Source Code
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These source-code files are part of a reconstructed copy of Luminary 69/2,
the flown, final release of the Apollo 10 Lunar Module (LM) Apollo Guidance Computer (AGC) software.
The reconstruction is based on the source code of Luminary 69 — i.e., the
initial, unflown version, "revision 0" — of which
a contemporary listing was available. The code was then updated by incorporating the
differences between Luminary 69 and Luminary 69/2, known from other contemporary
documentation. The only such difference is the implementation in
Luminary 69/2 of the "R-2 Lunar Potential Model", the source code for which was taken
from program Luminary 99/1 (Apollo 11 LM), of which a contemporary listing was also available.
Finally, the now-reconstructed Luminary 69/2 was then validated by assembling it to
executable form and verifying that its memory banks had the correct checksums,
known from still other contemporary documentation.
Note that page numbers in the reconstructed code match those in the original Luminary 69
program listing, or in the ORBITAL INTEGRATION log section, in Luminary 99/1. Page numbers
would certainly differ somewhat in a contemporary Luminary 69/2 listing.
Moreover, annotations that were not present in the contemporary source code have been added
to the reconstructed code to justify each change in Luminary 69/2 relative to
Luminary 69. Here's a guide to the Apollo documentation referenced in those annotations:
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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016266,000002: ## Copyright: Public domain.
016267,000003: ## Filename: GIMBAL_LOCK_AVOIDANCE.agc
016268,000004: ## Purpose: A section of LUM69 revision 2.
016269,000005: ## It is part of the reconstructed source code for the flown
016270,000006: ## version of the flight software for the Lunar Module's (LM)
016271,000007: ## Apollo Guidance Computer (AGC) for Apollo 10. The code has
016272,000008: ## been recreated from a copy of Luminary revsion 069, using
016273,000009: ## changes present in Luminary 099 which were described in
016274,000010: ## Luminary memos 75 and 78. The code has been adapted such
016275,000011: ## that the resulting bugger words exactly match those specified
016276,000012: ## for LUM69 revision 2 in NASA drawing 2021152B, which gives
016277,000013: ## relatively high confidence that the reconstruction is correct.
016278,000014: ## Reference: p. 377
016279,000015: ## Assembler: yaYUL
016280,000016: ## Contact: Ron Burkey <info@sandroid.org>.
016281,000017: ## Website: www.ibiblio.org/apollo/index.html
016282,000018: ## Mod history: 2019-07-27 MAS Created from Luminary 69.
016283,000019:
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Page 377
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016285,000021: 15,2050 BANK 15
016286,000022:
016287,000023: 22,2000 SETLOC KALCMON1
016288,000024: 22,2000 BANK
016289,000025:
016290,000026: # DETECTING GIMBAL LOCK
016291,000027: 22,2744 22,2744 LOCSKIRT EQUALS NOGIMLOC
016292,000028:
016293,000029: 22,2744 77614 NOGIMLOC SET
016294,000030: 22,2745 01074 CALCMAN3
016295,000031: 22,2746 70740 WCALC LXC,1 DLOAD*
016296,000032: 22,2747 01325 RATEINDX # CHOOSE THE DESIRED MANEUVER RATE
016297,000033: 22,2750 04772 ARATE,1 # FROM A LIST OF FOUR
016298,000034: 22,2751 45002 SR4 CALL # COMPUTE THE INCREMENTAL ROTATION MATRIX
016299,000035: 22,2752 44527 DELCOMP # DEL CORRESPONDING TO A 1 SEC ROTATION
016300,000036: # ABOUT COF
016301,000037: 22,2753 74343 DLOAD* VXSC
016302,000038: 22,2754 04772 ARATE,1
016303,000039: 22,2755 03267 COF
016304,000040: 22,2756 17324 STODL BRATE # COMPONENT MANEUVER RATES 45 DEG/SEC
016305,000041: 22,2757 03334 AM
016306,000042: 22,2760 55605 DMP DDV*
016307,000043: 22,2761 05002 ANGLTIME
016308,000044: 22,2762 04772 ARATE,1
016309,000045: 22,2763 77661 SR
016310,000046: 22,2764 20606 5
016311,000047: 22,2765 03332 STORE TM # MANEUVER EXECUTION TIME SCALED AS T2
016312,000048: 22,2766 77614 SETGO
016313,000049: 22,2767 01035 CALCMAN2 # 0(OFF) = CONTINUE MANEUVER
016314,000050: 22,2770 45010 NEWANGL +1 # 1(ON) = START MANEUVER
016315,000051:
016316,000052: # THE FOUR SELECTABLE FREE FALL MANEUVER RATES SELECTED BY
016317,000053: # LOADING RATEINDX WITH 0, 2, 4, 6, RESPECTIVELY
016318,000054:
016319,000055: 22,2771 00221 24255 ARATE 2DEC .0088888888 # = 0.2 DEG/SEC $ 22.5 DEG/SEC
016320,000056:
016321,000057: 22,2773 00554 02660 2DEC .0222222222 # = 0.5 DEG/SEC $ 22.5 DEG/SEC
016322,000058:
016323,000059: 22,2775 02660 13301 2DEC .0888888888 # = 2.0 DEG/SEC $ 22.5 DEG/SEC
016324,000060:
016325,000061: 22,2777 16161 30707 2DEC .4444444444 # = 10.0 DEG/SEC $ 22.5 DEG/SEC
016326,000062:
016327,000063: 22,3001 00003 04000 ANGLTIME 2DEC .0001907349 # = 100B-19 FUDGE FACTOR TO CONVERT
016328,000064: # MANEUVER ANGLE TO MANEUVER TIME
016329,000065:
016330,000066:
End of include-file GIMBAL_LOCK_AVOIDANCE.agc. Parent file is MAIN.agc