 35,2354 05024 OCT 05024 # GROUP 4 CONTINUES HERE
025171,000151: 35,2355 13000 OCT 13000
025172,000152:
025173,000153: 35,2356 01,2333 6P3SPT1 = 6.3SPOT
025174,000154: 35,2356 01262 TC PHSPRDT6
025175,000155:
025176,000156: 35,2357 57545 NOTSET DLOAD DCOMP
025177,000157: 35,2360 32365 MARSDP
025178,000158: 35,2361 03604 STORE +MGA
025179,000159: 35,2362 77634 RTB
025180,000160: 35,2363 72332 DISPMGA
025181,000161: 35,2364 00000 MARSDP OCT 00000 # (00000) (16440) = (+00001)
025182,000162: 35,2365 35100 OCT 35100
025183,000163: # ( .01 ) DEGREES IN THE LOW ORDER REGISTE
025184,000164:
025185,000165: 35,2366 01452 V06N42 VN 0642
025186,000166:
025187,000167:
025188,000168: # S30/31.1 SUBROUTINE USED BY P30/P31 CALCULATIONS
025189,000169: # MOD NO 1 LOG SECTION P30,P37
025190,000170:
025191,000171: # FUNCTIONAL DESCRIPTION
025192,000172: # THROUGH A SERIES OF CALLS COMPUTES APOGEE AND PERIGEE ALTITUDE
025193,000173:
025194,000174: # SUBROUTINES CALLED
025195,000175: # PERIAPO1
025196,000176: # MAXCHK
025197,000177:
025198,000178: # CALLING SEQUENCE
025199,000179: # L CALL
025200,000180: # L+1 S30/31.1
025201,000181:
025202,000182: # NORMAL EXIT MODE
025203,000183: # AT L+2 OR CALLING SEQUENCE
025204,000184:
025205,000185: # OUTPUT
025206,000186: # HAPO APOGEE ALT. DP B+29 M
025207,000187: # HPER PERIGEE ALT. DP B+29 M
025208,000188:
025209,000189: 26,2000 SETLOC P30S1A
025210,000190: 26,2000 BANK
025211,000191:
025212,000192: 26,2021 COUNT* $$/P30
025213,000193: 26,2021 45020 S30/31.1 STQ CALL
025214,000194: 26,2022 03635 QTEMP
025215,000195: 26,2023 45375 PERIAPO1
025216,000196: 26,2024 77624 CALL
025217,000197: 26,2025 46764 MAXCHK
025218,000198: 26,2026 16236 STODL HPER # PERIGEE ALT B+29
025219,000199: 26,2027 00005 4D
025220,000200: 26,2030 77624 CALL
025221,000201: 26,2031 46764 MAXCHK
025222,000202: 26,2032 36234 STCALL HAPO # APOGEE ALT B+29
025223,000203: 26,2033 03635 QTEMP
025224,000204:
025225,000205:
025226,000206:
025227,000207: 4000 SETLOC P30SUBS
025228,000208: 4000 BANK
025229,000209: 4564 COUNT* $$/P30
025230,000210: 4564 E4,1636 EBANK= SUBEXIT
025231,000211: 4564 00006 P20FLGON EXTEND
025232,000212: 4565 23636 QXCH SUBEXIT
025233,000213: 4566 07710 TC UPFLAG
025234,000214: 4567 00031 ADRES TRACKFLG
025235,000215: 4570 07710 TC UPFLAG
025236,000216: 4571 00027 ADRES UPDATFLG
025237,000217: 4572 07722 TC DOWNFLAG
025238,000218: 4573 00244 ADRES PCFLAG
025239,000219: 4574 01636 TC SUBEXIT
025240,000220:
025241,000221: 22,2000 SETLOC P38TAG
025242,000222: 22,2000 BANK
025243,000223: # PLANE CHANGE TARGETING PROGRAM P38
025244,000224: #
025245,000225: # PURPOSE
025246,000226: # TO COMPUTE PARAMETERS FOR PLANE CHANGE MANEUVER
025247,000227:
025248,000228: # INPUT
025249,000229: # LASTTIG
025250,000230: #
025251,000231: # OUTPUT
025252,000232: # TIG TIME OF PLANE CHANGE MANEUVER COMPUTED TO BE
025253,000233: # LASTTIG + 90 DEG TRANSFER TIME
025254,000234: # DELVLVC DELTA VELOCITY AT PC - LOCAL VERTICAL
025255,000235: # DELVSIN DELTA VELOCITY AT PC - REFERENCE
025256,000236:
025257,000237: 22,3271 COUNT* $$/P38
025258,000238: 22,3271 04564 P38 TC P20FLGON # SET TRACK,UPDATE - CLEAR PC FLAGS
025259,000239: 22,3272 07710 TC UPFLAG
025260,000240: 22,3273 00244 ADRES PCFLAG
025261,000241:
025262,000242: 22,3274 06006 TC INTPRET
025263,000243: 22,3275 71214 CLEAR DLOAD
025264,000244: 22,3276 01271 FINALFLG
025265,000245: 22,3277 03413 TIG
025266,000246: 22,3300 03726 STORE LASTTIG
025267,000247: 22,3301 77776 EXIT
025268,000248: 22,3302 33372 CAF V06N39
025269,000249: 22,3303 05550 TC VNFLASH
025270,000250: 22,3304 06006 TC INTPRET
025271,000251: 22,3305 71214 P38A SET DLOAD
025272,000252: 22,3306 01067 XDELVFLG
025273,000253: 22,3307 03726 LASTTIG
025274,000254: 22,3310 34041 STCALL TDEC1
025275,000255: 22,3311 11400 CSMPREC # INTEGRATE STATES TO LASTTIG
025276,000256: 22,3312 43145 DLOAD SET
025277,000257: 22,3313 15204 ZEROVECS
025278,000258: 22,3314 03466 RVSW
025279,000259: 22,3315 16726 STODL CSTH # COS 90 DEGREES
025280,000260: 22,3316 05371 CS359+
025281,000261: 22,3317 26724 STOVL SNTH # SINE 90 DEGREES
025282,000262: 22,3320 00001 RATT
025283,000263: 22,3321 26651 STOVL RVEC
025284,000264: 22,3322 00007 VATT
025285,000265: 22,3323 36740 STCALL VVEC # COMPUTE TRANSFER TIME OF 90 DEG
025286,000266: 22,3324 25004 TIMETHET
025287,000267: 22,3325 77615 DAD
025288,000268: 22,3326 03726 LASTTIG
025289,000269: 22,3327 03413 STORE TIG
025290,000270: 22,3330 77776 EXIT
025291,000271: 22,3331 35041 CAF V06N33
025292,000272: 22,3332 05550 TC VNFLASH
025293,000273: 22,3333 06006 TC INTPRET
025294,000274: 22,3334 77624 CALL
025295,000275: 22,3335 73430 VN1645
025296,000276: 22,3336 77775 P38RECYC VLOAD
025297,000277: 22,3337 15204 ZEROVECS
025298,000278: 22,3340 17405 STODL DELVLVC
025299,000279: 22,3341 03413 TIG
025300,000280: 22,3342 34041 STCALL TDEC1
025301,000281: 22,3343 45416 PRECSET
025302,000282: 22,3344 43014 BON SET
025303,000283: 22,3345 01311 FINALFLG
025304,000284: 22,3346 45350 +2
025305,000285: 22,3347 00470 UPDATFLG
025306,000286: 22,3350 77775 +2 VLOAD
025307,000287: 22,3351 03524 VACT3
025308,000288: 22,3352 27616 STOVL VTIG
025309,000289: 22,3353 03516 RACT3
025310,000290: 22,3354 37610 STCALL RTIG
025311,000291: 22,3355 15667 DISPN90
025312,000292: 22,3356 77624 CALL
025313,000293: 22,3357 73333 LOMAT
025314,000294: 22,3360 61375 VLOAD VXM
025315,000295: 22,3361 03405 DELVLVC # ROTATE DV (LV TO REF)
025316,000296: 22,3362 00001 0D
025317,000297: 22,3363 77772 VSL1
025318,000298: 22,3364 37624 STCALL DELVSIN
025319,000299: 22,3365 73430 VN1645
025320,000300: 22,3366 77650 GOTO
025321,000301: 22,3367 45336 P38RECYC
025322,000302:
025323,000303: 22,3370 17777 37776 CS359+ 2DEC +.499999992
025324,000304: 22,3372 01447 V06N39 VN 0639
End of include-file P30,P38.agc. Parent file is MAIN.agc