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.
|
050170,000002: ## Copyright: Public domain.
050171,000003: ## Filename: PLANETARY_INERTIAL_ORIENTATION.agc
050172,000004: ## Purpose: A section of Skylark revision 048.
050173,000005: ## It is part of the source code for the Apollo Guidance Computer (AGC)
050174,000006: ## for Skylab-2, Skylab-3, Skylab-4, and ASTP. No original listings of
050175,000007: ## this software are available; instead, this file was created via
050176,000008: ## disassembly of dumps of the core rope modules actually flown on
050177,000009: ## Skylab-2. Access to these modules was provided by the New Mexico
050178,000010: ## Museum of Space History.
050179,000011: ## Assembler: yaYUL
050180,000012: ## Contact: Ron Burkey <info@sandroid.org>.
050181,000013: ## Website: www.ibiblio.org/apollo/index.html
050182,000014: ## Mod history: 2023-09-04 MAS Created from Artemis 072.
050183,000015: ## 2024-03-05 MAS Updated for Skylark 48.
050184,000016:
050185,000017: # ..... RP-TO-R SUBROUTINE .....
050186,000018: # SUBROUTINE TO CONVERT RP (VECTOR IN PLANETARY COORDINATE SYSTEM, EITHER
050187,000019: # EARTH-FIXED OR MOON-FIXED) TO R (SAME VECTOR IN THE BASIC REF. SYSTEM)
050188,000020:
050189,000021: # R = MT(T) * (RP + LP X RP) MT = M MATRIX TRANSPOSE
050190,000022:
050191,000023: # CALLING SEQUENCE
050192,000024: # L CALL
050193,000025: # L+1 RP-TO-R
050194,000026:
050195,000027: # SUBROUTINES USED
050196,000028: # EARTHMX, MOONMX, EARTHL
050197,000029:
050198,000030: # ITEMS AVAILABLE FROM LAUNCH DATA
050199,000031: # 504LM = THE LIBRATION VECTOR L OF THE MOON AT TIME TIMSUBL, EXPRESSED
050200,000032: # IN THE MOON-FIXED COORD. SYSTEM RADIANS B0
050201,000033:
050202,000034: # ITEMS NECESSARY FOR SUBR. USED (SEE DESCRIPTION OF SUBR.)
050203,000035:
050204,000036: # INPUT
050205,000037: # MPAC = 0 FOR EARTH, NON-ZERO FOR MOON
050206,000038: # 0-5D = RP VECTOR
050207,000039: # 6-7D = TIME
050208,000040:
050209,000041: # OUTPUT
050210,000042: # MPAC = R VECTOR METERS B-29 FOR EARTH, B-27 FOR MOON
050211,000043:
050212,000044: 26,2000 SETLOC PLANTIN
050213,000045: 26,2000 BANK
050214,000046:
050215,000047: 26,3213 COUNT* $$/LUROT
050216,000048:
050217,000049: 26,3213 45020 RP-TO-R STQ CALL
050218,000050: 26,3214 00050 RPREXIT
050219,000051: 26,3215 55264 EARTHMX # M MATRIX B-1
050220,000052: # AND L VECTOR RADIANS B0
050221,000053: 26,3216 61375 VLOAD VXM
050222,000054: 26,3217 00001 504RPR
050223,000055: 26,3220 00025 MMATRIX # MPAC=R=MT(T)*(RP+LPXRP)
050224,000056: 26,3221 52105 VXM GOTO
050225,000057: 26,3222 02015 LMATRIX
050226,000058: 26,3223 55234 RPRPXXXX # RESET PUSHLOC TO 0 BEFORE EXITING
050227,000059:
050228,000060: # ..... R-TO-RP SUBROUTINE .....
050229,000061: # SUBROUTINE TO CONVERT R (VECTOR IN REFERENCE COORD. SYSTEM) TO RP
050230,000062: # (VECTOR IN PLANETARY COORD SYSTEM) EITHER EARTH-FIXED OR MOON-FIXED
050231,000063:
050232,000064: # RP = M(T) * (R - L X R)
050233,000065:
050234,000066: # CALLING SEQUENCE
050235,000067: # L CALL
050236,000068: # L+1 R-TO-RP
050237,000069:
050238,000070: # SUBROUTINES USED
050239,000071: # EARTHMX, MOONMX, EARTHL
050240,000072:
050241,000073: # INPUT
050242,000074: # MPAC = 0 FOR EARTH, NON-ZERO FOR MOON
050243,000075: # 0-5D = R VECTOR
050244,000076: # 6-7D = TIME
050245,000077:
050246,000078: # ITEMS AVAILABLE FROM LAUNCH DATA
050247,000079: # 504LM = THE LIBRATION VECTOR L OF THE MOON AT TIME TIMSUBL, EXPRESSED
050248,000080: # IN THE MOON-FIXED COORD. SYSTEM RADIANS B0
050249,000081:
050250,000082: # ITEMS NECESSARY FOR SUBROUTINES USED (SEE DESCRIPTION OF SUBR.)
050251,000083:
050252,000084: # OUTPUT
050253,000085: # MPAC = RP VECTOR METERS B-29 FOR EARTH, B-27 FOR MOON
050254,000086:
050255,000087: 26,3224 45020 R-TO-RP STQ CALL
050256,000088: 26,3225 00050 RPREXIT
050257,000089: 26,3226 55264 EARTHMX
050258,000090: 26,3227 64375 VLOAD MXV
050259,000091: 26,3230 00001 504RPR
050260,000092: 26,3231 02015 LMATRIX
050261,000093: 26,3232 77721 MXV # M(T)*(R-LXR) B-2
050262,000094: 26,3233 00025 MMATRIX
050263,000095: 26,3234 40372 RPRPXXXX VSL1 SETPD
050264,000096: 26,3235 00001 0D
050265,000097: 26,3236 77650 GOTO
050266,000098: 26,3237 00050 RPREXIT
050267,000099:
050268,000100: # COMPUTE X=X0+(XDOT)(T+T0)
050269,000101: # 8-9D= XO (REVS B-0), PUSHLOC SET AT 12D
050270,000102: # 10-11D=XDOT (REVS/CSEC) SCALED B+23 FOR WEARTH,B+28 FOR NODDOT AND BDOT
050271,000103: # AND B+27 FOR FDOT
050272,000104: # X1=DIFFERENCE IN 23 AND SCALING OF XDOT, =0 FOR WEARTH, 5 FOR NODDOT AND
050273,000105: # BDOT AND 4 FOR FDOT
050274,000106: # 6-7D=T (CSEC B-28), TIMSUBO= (CSEC B-42 TRIPLE PREC.)
050275,000107:
050276,000108: 26,3240 54345 NEWANGLE DLOAD SR # ENTER PD 12D
050277,000109: 26,3241 00007 6D
050278,000110: 26,3242 20617 14D
050279,000111: 26,3243 72371 TAD TLOAD # CHANGE MODE TO TP
050280,000112: 26,3244 01701 TIMSUBO
050281,000113: 26,3245 00155 MPAC
050282,000114: 26,3246 14017 STODL TIMSUBM # T+T0 CSEC B-42
050283,000115: 26,3247 00020 TIMSUBM +1
050284,000116: 26,3250 77605 DMP # PD 10D MULT BY XDOT IN 10-11D
050285,000117: 26,3251 43257 SL* DAD # PD 8D ADD XO IN 8-9D AFTER SHIFTING
050286,000118: 26,3252 20206 5,1 # SUCH THAT SCALING IS B-0
050287,000119: 26,3253 67206 PUSH SLOAD # PD 10D SAVE PARTIAL (X0+XDOT*T) IN 8-9D
050288,000120: 26,3254 00017 TIMSUBM
050289,000121: 26,3255 41261 SL DMP
050290,000122: 26,3256 20212 9D
050291,000123: 26,3257 00013 10D # XDOT
050292,000124: 26,3260 43257 SL* DAD # PD 8D SHIFT SUCH THAT THIS PART OF X
050293,000125: 26,3261 20213 10D,1 # IS SCALED REVS/CSEC B-0
050294,000126: 26,3262 43400 HERE BOV RVQ # TURN OFF OVERFLOW IF SET BY SHIFT
050295,000127: 26,3263 55262 HERE # INSTRUCTION BEFORE EXITING
050296,000128: # MPAC=X=X0+(XDOT)(T+T0) REVS B0
050297,000129:
050298,000130: # ..... EARTHMX SUBROUTINE .....
050299,000131: # SUBROUTINE TO COMPUTE THE TRANSFORMATION MATRIX M FOR THE EARTH
050300,000132:
050301,000133: # CALLING SEQUENCE
050302,000134: # L CALL
050303,000135: # L+1 EARTHMX
050304,000136:
050305,000137: # SUBROUTINES USED
050306,000138: # NEWANGLE
050307,000139:
050308,000140: # INPUT
050309,000141: # INPUT AVAILABLE FROM LAUNCH DATA AZO REVS B-0
050310,000142: # TEPHEM CSEC B-42
050311,000143: # 6-7D= TIME CSEC B-28
050312,000144:
050313,000145: # OUTPUT
050314,000146: # MMATRIX= 3X3 M MATRIX B-1 (STORED IN VAC AREA)
050315,000147:
050316,000148: 26,3264 40220 EARTHMX STQ SETPD # SET 8-9D=AZO
050317,000149: 26,3265 00051 EARTHMXX
050318,000150: 26,3266 00011 8D # 10-11D=WEARTH
050319,000151: 26,3267 77770 AXT,1 # FOR SL 5, AND SL 10 IN NEWANGLE
050320,000152: 26,3270 00000 0
050321,000153: 26,3271 65345 DLOAD PDDL # LEAVING PD SET AT 12D FOR NEWANGLE
050322,000154: 26,3272 02037 AZO
050323,000155: 26,3273 15317 WEARTH
050324,000156: 26,3274 45006 PUSH CALL
050325,000157: 26,3275 55240 NEWANGLE
050326,000158: 26,3276 41401 SETPD PUSH # 18-19D=504AZ
050327,000159: 26,3277 00023 18D # COS(AZ) SIN(AZ) 0
050328,000160: 26,3300 65346 COS PDDL # 20-37D= MMATRIX= -SIN(AZ) COS(AZ) 0 B-1
050329,000161: 26,3301 00023 504AZ # 0 0 1
050330,000162: 26,3302 65356 SIN PDDL
050331,000163: 26,3303 15204 HI6ZEROS
050332,000164: 26,3304 73525 PDDL SIN
050333,000165: 26,3305 00023 504AZ
050334,000166: 26,3306 65276 DCOMP PDDL
050335,000167: 26,3307 00023 504AZ
050336,000168: 26,3310 63346 COS PDVL
050337,000169: 26,3311 15204 HI6ZEROS
050338,000170: 26,3312 41525 PDDL PUSH
050339,000171: 26,3313 15202 HIDPHALF
050340,000172: 26,3314 77650 GOTO
050341,000173: 26,3315 00051 EARTHMXX
050342,000174: # CONSTANTS AND ERASABLE ASSIGNMENTS
050343,000175:
050344,000176: 26,3316 06,3723 1B1 = DP1/2 # 1 SCALED B-1
050345,000177: 26,3316 0000050 RPREXIT = S1 # R-TO-RP AND RP-TO-R SUBR EXIT
050346,000178: 26,3316 0000051 EARTHMXX = S2 # EARTHMX,MOONMX SUBR. EXITS
050347,000179: 26,3316 504RPR = 0D # 6 REGS R OR RP VECTOR
050348,000180: 26,3316 504AZ = 18D # 2 AZ
050349,000181: 26,3316 TIMSUBM = 14D # 3 TIME SUB M (MOON) T+T0 IN GETAZ
050350,000182: 26,3316 MMATRIX = 20D # 18 M MATRIX
050351,000183: 26,3316 37116 32631 WEARTH 2DEC* +1.160576171 E-7 B23* # REV/CS.
End of include-file PLANETARY_INERTIAL_ORIENTATION.agc. Parent file is MAIN.agc