LUNAR_AND_SOLAR_EPHEMERIDES_SUBROUTINES.agc
### FILE="Main.annotation"
## Copyright: Public domain.
## Filename: LUNAR_AND_SOLAR_EPHEMERIDES_SUBROUTINES.agc
## Purpose: A section of Luminary revision 116.
## It is part of the source code for the Lunar Module's (LM)
## Apollo Guidance Computer (AGC) for Apollo 12.
## This file is intended to be a faithful transcription, except
## that the code format has been changed to conform to the
## requirements of the yaYUL assembler rather than the
## original YUL assembler.
## Reference: pp. 976-979
## Assembler: yaYUL
## Contact: Ron Burkey <info@sandroid.org>.
## Website: www.ibiblio.org/apollo/index.html
## Mod history: 2017-01-22 MAS Created from Luminary 99.
## 2017-01-31 RRB Updated for Luminary 116.
## 2017-03-13 RSB Proofed comment text via 3-way diff vs
## Luminary 99 and 131.
## 2017-08-26 MAS Fixed comment-text errors found while transcribing Zerlina 56.
## Page 984
# NAME - LSPOS - LOCATE SUN AND MOON DATE - 25 OCT 67
# MOD NO. 1
# MOD BY NEVILLE ASSEMBLY SUNDANCE
# FUNCTIONAL DESCRIPTION
# COMPUTES UNIT POSITION VECTOR OF THE SUN AND MOON IN THE BASIC REFERENCE SYSTEM. THE SUN VECTOR S IS
# LOCATED VIA TWO ANGLES. THE FIRST ANGLE(OBLIQUITY) IS THE ANGLE BETWEEN THE EARTH EQUATOR AND THE ECLIPTIC. THE
# SECOND ANGLE IS THE LONGITUDE OF THE SUN MEASURED IN THE ECLIPTIC.
# THE POSITION VECTOR OF THE SUN IS
# -
# S = (COS(LOS), COS(OBL)*SIN(LOS), SIN(OBL)*SIN(LOS)), WHERE
# LOS = LOS +LOS *T-(C *SIN(2PI*T)/365.24 +C *COS(2PI*T)/365.24)
# 0 R 0 1
# LOS (RAD) IS THE LONGITUDE OF THE SUN FOR MIDNIGHT JUNE 30TH OF THE PARTICULAR YEAR.
# 0
# LOS (RAD/DAY) IS THE MEAN RATE FOR THE PARTICULAR YEAR.
# R
# LOS AND LOS ARE STORED AS LOSC AND LOSR IN RATESP.
# 0 R
# COS(OBL) AND SIN(OBL) ARE STORED IN THE MATRIX KONMAT.
# T, TIME MEASURED IN DAYS (24 HOURS), IS STORED IN TIMEP.
# C AND C ARE FUDGE FACTORS TO MINIMIZE THE DEVIATION. THEY ARE STORED AS ONE CONSTANT (CMOD), SINCE
# 0 1 2 2 1/2
# C *SIN(X)+C *COS(X) CAN BE WRITTEN AS (C +C ) *SIN(X+PHI), WHERE PHI=ARCTAN(C /C ).
# 0 1 0 1 1 0
# THE MOON IS LOCATED VIA FOUR ANGLES. THE FIRST IS THE OBLIQUITY. THE SECOND IS THE MEAN LONGITUDE OF THE MOON,
# MEASURED IN THE ECLIPTIC FROM THE MEAN EQUINOX TO THE MEAN ASCENDING NODE OF THE LUNAR ORBIT, AND THEN ALONG THE
# ORBIT. THE THIRD ANGLE IS THE ANGLE BETWEEN THE ECLIPTIC AND THE LUNAR ORBIT. THE FOURTH ANGLE IS THE LONGITUDE
# OF THE NODE OF THE MOON, MEASURED IN THE LUNAR ORBIT. LET THESE ANGLES BE OBL,LOM,IM, AND LON RESPECTIVELY.
# THE SIMPLIFIED POSITION VECTOR OF THE MOON IS
# -
# M=(COS(LOM), COS(OBL)*SIN(LOM)-SIN(OBL)*SIN(IM)*SIN(LOM-LON), SIN(OBL)*SIN(LOM)+COS(OBL)*SIN(IM)*SIN(LOM-LON))
# WHERE
# LOM=LOM +LOM *T-(A *SIN 2PI*T/27.5545+A *COS(2PI*T/27.5545)+B *SIN 2PI*T/32+B *COS(2PI*T/32)), AND
# 0 R 0 1 0 1
# LON=LON +LON
# 0 R
# A , A , B AND B ARE STORED AS AMOD AND BMOD (SEE DESCRIPTION OF CMOD, ABOVE). COS(OBL), SIN(OBL)*SIN(IM),
# 0 1 0 1
# SIN(OBL), AND COS(OBL)*SIN(IM) ARE STORED IN KONMAT AS K1, K2, K3 AND K4, RESPECTIVELY. LOM , LOM , LON , LON
# ARE STORED AS LOMO, LOMR, LONO, AND LONR IN RATESP. 0 R 0 R
# THE THREE PHIS ARE STORED AS AARG, BARG, AND CARG(SUN). ALL CONSTANTS ARE UPDATED BY YEAR.
# CALLING SEQUENCE
## Page 977
# CALL LSPOS. RETURN IS VIA CPRET.
# ALARMS OR ABORTS
# NONE
# ERASABLE INITIALIZATION REQUIRED
# TEPHEM - TIME FROM MIDNIGHT 1 JULY PRECEDING THE LAUNCH TO THE TIME OF THE LAUNCH (WHEN THE AGC CLOCK WENT
# TO ZERO). TEPHEM IS TP WITH UNITS OF CENTI-SECONDS.
# TIME2 AND TIME1 ARE IN MPAC AND MPAC +1 WHEN PROGRAM IS CALLED.
# OUTPUT
# UNIT POSITIONAL VECTOR OF SUN IN VSUN. (SCALED B-1)
# UNIT POSITIONAL VECTOR OF MOON IN VMOON. (SCALED B-1)
# SUBROUTINES USED
# NONE
# DEBRIS
# CURRENT CORE SET, WORK AREA AND FREEFLAG
BANK 04
SETLOC EPHEM
BANK
EBANK= VSUN
COUNT* $$/EPHEM
LUNPOS EQUALS LSPOS
LSPOS SETPD SR
0
14D # TP
TAD DDV
TEPHEM # TIME OF LAUNCH
CSTODAY # 24 HOURS-8640000 CENTI-SECS/DAY B-33
STORE TIMEP # T IN DAYS
AXT,1 AXT,2
0
0
CLEAR
FREEFLAG # SWITCH BIT
POSITA DLOAD
KONMAT +2 # ZEROS
STORE GTMP
POSITB DLOAD DMP*
TIMEP # T
VAL67 +4,1 # 1/27 OR 1/32 OR 1/365
## Page 978
SL DAD*
8D
VAL67 +2,1 # AARG
SIN DMP* # SIN(T/27+PHI) OR T/32 OR T/365
VAL67,1 # (A0**2+A1**2)**1/2 SIN(X+PHIA)
DAD INCR,1 # PLUS
GTMP # (B0**2+B1**2)**1/2 SIN(X+PHIB)
DEC -6
STORE GTMP # OR (C0**2+C1**2)**1/2 SIN(X+PHIC)
BOFSET
FREEFLAG
POSITB
POSITD DLOAD DMP*
TIMEP # T
RATESP,2 # LOMR,LOSR,LONR
SL DAD*
5D
RATESP +6,2 # LOMO,LOSO,LONO
DSU
GTMP
STORE STMP,2 # LOM,LOS,LON
SLOAD INCR,2
X2
DEC -2
DAD BZE
RCB-13 # PLUS 2
POSITE # 2ND
BPL
POSITA # 1ST
POSITF DLOAD DSU # 3RD
STMP # LOM
STMP +4 # LON
SIN PDDL # SIN(LOM-LON)
STMP
SIN PDDL # SIN LOM
STMP
COS VDEF # COS LOM
MXV UNIT
KONMAT # K1,K2,K3,K4,
STORE VMOON
DLOAD PDDL
KONMAT +2 # ZERO
STMP +2
SIN PDDL # SIN LOS
STMP +2
COS VDEF # COS LOS
MXV UNIT
KONMAT
STORE VSUN
RVQ
## Page 979
POSITE DLOAD
KONMAT +2 # ZEROS
STORE GTMP
GOTO
POSITD
SETLOC EPHEM1
BANK
COUNT* $$/EPHEM
STMP EQUALS 16D
GTMP EQUALS 22D
TIMEP EQUALS 24D
