Source Code
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These source-code files are part of a reconstructed copy of Comanche 44, the
initial release (though not the final mission release) of the Apollo 10
Command Module (CM) Apollo Guidance Computer (AGC) software. Subsequent releases
were Comanche 45 and Comanche 45/2 (the flown release on Apollo 10). The reconstruction
is believed to be exactly accurate, but in the absence of an actual Apollo-era
listing of Comanche 44, some explanation of the reconstruction process is needed
to insure confidence in that accuracy.
The starting point was the source code of Comanche 51
(separately previously reconstructed from an Apollo-era listing of Comanche 55,
flown on Apollo 11). Comanche 51 source code was then modified
by undoing changes known to have been made between revisions 44 and 51. The now-reconstructed
Comanche 44 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 printout,
although the source code would likely have different page numbers in a contemporary
Comanche 44 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 51. Here's a guide to the Apollo documentation referenced
in those annotations:
In most cases, only the titles (rather than the full texts) of PCRs are known. In addition to the
explanatory annotations, there is also
a step-by-step 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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017834,000002: ## Copyright: Public domain.
017835,000003: ## Filename: GIMBAL_LOCK_AVOIDANCE.agc
017836,000004: ## Purpose: A section of Comanche revision 044.
017837,000005: ## It is part of the reconstructed source code for the
017838,000006: ## original release of the flight software for the Command
017839,000007: ## Module's (CM) Apollo Guidance Computer (AGC) for Apollo 10.
017840,000008: ## The code has been recreated from a copy of Comanche 055. It
017841,000009: ## has been adapted such that the resulting bugger words
017842,000010: ## exactly match those specified for Comanche 44 in NASA drawing
017843,000011: ## 2021153D, which gives relatively high confidence that the
017844,000012: ## reconstruction is correct.
017845,000013: ## Assembler: yaYUL
017846,000014: ## Contact: Ron Burkey <info@sandroid.org>.
017847,000015: ## Website: www.ibiblio.org/apollo/index.html
017848,000016: ## Mod history: 2020-12-03 MAS Created from Comanche 51.
017849,000017: ## 2020-12-04 MAS Changed the last ARATE entry back to 4 deg/s.
017850,000018: ## 2020-12-11 RSB Added justifying annotations for Mike's
017851,000019: ## reconstruction steps.
017852,000020:
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Page 412
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017854,000022: 15,2000 BANK 15
017855,000023: 22,2000 SETLOC KALCMON1
017856,000024: 22,2000 BANK
017857,000025:
017858,000026: 22,2737 E6,1661 EBANK= BCDU
017859,000027:
017860,000028: # DETECTING GIMBAL LOCK
017861,000029: 22,2737 22,2737 LOCSKIRT EQUALS WCALC
017862,000030: 22,2737 70740 WCALC LXC,1 DLOAD*
017863,000031: 22,2740 01130 RATEINDX
017864,000032: 22,2741 04771 ARATE,1
017865,000033: 22,2742 45002 SR4 CALL # COMPUTE THE INCREMENTAL ROTATION MATRIX
017866,000034: 22,2743 44530 DELCOMP # DEL CORRESPONDING TO A 1 SEC ROTATION
017867,000035: # ABOUT COF
017868,000036: 22,2744 74343 DLOAD* VXSC
017869,000037: 22,2745 04771 ARATE,1
017870,000038: 22,2746 03343 COF
017871,000039: 22,2747 77721 MXV
017872,000040: 22,2750 05003 QUADROT
017873,000041: 22,2751 17311 STODL BRATE
017874,000042: 22,2752 03365 AM
017875,000043: 22,2753 55605 DMP DDV*
017876,000044: 22,2754 05001 ANGLTIME
017877,000045: 22,2755 04771 ARATE,1
017878,000046: 22,2756 77661 SR
017879,000047: 22,2757 20606 5
017880,000048: 22,2760 27317 STOVL TM
017881,000049: 22,2761 03311 BRATE
017882,000050: 22,2762 77761 VXSC
017883,000051: 22,2763 05025 BIASCALE
017884,000052: 22,2764 03275 STORE BIASTEMP # ATTITUDE ERROR BIAS TO PREVENT OVERSHOOT
017885,000053: # IN SYSTEM
017886,000054: 22,2765 77614 SETGO # STATE SWITCH CALCMAN2 (43D)
017887,000055: 22,2766 01035 CALCMAN2 # 0(OFF) = BYPASS STARTING PROCEDURE
017888,000056: 22,2767 45032 NEWANGL +1 # 1(ON) = START MANEUVER
017889,000057:
017890,000058:
017891,000059: 22,2770 00044 15053 ARATE 2DEC .0022222222 # = .05 DEG/SEC
017892,000060:
017893,000061: 22,2772 00221 24255 2DEC .0088888889 # = .2 DEG/SEC
017894,000062:
017895,000063: 22,2774 00554 02660 2DEC .0222222222 # = .5 DEG/SEC
017896,000064:
017902,000070: 22,2776 05540 26603 2DEC .1777777777 # = 4 DEG/SEC $ 22.5 DEG/SEC
017903,000071:
017904,000072: 22,3000 00003 04000 ANGLTIME 2DEC .000190735 # = 100B - 19
017905,000073:
017906,000074: # MANEUVER ANGLE TO MANEUVER TIME
017907,000075: 22,3002 03146 14632 QUADROT 2DEC .1 # ROTATION MATRIX FROM S/C AXES TO CONTROL
017908,000076:
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Page 413
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017910,000078: 22,3004 00000 00000 2DEC 0 B-28 # AXES (X ROT = -7.25 DEG)
017911,000079:
017912,000080: 22,3006 00000 00000 2DEC 0 B-28
017913,000081:
017914,000082: 22,3010 00000 00000 2DEC 0 B-28
017915,000083:
017916,000084: 22,3012 03131 11275 2DEC .099200 # =(.1)COS7.25
017917,000085:
017918,000086: 22,3014 77461 47370 2DEC -.012620 # =-(.1)SIN7.25
017919,000087:
017920,000088: 22,3016 00000 00000 2DEC 0 B-28
017921,000089:
017922,000090: 22,3020 00316 30407 2DEC .012620 # (.1)SIN7.25
017923,000091:
017924,000092: 22,3022 03131 11275 2DEC .099200 # (.1)COS7.25
017925,000093:
017926,000094: 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