Source Code
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These source-code files are part of a reconstructed copy of Comanche 45, the
second release, though not the final mission release, of the Apollo 10
Command Module (CM) Apollo Guidance Computer (AGC) software. Comanche 45 was
preceded by Comanche 44 and followed by Comanche 45/2 (the flown release). The reconstruction
is believed to be exactly accurate, but in the absence of an actual Apollo-era
listing of Comanche 45, some explanation of the reconstruction process is needed
to insure confidence in that accuracy.
The starting point was the source code of Comanche 44 (itself previously accurately
reconstructed). Comanche 44 source code was then modified
by incorporating changes known from contemporary documentation to have been
made between revisions 44 and 45. The now-reconstructed Comanche 45 source code was
verified by assembling it and checking that the assembled code had
the expected known-correct memory-bank checksums.
Note that page numbers in the reconstructed code tend to match those in the Comanche 55, the
most-similar revision of Comanche for which we have access to an actual non-reconstructed hardcopy;
the source code would likely have different page numbers in a contemporary
Comanche 45 listing.
Annotations that were not present in the contemporary source code have been added to the reconstructed
code to justify each change relative to Comanche 44. Here's a guide to the Apollo documentation referenced
in those annotations:
There is also
a detailed commentary about the reconstruction process.
Comments expected to have been present in 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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017671,000002: ## Copyright: Public domain.
017672,000003: ## Filename: GIMBAL_LOCK_AVOIDANCE.agc
017673,000004: ## Purpose: A section of Comanche revision 045.
017674,000005: ## It is part of the reconstructed source code for the
017675,000006: ## second release of the flight software for the Command
017676,000007: ## Module's (CM) Apollo Guidance Computer (AGC) for Apollo 10.
017677,000008: ## The code has been recreated from a copy of Comanche 055. It
017678,000009: ## has been adapted such that the resulting bugger words
017679,000010: ## exactly match those specified for Comanche 45 in NASA drawing
017680,000011: ## 2021153D, which gives relatively high confidence that the
017681,000012: ## reconstruction is correct.
017682,000013: ## Assembler: yaYUL
017683,000014: ## Contact: Ron Burkey <info@sandroid.org>.
017684,000015: ## Website: www.ibiblio.org/apollo/index.html
017685,000016: ## Mod history: 2020-12-06 MAS Created from Comanche 44.
017686,000017:
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Page 412
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017688,000019: 15,2000 BANK 15
017689,000020: 22,2000 SETLOC KALCMON1
017690,000021: 22,2000 BANK
017691,000022:
017692,000023: 22,2737 E6,1661 EBANK= BCDU
017693,000024:
017694,000025: # DETECTING GIMBAL LOCK
017695,000026: 22,2737 22,2737 LOCSKIRT EQUALS WCALC
017696,000027: 22,2737 70740 WCALC LXC,1 DLOAD*
017697,000028: 22,2740 01130 RATEINDX
017698,000029: 22,2741 04771 ARATE,1
017699,000030: 22,2742 45002 SR4 CALL # COMPUTE THE INCREMENTAL ROTATION MATRIX
017700,000031: 22,2743 44530 DELCOMP # DEL CORRESPONDING TO A 1 SEC ROTATION
017701,000032: # ABOUT COF
017702,000033: 22,2744 74343 DLOAD* VXSC
017703,000034: 22,2745 04771 ARATE,1
017704,000035: 22,2746 03343 COF
017705,000036: 22,2747 77721 MXV
017706,000037: 22,2750 05003 QUADROT
017707,000038: 22,2751 17311 STODL BRATE
017708,000039: 22,2752 03365 AM
017709,000040: 22,2753 55605 DMP DDV*
017710,000041: 22,2754 05001 ANGLTIME
017711,000042: 22,2755 04771 ARATE,1
017712,000043: 22,2756 77661 SR
017713,000044: 22,2757 20606 5
017714,000045: 22,2760 27317 STOVL TM
017715,000046: 22,2761 03311 BRATE
017716,000047: 22,2762 77761 VXSC
017717,000048: 22,2763 05025 BIASCALE
017718,000049: 22,2764 03275 STORE BIASTEMP # ATTITUDE ERROR BIAS TO PREVENT OVERSHOOT
017719,000050: # IN SYSTEM
017720,000051: 22,2765 77614 SETGO # STATE SWITCH CALCMAN2 (43D)
017721,000052: 22,2766 01035 CALCMAN2 # 0(OFF) = BYPASS STARTING PROCEDURE
017722,000053: 22,2767 45032 NEWANGL +1 # 1(ON) = START MANEUVER
017723,000054:
017724,000055:
017725,000056: 22,2770 00044 15053 ARATE 2DEC .0022222222 # = .05 DEG/SEC
017726,000057:
017727,000058: 22,2772 00221 24255 2DEC .0088888889 # = .2 DEG/SEC
017728,000059:
017729,000060: 22,2774 00554 02660 2DEC .0222222222 # = .5 DEG/SEC
017730,000061:
017731,000062: 22,2776 05540 26603 2DEC .1777777777 # = 4 DEG/SEC $ 22.5 DEG/SEC
017732,000063:
017733,000064: 22,3000 00003 04000 ANGLTIME 2DEC .000190735 # = 100B - 19
017734,000065:
017735,000066: # MANEUVER ANGLE TO MANEUVER TIME
017736,000067: 22,3002 03146 14632 QUADROT 2DEC .1 # ROTATION MATRIX FROM S/C AXES TO CONTROL
017737,000068:
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Page 413
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017739,000070: 22,3004 00000 00000 2DEC 0 B-28 # AXES (X ROT = -7.25 DEG)
017740,000071:
017741,000072: 22,3006 00000 00000 2DEC 0 B-28
017742,000073:
017743,000074: 22,3010 00000 00000 2DEC 0 B-28
017744,000075:
017745,000076: 22,3012 03131 11275 2DEC .099200 # =(.1)COS7.25
017746,000077:
017747,000078: 22,3014 77461 47370 2DEC -.012620 # =-(.1)SIN7.25
017748,000079:
017749,000080: 22,3016 00000 00000 2DEC 0 B-28
017750,000081:
017751,000082: 22,3020 00316 30407 2DEC .012620 # (.1)SIN7.25
017752,000083:
017753,000084: 22,3022 03131 11275 2DEC .099200 # (.1)COS7.25
017754,000085:
017755,000086: 22,3024 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