Source Code
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These source-code files are part of a reconstructed copy of Artemis 071, the
first release of the Apollo 15 through 17 Command Module (CM) Apollo Guidance
Computer (AGC) software.
The reconstruction began with source code of Artemis 072 previously transcribed
from a digitized copy of that program. The code was then updated by undoing
changes between the two versions. The reconstruction was verified by matching
memory-bank checksums to those listed in drawing 2021154-. Note that page
numbers in the reconstructed code match those on the Artemis 072 printout,
although the changed code would likely have changed page numbers for a real
Artemis 071 listing.
Comments from the original source code are prefixed with a single '#' symbol,
whereas comments added later are prefixed by "##" or "###". Report any errors
noted by creating an
issue report at the Virtual AGC
project's GitHub repository.
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018402,000002: ## Copyright: Public domain.
018403,000003: ## Filename: GIMBAL_LOCK_AVOIDANCE.agc
018404,000004: ## Purpose: A section of Artemis revision 071.
018405,000005: ## It is part of the reconstructed source code for the first
018406,000006: ## release of the flight software for the Command Module's
018407,000007: ## (CM) Apollo Guidance Computer (AGC) for Apollo 15 through
018408,000008: ## 17. The code has been recreated from a copy of Artemis 072.
018409,000009: ## It has been adapted such that the resulting bugger words
018410,000010: ## exactly match those specified for Artemis 071 in NASA
018411,000011: ## drawing 2021154-, which gives relatively high confidence
018412,000012: ## that the reconstruction is correct.
018413,000013: ## Reference: 416
018414,000014: ## Assembler: yaYUL
018415,000015: ## Contact: Ron Burkey <info@sandroid.org>.
018416,000016: ## Website: www.ibiblio.org/apollo/index.html
018417,000017: ## Mod history: 2019-08-14 MAS Created from Artemis 072.
018418,000018:
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Page 416
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018420,000020:
018421,000021: 22,2000 SETLOC KALCMON1
018422,000022: 22,2000 BANK
018423,000023:
018424,000024: 22,2745 COUNT* $$/KALC
018425,000025: 22,2745 E6,1661 EBANK= BCDU
018426,000026:
018427,000027: # DETECTING GIMBAL LOCK
018428,000028: 22,2745 22,2745 LOCSKIRT EQUALS WCALC
018429,000029: 22,2745 70740 WCALC LXC,1 DLOAD*
018430,000030: 22,2746 00774 RATEINDX
018431,000031: 22,2747 05002 ARATE,1
018432,000032: 22,2750 45002 SR4 CALL # COMPUTE THE INCREMENTAL ROTATION MATRIX
018433,000033: 22,2751 44522 DELCOMP # DEL CORRESPONDING TO A 1 SEC ROTATION
018434,000034: # ABOUT COF
018435,000035: 22,2752 74343 DLOAD* VXSC
018436,000036: 22,2753 05002 ARATE,1
018437,000037: 22,2754 03343 COF
018438,000038: 22,2755 77721 MXV
018439,000039: 22,2756 05014 QUADROT
018440,000040: 22,2757 17311 STODL BRATE
018441,000041: 22,2760 03365 AM
018442,000042: 22,2761 55605 DMP DDV*
018443,000043: 22,2762 05012 ANGLTIME
018444,000044: 22,2763 05002 ARATE,1
018445,000045: 22,2764 77661 SR
018446,000046: 22,2765 20606 5
018447,000047: 22,2766 03317 STORE TM
018448,000048: 22,2767 77214 BON VLOAD
018449,000049: 22,2770 00313 CYC61FLG
018450,000050: 22,2771 71747 RCYCLR61
018451,000051: 22,2772 03311 BRATE
018452,000052: 22,2773 77761 VXSC
018453,000053: 22,2774 05036 BIASCALE
018454,000054: 22,2775 03275 STORE BIASTEMP # ATTITUDE ERROR BIAS TO PREVENT OVERSHOOT
018455,000055: # IN SYSTEM
018456,000056: 22,2776 77614 SETGO # STATE SWITCH CALCMAN2 (43D)
018457,000057: 22,2777 01035 CALCMAN2 # 0(OFF) = BYPASS STARTING PROCEDURE
018458,000058: 22,3000 45053 NEWANGL +1 # 1(ON) = START MANEUVER
018459,000059:
018460,000060:
018461,000061: 22,3001 00044 15053 ARATE 2DEC .0022222222 # = .05 DEG/SEC
018462,000062: 22,3003 00221 24255 2DEC .0088888889 # = .2 DEG/SEC
018463,000063: 22,3005 00554 02660 2DEC .0222222222 # = .5 DEG/SEC
018464,000064: 22,3007 02660 13301 2DEC .0888888889 # = 2 DEG/SEC $22.5 DEG/SEC
018465,000065: 22,3011 00003 04000 ANGLTIME 2DEC .000190735 # = 100B - 19
018466,000066: # MANEUVER ANGLE TO MANEUVER TIME
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Page 417
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018468,000068: 22,3013 03146 14632 QUADROT 2DEC .1 # ROTATION MATRIX FROM S/C AXES TO CONTROL
018469,000069: 22,3015 00000 00000 2DEC 0 B-28 # AXES (X ROT = -7.25 DEG)
018470,000070: 22,3017 00000 00000 2DEC 0 B-28
018471,000071: 22,3021 00000 00000 2DEC 0 B-28
018472,000072: 22,3023 03131 11275 2DEC .099200 # =(.1)COS7.25
018473,000073: 22,3025 77461 47370 2DEC -.012620 # =-(.1)SIN7.25
018474,000074: 22,3027 00000 00000 2DEC 0 B-28
018475,000075: 22,3031 00316 30407 2DEC .012620 # (.1)SIN7.25
018476,000076: 22,3033 03131 11275 2DEC .099200 # (.1)COS7.25
018477,000077: 22,3035 00004 05253 BIASCALE 2DEC .0002543132 # = (450/180)(1/0.6)(1/16384)
End of include-file GIMBAL_LOCK_AVOIDANCE.agc. Parent file is MAIN.agc