GAP: ASSEMBLE REVISION 131 OF AGC PROGRAM LUMINARY BY NASA 2021112-091 17:53 DEC. 19, 1969Note that the date is the date the printout was made, not the date on which the program revision was released, although these happen to be very close together.
Source Code
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This source code is very close to the Apollo Guidance Computer software for the
Apollo 13 Lunar module. This revision of the Luminary 131 program is from December
of 1969, whereas there was a later revision in January of 1970, and still another
revision in February, which is the code that flew on the mission.
As far as this transcription is concerned, it was originally from a copy made in 1991 of
a printout from the collection of AGC developer Don Eyles for collector David Craig.
It was subsequently scanned by Gary Neff, reprocessed for online
presentation at the now-discontinued History of Recent Science and Technology (HRST) website
of MIT's Dibner Institute (the full-quality scans being discarded in the process),
and finally transcribed by Ron Burkey for the Virtual AGC Project. Although a
high-quality replacement scan for a completely illegible page was later provided by Gary
Neff, the reduced legibility of the reprocessed HRST posting nevertheless caused many
errors to be introduced into the transcription. Accordingly, a second scan of the same physical
printout was made in 2017 for the Virtual AGC Project's collection at the Internet Archive,
and used to correct the transcription errors. All of the scanned materials mentioned,
as well as other Luminary 131 related material, are available online.
Don Eyles apprently made additional hand-written notes in printout between 1991 and 2017,
so the two scans are not identical in that respect. The page-headings in the printout read, in part:GAP: ASSEMBLE REVISION 131 OF AGC PROGRAM LUMINARY BY NASA 2021112-091 17:53 DEC. 19, 1969Note that the date is the date the printout was made, not the date on which the program revision was released, although these happen to be very close together. |
033550,000002: ## Copyright: Public domain.
033551,000003: ## Filename: THROTTLE_CONTROL_ROUTINES.agc
033552,000004: ## Purpose: A section of Luminary 1C, revision 131.
033553,000005: ## It is part of the source code for the Lunar Module's (LM)
033554,000006: ## Apollo Guidance Computer (AGC) for Apollo 13.
033555,000007: ## This file is intended to be a faithful transcription, except
033556,000008: ## that the code format has been changed to conform to the
033557,000009: ## requirements of the yaYUL assembler rather than the
033558,000010: ## original YUL assembler.
033559,000011: ## Reference: pp. 788-792
033560,000012: ## Contact: Ron Burkey <info@sandroid.org>.
033561,000013: ## Website: www.ibiblio.org/apollo/index.html
033562,000014: ## Mod history: 05/24/03 RSB. Began transcribing.
033563,000015: ## 05/14/05 RSB Corrected website reference above.
033564,000016: ## 2017-01-06 RSB Page numbers now agree with those on the
033565,000017: ## original hardcopy, as opposed to the PDF page
033566,000018: ## numbers in 1701.pdf.
033567,000019: ## 2017-02-25 RSB Proofed comment text using octopus/ProoferComments.
033568,000020: ## 2017-03-16 RSB Comment-text fixes identified in 5-way
033569,000021: ## side-by-side diff of Luminary 69/99/116/131/210.
033570,000022:
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Page 788 |
033572,000024: 31,2144 BANK 31
033573,000025: 31,2000 SETLOC FTHROT
033574,000026: 31,2000 BANK
033575,000027: 31,2144 E7,1612 EBANK= PIF
033576,000028: 31,2144 COUNT* $$/THROT
033577,000029:
033578,000030: # * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
033579,000031: # HERE FC, DESIRED THRUST, AND FP, PRESENT THRUST, UNWEIGHTED, ARE COMPUTED.
033580,000032:
033581,000033: 31,2144 31245 THROTTLE CA ABDELV # COMPUTE PRESENT ACCELERATION IN UNITS OF
033582,000034: 31,2145 00006 EXTEND # 2(-4) M/CS/CS, SAVING SERVICER TROUBLE
033583,000035: 31,2146 72356 MP /AF/CNST
033584,000036: 31,2147 00006 +3 EXTEND
033585,000037: 31,2150 23607 QXCH RTNHOLD
033586,000038: 31,2151 02337 AFDUMP TC MASSMULT
033587,000039: 31,2152 53470 DXCH FP # FP = PRESENT THRUST
033588,000040: 31,2153 00006 EXTEND
033589,000041: 31,2154 31464 DCA /AFC/
033590,000042: 31,2155 02337 TC MASSMULT
033591,000043: 31,2156 55615 TS FC # FC = THRUST DESIRED BY GUIDANCE
033592,000044: 31,2157 53466 DXCH FCODD # FCODD = WHAT IT IS GOING TO GET
033593,000045:
033594,000046: # COMPUTE DESIRED THRUST FOR DISPLAY AS A PERCENTAGE OF 10,500 POUNDS
033595,000047:
033596,000048: 31,2160 32360 CAF 4FMAXNOM # MOVE 4FMAXNOM TO ERASABLE FOR DV BELOW
033597,000049: 31,2161 54002 TS Q
033598,000050: 31,2162 31615 CA FC
033599,000051: 31,2163 72357 MASK OCT17777 # FOR SAFETY
033600,000052: 31,2164 00006 EXTEND
033601,000053: 31,2165 10002 DV Q
033602,000054: 31,2166 00006 EXTEND
033603,000055: 31,2167 75003 MP 4SECS
033604,000056: 31,2170 55750 TS THRDISP # FOR DISPLAY IN N92
033605,000057:
033606,000058: # IF IT HAS BEEN LESS THAN 3 SECONDS SINCE THE LAST THROTTLING, AUGMENT FP USING THE FWEIGHT CALCULATED THEN.
033607,000059:
033608,000060: 31,2171 41617 CS TTHROT # THIS CODING ASSUMES A FLATOUT WITHIN
033609,000061: 31,2172 60025 AD TIME1 # 80 SECONDS BEFORE FIRST THROTTLE CALL
033610,000062: 31,2173 74733 MASK POSMAX
033611,000063: 31,2174 40000 COM
033612,000064: 31,2175 65002 AD 3SECS
033613,000065: 31,2176 00006 EXTEND
033614,000066: 31,2177 62203 BZMF WHERETO # BRANCH IF (TIME1-TTHROT +1) > 3 SECONDS
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Page 789 |
033616,000068: 31,2200 00006 EXTEND
033617,000069: 31,2201 31611 DCA FWEIGHT
033618,000070: 31,2202 21470 DAS FP
033619,000071:
033620,000072: # THIS LOGIC DETERMINES THE THROTTLING IN THE REGION 10% - 94%. THE MANUAL THROTTLE, NOMINALLY SET AT
033621,000073: # MINIMUM BY ASTRONAUT OR MISSION CONTROL PROGRAMS, PROVIDES THE LOWER BOUND. A STOP IN THE THROTTLE HARDWARE
033622,000074: # PROVIDES THE UPPER.
033623,000075:
033624,000076: 31,2203 35014 WHERETO CA EBANK5 # INITIALIZE L*WCR*T AND H*GHCR*T FROM
033625,000077: 31,2204 54003 TS EBANK # PAD LOADED ERASABLES IN W-MATRIX
033626,000078: 31,2205 E5,1506 EBANK= LOWCRIT
033627,000079: 31,2205 00006 EXTEND
033628,000080: 31,2206 31507 DCA LOWCRIT
033629,000081: 31,2207 52131 DXCH L*WCR*T
033630,000082: 31,2210 35016 CA EBANK7
033631,000083: 31,2211 54003 TS EBANK
033632,000084: 31,2212 E7,1612 EBANK= PIF
033633,000085: 31,2212 44755 CS ZERO # INITIALIZE PIFPSET
033634,000086: 31,2213 55606 TS PIFPSET
033635,000087: 31,2214 40131 CS H*GHCR*T
033636,000088: 31,2215 61620 AD FCOLD
033637,000089: 31,2216 00006 EXTEND
033638,000090: 31,2217 62231 BZMF LOWFCOLD # BRANCH IF FCOLD < OR = HIGHCRIT
033639,000091: 31,2220 40130 CS L*WCR*T
033640,000092: 31,2221 61465 AD FCODD
033641,000093: 31,2222 00006 EXTEND
033642,000094: 31,2223 62226 BZMF FCOMPSET # BRANCH IF FC < OR = LOWCRIT
033643,000095: 31,2224 31467 CA FP # SEE NOTE 1
033644,000096: 31,2225 12236 TCF FLATOUT1
033645,000097:
033646,000098: 31,2226 42002 FCOMPSET CS FMAXODD # SEE NOTE 2
033647,000099: 31,2227 61467 AD FP
033648,000100: 31,2230 12240 TCF FLATOUT2
033649,000101:
033650,000102: 31,2231 40131 LOWFCOLD CS H*GHCR*T
033651,000103: 31,2232 61465 AD FCODD
033652,000104: 31,2233 00006 EXTEND
033653,000105: 31,2234 62241 BZMF DOPIF # BRANCH IF FC < OR = HIGHCRIT
033654,000106:
033655,000107: 31,2235 32003 CA FMAXPOS # NO: THROTTLE-UP
033656,000108: 31,2236 53466 FLATOUT1 DXCH FCODD
033657,000109: 31,2237 34737 CA FEXTRA
033658,000110: 31,2240 55606 FLATOUT2 TS PIFPSET
033659,000111:
033660,000112: # NOTE 1 FC IS SET EQUAL TO FP SO PIF WILL BE ZERO. THIS IS DESIRABLE
033661,000113: # AS THERE IS ACTUALLY NO THROTTLE CHANGE.
033662,000114:
033663,000115: # NOTE2 HERE, SINCE WE ARE ABOUT TO RETURN TO THE THROTTLEABLE REGION
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Page 790 |
033665,000117: # (BELOW 55%) THE QUANTITY -(FMAXODD-FP) IS COMPUTED AND PUT
033666,000118: # INTO PIFPSET TO COMPENSATE FOR THE DIFFERENCE BETWEEN THE
033667,000119: # NUMBER OF BITS CORRESPONDING TO FULL THROTTLE (FMAXODD) AND THE
033668,000120: # NUMBER CORRESPONDING TO ACTUAL THRUST (FP). THUS THE TOTAL
033669,000121: # THROTTLE COMMAND PIF = FC - FP - (FMAXODD - FP) = FC - FMAXODD.
033670,000122:
033671,000123: 31,2241 03677 DOPIF TC FASTCHNG
033672,000124: 31,2242 00006 EXTEND
033673,000125: 31,2243 31466 DCA FCODD
033674,000126: 31,2244 55620 TS FCOLD
033675,000127: 31,2245 53613 DXCH PIF
033676,000128: 31,2246 00006 EXTEND
033677,000129: 31,2247 41470 DCS FP
033678,000130: 31,2250 21613 DAS PIF # PIF = FC - FP, NEVER EQUALS +0
033679,000131:
033680,000132: 31,2251 31612 DOIT CA PIF
033681,000133: 31,2252 61606 AD PIFPSET # ADD IN PIFPSET, WITHOUT CHANGING PIF
033682,000134: 31,2253 55614 TS PSEUDO55
033683,000135: 31,2254 54055 TS THRUST
033684,000136: 31,2255 34750 CAF BIT4
033685,000137: 31,2256 00006 EXTEND
033686,000138: 31,2257 05014 WOR CHAN14
033687,000139: 31,2260 30025 CA TIME1
033688,000140: 31,2261 55617 TS TTHROT
033689,000141:
033690,000142: # SINCE /AF/ IS NOT AN INSTANTANEOUS ACCELERATION, BUT RATHER AN "AVERAGE" OF THE ACCELERATION LEVELS DURING
033691,000143: # THE PRECEEDING PIPA INTERVAL, AND SINCE FP IS COMPUTED DIRECTLY FROM /AF/, FP IN ORDER TO CORRESPOND TO THE
033692,000144: # ACTUAL THRUST LEVEL AT THE END OF THE INTERVAL MUST BE WEIGHTED BY
033693,000145: # PIF(PPROCESS + TL) PIF /PIF/
033694,000146: # FWEIGHT = ------------------ + -------------
033695,000147: # PGUID 2 PGUID FRATE
033696,000148: # WHERE PPROCESS IS THE TIME BETWEEN PIPA READING AND THE START OF THROTTLING, PGUID IS THE GUIDANCE PERIOD, AND
033697,000149: # FRATE IS THE THROTTLING RATE (32 UNITS PER CENTISECOND). PGUID IS EITHER 1 OR 2 SECONDS. THE "TL" IN THE
033698,000150: # FIRST TERM REPRESENTS THE ENGINE'S RESPONSE LAG. HERE FWEIGHT IS COMPUTED FOR USE NEXT PASS.
033699,000151:
033700,000152: 31,2262 31762 CA THISTPIP +1 # INITIALIZE FWEIGHT COMP AS IF FOR P66
033701,000153: 31,2263 54130 TS BUF
033702,000154:
033703,000155: 31,2264 41010 CS MODREG # ARE WE IN FACT IN P66?
033704,000156: 31,2265 62452 AD DEC66
033705,000157: 31,2266 00006 EXTEND
033706,000158: 31,2267 12274 BZF FWCOMP # YES
033707,000159:
033708,000160: 31,2270 31234 CA PIPTIME +1 # NO: INITIALIZE FOR TWO SECOND PERIOD
033709,000161: 31,2271 54130 TS BUF
033710,000162: 31,2272 35003 CAF 4SECS
033711,000163: 31,2273 12275 TCF FWCOMP +1
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Page 791 |
033713,000165:
033714,000166: 31,2274 35000 FWCOMP CAF 2SECS
033715,000167: 31,2275 54002 +1 TS Q
033716,000168: 31,2276 00006 EXTEND
033717,000169: 31,2277 74746 MP BIT6
033718,000170: 31,2300 22131 LXCH BUF +1
033719,000171: 31,2301 40130 CS BUF # TIME OF LAST PIPA READING.
033720,000172: 31,2302 60025 AD TIME1
033721,000173: 31,2303 62004 AD THROTLAG # COMPENSATE FOR ENGINE RESPONSE LAG
033722,000174: 31,2304 74357 MASK LOW8 # MAKE SURE SMALL AND POSITIVE
033723,000175: 31,2305 22007 ZL
033724,000176: 31,2306 00006 EXTEND
033725,000177: 31,2307 10002 DV Q
033726,000178: 31,2310 00006 EXTEND
033727,000179: 31,2311 71612 MP PIF
033728,000180: 31,2312 60000 DOUBLE
033729,000181: 31,2313 53611 DXCH FWEIGHT
033730,000182: 31,2314 11612 CCS PIF
033731,000183: 31,2315 64753 AD ONE
033732,000184: 31,2316 12320 TCF +2
033733,000185: 31,2317 64753 AD ONE
033734,000186: 31,2320 00006 EXTEND
033735,000187: 31,2321 71612 MP PIF
033736,000188: 31,2322 00006 EXTEND
033737,000189: 31,2323 10131 DV BUF +1
033738,000190: 31,2324 22007 ZL
033739,000191: 31,2325 21611 DAS FWEIGHT
033740,000192:
033741,000193: 31,2326 01607 THDUMP TC RTNHOLD
033742,000194:
033743,000195: # FLATOUT THROTTLES UP THE DESCENT ENGINE, AND IS CALLED AS A BASIC SUBROUTINE.
033744,000196:
033745,000197: 31,2327 34737 FLATOUT CAF BIT13 # 4096 PULSES
033746,000198: 31,2330 55606 WHATOUT TS PIFPSET # USE PIFPSET SO FWEIGHT WILL BE ZERO
033747,000199: 31,2331 44755 CS ZERO
033748,000200: 31,2332 55620 TS FCOLD
033749,000201: 31,2333 55612 TS PIF
033750,000202: 31,2334 00006 EXTEND
033751,000203: 31,2335 23607 QXCH RTNHOLD
033752,000204: 31,2336 12251 TCF DOIT
033753,000205:
033754,000206: # MASSMULT SCALES ACCELERATION, ARRIVING IN A AND L IN UNITS OF 2(-4) M/CS/CS, TO FORCE IN PULSE UNITS.
033755,000207:
033756,000208: 31,2337 00006 MASSMULT EXTEND
033757,000209: 31,2340 22130 QXCH BUF
033758,000210: 31,2341 52155 DXCH MPAC
033759,000211: 31,2342 07106 TC DMP
033760,000212: 31,2343 01243 ADRES MASS
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Page 792 |
033762,000214: 31,2344 07106 TC DMP # LEAVES PROPERLY SCALED FORCE IM MPAC
033763,000215: 31,2345 02005 ADRES SCALEFAC
033764,000216: 31,2346 07262 TC TPAGREE
033765,000217: 31,2347 30154 CA MPAC
033766,000218: 31,2350 00006 EXTEND
033767,000219: 31,2351 12354 BZF +3
033768,000220: 31,2352 34733 CAF POSMAX
033769,000221: 31,2353 00130 TC BUF
033770,000222: 31,2354 52156 DXCH MPAC +1
033771,000223: 31,2355 00130 TC BUF
033772,000224:
033773,000225: # CONSTANTS:-
033774,000226:
033775,000227: 31,2356 4737 FEXTRA = BIT13 # FEXT +5.13309020 E+4
033776,000228:
033777,000229: 31,2356 04143 /AF/CNST DEC .13107
033778,000230:
033779,000231: 31,2357 17777 OCT17777 OCT 17777
033780,000232: 31,2360 35074 4FMAXNOM DEC 14908 B-14 # EQUIVALENT TO 10,500 LBS.
033781,000233:
033782,000234: # * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
End of include-file THROTTLE_CONTROL_ROUTINES.agc. Parent file is MAIN.agc