Source Code
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These source-code files are part of a reconstructed copy of Comanche 51, the
initial release (though not the final mission release) of the Apollo 11
Command Module (CM) Apollo Guidance Computer (AGC) software. The flown, final
release was Comanche 55. The reconstruction is believed to be exactly accurate,
but in the absence of an actual Apollo-era listing of Comanche 51, some
explanation of the reconstruction process is needed to insure confidence in
that accuracy.
The starting point was the source code of Comanche 55, whose original source code
is available. Comanche 55 source code was then modified by undoing changes known
to have been made between revisions 51 and 55. The most-significant steps involved
reverting changes related to the R-2 lunar potential model, the details of which
were known from the previous, separate, independent reconstruction of the Apollo 10
Lunar Module software Luminary 69/2. The now-reconstructed
Comanche 51 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 match those on the Comanche 55 or Luminary 69 printouts, although
the source code would likely have different page numbers in a contemporary Comanche 51 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 55. Here's a guide
to some of the Apollo documentation relevant to those annotations:
Among documentation not actually referenced in the annotations, there is
a short writeup about the reconstruction process in our software repository
that may be helpful in understanding it from a different perspective. There's also
a handy table
that lists what the number of memory-words should be for each routine in Comanche 51,
which could make a nice double-check; however, we've not performed that double-check ourselves.
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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017689,000002: ## Copyright: Public domain.
017690,000003: ## Filename: GIMBAL_LOCK_AVOIDANCE.agc
017691,000004: ## Purpose: A section of Comanche revision 051.
017692,000005: ## It is part of the reconstructed source code for the
017693,000006: ## original release of the flight software for the Command
017694,000007: ## Module's (CM) Apollo Guidance Computer (AGC) for Apollo 11.
017695,000008: ## The code has been recreated from a copy of Comanche 055. It
017696,000009: ## has been adapted such that the resulting bugger words
017697,000010: ## exactly match those specified for Comanche 51 in NASA drawing
017698,000011: ## 2021153D, which gives relatively high confidence that the
017699,000012: ## reconstruction is correct.
017700,000013: ## Reference: pp. 412-413
017701,000014: ## Assembler: yaYUL
017702,000015: ## Contact: Ron Burkey <info@sandroid.org>.
017703,000016: ## Website: www.ibiblio.org/apollo/index.html
017704,000017: ## Mod history: 2019-07-30 MAS Created from Comanche 55.
017705,000018:
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Page 412
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017707,000020: 15,2000 BANK 15
017708,000021: 22,2000 SETLOC KALCMON1
017709,000022: 22,2000 BANK
017710,000023:
017711,000024: 22,2737 E6,1661 EBANK= BCDU
017712,000025:
017713,000026: # DETECTING GIMBAL LOCK
017714,000027: 22,2737 22,2737 LOCSKIRT EQUALS WCALC
017715,000028: 22,2737 70740 WCALC LXC,1 DLOAD*
017716,000029: 22,2740 01130 RATEINDX
017717,000030: 22,2741 04771 ARATE,1
017718,000031: 22,2742 45002 SR4 CALL # COMPUTE THE INCREMENTAL ROTATION MATRIX
017719,000032: 22,2743 44530 DELCOMP # DEL CORRESPONDING TO A 1 SEC ROTATION
017720,000033: # ABOUT COF
017721,000034: 22,2744 74343 DLOAD* VXSC
017722,000035: 22,2745 04771 ARATE,1
017723,000036: 22,2746 03343 COF
017724,000037: 22,2747 77721 MXV
017725,000038: 22,2750 05003 QUADROT
017726,000039: 22,2751 17311 STODL BRATE
017727,000040: 22,2752 03365 AM
017728,000041: 22,2753 55605 DMP DDV*
017729,000042: 22,2754 05001 ANGLTIME
017730,000043: 22,2755 04771 ARATE,1
017731,000044: 22,2756 77661 SR
017732,000045: 22,2757 20606 5
017733,000046: 22,2760 27317 STOVL TM
017734,000047: 22,2761 03311 BRATE
017735,000048: 22,2762 77761 VXSC
017736,000049: 22,2763 05025 BIASCALE
017737,000050: 22,2764 03275 STORE BIASTEMP # ATTITUDE ERROR BIAS TO PREVENT OVERSHOOT
017738,000051: # IN SYSTEM
017739,000052: 22,2765 77614 SETGO # STATE SWITCH CALCMAN2 (43D)
017740,000053: 22,2766 01035 CALCMAN2 # 0(OFF) = BYPASS STARTING PROCEDURE
017741,000054: 22,2767 45032 NEWANGL +1 # 1(ON) = START MANEUVER
017742,000055:
017743,000056:
017744,000057: 22,2770 00044 15053 ARATE 2DEC .0022222222 # = .05 DEG/SEC
017745,000058:
017746,000059: 22,2772 00221 24255 2DEC .0088888889 # = .2 DEG/SEC
017747,000060:
017748,000061: 22,2774 00554 02660 2DEC .0222222222 # = .5 DEG/SEC
017749,000062:
017750,000063: 22,2776 02660 13301 2DEC .0888888889 # = 2 DEG/SEC $22.5 DEG/SEC
017751,000064:
017752,000065: 22,3000 00003 04000 ANGLTIME 2DEC .000190735 # = 100B - 19
017753,000066:
017754,000067: # MANEUVER ANGLE TO MANEUVER TIME
017755,000068: 22,3002 03146 14632 QUADROT 2DEC .1 # ROTATION MATRIX FROM S/C AXES TO CONTROL
017756,000069:
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Page 413
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017758,000071: 22,3004 00000 00000 2DEC 0 B-28 # AXES (X ROT = -7.25 DEG)
017759,000072:
017760,000073: 22,3006 00000 00000 2DEC 0 B-28
017761,000074:
017762,000075: 22,3010 00000 00000 2DEC 0 B-28
017763,000076:
017764,000077: 22,3012 03131 11275 2DEC .099200 # =(.1)COS7.25
017765,000078:
017766,000079: 22,3014 77461 47370 2DEC -.012620 # =-(.1)SIN7.25
017767,000080:
017768,000081: 22,3016 00000 00000 2DEC 0 B-28
017769,000082:
017770,000083: 22,3020 00316 30407 2DEC .012620 # (.1)SIN7.25
017771,000084:
017772,000085: 22,3022 03131 11275 2DEC .099200 # (.1)COS7.25
017773,000086:
017774,000087: 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