Assembly listing generated by yaYUL

Source Code

These source-code files are part of a reconstructed copy of Skylark 048, the Block II Command Module (CM) Apollo Guidance Computer (AGC) software for the Skylab-2, Skylab-3, Skylab-4, and Apollo-Soyuz Test Project missions.

They have been created via disassembly of binary dumps of the original core rope memory modules actually flown on Skylab-2, part numbers 2010802-541, 2010802-551, 2010802-561, 2010802-571, 2010802-581, and 2010802-591. Access to these modules was provided by the New Mexico Museum of Space History, who we are much indebted to.

The source code for the Apollo 15, 16, and 17 software, Artemis 072, was used as a starting point. Heavy use was made of TRW 4900.5-244, Programmed Guidance Equations for Skylark Command Module Earth Orbital Program, dated 14 February 1972. This document contains pseudocode of essentially all of Skylark, using original program labels which have been copied for this source reconstruction.

Since only binary dumps (rather than listings) of Skylark are available as source material, all comments and labels are approximate. They have been taken from the Programmed Guidance Equations or other AGC programs where possible, or, in some places, written from scratch to match what we believe would have been in the original listing.

016639,000002: 016640,000003: 016641,000004: 016642,000005: 016643,000006: 016644,000007: 016645,000008: 016646,000009: 016647,000010: 016648,000011: 016649,000012: 016650,000013: 016651,000014: 016652,000015: 016653,000016: 016654,000017: 27,2000 016655,000018: 27,2000 016656,000019: 016657,000020: 27,2000 016658,000021: 016659,000022: 27,2000 016660,000023: 016661,000024: 016662,000025: 016663,000026: < 016958,000321: 27,2320 016959,000322: 27,2321 016960,000323: 27,2000 016961,000324: 27,2000 016962,000325: 016963,000326: 27,2322 ## Copyright: Public domain. ## Filename: R60,R62.agc ## Purpose: A section of Skylark revision 048. ## It is part of the source code for the Apollo Guidance Computer (AGC) ## for Skylab-2, Skylab-3, Skylab-4, and ASTP. No original listings of ## this software are available; instead, this file was created via ## disassembly of dumps of the core rope modules actually flown on ## Skylab-2. Access to these modules was provided by the New Mexico ## Museum of Space History. ## Assembler: yaYUL ## Contact: Ron Burkey <info@sandroid.org>. ## Website: www.ibiblio.org/apollo/index.html ## Mod history: 2023-09-04 MAS Created from Artemis 072. ## 2024-03-05 MAS Updated for Skylark 48. SETLOC MANUVER BANK 0777 EBANK= TEMPR60 COUNT* $$/R60 # R60CSM # REV 13 CONFORMS TO GSOP CHAPTER FOUR REVISION LOGIC 09 JAN 18,1968 >016664,000027: 27,2000 04676 R60CSM TC MAKECADR 54777 TS TEMPR60 E4E">016667,000030: 27,2002 06006 REDOMANN TC INTPRET 45014 BON CALL # IS 3-AXIS FLAG SET 02711 3AXISFLG 56010 TOBALL1 # YES 56135 VECPOINT # NO CALL VECPOINT 01300 STORE CPHI 1">016673,000036: 27,2010 77776 TOBALL1 EXIT >016675,000038: 27,2011 35044 TOBALL CAF V06N18 04647 TC BANKCALL 21034 CADR GOPERF2R # DISPLAY PLEASE PERFORM AUTO MANEUVER 02125 TC R61TEST 02021 TC REDOMANC -1 12054 TCF ENDMANU1 # ENTER I.E. FINISHED WITH R60 02056 TC CHKLINUS # TO CHECK FOR PRIORITY DISPLAYS 05220 TC ENDOFJOB 06006 -1 TC INTPRET E43">016686,000049: 27,2022 45014 REDOMANC BON CALL # IS 3-AXIS FLAG SET 02711 3AXISFLG 56027 +3 # YES 56135 VECPOINT # NO CALL VECPOINT 01300 STORE CPHI # STORE ANGLES 77776 EXIT 3">016693,000056: 27,2030 37673 TOBALLC CAF FURST3 # BITS 15,14,13 OF CHAN31 = 011 05627 TC C31BTCHK # FOR AUTO AND G&N CONTROL 12033 TCF +1 67671 AD NEG30000 00006 EXTEND 12037 BZF +2 # AUTO, NON-FLASH N18 12011 TCF TOBALL # NOT AUTO 35044 CAF V06N18 # SET UP NON-FLASHING V06 N18 04647 TC BANKCALL 20570 CADR GODSPR 02056 TC CHKLINUS E56">016705,000068: 27,2043 04666 STARTMNV TC POSTJUMP 44000 CADR KALCMAN3 556">016708,000071: 27,2045 06006 ENDMANUV TC INTPRET 43014 BOFF BOFF 05350 AUTOSEQ 56010 TOBALL1 00752 TRACKFLG 56010 TOBALL1 77776 EXIT 531">016716,000079: 27,2054 30777 ENDMANU1 CA TEMPR60 04671 TC BANKJUMP # - 553">016719,000082: 27,2056 40100 CHKLINUS CS FLAGWRD4 74766 MASK PDSPFBIT # IS PRIORITY DISPLAY FLAG SET 10000 CCS A # - 00002 TC Q # NO - EXIT 30002 CA Q 54156 TS MPAC +2 # SAVE RETURN 46214 CS THREE # OBTAIN LOCATION FOR RESTART. 60133 AD BUF2 # HOLDS Q OF LAST DISPALY 55247 TS TBASE1 05415 TC PHASCHNG 00071 OCT 71 # 1.7SPOT FOR RELINUS 1">016732,000095: 27,2071 01,2022 1P7SPT1 = 1.7SPOT 34773 CAF BIT7 05531 TC LINUS # GO SET BITS FOR PRIORITY DISPLAY - 00156 TC MPAC +2 3">016737,000100: 27,2074 34775 RELINUS CAF TRACKBIT # IS TRACK FLAG ON 70075 MASK FLAGWRD1 00006 EXTEND 12123 BZF GOREDO20 # NO 07710 TC UPFLAG 00077 ADRES PDSPFLAG # R60 PRIODSP FLAG 30104 CA FLAGWRD8 74771 MASK UTBIT 10000 CCS A 02120 TC RELINUSX # UTFLAG SET,DO NOT SET TARG1FLG,OPTIND 07710 TC UPFLAG 00024 ADRES TARG1FLG # FOR R52 35003 CAF ZERO # RESET TO ZERO, SINCE 55313 TS OPTIND # OPTIND WAS SET TO -1 BY V379 35001 CAF BIT1 05246 TC WAITLIST 1333 EBANK= FIXTIME 02264 60062 2CADR CTASK 07710 TC UPFLAG 00037 ADRES R21MARK # ALLOW OPTICS MARKING DURING P2 358">016763,000126: 27,2120 35065 RELINUSX CAF PRIO14 # RESTORE ORIGINAL PRIORITY 05211 TC PRIOCHNG 01247 TC TBASE1 230">016768,000131: 27,2123 04666 GOREDO20 TC POSTJUMP # RESTORE R03 DEADBAND, DO STOPRATE, 74662 CADR FIXDB # SET UP 1.11 RESTART, EOJ. 4">016770,000133: 27,2125 31204 R61TEST CA MODREG # ARE WE IN P00. IF YES THIS MUST BE 00006 EXTEND # VERB49 OR VERB89 SO DO ENDEXT. 12054 BZF ENDMANU1 # RESET 3-AXIS & RUTURN. USER DOES ENDEXT 30100 CA FLAGWRD4 # ARE WE IN R61 (P20) 74766 MASK PDSPFBIT 00006 EXTEND 14103 BZF GOTOPOOH # NO 04557 TC GOTOV56 # YES # PROGRAM DESCRIPTION - VECPOINT # THIS INTERPRETIVE SUBROUTINE MAY BE USED TO POINT A SPACECRAFT AXIS IN A DESIRED DIRECTION. THE AXIS # TO BE POINTED MUST APPEAR AS A HALF UNIT DOUBLE PRECISION VECTOR IN SUCCESSIVE LOCATIONS OF ERASABLE MEMORY # BEGINNING WITH THE LOCATION CALLED SCAXIS. THE COMPONENTS OF THIS VECTOR ARE GIVEN IN SPACECRAFT COORDINATES. # THE DIRECTION IN WHICH THIS AXIS IS TO BE POINTED MUST APPEAR AS A HALF UNIT DOUBLE PRECISION VECTOR IN # SUCCESSIVE LOCATIONS OF ERASABLE MEMORY BEGINNING WITH THE ADDRESS CALLED POINTVSM. THE COMPONENTS OF THIS # VECTOR ARE GIVEN IN STABLE MEMBER COORDINATES. WITH THIS INFORMATION VECPOINT COMPUTES A SET OF THREE GIMBAL # ANGLES (2S COMPLEMENT) CORRESPONDING TO THE CROSS-PRODUCT ROTATION BETWEEN SCAXIS AND POINTVSM AND STORES THEM # IN T(MPAC) BEFORE RETURNING TO THE CALLER. # THIS ROTATION, HOWEVER, MAY BRING THE S/C INTO GIMBAL LOCK. WHEN POINTING A VECTOR IN THE Y-Z PLANE, # THE TRANSPONDER AXIS, OR THE AOT FOR THE LEM, THE PROGRAM WILL CORRECT THIS PROBLEM BY ROTATING THE CROSS- # PRODUCT ATTITUDE ABOUT POINTVSM BY A FIXED AMOUNT SUFFICIENT TO ROTATE THE DESIRED S/C ATTITUDE OUT OF GIMBAL # LOCK. IF THE AXIS TO BE POINTED IS MORE THAN 40.6 DEGREES BUT LESS THAN 60.5 DEG FROM THE +X (OR -X) AXIS, # THE ADDITIONAL ROTATION TO AVOID GIMAL LOCK IS 35 DEGREES. IF THE AXIS IS MORE THAN 60.5 DEGEES FROM +X (OR -X) # THE ADDITIONAL ROTATION IS 35 DEGREES. THE GIMBAL ANGLES CORRESPONDING TO THIS ATTITUDE ARE THEN COMPUTED AND # STORED AS 2S COMPLIMENT ANGLES IN T(MPAC) BEFORE RETURNING TO THE CALLER. # WHEN POINTING THE X-AXIS, OR THE THRUST VECTOR, OR ANY VECTOR WITHIN 40.6 DEG OF THE X-AXIS, VECPOINT # CANNOT CORRECT FOR A CROSS-PRODUCT ROTATION INTO GIMBAL LOCK. IN THIS CASE A PLATFORM REALIGNMENT WOULD BE # REQUIRED TO POINT THE VECTOR IN THE DESIRED DIRECTION. AT PRESENT NO INDICATION IS GIVEN FOR THIS SITUATION # EXCEPT THAT THE FINAL MIDDLE GIMBAL ANGLE IN MPAC +2 IS GREATER THAN 59 DEGREES. # CALLING SEQUENCE - # 1) LOAD SCAXIS, POINTVSM # 2) CALL # VECPOINT # RETURNS WITH # 1) DESIRED OUTER GIMBAL ANGLE IN MPAC # 2) DESIRED INNER GIMBAL ANGLE IN MPAC +1 # 3) DESIRED MIDDLE GIMBAL ANGLE IN MPAC +2 # ERASABLES USED - # 1) SCAXIS 6 # 2) POINTVSM 6 # 3) MIS 18 # 4) DEL 18 # 5) COF 6 # 6) VECQTEMP 1 # 7) ALL OF VAC AREA 43 # TOTAL 99 SETLOC VECPT BANK EBANK= BCDU COUNT* $$/VECPT E54">016831,000194: 27,2135 40020 VECPOINT STQ BOV # SAVE RETURN ADDRESS 03341 VECQTEMP 56140 VECLEAR # AND CLEAR OVFIND 2">016834,000197: 27,2140 47164 VECLEAR AXC,2 RTB 02271 MIS # READ THE PRESENT CDU ANGLES AND 44370 READCDUK # STORE THEM IN PD25, 26, 27 34032 STCALL 25D 44377 CDUTODCM # S/C AXES TO STABLE MEMBER AXES (MIS) 61375 VLOAD VXM 03362 POINTVSM # RESOLVE THE POINTING DIRECTION VF INTO 02272 MIS # INITIAL S/C AXES (VF = POINTVSM) 77656 UNIT 00035 STORE 28D # PD 28 29 30 31 32 33 53435 VXV UNIT # TAKE THE CROSS PRODUCT VF X VI 03354 SCAXIS # WHERE VI = SCAXIS 57400 BOV VCOMP 56265 PICKAXIS 16314 STODL COF # CHECK MAGNITUDE 00045 36D # OF CROSS PRODUCT 50025 DSU BMN # VECTOR, IF LESS 16336 DPB-14 # THAN B-14 ASSUME 56265 PICKAXIS # UNIT OPERATION 50375 VLOAD DOT # INVALID. 03354 SCAXIS 00035 28D 65552 SL1 ARCCOS 458">016858,000221: 27,2167 77624 COMPMATX CALL # NOW COMPUTE THE TRANSFORMATION FROM 44522 DELCOMP # FINAL S/C AXES TO INITIAL S/C AXES MFI 75160 AXC,1 AXC,2 02271 MIS # COMPUTE THE TRANSFORMATION FROM FINAL 03425 DEL # S/C AXES TO STABLE MEMBER AXES 77624 CALL # MFS = MIS MFI 44304 MXM3 # (IN PD LIST) 51545 DLOAD ABS 00007 6 # MFS6 = SIN(CPSI) $2 50025 DSU BMN 16323 SINGIMLC # = SIN(59 DEGS) $2 56255 FINDGIMB # /CPSI/ LESS THAN 59 DEGS # I.E. DESIRED ATTITUDE NOT IN GIMBAL LOCK 51545 DLOAD ABS # CHECK TO SEE IF WE ARE POINTING 03354 SCAXIS # THE THRUST AXIS 51025 DSU BPL 16325 SINVEC1 # SIN 49.4 DEGS $2 56255 FINDGIMB # IF SO, WE ARE TRYING TO POINT IT INTO 77775 VLOAD # GIMBAL LOCK, ABORT COULD GO HERE 77626 STADR 51471 STOVL MIS +12D 77626 STADR # STORE MFS (IN PD LIST) IN MIS 51477 STOVL MIS +6 77626 STADR 51505 STOVL MIS 02300 MIS +6 # INNER GIMBAL AXIS IN FINAL S/C AXES 57444 BPL VCOMP # LOCATE THE IG AXIS DIRECTION CLOSEST TO 56222 IGSAMEX # FINAL X S/C AXIS 8">016889,000252: 27,2222 50035 IGSAMEX VXV BMN # FIND THE SHORTEST WAY OF ROTATING THE 03354 SCAXIS # S/C OUT OF GIMBAL LOCK BY A ROTATION 56231 U=SCAXIS # ABOUT +- SCAXIS, I.E. IF (IG (SGN MFS3) # X SCAXIS . XF) LESS THAN 0, U = SCAXIS # OTHERWISE U = -SCAXIS 57575 VLOAD VCOMP 03354 SCAXIS 36314 STCALL COF # ROTATE ABOUT -SCAXIS 56234 CHEKAXIS 953">016899,000262: 27,2231 77775 U=SCAXIS VLOAD 03354 SCAXIS 02314 STORE COF # ROTATE ABOUT + SCAXIS 953">016902,000265: 27,2234 51545 CHEKAXIS DLOAD ABS 03354 SCAXIS # SEE IF WE ARE POINTING THE AOT 51025 DSU BPL 16327 SINVEC2 # SIN 29.5 DEGS $2 56244 PICKANG1 # IF SO, ROTATE 50 DEGS ABOUT +- SCAXIS 52145 DLOAD GOTO # IF NOT, MUST BE POINTING THE TRANSPONDER 16333 VECANG2 # OR SOME VECTOR IN THE Y, OR Z PLANE 56246 COMPMFSN # IN THIS CASE ROTATE 35 DEGS TO GET OUT # OF GIMBAL LOCK (VECANG2 $360) 731">016911,000274: 27,2244 77745 PICKANG1 DLOAD 16331 VECANG1 # = 50 DEGS $ 360 34E">016913,000276: 27,2246 77624 COMPMFSN CALL 44522 DELCOMP # COMPUTE THE ROTATION ABOUT SCAXIS TO 75160 AXC,1 AXC,2 # BRING MFS OUT OF GIMBAL LOCK 02271 MIS 03425 DEL 77624 CALL # COMPUTE THE NEW TRANSFORMATION FROM 44304 MXM3 # DESIRED S/C AXES TO STABLE MEMBER AXES # WHICH WILL ALIGN VI WITH VF AND AVOID # GIMBAL LOCK D42">016922,000285: 27,2255 45160 FINDGIMB AXC,1 CALL 00000 0 # EXTRACT THE COMMANDED CDU ANGLES FROM 44647 DCMTOCDU # THIS MATRIX 77634 RTB 45625 V1STO2S # CONVERT TO 2:S COMPLEMENT 554">016927,000290: 27,2262 52001 VECPTRET SETPD GOTO 00001 0 03341 VECQTEMP # RETURN TO CALLER 953">016931,000294: 27,2265 50375 PICKAXIS VLOAD DOT # IF VF X VI = 0, FIND VF . VI 00035 28D 03354 SCAXIS 72240 BMN TLOAD 56275 ROT180 00032 25D 77650 GOTO # IF VF = VI, CDU DESIRED = PRESENT CDU 56262 VECPTRET # PRESENT CDU ANGLES >016939,000302: 27,2275 47375 ROT180 VLOAD VXV # IF VF, VI ANTIPARALLEL, 180 DEG ROTATION 02300 MIS +6 # IS REQUIRED. Y STABLE MEMBER AXIS IN 15202 HIUNITX # INITIAL S/C AXIS. 47256 UNIT VXV # FIND Y(SM) X X(I) 03354 SCAXIS # FIND UNIT(VI X UNIT(Y(SM) X X(I))) 40056 UNIT BOV # I.E. PICK A VECTOR IN THE PLANE OF X(I), 56317 PICKX # Y(SM) PERPENDICULAR TO VI 16314 STODL COF 00045 36D # CHECK MAGNITUDE 50025 DSU BMN # OF THIS VECTOR. 16336 DPB-14 # IF LESS THAN B-14, 56317 PICKX # PICK X-AXIS. 77775 VLOAD 02314 COF >016953,000316: 27,2313 16314 XROT STODL COF 15202 HIDPHALF 77650 GOTO 56167 COMPMATX /a>016957,000320: 27,2317 52175 PICKX VLOAD GOTO # PICK THE XAXIS IN THIS CASE 15202 HIUNITX 56313 XROT SETLOC MANUVER1 BANK COUNT* $$/VECPT C43">016964,000327: 27,2322 15555 35172 SINGIMLC 2DEC .4285836003 # = SIN(59) $2 1">016965,000328: 27,2324 14113 36326 SINVEC1 2DEC .3796356537 # = SIN(49.4) $2 2">016966,000329: 27,2326 07701 35703 SINVEC2 2DEC .2462117800 # = SIN(29.5) $2 1">016967,000330: 27,2330 04343 21616 VECANG1 2DEC .1388888889 # = 50 DEGREES $360 2">016968,000331: 27,2332 03070 34344 VECANG2 2DEC .09722222222 # = 35 DEGREES $360 >016970,000333: 27,2334 00000 1BITDP OCT 0 # KEEP THIS BEFORE DPB(-14) ********* >016971,000334: 27,2335 00001 DPB-14 OCT 00001 00000 OCT 00000 SETLOC MANUVER BANK # ROUTINE FOR INITIATING AUTOMATIC MANEUVER VIA KEYBOARD (V49) 1277 EBANK= CPHI COUNT* $$/R62 0">016981,000344: 27,2337 35040 R62DISP CAF V06N22 # DISPLAY COMMAND ICDUS CPHI, CTHETA, CPHI 04647 TC BANKCALL 20623 CADR GOFLASH 15537 TCF ENDEXT 12345 TCF GOMOVE # PROCEED 12337 TCF R62DISP # ENTER # ASTRONAUT MAY LOAD NEW ICDUS AT THIS # POINT >016990,000353: 27,2345 07710 GOMOVE TC UPFLAG # SET 3-AXIS FLAG 00124 ADRES 3AXISFLG # BIT 6 FLAG 5 04647 TC BANKCALL 56000 CADR R60CSM 15537 TCF ENDEXT Parent file is MAIN.agc