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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038134,000002: ## Copyright: Public domain.
038135,000003: ## Filename: TVCMASSPROP.agc
038136,000004: ## Purpose: A section of Skylark revision 048.
038137,000005: ## It is part of the source code for the Apollo Guidance Computer (AGC)
038138,000006: ## for Skylab-2, Skylab-3, Skylab-4, and ASTP. No original listings of
038139,000007: ## this software are available; instead, this file was created via
038140,000008: ## disassembly of dumps of the core rope modules actually flown on
038141,000009: ## Skylab-2. Access to these modules was provided by the New Mexico
038142,000010: ## Museum of Space History.
038143,000011: ## Assembler: yaYUL
038144,000012: ## Contact: Ron Burkey <info@sandroid.org>.
038145,000013: ## Website: www.ibiblio.org/apollo/index.html
038146,000014: ## Mod history: 2023-09-04 MAS Created from Artemis 072.
038147,000015:
038148,000016:
038149,000017: # PROGRAM NAME....MASSPROP
038150,000018: # LOG SECTION....TVCMASSPROP PROGRAMMER...MELANSON (ENGEL, SCHLUNDT)
038151,000019:
038152,000020:
038153,000021: # FUNCTIONAL DESCRIPTION:
038154,000022:
038155,000023: # MASSPROP OPERATES IN TWO MODES:(1)IF LEM MASS OR CONFIGURATION ARE UPDATED (MASSPROP DOES NOT TEST
038156,000024: # FOR THIS) THE ENTIRE PROGRAM MUST BE RUN THROUGH, BREAKPOINT VALUES AND DERIVATIVES OF THE OUTPUTS WITH
038157,000025: # RESPECT TO CSM MASS BEING CALCULATED PRIOR TO CALCULATION OF THE OUTPUTS. (2)OTHERWISE, THE OUTPUTS CAN BE
038158,000026: # CALCULATED USING PREVIOUSLY COMPUTED BREAKPOINT VALUES AND DERIVATIVES.
038159,000027:
038160,000028: # CALLING SEQUENCES
038161,000029:
038162,000030: # IF LEM MASS OR CONFIGURATION HAS BEEN UPDATED, TRANSFER TO MASSPROP, OTHERWISE TRANSFER TO FIXCW.
038163,000031: # L TC BANKCALL OR IBNKCALL
038164,000032: # L+1 CADR MASSPROP
038165,000033: # OR
038166,000034: # L+1 CADR FIXCW
038167,000035:
038168,000036: # L+2 RETURNS VIA Q
038169,000037:
038170,000038: # CALLED IN PARTICULAR BY DONOUN47 (JOB) AND TVCEXECUTIVE (TASK)
038171,000039:
038172,000040: # JOBS OR TASKS INITIATED - NONE
038173,000041:
038174,000042: # SUBROUTINES CALLED - NONE
038175,000043:
038176,000044: # ERASABLE INITIALIZATION REQUIRED
038177,000045:
038178,000046: # LEMMASS MUST CONTAIN LEM MASS SCALED AT B+16 IN KILOGRAMS
038179,000047: # CSMMASS MUST CONTAIN CSM MASS SCALED AT B+16 IN KILOGRAMS
038180,000048:
038181,000049: # DAPDATR1 MUST BE SET TO INDICATE VEHICLE CONFIGURATION.
038182,000050: # BITS (15,14,13) = ( 0 , 0 , 1 ) LEM OFF
038183,000051: # ( 0 , 1 , 0 ) LEM ON (ASCNT,DSCNT)
038184,000052: # ( 1 , 1 , 0 ) LEM ON (ASCNT ONLY)
038185,000053:
038186,000054:
038187,000055: # ALARMS - NONE
038188,000056:
038189,000057: # EXIT - TC Q
038190,000058:
038191,000059: # OUTPUTS:
038192,000060:
038193,000061: # (1)IXX, SINGLE PRECISION SCALED AT B+20 IN KG-M SQ.
038194,000062: # (2)IAVG, SINGLE PRECISION SCALED AT B+20 IN KG-M SQ.
038195,000063: # (3)IAVG/TLX, SINGLE PRECISION, SCALED AT B+2 SEC-SQD
038196,000064: # THEY ARE STORED IN CONSECUTIVE REGISTERS IXX0, IXX1, IXX2
038197,000065:
038198,000066: # CONVERSION FACTOR: (SLUG-FTSQ) = 0.737562 (KG-MSQ)
038199,000067:
038200,000068:
038201,000069: # OUTPUTS ARE CALCULATED AS FOLLOWS :
038202,000070:
038203,000071: # (1) IF LEM DOCKED, LEMMASS IS FIRST ELIMINATED AS A PARAMETER
038204,000072:
038205,000073: # VARST0 = INTVALUE0 + LEMMASS(SLOPEVAL0) IXX BREAKPOINT VALUE
038206,000074: # VARST1 = INTVALUE1 + LEMMASS(SLOPEVAL1) IAVG BREAKPOINT VALUE
038207,000075: # VARST2 = INTVALUE2 + LEMMASS(SLOPEVAL2) IAVG/TLX BREAKPOINT VALUE
038208,000076:
038209,000077: # VARST3 = INTVALUE3 + LEMMASS(SLOPEVAL3) IAVG/TLX SLOPE FOR CSMMASS > 33956 LBS ( SPS > 10000 LBS)
038210,000078: # VARST4 = INTVALUE4 + LEMMASS(SLOPEVAL4) IAVG SLOPE FOR CSMMASS > 33956 LBS ( SPS > 10000 LBS)
038211,000079:
038212,000080: # VARST5 = INTVALUE5 + LEMMASS(SLOPEVAL5) IXX SLOPE FOR ALL VALUES OF CSMMASS
038213,000081:
038214,000082: # VARST6 = INTVALUE6 + LEMMASS(SLOPEVAL6) IAVG SLOPE FOR CSMMASS < 33956 LBS ( SPS < 10000 LBS)
038215,000083: # VARST7 = INTVALUE7 + LEMMASS(SLOPEVAL7) IAVG/TLX SLOPE FOR CSMMASS < 33956 LBS ( SPS < 10000 LBS)
038216,000084:
038217,000085: # VARST8 = INTVALUE8 + LEMMASS(SLOPEVAL8) IAVG DECREMENT TO BRKPT VALUE WHEN LEM DSCNT STAGE OFF
038218,000086: # VARST9 = INTVALUE9 + LEMMASS(SLOPEVAL9) IAVG/TLX DECREMENT TO BRKPT VALUE WHEN LEM DSCNT STAGE OFF
038219,000087:
038220,000088: # (2) IF LEM NOT DOCKED
038221,000089:
038222,000090: # VARST0 = NOLEMVAL0 WHERE THE MEANING AND SCALING OF VARST0
038223,000091: # . . TO VARST9 ARE THE SAME AS GIVEN ABOVE
038224,000092: # . .
038225,000093: # . . NOTE... FOR THIS CASE, VARST8,9 HAVE NO
038226,000094: # VARST9 = NOLEMVAL9 MEANING (THEY ARE COMPUTED BUT NOT USED)
038227,000095:
038228,000096: # (3) THE FINAL OUTPUT CALCULATIONS ARE THEN DONE
038229,000097:
038230,000098: # IXX0 = VARST0 + (CSMMASS + NEGBPW)VARST5 IXX
038231,000099:
038232,000100: # IXX1 = VARST1 + (CSMMASS + NEGBPW)VARST(4 OR 6) IAVG
038233,000101:
038234,000102: # IXX2 = VARST2 + (CSMMASS + NEGBPW)VARST(3 OR 7) IAVG/TLX
038235,000103:
038236,000104: # THE DATA USED CAME FROM CSM/LM SPACECRAFT OPERATIONAL DATA BOOK.
038237,000105: # VOL. 3, NASA DOCUMENT SNA-8-D-027 (MARCH 1968)
038238,000106:
038239,000107: # PERTINENT MASS DATA : CSM WEIGHT (FULL) 64100 LBS
038240,000108: # (EMPTY) 23956 LBS
038241,000109: # LEM WEIGHT (FULL) 32000 LBS
038242,000110: # (EMPTY) 14116 LBS
038243,000111:
038244,000112: # (WEIGHTS ARE FROM AMENDMENT #1 (APRIL 24,1968) TO ABOVE DATA BOOK)
038245,000113:
038246,000114: 05,2000 SETLOC DAPMASS
038247,000115: 05,2000 BANK
038248,000116: 05,3311 E6,1453 EBANK= CNTR
038249,000117: 05,3311 COUNT* $$/MASP
038250,000118:
038251,000119:
038252,000120: 05,3311 34322 MASSPROP CAF NINE # MASSPROP USES TVC/RCS INTERUPT TEMPS
038253,000121: 05,3312 55535 +1 TS PHI333 # SET UP TEN PASSES
038254,000122: 05,3313 31514 LEMTEST CAE DAPDATR1 # DETERMINE LEM STATUS
038255,000123: 05,3314 74765 MASK BIT13
038256,000124: 05,3315 00006 EXTEND
038257,000125: 05,3316 13322 BZF LEMYES
038258,000126:
038259,000127: 05,3317 51535 LEMNO INDEX PHI333 # LEM NOT ATTACHED
038260,000128: 05,3320 33406 CAF NOLEMVAL
038261,000129: 05,3321 13332 TCF STOINST
038262,000130:
038263,000131: 05,3322 31521 LEMYES CAE LEMMASS # LEM IS ATTACHED
038264,000132: 05,3323 60000 DOUBLE
038265,000133: 05,3324 00006 EXTEND
038266,000134: 05,3325 51535 INDEX PHI333
038267,000135: 05,3326 73430 MP SLOPEVAL
038268,000136: 05,3327 20001 DDOUBL
038269,000137: 05,3330 51535 INDEX PHI333
038270,000138: 05,3331 63416 AD INTVALUE
038271,000139:
038272,000140: 05,3332 51535 STOINST INDEX PHI333 # STORAGE INST BEGIN HERE
038273,000141: 05,3333 55540 TS VARST0
038274,000142: 05,3334 11535 CCS PHI333 # ARE ALL TEN PASSES COMPLETED
038275,000143: 05,3335 13312 TCF MASSPROP +1 # NO - GO DECREMENT PHI333
038276,000144:
038277,000145: 05,3336 11514 DXTEST CCS DAPDATR1 # IF NEG, BIT15 IS 1, LEM DSCNT STAGE OFF
038278,000146: 05,3337 13345 TCF FIXCW
038279,000147: 05,3340 13345 TCF FIXCW
038280,000148: 05,3341 53551 DXCH VARST0 +8D
038281,000149: 05,3342 21542 DAS VARST0 +1
038282,000150: 05,3343 33443 CA DXITFIX
038283,000151: 05,3344 27547 ADS VARST0 +7
038284,000152:
038285,000153: 05,3345 35000 FIXCW CAF BIT2 # COMPUTATION PHASE BEGINS HERE. SET UP
038286,000154: 05,3346 55535 TS PHI333 # THREE PASSES
038287,000155: 05,3347 55536 TS PSI333
038288,000156:
038289,000157: 05,3350 31522 CAE CSMMASS # GET DELTA CSM WEIGHT - SIGN DETERMINES
038290,000158: 05,3351 63442 AD NEGBPW # SLOPE LOCATIONS.
038291,000159: 05,3352 60000 DOUBLE
038292,000160: 05,3353 55537 TS TEMP333
038293,000161:
038294,000162: 05,3354 00006 EXTEND
038295,000163: 05,3355 63360 BZMF PEGGY # DETERMINE CORRECT SLOPE
038296,000164: 05,3356 37701 CAF NEG2
038297,000165: 05,3357 55535 TS PHI333
038298,000166:
038299,000167: 05,3360 51535 PEGGY INDEX PHI333 # ALL IS READY - CALCULATE OUTPUTS NOW
038300,000168: 05,3361 31545 CAE VARST5 # GET SLOPE
038301,000169: 05,3362 00006 EXTEND
038302,000170: 05,3363 71537 MP TEMP333 # MULT BY DELTA CSM WEIGHT
038303,000171: 05,3364 60000 DOUBLE
038304,000172: 05,3365 51536 INDEX PSI333
038305,000173: 05,3366 61540 AD VARST0 # ADD BREAKPOINT VALUE
038306,000174: 05,3367 51536 INDEX PSI333
038307,000175: 05,3370 55516 TS IXX # ****** OUTPUTS (IXX0, IXX1, IXX2) ******
038308,000176:
038309,000177:
038310,000178: 05,3371 11536 CCS PSI333 # BOOKKEEPING - MASSPROP FINISHED OR NOT
038311,000179: 05,3372 13402 TCF BOKKEP2 # NO - GO TAKE CARE OF INDEXING REGISTERS
038312,000180:
038313,000181: 05,3373 31514 CAE DAPDATR1 # UPDATE WEIGHT/G
038314,000182: 05,3374 74764 MASK BIT14
038315,000183: 05,3375 10000 CCS A
038316,000184: 05,3376 31521 CA LEMMASS
038317,000185: 05,3377 61522 AD CSMMASS
038318,000186: 05,3400 55524 TS WEIGHT/G # SCALED AT B+16 IN KILOGRAMS
038319,000187: 05,3401 00002 ENDMASSP TC Q
038320,000188:
038321,000189: 05,3402 55536 BOKKEP2 TS PSI333 # REDUCE PSI BY ONE
038322,000190: 05,3403 00006 EXTEND
038323,000191: 05,3404 27535 DIM PHI333
038324,000192: 05,3405 13360 TCF PEGGY
038325,000193:
038326,000194:
038327,000195: 05,3406 00616 NOLEMVAL DEC 25445. B-20
038328,000196: 05,3407 02526 DEC 87450. B-20
038329,000197: 05,3410 02352 DEC .30715 B-2
038330,000198: 05,3411 01471 DEC 1.22877 E-5 B+12
038331,000199: 05,3412 00634 DEC 1.6096 B-6
038332,000200: 05,3413 00612 DEC 1.54 B-6
038333,000201: 05,3414 03706 DEC 7.77177 B-6
038334,000202: 05,3415 04425 DEC 3.46458 E-5 B+12
038335,000203:
038336,000204: 05,3416 00644 INTVALUE DEC 26850 B-20
038337,000205: 05,3417 03710 DEC 127518 B-20
038338,000206: 05,3420 04246 DEC .54059 B-2
038339,000207: 05,3421 02011 DEC .153964 E-4 B+12
038340,000208: 05,3422 77501 DEC -.742923 B-6
038341,000209: 05,3423 00612 DEC 1.5398 B-6
038342,000210: 05,3424 04656 DEC 9.68 B-6
038343,000211: 05,3425 10372 DEC .647625 E-4 B+12
038344,000212: 05,3426 77126 DEC -27228. B-20
038345,000213: 05,3427 76261 DEC -.206476 B-2
038346,000214:
038347,000215: 05,3430 00767 SLOPEVAL DEC 1.96307 B-6
038348,000216: 05,3431 15624 DEC 27.5774 B-6
038349,000217: 05,3432 03054 DEC 2.3548 E-5 B+12
038350,000218: 05,3433 04532 DEC 2.1777 E-9 B+26
038351,000219: 05,3434 10433 DEC 1.044 E-3 B+8
038352,000220: 05,3435 00000 DEC 0 B-14
038353,000221: 05,3436 22070 DEC 2.21068 E-3 B+8
038354,000222: 05,3437 03204 DEC 1.5166 E-9 B+26
038355,000223: 05,3440 77266 DEC -1.284 B-6
038356,000224: 05,3441 02476 DEC 2. E-5 B+12
038357,000225:
038358,000226: 05,3442 70364 NEGBPW DEC -15402.17 B-16
038359,000227: 05,3443 75420 DXITFIX DEC* -1.88275 E-5 B+12*
End of include-file TVCMASSPROP.agc. Parent file is MAIN.agc