Source Code

This is a reconstruction of the AGC program Luminary 99 Rev 0. It was the second release of the Lunar Module flight software targeted for use in Apollo 11, after Luminary 97. A bug (which had been around since at least Apollo 10, Luminary 69) was discovered in Rev 0 shortly before the Apollo 11 flight, resulting in a last minute revision into Rev 1, which is what actually flew rather than the Rev 0 presented here. A hardcopy of Rev 0 is known to exist — it belonged to AGC developer Allan Klumpp for many years — but unfortunately the Virtual AGC Project has not had access to that hardcopy. Thus the code you see here had been reconstructed (we believe accurately) rather than transcribed. The first step of the reconstruction of the Rev 0 source code was the transcription of the Rev 1 source code from a hardcopy in the MIT Museum collection. The process of reverting the active portion of the source code (i.e., other than program comments) from Rev 1 to Rev 0 was very minor, consisting only of moving the position of the STARTSB1 label in FRESH START AND RESTART. Allan had previously given us the checksums of the memory banks of Rev 0, and we have verified the program presented here has checksums identical to all banks of Allan's listing of Rev 0. The notations on Allan's Rev 0 program listing read, in part:

	GAP:  ASSEMBLE REVISION 099 OF AGC PROGRAM LUMINARY BY NASA 2021112-051

A single program comment is known to differ between Rev 0 and Rev 1, but these are harder to reconstruct and verify than changes to the active portion of the code. Thus it is possible that there are additional differences between the program comments in Rev 0 and Rev 1 that are unknown to us, and therefore are not reflected in the code presented here.

015553,000002:                                                                                                  ## Copyright:   Public domain.
015554,000003:                                                                                                  ## Filename:    GIMBAL_LOCK_AVOIDANCE.agc
015555,000004:                                                                                                  ## Purpose:     Part of the reconstructed source code for LMY99 Rev 0,
015556,000005:                                                                                                  ##              otherwise known as Luminary Rev 99, the second release
015557,000006:                                                                                                  ##              of the Apollo Guidance Computer (AGC) software for Apollo 11.
015558,000007:                                                                                                  ##              It differs from LMY99 Rev 1 (the flown version) only in the
015559,000008:                                                                                                  ##              placement of a single label. The corrections shown here have
015560,000009:                                                                                                  ##              been verified to have the same bank checksums as AGC developer
015561,000010:                                                                                                  ##              Allan Klumpp's copy of Luminary Rev 99, and so are believed
015562,000011:                                                                                                  ##              to be accurate. This file is intended to be a faithful 
015563,000012:                                                                                                  ##              recreation, except that the code format has been changed to 
015564,000013:                                                                                                  ##              conform to the requirements of the yaYUL assembler rather than 
015565,000014:                                                                                                  ##              the original YUL assembler.
015566,000015:                                                                                                  ##
015567,000016:                                                                                                  ## Assembler:   yaYUL
015568,000017:                                                                                                  ## Contact:     Ron Burkey <info@sandroid.org>.
015569,000018:                                                                                                  ## Website:     www.ibiblio.org/apollo.
015570,000019:                                                                                                  ## Pages:       364
015571,000020:                                                                                                  ## Mod history: 2009-05-17 RSB  Adapted from the corresponding 
015572,000021:                                                                                                  ##                              Luminary131 file, using page 
015573,000022:                                                                                                  ##                              images from Luminary 1A.
015574,000023:                                                                                                  ##              2010-12-31 JL   Fixed page number comment.
015575,000024:                                                                                                  ##              2016-12-14 RSB  Proofed text comments with octopus/ProoferComments
015576,000025:                                                                                                  ##                              but no errors found.
015577,000026:                                                                                                  ##              2017-08-01 MAS  Created from LMY99 Rev 1.
015578,000027:                                                                                                  ##              2017-08-22 RSB  Fixed comment-text typo identified in ZERLINA 56.
015579,000028: 
015580,000029:                                                                                                  ## This source code has been transcribed or otherwise adapted from
015581,000030:                                                                                                  ## digitized images of a hardcopy from the MIT Museum.  The digitization
015582,000031:                                                                                                  ## was performed by Paul Fjeld, and arranged for by Deborah Douglas of
015583,000032:                                                                                                  ## the Museum.  Many thanks to both.  The images (with suitable reduction
015584,000033:                                                                                                  ## in storage size and consequent reduction in image quality as well) are
015585,000034:                                                                                                  ## available online at www.ibiblio.org/apollo.  If for some reason you
015586,000035:                                                                                                  ## find that the images are illegible, contact me at info@sandroid.org
015587,000036:                                                                                                  ## about getting access to the (much) higher-quality images which Paul
015588,000037:                                                                                                  ## actually created.
015589,000038:                                                                                                  ##
015590,000039:                                                                                                  ## The code has been modified to match LMY99 Revision 0, otherwise
015591,000040:                                                                                                  ## known as Luminary Revision 99, the Apollo 11 software release preceeding
015592,000041:                                                                                                  ## the listing from which it was transcribed. It has been verified to
015593,000042:                                                                                                  ## contain the same bank checksums as AGC developer Allan Klumpp's listing
015594,000043:                                                                                                  ## of Luminary Revision 99 (for which we do not have scans).
015595,000044:                                                                                                  ##
015596,000045:                                                                                                  ## Notations on Allan Klumpp's listing read, in part:
015597,000046:                                                                                                  ##
015598,000047:                                                                                                  ##      ASSEMBLE REVISION 099 OF AGC PROGRAM LUMINARY BY NASA 2021112-51
015599,000048: 

Page 364

015601,000050: 15,2050                                           BANK     15                                    
015602,000051: 
015603,000052: 22,2000                                           SETLOC   KALCMON1                              
015604,000053: 22,2000                                           BANK                                           
015605,000054: 
015606,000055:                                                                                                  #  DETECTING GIMBAL LOCK
015607,000056: 22,2744  22,2744               LOCSKIRT           EQUALS   NOGIMLOC                              
015608,000057: 
015609,000058: 22,2744           77614        NOGIMLOC           SET                                            
015610,000059: 22,2745           01074                                    CALCMAN3                              
015611,000060: 22,2746           70740        WCALC              LXC,1    DLOAD*                                
015612,000061: 22,2747           01325                                    RATEINDX                              #  CHOOSE THE DESIRED MANEUVER RATE
015613,000062: 22,2750           04772                                    ARATE,1                               #  FROM A LIST OF FOUR
015614,000063: 22,2751           45002                           SR4      CALL                                  #  COMPUTE THE INCREMENTAL ROTATION MATRIX
015615,000064: 22,2752           44527                                    DELCOMP                               #  DEL CORRESPONDING TO A 1 SEC ROTATION
015616,000065:                                                                                                  #  ABOUT COF
015617,000066: 22,2753           74343                           DLOAD*   VXSC                                  
015618,000067: 22,2754           04772                                    ARATE,1                               
015619,000068: 22,2755           03271                                    COF                                   
015620,000069: 22,2756           17326                           STODL    BRATE                                 #  COMPONENT MANEUVER RATES 45 DEG/SEC
015621,000070: 22,2757           03336                                    AM                                    
015622,000071: 22,2760           55605                           DMP      DDV*                                  
015623,000072: 22,2761           05002                                    ANGLTIME                              
015624,000073: 22,2762           04772                                    ARATE,1                               
015625,000074: 22,2763           77661                           SR                                             
015626,000075: 22,2764           20606                                    5                                     
015627,000076: 22,2765           03334                           STORE    TM                                    #  MANEUVER EXECUTION TIME SCALED AS T2
015628,000077: 22,2766           77614                           SETGO                                          
015629,000078: 22,2767           01035                                    CALCMAN2                              #  0(OFF) = CONTINUE MANEUVER
015630,000079: 22,2770           45010                                    NEWANGL    +1                         #  1(ON) = START MANEUVER
015631,000080: 
015632,000081:                                                                                                  #  THE FOUR SELECTABLE FREE FALL MANEUVER RATES SELECTED BY
015633,000082:                                                                                                  #  LOADING RATEINDX WITH 0, 2, 4, 6, RESPECTIVELY
015634,000083: 
015635,000084: 22,2771           00221 24255  ARATE              2DEC     .0088888888                            #  = 0.2 DEG/SEC         $ 22.5 DEG/SEC
015636,000085: 
015637,000086: 22,2773           00554 02660                     2DEC     .0222222222                            #  = 0.5 DEG/SEC         $ 22.5 DEG/SEC
015638,000087: 
015639,000088: 22,2775           02660 13301                     2DEC     .0888888888                            #  = 2.0 DEG/SEC         $ 22.5 DEG/SEC
015640,000089: 
015641,000090: 22,2777           16161 30707                     2DEC     .4444444444                            #  = 10.0 DEG/SEC        $ 22.5 DEG/SEC
015642,000091: 
015643,000092: 22,3001           00003 04000  ANGLTIME           2DEC     .0001907349                            #  = 100B-19 FUDGE FACTOR TO CONVERT
015644,000093:                                                                                                  #  MANEUVER ANGLE TO MANEUVER TIME
015645,000094: 
015646,000095: 

End of include-file GIMBAL_LOCK_AVOIDANCE.agc.  Parent file is MAIN.agc