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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019710,000002: ## Copyright: Public domain.
019711,000003: ## Filename: GROUND_TRACKING_DETERMINATION_PROGRAM_-_P21.agc
019712,000004: ## Purpose: A section of Comanche revision 044.
019713,000005: ## It is part of the reconstructed source code for the
019714,000006: ## original release of the flight software for the Command
019715,000007: ## Module's (CM) Apollo Guidance Computer (AGC) for Apollo 10.
019716,000008: ## The code has been recreated from a copy of Comanche 055. It
019717,000009: ## has been adapted such that the resulting bugger words
019718,000010: ## exactly match those specified for Comanche 44 in NASA drawing
019719,000011: ## 2021153D, which gives relatively high confidence that the
019720,000012: ## reconstruction is correct.
019721,000013: ## Assembler: yaYUL
019722,000014: ## Contact: Ron Burkey <info@sandroid.org>.
019723,000015: ## Website: www.ibiblio.org/apollo/index.html
019724,000016: ## Mod history: 2020-12-03 MAS Created from Comanche 51.
019725,000017: ## 2020-12-04 MAS Removed the SL* 0,2 for P21VEL in P21VSAVE.
019726,000018: ## 2020-12-11 RSB Added justification annotations for Mike's
019727,000019: ## reconstruction steps.
019728,000020: ## 2020-12-13 RSB Added feedback about the annotations.
019729,000021:
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Page 456
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019731,000023: # GROUND TRACKING DETERMINATION PROGRAM P21
019732,000024:
019733,000025: # PROGRAM DESCRIPTION
019734,000026: # MOD NO - 1
019735,000027: # MOD BY - N. M. NEVILLE
019736,000028: # FUNCTIONAL DECRIPTION-
019737,000029:
019738,000030: # TO PROVIDE THE ASTRONAUT DETAILS OF THE LM OR CSM GROUND TRACK WITHOUT
019739,000031: # THE NEED FOR GROUND COMMUNICATION (REQUESTED BY DSKY).
019740,000032: # CALLING SEQUENCE-
019741,000033:
019742,000034: # ASTRONAUT REQUEST THROUGH DSKY V37E21E
019743,000035: # SUBROUTINES CALLED-
019744,000036:
019745,000037: # GOPERF4
019746,000038: # GOFLASH
019747,000039: # THISPREC
019748,000040: # OTHPREC
019749,000041: # LAT-LONG
019750,000042: # NORMAL EXIT MODES-
019751,000043:
019752,000044: # ASTRONAUT REQUEST TROUGH DSKY TO TERMINATE PROGRAM V34E
019753,000045: # ALARM OR ABORT EXIT MODES-
019754,000046:
019755,000047: # NONE
019756,000048: # OUTPUT-
019757,000049:
019758,000050: # OCTAL DISPLAY OF OPTION CODE AND VEHICLE WHOSE GROUND TRACK IS TO BE
019759,000051: # COMPUTED
019760,000052: # OPTION CODE 00002
019761,000053: # THIS 00001
019762,000054: # OTHER 00002
019763,000055: # DECIMAL DISPLAY OF TIME TO BE INTEGRATED TO HOURS , MINUTES , SECONDS
019764,000056: # DECIMAL DISPLAY OF LAT,LONG,ALT
019765,000057: # ERASABLE INITIALIZATION REQUIRED
019766,000058:
019767,000059: # AX0 2DEC 4.652459653 E-5 RADIANS %68-69 CONSTANTS"
019768,000060:
019769,000061: # -AY0 2DEC 2.147535898 E-5 RADIANS
019770,000062:
019771,000063: # AZ0 2DEC .7753206164 REVOLUTIONS
019772,000064: # FOR LUNAR ORBITS 504LM VECTOR IS NEEDED
019773,000065:
019774,000066: # 504LM 2DEC -2.700340600 E-5 RADIANS
019775,000067:
019776,000068: # 504LM _2 2DEC -7.514128400 E-4 RADIANS
019777,000069:
019778,000070: # 504LM _4 2DEC _2.553198641 E-4 RADIANS
019779,000071:
019780,000072: # NONE
019781,000073: # DEBRIS
019782,000074:
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Page 457
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019784,000076: # CENTRALS-A,Q,L
019785,000077: # OTHER-THOSE USED BY THE ABOVE LISTED SUBROUTINES
019786,000078: # SEE LEMPREC, LAT-LONG
019787,000079:
019788,000080: 33,3776 30,2000 SBANK= LOWSUPER # FOR LOW 2CADR'S.
019789,000081:
019790,000082: 33,3776 BANK 33
019791,000083: 37,2000 SETLOC P20S
019792,000084: 37,2000 BANK
019793,000085:
019794,000086: 37,2001 E4,1715 EBANK= P21TIME
019795,000087: 37,2001 COUNT 24/P21
019796,000088:
019797,000089: 37,2001 35017 PROG21 CAF ONE
019798,000090: 37,2002 55132 TS OPTION2 # ASSUMED VEHICLE IS LM, R2 = 00001
019799,000091: 37,2003 35016 CAF BIT2 # OPTION 2
019800,000092: 37,2004 04662 TC BANKCALL
019801,000093: 37,2005 21055 CADR GOPERF4
019802,000094: 37,2006 04106 TC GOTOPOOH # TERMINATE
019803,000095: 37,2007 02011 TC +2 # PROCEED VALUE OF ASSUMED VEHICLE OK
019804,000096: 37,2010 02003 TC -5 # R2 LOADED THROUGH DSKY
019805,000097: 37,2011 32151 P21PROG1 CAF V6N34 # LOAD DESIRED TIME OF LAT-LONG.
019806,000098: 37,2012 04662 TC BANKCALL
019807,000099: 37,2013 20720 CADR GOFLASH
019808,000100: 37,2014 04106 TC GOTOPOOH # TERM
019809,000101: 37,2015 02017 TC +2 # PROCEED VALUES OK
019810,000102: 37,2016 02011 TC -5 # TIME LOADED THROUGH DSKY
019811,000103: 37,2017 06006 TC INTPRET
019812,000104: 37,2020 77745 DLOAD
019813,000105: 37,2021 01046 DSPTEM1
019814,000106: 37,2022 34041 STCALL TDEC1 # INTEG TO TIME SPECIFIED IN TDEC
019815,000107: 37,2023 27442 INTSTALL
019816,000108: 37,2024 43014 BON SET
019817,000109: 37,2025 01303 P21FLAG
019818,000110: 37,2026 76044 P21CONT # ON...RECYCLE USING BASE VECTOR
019819,000111: 37,2027 01474 VINTFLAG # OFF..1ST PASS CALC BASE VECTOR
019820,000112: 37,2030 70535 SLOAD SR1
019821,000113: 37,2031 01133 OPTION2
019822,000114: 37,2032 43030 BHIZ CLEAR
019823,000115: 37,2033 76035 +2 # ZERO..THIS VEHICLE (CM)
019824,000116: 37,2034 01674 VINTFLAG # ONE...OTHER VEHICLE(LM)
019825,000117: 37,2035 43014 CLEAR CLEAR
019826,000118: 37,2036 01676 DIM0FLAG
019827,000119: 37,2037 01673 INTYPFLG # PRECISION
019828,000120: 37,2040 77624 CALL
019829,000121: 37,2041 27162 INTEGRV # CALCULATE
019830,000122: 37,2042 77650 GOTO # .AND
019831,000123: 37,2043 76065 P21VSAVE # ..SAVE BASE VECTOR
019832,000124: 37,2044 77775 P21CONT VLOAD # RECYCLE..INTEG FROM BASE VECTOR
019833,000125: 37,2045 03605 P21BASER
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Page 458
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019835,000127: 37,2046 25535 STOVL RCV # ..POS
019836,000128: 37,2047 03613 P21BASEV
019837,000129: 37,2050 15543 STODL VCV # ..VEL
019838,000130: 37,2051 02316 P21TIME
019839,000131: 37,2052 01517 STORE TET # ..TIME
019840,000132: 37,2053 43014 CLEAR CLEAR
019841,000133: 37,2054 01676 DIM0FLAG
019842,000134: 37,2055 00263 MOONFLAG
019843,000135: 37,2056 53135 SLOAD BZE
019844,000136: 37,2057 03604 P21ORIG
019845,000137: 37,2060 76063 +3 # ZERO = EARTH
019846,000138: 37,2061 77614 SET # ...2 = MOON
019847,000139: 37,2062 00063 MOONFLAG
019848,000140: 37,2063 77624 CALL
019849,000141: 37,2064 27135 INTEGRVS
019850,000142: 37,2065 77745 P21VSAVE DLOAD # SAVE CURRENT BASE VECTOR
019851,000143: 37,2066 00015 TAT
019852,000144: 37,2067 26316 STOVL P21TIME # ..TIME
019853,000145: 37,2070 00017 RATT1
019854,000146: 37,2071 27605 STOVL P21BASER # ..POS B-29 OR B-27
019855,000147: 37,2072 00025 VATT1
019856,000148: 37,2073 03613 STORE P21BASEV # ..VEL B-7 OR B-5
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Reconstruction: This change, from
ABVAL SL*
0,2
to simply ABVAL, is justified by
Programmed Guidance Equations for Colossus 2, p. ORVN-3. (The indicated change,
from Comanche 45/2 to Comanche 55, is that an absolute value is taken, shifted right by
two bits, and then stored, so the only actual change in the code is the shift, with the
the absolute value and storage remain unchanged. The change bars refer to changes in the
document rather than changes in the code.)
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019869,000161: 37,2074 77646 ABVAL
019870,000162: 37,2075 27623 STOVL P21VEL # /VEL/ FOR N73 DSP
019871,000163: 37,2076 00001 RATT
019872,000164: 37,2077 50256 UNIT DOT
019873,000165: 37,2100 00007 VATT # U(R).(V)
019874,000166: 37,2101 67471 DDV ASIN # U(R).U(V)
019875,000167: 37,2102 03623 P21VEL
019876,000168: 37,2103 03625 STORE P21GAM # SIN-1 U(R).U(V), -90 TO +90
019877,000169: 37,2104 43134 SXA,2 SET
019878,000170: 37,2105 03603 P21ORIG # 0 = EARTH 2 = MOON
019879,000171: 37,2106 01063 P21FLAG
019880,000172: 37,2107 67214 P21DSP CLEAR SLOAD # GENERATE DISPLAY DATA
019881,000173: 37,2110 01663 LUNAFLAG
019882,000174: 37,2111 00050 X2
019883,000175: 37,2112 43054 BZE SET
019884,000176: 37,2113 76115 +2 # 0 = EARTH
019885,000177: 37,2114 01463 LUNAFLAG
019886,000178: 37,2115 77775 VLOAD
019887,000179: 37,2116 00001 RATT
019888,000180: 37,2117 16152 STODL ALPHAV
019889,000181: 37,2120 00015 TAT
019890,000182: 37,2121 45014 CLEAR CALL
019891,000183: 37,2122 00662 ERADFLAG
019892,000184: 37,2123 26370 LAT-LONG
019893,000185: 37,2124 77605 DMP # MPAC = ALT, METERS B-29
019894,000186: 37,2125 36153 K.01
019895,000187: 37,2126 03621 STORE P21ALT # ALT/100 FOR N73 DSP
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Page 459
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019897,000189: 37,2127 77776 EXIT
019898,000190: 37,2130 32150 CAF V06N43 # DISPLAY LAT,LONG,ALT
019899,000191: 37,2131 04662 TC BANKCALL # LAT,LONG = REVS B0 BOTH EARTH/MOON
019900,000192: 37,2132 20720 CADR GOFLASH # ALT = METERS B-29 BOTH EARTH/MOON
019901,000193: 37,2133 04106 TC GOTOPOOH # TERM
019902,000194: 37,2134 04106 TC GOTOPOOH
019903,000195: 37,2135 06006 TC INTPRET # V32E RECYCLE
019904,000196: 37,2136 43345 DLOAD DAD
019905,000197: 37,2137 02316 P21TIME
019906,000198: 37,2140 36145 600SEC # 600 SECONDS OR 10 MIN
019907,000199: 37,2141 01046 STORE DSPTEM1
019908,000200: 37,2142 77634 RTB
019909,000201: 37,2143 76011 P21PROG1
019910,000202:
019911,000203: 37,2144 00003 25140 600SEC 2DEC 60000 B-28 # 10 MIN
019912,000204:
019913,000205: 37,2146 00001 P21ONENN OCT 00001 # NEEDED TO DETERMINE VEHICLE
019914,000206: 37,2147 00000 OCT 00000 # TO BE INTEGRATED
019915,000207: 37,2150 01453 V06N43 VN 00643
019916,000208: 37,2151 01442 V6N34 VN 00634
019917,000209: 37,2152 00243 32703 K.01 2DEC .01
019918,000210:
End of include-file GROUND_TRACKING_DETERMINATION_PROGRAM_-_P21.agc. Parent file is MAIN.agc