Source Code
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These source-code files are part of a reconstructed copy of LM131 revision 1,
the final release of the Apollo 13 Lunar Module (LM) Apollo Guidance Computer
(AGC) software.
The source reconstruction began with source code of Luminary 131 previously
transcribed from a digitized copy of that program. A dump of the flight spare
core rope memory module B5, part number 2010802-171, serial number RAY 411,
was obtained. This module is the only module different between Luminary 131
and LM131 revision 1. The dump was disassembled and all changes were incorporated
into these source files. Note that page numbers in the reconstructed code match
those on the Luminary 131 printout, although the changed code would likely have
changed page numbers for a real LM131 revision 1 listing.
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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027679,000002: ## Copyright: Public domain.
027680,000003: ## Filename: GROUND_TRACKING_DETERMINATION_PROGRAM_-_P21.agc
027681,000004: ## Purpose: A section of LM131 revision 1.
027682,000005: ## It is part of the reconstructed source code for the final
027683,000006: ## release of the flight software for the Lunar Module's (LM)
027684,000007: ## Apollo Guidance Computer (AGC) for Apollo 13. The code has
027685,000008: ## been reconstructed from a listing of Luminary 131 and a dump
027686,000009: ## of a core rope memory module B5, part number 2010802-171,
027687,000010: ## which is the only module different between LM131 revision 1
027688,000011: ## and Luminary 131. The executable generated from this source
027689,000012: ## has been verified against the module dump, so while the names,
027690,000013: ## comments, and ordering may not be exactly correct, the
027691,000014: ## resulting binary is.
027692,000015: ## Reference: pp. 656-659
027693,000016: ## Assembler: yaYUL
027694,000017: ## Contact: Ron Burkey <info@sandroid.org>.
027695,000018: ## Website: www.ibiblio.org/apollo/index.html
027696,000019: ## Mod history: 2022-10-28 MAS Created from Luminary 131.
027697,000020:
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Page 656
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027699,000022: # GROUND TRACKING DETERMINATION PROGRAM P21
027700,000023:
027701,000024: # PROGRAM DESCRIPTION
027702,000025: # MOD NO - 1
027703,000026: # MOD BY - N. M. NEVILLE
027704,000027:
027705,000028: # FUNCTIONAL DECRIPTION -
027706,000029: # TO PROVIDE THE ASTRONAUT DETAILS OF THE LM OR CSM GROUND TRACK WITHOUT
027707,000030: # THE NEED FOR GROUND COMMUNICATION (REQUESTED BY DSKY).
027708,000031:
027709,000032: # CALLING SEQUENCE -
027710,000033: # ASTRONAUT REQUEST THROUGH DSKY V37E21E
027711,000034:
027712,000035: # SUBROUTINES CALLED -
027713,000036: # GOPERF4
027714,000037: # GOFLASH
027715,000038: # THISPREC
027716,000039: # OTHPREC
027717,000040: # LAT-LONG
027718,000041:
027719,000042: # NORMAL EXIT MODES -
027720,000043: # ASTRONAUT REQUEST TROUGH DSKY TO TERMINATE PROGRAM V34E
027721,000044:
027722,000045: # ALARM OR ABORT EXIT MODES -
027723,000046: # NONE
027724,000047:
027725,000048: # OUTPUT -
027726,000049: # OCTAL DISPLAY OF OPTION CODE AND VEHICLE WHOSE GROUND TRACK IS TO BE
027727,000050: # COMPUTED
027728,000051: # OPTION CODE 00002
027729,000052: # THIS 00001
027730,000053: # OTHER 00002
027731,000054: # DECIMAL DISPLAY OF TIME TO BE INTEGRATED TO HOURS, MINUTES, SECONDS
027732,000055: # DECIMAL DISPLAY OF LAT,LONG,ALT
027733,000056:
027734,000057: # ERASABLE INITIALIZATION REQUIRED
027735,000058: # AX0 2DEC 4.652459653 E-5 RADIANS %68-69 CONSTANTS"
027736,000059: # -AY0 2DEC 2.147535898 E-5 RADIANS
027737,000060: # AZ0 2DEC .7753206164 REVOLUTIONS
027738,000061: # FOR LUNAR ORBITS 504LM VECTOR IS NEEDED
027739,000062: # 504LM 2DEC -2.700340600 E-5 RADIANS
027740,000063: # 504LM _2 2DEC -7.514128400 E-4 RADIANS
027741,000064: # 504LM _4 2DEC _2.553198641 E-4 RADIANS
027742,000065:
027743,000066: # NONE
027744,000067: # DEBRIS
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Page 657
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027746,000069: # CENTRALS - A,Q,L
027747,000070: # OTHER - THOSE USED BY THE ABOVE LISTED SUBROUTINES
027748,000071: # SEE LEMPREC, LAT-LONG
027749,000072:
027750,000073: 35,2455 30,2000 SBANK= LOWSUPER # FOR LOW 2CADR'S.
027751,000074:
027752,000075: 33,2200 BANK 33
027753,000076: 24,2000 SETLOC P20S
027754,000077: 24,2000 BANK
027755,000078:
027756,000079: 24,3506 E7,1762 EBANK= P21TIME
027757,000080: 24,3506 COUNT* $$/P21
027758,000081: 24,3506 34753 PROG21 CAF ONE
027759,000082: 24,3507 55144 TS OPTION2 # ASSUMED VEHICLE IS LM, R2 = 00001
027760,000083: 24,3510 34752 CAF BIT2 # OPTION 2
027761,000084: 24,3511 04616 TC BANKCALL
027762,000085: 24,3512 20634 CADR GOPERF4
027763,000086: 24,3513 06001 TC GOTOPOOH # TERMINATE
027764,000087: 24,3514 03516 TC +2 # PROCEED VALUE OF ASSUMED VEHICLE OK
027765,000088: 24,3515 03510 TC -5 # R2 LOADED THROUGH DSKY
027766,000089: 24,3516 34755 CAF ZERO # INITIAL TIME = PRESENT TIME
027767,000090: 24,3517 55044 TS DSPTEM1
027768,000091: 24,3520 55045 TS DSPTEM1 +1
027769,000092: 24,3521 33675 P21PROG1 CAF V6N34 # LOAD DESIRED TIME OF LAT-LONG.
027770,000093: 24,3522 04616 TC BANKCALL
027771,000094: 24,3523 20477 CADR GOFLASH
027772,000095: 24,3524 06001 TC GOTOPOOH # TERM
027773,000096: 24,3525 03527 TC +2 # PROCEED VALUES OK
027774,000097: 24,3526 03521 TC -5 # TIME LOADED THROUGH DSKY
027775,000098: 24,3527 06042 TC INTPRET
027776,000099: 24,3530 53145 DLOAD BZE
027777,000100: 24,3531 01045 DSPTEM1
027778,000101: 24,3532 51667 P21PRTM
027779,000102: 24,3533 34041 P21PROG2 STCALL TDEC1 # INTEG TO TIME SPECIFIED IN TDEC1
027780,000103: 24,3534 27410 INTSTALL
027781,000104: 24,3535 43014 BON CLEAR
027782,000105: 24,3536 00304 P21FLAG
027783,000106: 24,3537 51555 P21CONT # ON---RECYCLE USING BASE VECTOR
027784,000107: 24,3540 01674 VINTFLAG # OFF--1ST PASS CALL BASE VECTOR
027785,000108: 24,3541 70535 SLOAD SR1
027786,000109: 24,3542 01145 OPTION2
027787,000110: 24,3543 43030 BHIZ SET
027788,000111: 24,3544 51546 +2 # ZERO--THIS VEHICLE (LM)
027789,000112: 24,3545 01474 VINTFLAG # ONE--OTHER VEHICLE (CM)
027790,000113: 24,3546 43014 CLEAR CLEAR
027791,000114: 24,3547 01676 DIM0FLAG
027792,000115: 24,3550 01673 INTYPFLG # PRECISION
027793,000116: 24,3551 77624 CALL
027794,000117: 24,3552 27133 INTEGRV # CALCULATE
027795,000118: 24,3553 77650 GOTO # -AND
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Page 658
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027797,000120: 24,3554 51576 P21VSAVE # -SAVE BASE VECTOR
027798,000121: 24,3555 77775 P21CONT VLOAD
027799,000122: 24,3556 03676 P21BASER # RECYCLE--INTEG FROM BASE VECTOR
027800,000123: 24,3557 25535 STOVL RCV # --POS
027801,000124: 24,3560 03704 P21BASEV
027802,000125: 24,3561 15543 STODL VCV # --VEL
027803,000126: 24,3562 03763 P21TIME
027804,000127: 24,3563 01517 STORE TET # --TIME
027805,000128: 24,3564 43014 CLEAR CLEAR
027806,000129: 24,3565 01676 DIM0FLAG
027807,000130: 24,3566 00263 MOONFLAG
027808,000131: 24,3567 53135 SLOAD BZE
027809,000132: 24,3570 01163 P21ORIG
027810,000133: 24,3571 51574 +3 # ZERO = EARTH
027811,000134: 24,3572 77614 SET # ---2 = MOON
027812,000135: 24,3573 00063 MOONFLAG
027813,000136: 24,3574 77624 +3 CALL
027814,000137: 24,3575 27106 INTEGRVS
027815,000138: 24,3576 77745 P21VSAVE DLOAD # SAVE CURRENT BASE VECTOR
027816,000139: 24,3577 00015 TAT
027817,000140: 24,3600 27763 STOVL P21TIME # --TIME
027818,000141: 24,3601 00017 RATT1
027819,000142: 24,3602 27676 STOVL P21BASER # --POS B-29 OR B-27
027820,000143: 24,3603 00025 VATT1
027821,000144: 24,3604 03704 STORE P21BASEV # --VEL B-07 OR B-05
027822,000145: 24,3605 53646 ABVAL SL*
027823,000146: 24,3606 57576 0,2
027824,000147: 24,3607 27712 STOVL P21VEL # VEL/ FOR N91 DISP
027825,000148: 24,3610 00001 RATT
027826,000149: 24,3611 50256 UNIT DOT
027827,000150: 24,3612 00007 VATT # U(R).V
027828,000151: 24,3613 67471 DDV ASIN # U(R).U(V)
027829,000152: 24,3614 03712 P21VEL
027830,000153: 24,3615 03714 STORE P21GAM # SIN-1 U(R).U(V) , -90 TO &90
027831,000154: 24,3616 67334 SXA,2 SLOAD
027832,000155: 24,3617 01162 P21ORIG # 0 = EARTH
027833,000156: 24,3620 01145 OPTION2
027834,000157: 24,3621 46142 SR1 BHIZ
027835,000158: 24,3622 51625 +3
027836,000159: 24,3623 77650 GOTO
027837,000160: 24,3624 51630 +4
027838,000161: 24,3625 77614 +3 BON
027839,000162: 24,3626 04307 SURFFLAG
027840,000163: 24,3627 51632 P21DSP
027841,000164: 24,3630 77614 +4 SET
027842,000165: 24,3631 00064 P21FLAG
027843,000166: 24,3632 67214 P21DSP CLEAR SLOAD # GENERATE DISPLAY DATA
027844,000167: 24,3633 01663 LUNAFLAG
027845,000168: 24,3634 00050 X2
027846,000169: 24,3635 43054 BZE SET
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Page 659
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027848,000171: 24,3636 51640 +2 # 0 = EARTH
027849,000172: 24,3637 01463 LUNAFLAG
027850,000173: 24,3640 77775 VLOAD
027851,000174: 24,3641 00001 RATT
027852,000175: 24,3642 16032 STODL ALPHAV
027853,000176: 24,3643 00015 TAT
027854,000177: 24,3644 45014 CLEAR CALL
027855,000178: 24,3645 00662 ERADFLAG
027856,000179: 24,3646 26347 LAT-LONG
027857,000180: 24,3647 77605 DMP # MPAC = ALT, METERS B-29
027858,000181: 24,3650 11677 K.01
027859,000182: 24,3651 03716 STORE P21ALT # ALT/100 FOR N91 DISP
027860,000183: 24,3652 77776 EXIT
027861,000184: 24,3653 33674 CAF V06N43 # DISPLAY LAT, LONG, ALT
027862,000185: 24,3654 04616 TC BANKCALL # LAT, LONG = 1/2 REVS B0
027863,000186: 24,3655 20477 CADR GOFLASH # ALT = KM B14
027864,000187: 24,3656 06001 TC GOTOPOOH # TERM
027865,000188: 24,3657 06001 TC GOTOPOOH
027866,000189: 24,3660 06042 TC INTPRET # V32E RECYCLE
027867,000190: 24,3661 43345 DLOAD DAD
027868,000191: 24,3662 03763 P21TIME
027869,000192: 24,3663 11673 600SEC # 600 SECONDS OR 10 MIN
027870,000193: 24,3664 01045 STORE DSPTEM1
027871,000194: 24,3665 77634 RTB
027872,000195: 24,3666 51521 P21PROG1
027873,000196: 24,3667 52034 P21PRTM RTB GOTO
027874,000197: 24,3670 21574 LOADTIME
027875,000198: 24,3671 51533 P21PROG2
027876,000199: 24,3672 00003 25140 600SEC 2DEC 60000 B-28 # 10 MIN
027877,000200:
027878,000201: 24,3674 01453 V06N43 VN 00643
027879,000202: 24,3675 01442 V6N34 VN 00634
027880,000203: 24,3676 00243 32703 K.01 2DEC .01
027881,000204:
End of include-file GROUND_TRACKING_DETERMINATION_PROGRAM_-_P21.agc. Parent file is MAIN.agc