309 lines
6.9 KiB
Plaintext
309 lines
6.9 KiB
Plaintext
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# Copyright: Public domain.
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# Filename: LATITUDE_LONGITUDE_SUBROUTINES.agc
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# Purpose: Part of the source code for Luminary 1A build 099.
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# It is part of the source code for the Lunar Module's (LM)
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# Apollo Guidance Computer (AGC), for Apollo 11.
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#
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# Assembler: yaYUL
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# Contact: Jim Lawton <jim DOT lawton AT gmail DOT com>
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# Website: www.ibiblio.org/apollo.
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# Pages: 1133-1139
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# Mod history: 2009-05-28 JL Updated from page images.
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# 2011-01-06 JL Fixed interpretive indentation.
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#
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# This source code has been transcribed or otherwise adapted from digitized
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# images of a hardcopy from the MIT Museum. The digitization was performed
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# by Paul Fjeld, and arranged for by Deborah Douglas of the Museum. Many
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# thanks to both. The images (with suitable reduction in storage size and
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# consequent reduction in image quality as well) are available online at
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# www.ibiblio.org/apollo. If for some reason you find that the images are
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# illegible, contact me at info@sandroid.org about getting access to the
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# (much) higher-quality images which Paul actually created.
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#
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# Notations on the hardcopy document read, in part:
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#
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# Assemble revision 001 of AGC program LMY99 by NASA 2021112-061
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# 16:27 JULY 14, 1969
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# Page 1133
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# SUBROUTINE TO CONVERT RAD VECTOR AT GIVEN TIME TO LAT,LONG AND ALT
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#
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# CALLING SEQUENCE
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# L-1 CALL
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# L LAT-LONG
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#
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# SUBROUTINES USED
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# R-TO-RP, ARCTAN, SFTGAMMA, SETRE
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#
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# ERASABLE INIT. REQ.
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# AXO, -AYO, AZO, TEPHEM (SET AT LAUNCH TIME)
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# ALPHAV = POSITION VECTOR METERS B-29
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# MPAC -- TIME (CSECS B-28)
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# ERADFLAG =1, TO COMPUTE EARTH RADIUS, =0 FOR FIXED EARTH RADIUS
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# LUNAFLAG=0 FOR EARTH, 1 FOR MOON
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#
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# OUTPUT
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# LATITUDE IN LAT (REVS. B-0)
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# LONGITUDE IN LONG (REVS. B-0)
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# ALTITUDE IN ALT METERS B-29
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BANK 30
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SETLOC LATLONG
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BANK
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COUNT* $$/LT-LG
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EBANK= ALPHAV
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LAT-LONG STQ SETPD
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INCORPEX
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0D
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STOVL 6D # SAVE TIME IN 6-7D FOR R-TO-RP
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ALPHAV
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PUSH ABVAL # 0-5D= R FOR R-TO-RP
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STODL ALPHAM # ABS. VALUE OF R FOR ALT FORMULA BELOW
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ZEROVEC # SET MPAC=0 FOR EARTH, NON-ZERO FOR MOON
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BOFF COS # USE COS(0) TO GET NON-ZERO IN MPAC
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LUNAFLAG # 0=EARTH, 1=MOON
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CALLRTRP
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CALLRTRP CALL
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R-TO-RP # RP VECTOR CONVERTED FROM R B-29
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UNIT # UNIT RP B-1
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STCALL ALPHAV # U2= 1/2 SINL FOR SETRE SUBR BELOW
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SETGAMMA # SET GAMMA=B2/A2 FOR EARTH, =1 FOR MOON
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CALL # SCALED B-1
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SETRE # CALC RE METERS B-29
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DLOAD DSQ
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ALPHAV
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PDDL DSQ
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ALPHAV +2
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DAD SQRT
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# Page 1134
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DMP SL1R
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GAMRP
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STODL COSTH # COS(LAT) B-1
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ALPHAV +4
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STCALL SINTH # SIN(LAT) B-1
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ARCTAN
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STODL LAT # LAT B0
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ALPHAV
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STODL COSTH # COS(LONG) B-1
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ALPHAV +2
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STCALL SINTH # SIN(LONG) B-1
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ARCTAN
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STODL LONG # LONG. REVS B-0 IN RANGE -1/2 TO 1/2
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ALPHAM
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DSU # ALT= R-RE METERS B-29
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ERADM
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STCALL ALT # EXIT WITH ALT METERS B-29
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INCORPEX
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# Page 1135
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# SUBROUTINE TO CONVERT LAT,LONG.ALT AT GIVEN TIME TO RADIUS VECTOR
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#
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# CALLING SEQUENCE
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# L-1 CALL
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# L LALOTORV
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#
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# SUBROUTINES USED
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# SETGAMMA, SETRE, RP-TO-R
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#
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# ERASABLE INIT. REQ.
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# AXO, AYO, AZO, TEPHEM SET AT LAUNCH TIME
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# LAT -- LATITUDE (REVS B0)
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# LONG -- LONGITUDE (REVS B0)
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# ALT -- ALTITUDE (METERS) B-29
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# MPAC -- TIME (CSECS B-28)
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# ERADFLAG =1 TO COMPUTE EARTH RADIUS, =0 FOR FIXED EARTH RADIUS
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# LUNAFLAG=0 FOR EARTH, 1 FOR MOON
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#
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# OUTPUT
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# R-VECTOR IN ALPHAV (METERS B-29)
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LALOTORV STQ SETPD # LAT,LONG,ALT TO R VECTOR
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INCORPEX
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0D
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STCALL 6D # 6-7D= TIME FOR RP-TO-R
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SETGAMMA # GAMMA=B2/A2 FOR EARTH, 1 FOR MOON B-1
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DLOAD SIN # COS(LONG)COS(LAT) IN MPAC
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LAT # UNIT RP = SIN(LONG)COS(LAT) 2-3D
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DMPR PDDL # PD 2 GAMMA*SIN(LAT) 0-1D
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GAMRP
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LAT # 0-1D = GAMMA*SIN(LAT) B-2
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COS PDDL # PD4 2-3D = COS(LAT) B-1 TEMPORARILY
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LONG
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SIN DMPR # PD 2
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PDDL COS # PD 4 2-3D = SIN(LONG)COS(LAT) B-2
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LAT
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PDDL COS # PD 6 4-5D = COS(LAT) B-1 TEMPORARILY
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LONG
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DMPR VDEF # PD 4 MPAC = COS(LONG)COS(LAT) B-2
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UNIT PUSH # 0-5D= UNIT RP FOR RP-TO-R SUBR.
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STCALL ALPHAV # ALPHAV +4= SINL FOR SETRE SUBR.
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SETRE # RE METERS B-29
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DLOAD BOFF # SET MPAC=0 FOR EARTH, NON-ZERO FOR MOON
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ZEROVEC
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LUNAFLAG
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CALLRPRT
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COS # USE COS(0) TO GET NON-ZERO IN MPAC
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CALLRPRT CALL
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RP-TO-R # EXIT WITH UNIT R VECTOR IN MPAC
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STODL ALPHAV
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ERADM
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# Page 1136
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DAD VXSC # (RE + ALT)(UNIT R) METERS B-30
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ALT
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ALPHAV
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VSL1 # R METERS B-29
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STCALL ALPHAV # EXIT WITH R IN METERS B-29
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INCORPEX
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# SUBROUTINE TO COMPUTE EARTH RADIUS
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#
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# INPUT
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# 1/2 SIN LAT IN ALPHAV +4
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#
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# OUTPUT
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# EARTH RADIUS IN ERADM AND MPAC (METERS B-29)
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GETERAD DLOAD DSQ
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ALPHAV +4 # SIN**2(L)
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SL1 BDSU
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DP1/2 # COS**2(L)
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DMPR BDSU
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EE
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DP1/2
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BDDV SQRT
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B2XSC
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SR4R
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STORE ERADM
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RVQ
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# THE FOLLOWING CONSTANTS WERE COMPUTED WITH A=6378166, B=6356784 METERS
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# B2XSC = B**2 SCALED B-51
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# B2/A2 = B**2/A**2 SCALED B-1
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# EE = (1-B**2/A**2) SCALED B-0
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B2XSC 2DEC .0179450689 # B**2 SCALED B-51
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DP1/2 = XUNIT
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B2/A2 2DEC .9933064884 B-1 # GAMMA= B**2/A**2 B-1
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EE 2DEC 6.6935116 E-3 # (1-B**2/A**2) B-0
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# Page 1137
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# ARCTAN SUBROUTINE
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#
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# CALLING SEQUENCE
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# SIN THETA IN SINTH B-1
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# COS THETA IN COSTH B-1
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# CALL ARCTAN
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#
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# OUTPUT
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# ARCTAN THETA IN MPAC AND THETA B-0 IN RANGE -1/2 TO +1/2
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ARCTAN BOV
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CLROVFLW
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CLROVFLW DLOAD DSQ
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SINTH
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PDDL DSQ
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COSTH
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DAD
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BZE SQRT
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ARCTANXX # ATAN=0/0 SET THETA=0
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BDDV BOV
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SINTH
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ATAN=90
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SR1 ASIN
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STORE THETA
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PDDL BMN
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COSTH
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NEGCOS
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DLOAD RVQ
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NEGCOS DLOAD DCOMP
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BPL DAD
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NEGOUT
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DP1/2
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ARCTANXX STORE THETA
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RVQ
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NEGOUT DSU GOTO
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DP1/2
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ARCTANXX
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ATAN=90 DLOAD SIGN
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LODP1/4
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SINTH
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STORE THETA
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RVQ
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2DZERO = DPZERO
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# Page 1138
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# ***** SETGAMMA SUBROUTINE *****
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# SUBROUTINE TO SET GAMMA FOR THE LAT-LONG AND LALOTORV SUBROUTINES
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#
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# GAMMA = B**2/A**2 FOR EARTH (B-1)
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# GAMMA = 1 FOR MOON (B-1)
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#
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# CALLING SEQUENCE
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# L CALL
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# L+1 SETGAMMA
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#
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# INPUT
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# LUNAFLAG=0 FOR EARTH, =1 FOR MOON
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#
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# OUTPUT
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# GAMMA IN GAMRP (B-1)
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SETGAMMA DLOAD BOFF # BRANCH FOR EARTH
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B2/A2 # EARTH GAMMA
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LUNAFLAG
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SETGMEX
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SLOAD
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1B1 # MOON GAMMA
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SETGMEX STORE GAMRP
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RVQ
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GAMRP = 8D
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# Page 1139
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# ***** SETRE SUBROUTINE *****
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# SUBROUTINE TO SET RE (EARTH OR MOON RADIUS)
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#
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# RE = RM FOR MOON
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# RE = RREF FOR FIXED EARTH RADIUS OR COMPUTED RF FOR FISCHER ELLIPSOID
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#
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# CALLING SEQUENCE
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# L CALL
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# L+1 SETRE
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#
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# SUBROUTINES USED
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# GETERAD
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#
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# INPUT
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# ERADFLAG = 0 FOR FIXED RE, 1 FOR COMPUTED RE
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# ALPHAV +4 = 1/2 SINL IF GETERAD IS CALLED
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# LUNAFLAG = 0 FOR EARTH, =1 FOR MOON
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#
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# OUTPUT
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# ERADM = 504RM FOR MOON (METERS B-29)
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# ERADM = ERAD OR COMPUTED RE FOR EARTH (METERS B-29)
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SETRE STQ DLOAD
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SETREX
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504RM
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BON DLOAD # BRANCH FOR MOON
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LUNAFLAG
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TSTRLSRM
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ERAD
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BOFF CALL # ERADFLAG=0 FOR FIXED RE, 1 FOR COMPUTED
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ERADFLAG
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SETRXX
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GETERAD
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SETRXX STCALL ERADM # EXIT WITH RE OR RM METERS B-29
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SETREX
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TSTRLSRM BON VLOAD # ERADFLAG=0, SET R0=RLS
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ERADFLAG # =1 R0=RM
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SETRXX
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RLS
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ABVAL SR2R # SCALE FROM B-27 TO B-29
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GOTO
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SETRXX
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SETREX = S2
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