GROUND_TRACKING_DETERMINATION_PROGRAM_-_P21.agc
### FILE="Main.annotation"
## Copyright: Public domain.
## Filename: GROUND_TRACKING_DETERMINATION_PROGRAM_-_P21.agc
## Purpose: Part of the source code for Artemis (i.e., Colossus 3),
## build 072. This is for the Command Module's (CM)
## Apollo Guidance Computer (AGC), for
## Apollo 15-17.
## Assembler: yaYUL
## Contact: Sergio Navarro <sergionavarrog@gmail.com>
## Website: www.ibiblio.org/apollo/index.html
## Page Scans: www.ibiblio.org/apollo/ScansForConversion/Artemis072/
## Mod history: 2009-08-19 SN Adapted from corresponding Comanche 055 file.
## 2009-09-03 JL Fixed symbol names.
## 2009-09-04 JL Fixed a bunch of typos.
## 2009-09-05 JL Fixed typos.
## 2010-01-31 JL Fixed build errors.
## 2010-02-20 RSB Un-##'d this header.
## 2017-02-05 RSB Proofed comment text by diff'ing vs Comanche 55
## and fixed errors found.
## Page 455
# GROUND TRACKING DETERMINATION PROGRAM P21
#
# PROGRAM DESCRIPTION
# MOD NO - 1
# MOD BY - N. M. NEVILLE
#
# FUNCTIONAL DECRIPTION-
#
# TO PROVIDE THE ASTRONAUT DETAILS OF THE LM OR CSM GROUND TRACK WITHOUT
# THE NEED FOR GROUND COMMUNICATION (REQUESTED BY DSKY).
#
# CALLING SEQUENCE -
#
# ASTRONAUT REQUEST THROUGH DSKY V37E21E
#
# SUBROUTINES CALLED-
#
# GOPERF4
# GOFLASH
# THISPREC
# OTHPREC
# LAT-LONG
#
# NORMAL EXIT MODES-
#
# ASTRONAUT REQUEST TROUGH DSKY TO TERMINATE PROGRAM V34E
#
# ALARM OR ABORT EXIT MODES-
#
# NONE
#
# OUTPUT -
#
# OCTAL DISPLAY OF OPTION CODE AND VEHICLE WHOSE GROUND TRACK IS TO BE
# COMPUTED
# OPTION CODE 00002
# THIS 00001
# OTHER 00002
# DECIMAL DISPLAY OF TIME TO BE INTEGRATED TO HOURS , MINUTES , SECONDS
# DECIMAL DISPLAY OF LAT,LONG,ALT
#
# ERASABLE INITIALIZATION REQUIRED
#
# AX0 2DEC 4.652459653 E-5 RADIANS %68-69 CONSTANTS"
#
# -AY0 2DEC 2.147535898 E-5 RADIANS
#
# AZ0 2DEC .7753206164 REVOLUTIONS
#
# FOR LUNAR ORBITS 504LM VECTOR IS NEEDED
#
# 504LM 2DEC -2.700340600 E-5 RADIANS
#
# 504LM _2 2DEC -7.514128400 E-4 RADIANS
#
# 504LM _4 2DEC _2.553198641 E-4 RADIANS
#
# NONE
#
# DEBRIS
#
## Page 456
# CENTRALS - A,Q,L
# OTHER - THOSE USED BY THE ABOVE LISTED SUBROUTINES
# SEE LEMPREC,LAT-LONG
SBANK= LOWSUPER # FOR LOW 2CADR'S.
SETLOC P20S
BANK
EBANK= P21TIME
COUNT* $$/P21
PROG21 CAF ONE
TS OPTION2 # ASSUMED VEHICLE IS LM, R2 = 00001
TC UPFLAG
ADRES TRACKFLG
CAF BIT2 # OPTION 2
TC BANKCALL
CADR GOPERF4
TC GOTOPOOH # TERMINATE
TC +2 # PROCEED VALUE OF ASSUMED VEHICLE OK
TC -5 # R2 LOADED THROUGH DSKY
CAF ZERO # ZERO DSPTEM
TS DSPTEM1
TS DSPTEM1 +1
P21PROG1 CAF V6N34 # LOAD DESIRED TIME OF LAT-LONG.
TC VNFLASH
TC INTPRET
DLOAD BZE
DSPTEM1
P21PRTM # SET TO INTEG TO PRES TIME
P21PROG2 STCALL TDEC1 # INTEG TO TIME SPECIFIED IN TDEC
INTSTALL
BON SET
P21FLAG
P21CONT # ON...RECYCLE USING BASE VECTOR
VINTFLAG # OFF..1ST PASS CALC BASE VECTOR
SLOAD SR1
OPTION2
BHIZ CLEAR
+2 # ZERO..THIS VEHICLE (CM)
VINTFLAG # ONE...OTHER VEHICLE(LM)
CLEAR CLEAR
DIM0FLAG
INTYPFLG # PRECISION
CALL
INTEGRV # CALCULATE
GOTO # .AND
P21VSAVE # ..SAVE BASE VECTOR
P21CONT VLOAD # RECYCLE..INTEG FROM BASE VECTOR
## Page 457
P21BASER
STOVL RCV # ..POS
P21BASEV
STODL VCV # ..VEL
P21TIME
STORE TET # ..TIME
CLEAR CLEAR
DIM0FLAG
MOONFLAG
SLOAD BZE
P21ORIG
+3 # ZERO = EARTH
SET # ...2 = MOON
MOONFLAG
CALL
INTEGRVS
P21VSAVE DLOAD # SAVE CURRENT BASE VECTOR
TAT
STOVL P21TIME # ..TIME
RATT1
STOVL P21BASER # ..POS B-29 OR B-27
VATT1
STORE P21BASEV # ..VEL B-7 OR B-5
BONCLR # WITH ADJUSTED P29 BASE TIME, SKIP
NEWTFLAG # P29 DISPLAYS
HOP29DSP
BOFF RTB # RETURN TO P29 IF P29FLAG IS SET
P29FLAG
+2
LONGPASS
ABVAL SL*
0,2
STOVL P21VEL # /VEL/ FOR N73 DSP
RATT
UNIT DOT
VATT # U(R).(V)
DDV ASIN # U(R).U(V)
P21VEL
STORE P21GAM # SIN-1 U(R).U(V), -90 TO +90
SXA,2 SET
P21ORIG # 0 = EARTH 2 = MOON
P21FLAG
P21DSP CLEAR SLOAD # GENERATE DISPLAY DATA
LUNAFLAG
X2
BZE SET
+2 # 0 = EARTH
LUNAFLAG
VLOAD
RATT
## Page 458
STODL ALPHAV
TAT
CLEAR CALL
ERADFLAG
LAT-LONG
DMP # MPAC = ALT, METERS B-29
K.01
STORE P21ALT # ALT/100 FOR N73 DSP
EXIT
CAF V06N43 # DISPLAY LAT,LONG,ALT
TC BANKCALL # LAT,LONG = REVS B0 BOTH EARTH/MOON
CADR GOFLASH # ALT = METERS B-29 BOTH EARTH/MOON
TC GOTOPOOH # TERM
TC GOTOPOOH
TC INTPRET # V32E RECYCLE
DLOAD DAD
P21TIME
600SEC # 600 SECONDS OR 10 MIN
STORE DSPTEM1
RTB
P21PROG1
P21PRTM RTB GOTO
LOADTIME
P21PROG2
600SEC 2DEC 60000 # 10 MIN
P21ONENN OCT 00001 # NEEDED TO DETERMINE VEHICLE
OCT 00000 # TO BE INTEGRATED
V06N43 VN 00643
V6N34 = V06N34
K.01 2DEC .01
SETLOC P29TAG1
BANK
COUNT* $$/P29
EBANK= LONGFOR
P29 TC INTPRET # TIME-TO-LONGITUDE PROGRAM
SET RTB # SET=P29,CLEARED=P21--CHECKED IN P21
P29FLAG # FLAG ALSO MARKS FIRST PASS THRU P29
PROG21 # GET BASE TIME + STATE VECTOR FROM P21
LONGPASS CAF V06N43LP
TC VNFLASHR # ASTRONAUT LOADS DESIRED LONGITUDE
TCF +4
CAF FIVE # BLANK R1,R3
TC BLANKET
TC ENDOFJOB
DXCH LONG
DXCH LONGFOR # STORE DESIRED LONGITUDE
## Page 459
TC INTPRET
HOP29DSP VLOAD PDDL # STORE UNIT NORTH(IN PLANETARY COORDS )
UNITZ # AND BASE TIME ON PUSHLIST FOR
P29BASET # RP-TO-R
STORE PASSTIME # INITIALIZE TIME OF CROSSING
PDDL SET
ZEROVECS
P29FLAG # IN CASE OF RESTART OR REPEAT INTEGRATION
STORE DELTLONG # INITIALIZE LONGITUDE DIFFERENCE TO ZERO
CLEAR BOFF
LUNAFLAG
CMOONFLG
+4
SET DLOAD
LUNAFLAG # SET LUNAFLAG=CMOONFLG FOR LAT-LONG
FMOON # MPAC NONZERO FOR MOON, ZERO FOR EARTH
CALL # GET UNIT PLANETARY NORTH IN BASE COORDS.
RP-TO-R
PUSH PUSH # PD=12D,MUSUBZ(UNIT PLANETARY NORTH)
VXV UNIT
P29BASER
STOVL MUSUBE # PD=6D,MUSUBE=UNIT LOCAL EAST AT P29BASER
VXV UNIT
MUSUBE
STOVL MUSUBC # UNIT EQUATORIAL CENTRAL-DIRECTED VECTOR
P29BASER
VXV UNIT # FORM MUSUBN(UNIT ORBITAL LOCAL NORTH)
P29BASEV
PUSH PUSH # PD=18D
VXV UNIT
P29BASER
STOVL MUSUBS # PD=12D,MUSUBS=UNIT ORBITAL TANG. VEL.
DOT PDVL # PD=8D,MUSUBZ AT 0D, EXCHANGE DOT-PRODUCT
0D # WITH MUSUBN IN PUSHLIST
SIGN STADR # PD=6D, PUT MUSUBN IN HEMI. OF MUSUBZ
STOVL MUSUBN
P29BASER
HOPALONG BOFF VSR2 # MUST BE B+29 FOR LAT-LONG
CMOONFLG
+1
STODL ALPHAV # STORE FOR LAT-LONG
PASSTIME
CLEAR CALL # FIND LONGITUDE FOR PRESENT ITERATION OF
ERADFLAG # POSITION VECTOR
LAT-LONG
DLOAD DSU # COMPARE WITH DESIRED LONGITUDE
LONGFOR
LONG
PUSH ABS # PD=2D, SAVE DELTA
DSU BMN # IF WITHIN EPSILONG, DISPLAY RESULTS
## Page 460
EPSILONG # .01 DEGREES
PASSOUT
BOV # CLEAR OVERFLOW INDICATOR
+1
DAD BOV # CHECK WHETHER WITHIN EPSILON OF 360 DEG.
TWICEEPS # .02 DEGREES
PASSOUT
BOFCLR DLOAD # P29FLAG CLEARED FOR LATER PASSES
P29FLAG # PD=0D
MODULO
BPL DAD # MAKE DELTA>0
+2
DPPOSMAX
BOFF DSU # FOR EARTH,DELTA>0
CMOONFLG # FOR MOON, DELTA.0
HOP1
DPPOSMAX
PDDL GOTO # PD=2D
FMOON # 327.8/328.8, 8+1
HOP2
SETLOC P29TAG2
BANK
COUNT* $$/P29
HOP1 PDDL # PD=2D
FEARTH # 16/15, B+1
HOP2 STORE FUDGE
DELTLOAD DLOAD # PD=0D, LOAD DELTA
THETCOMP DMP BOV
FUDGE
+1 # CLEAR OVERFLOW INDICATOR
SL1 DAD # SHIFT TO GET B0, SINCE FUDGE IS B+1
DELTLONG
PUSH BOV # PD=2D, IF FUDGE FACTOR MAKES DELTLONG>
ADDTEN # 360, MODIFY BASE TIME
STORE DELTLONG # CUMULATIVE EQUATORIAL DELTA
COS VXSC
MUSUBE
PDDL SIN # PD=6D
VXSC VAD # PD=0D
MUSUBC # ROTATE MUSUBE THRU ANGLE DELTLONG
VXV UNIT # FORM MUSUBD=ROTATED ORBITAL UNIT
MUSUBN # POSITION VECTOR, OUTWARD-DIRECTED
PUSH PDVL # PD=12D
P29BASER
UNIT DOT # PD=6D, DOT PRODUCT IS B+2
SL1 PDVL # PD=2D, MAKE B+1 FOR ACOS, EXCHANGE
DOT PDDL # PD=2D, EXCHANGE WITH PUSHLIST
MUSUBS
ACOS SIGN # PD=0D
## Page 461
PUSH SIN # PD=2D, FORM THETA=ORBITAL DELTA
STODL SNTH # PD=0D
COS AXC,1
2D
STOVL CSTH # STORE ANGLE DATA AND BASE STATE VECTOR
P29BASER # FOR TIME-THETA
STOVL RVEC
P29BASEV
STORE VVEC
BOFF AXC,1 # SET X1=-2D FOR EARTH, -10D FOR MOON
CMOONFLG
+2
10D
CLEAR CALL # INTEGRATE BASE STATE VECTOR THRU THETA
RVSW
TIMETHET
DLOAD DAD
T # T=TIME TO TRAVERSE THETA
P29BASET
STOVL PASSTIME # TIME OF LONGITUDE CROSSING
GOTO # UPDATED POSITION VECTOR LOADED FOR
HOPALONG # LAT-LONG
MODULO DSU BMN # MPAC CONTAINS ABS(DELTA)+EPSILONG
DPHALF # IF THIS IS NEAR 360, MUST ADJUST DELTA
DELTLOAD # BY 360 TO GET ANGLE NEAR ZERO
DSU # TO ADJUST, SUBTRACT DPHALF (TWICE) AND
EPSILONG # EPSILONG TO GET NEGATIVE NUMBER,
DSU SIGN # AND SIGN BY UNADJUSTED DIFFERENCE,
DPHALF # AT TOP OF PUSHLIST, PD=0D.
GOTO
THETCOMP
ADDTEN DLOAD DAD # ADD 10 MINUTES TO BASE TIME
P29BASET
600SEC
SET GOTO # SET FLAG TO SKIP DISPLAYS ON RETURN TO
NEWTFLAG # P29
P21PROG2 # GO TO P21 FOR INTEGRATION
SETLOC P29TAG1
BANK
COUNT* $$/P29
PASSOUT EXIT
DXCH PASSTIME
DXCH DSPTEM1
CAF V06N34LP
TC BANKCALL
CADR GOFLASH # DISPLAY PASSTIME
TC GOTOPOOH
TC +2
TC LONGPASS # RECYCLE TO LONGITUDE INPUT
## Page 462
CAF V06N43LP
TC BANKCALL # DISPLAY LAT,LONG,ALT AT DESIRED
CADR GOFLASH # LONGITUDE
TC GOTOPOOH
TC GOTOPOOH
TC P29 # RECYCLE TO START OF PROGRAM
EPSILONG 2DEC .2777778E-04 # .01 DEGREES
TWICEEPS 2DEC .5555556E-04 # .02 DEGREES
FEARTH 2DEC 1.06666667 B-01 # 16/15
FMOON 2DEC .996958637 B-01 # 327.8/328.8
V06N34LP VN 0634
V06N43LP VN 0643
