LEM_GEOMETRY.agc

# Copyright:	Public domain.
# Filename:	LEM_GEOMETRY.agc
# Purpose: 	Part of the source code for Luminary 1A build 099.
#		It is part of the source code for the Lunar Module's (LM)
#		Apollo Guidance Computer (AGC), for Apollo 11.
# Assembler:	yaYUL
# Contact:	Ron Burkey <info@sandroid.org>.
# Website:	www.ibiblio.org/apollo.
# Pages:	320-325
# Mod history:	2009-05-16 RSB	Adapted from the corresponding
#				Luminary131 file, using page
#				images from Luminary 1A.
#
# This source code has been transcribed or otherwise adapted from
# digitized images of a hardcopy from the MIT Museum.  The digitization
# was performed by Paul Fjeld, and arranged for by Deborah Douglas of
# the Museum.  Many thanks to both.  The images (with suitable reduction
# in storage size and consequent reduction in image quality as well) are
# available online at www.ibiblio.org/apollo.  If for some reason you
# find that the images are illegible, contact me at info@sandroid.org
# about getting access to the (much) higher-quality images which Paul
# actually created.
#
# Notations on the hardcopy document read, in part:
#
#	Assemble revision 001 of AGC program LMY99 by NASA 2021112-061
#	16:27 JULY 14, 1969

# Page 320
		BANK	23
		SETLOC	LEMGEOM
		BANK

		SBANK=	LOWSUPER
		EBANK=	XSM

# THESE TWO ROUTINES COMPUTE THE ACTUAL STATE VECTOR FOR LM,CSM BY ADDING
# THE CONIC R,V AND THE DEVIATIONSR,V. THE STATE VECTORS ARE CONVERTED TO
# METERS B-29 AND METERS/CSEC B-7 AND STORED APPROPRIATELY IN RN,VN OR
# R-OTHER , V-OTHER FOR DOWNLINK. THE ROUTINES NAMES ARE SWITCHED IN THE
# OTHER VEHICLES COMPUTER.
#
# INPUT
#   STATE VECTOR IN TEMPORARY STORAGE AREA
#   IF STATE VECTOR IS SCALED POS B27 AND VEL B5
#      SET X2 TO +2
#   IF STATE VECTOR IS SCALED POS B29 AND VEL B7
#      SET X2 TO 0
#
# OUTPUT
#   R(T) IN RN, V(T) IN VN, T IN PIPTIME
# OR
#   R(T) IN R-OTHER, V(T) IN V-OTHER   (T IS DEFINED BY T-OTHER)

		COUNT*	$$/GEOM
SVDWN2		BOF	RVQ		# SW=1=AVETOMID DOING W-MATRIX INTEG.
			AVEMIDSW
			+1
		VLOAD	VSL*
			TDELTAV
			0 -7,2
		VAD	VSL*
			RCV
			0,2
		STOVL	RN
			TNUV
		VSL*	VAD
			0 -4,2
			VCV
		VSL*
			0,2
		STODL	VN
			TET
		STORE	PIPTIME
		RVQ
# Page 321
SVDWN1		VLOAD	VSL*
			TDELTAV
			0 -7,2
		VAD	VSL*
			RCV
			0,2
		STOVL	R-OTHER
			TNUV
		VSL*	VAD
			0 -4,2
			VCV
		VSL*
			0,2
		STORE	V-OTHER
		RVQ

# Page 322
#	   THE FOLLOWING ROUTINE TAKES A HALF UNIT TARGET VECTOR REFERRED TO NAV BASE COORDINATES AND FINDS BOTH
# GIMBAL ORIENTATIONS AT WHICH THE RR MIGHT SIGHT THE TARGET. THE GIMBAL ANGLES CORRESPONDING TO THE PRESENT MODE
# ARE LEFT IN MODEA AND THOSE WHICH WOULD BE USED AFTER A REMODE IN MODEB. THIS ROUTINE ASSUMES MODE 1 IS TRUNNION
# ANGLE LESS THAN 90 DEGS IN ABS VALUE WITH ARBITRARY SHAFT, WITH A CORRESPONDING DEFINITION FOR MODE 2. MODE
# SELECTION AND LIMIT CHECKING ARE DONE ELSEWHERE.
#
#	   THE MODE 1 CONFIGURATION IS CALCULATED FROM THE VECTOR AND THEN MODE 2 IS FOUND USING THE RELATIONS
#
#	   S(2) = 180 + S(1)
#	   T(2) = 180 - T(1)
#
#     THE VECTOR ARRIVES IN MPAC WHERE TRG*SMNB OR *SMNB* WILL HAVE LEFT IT.

RRANGLES	STORE	32D
		DLOAD	DCOMP		# SINCE WE WILL FIND THE MODE 1 SHAFT
			34D		# ANGLE LATER, WE CAN FIND THE MODE 1
		SETPD	ASIN		# TRUNNION BY SIMPLY TAKING THE ARCSIN OF
			0		# THE Y COMPONENT, THE ASIN GIVIN AN
		PUSH	BDSU		# ANSWER WHOSE ABS VAL IS LESS THAN 90 DEG
			LODPHALF
		STODL	4		# MODE 2 TRUNNION TO 4.

			LO6ZEROS
		STOVL	34D		# UNIT THE PROJECTION OF THE VECTOR
			32D		#   IN THE X-Z PLANE
		UNIT	BOVB		# IF OVERFLOW,TARGET VECTOR IS ALONG Y
			LUNDESCH	# CALL FOR MANEUVER UNLESS ON LUNAR SURF
		STODL	32D		# PROJECTION VECTOR.
			32D
		SR1	STQ
			S2
		STODL	SINTH		# USE ARCTRIG SINCE SHAFT COULD BE ARB.
			36D
		SR1
		STCALL	COSTH
			ARCTRIG
# Page 323
		PUSH	DAD		# MODE 1 SHAFT TO 2.
			LODPHALF
		STOVL	6
			4
		RTB			# FIND MODE 2 CDU ANGLES.
			2V1STO2S
		STOVL	MODEB
			0
		RTB			# MODE 1 ANGLES TO MODE A.
			2V1STO2S
		STORE	MODEA
		EXIT

		CS	RADMODES	# SWAP MODEA AND MODEB IF RR IN MODE 2.
		MASK	ANTENBIT
		CCS	A
		TCF	+4

		DXCH	MODEA
		DXCH	MODEB
		DXCH	MODEA

		TC	INTPRET
		GOTO
			S2
# Page 324
# GIVEN RR TRUNNION AND SHAFT (T,S) IN TANGNB,+1,FIND THE ASSOCIATED
# LINE OF SIGHT IN NAV BASE AXES.  THE HALF UNIT VECTOR, .5(SIN(S)COS(T),
# -SIN(T),COS(S)COS(T)) IS LEFT IN MPAC AND 32D.

		SETLOC	INFLIGHT
		BANK

		COUNT*	$$/GEOM

RRNB		SLOAD	RTB
			TANGNB
			CDULOGIC
		SETPD	PUSH		# TRUNNION ANGLE TO 0
			0
		SIN	DCOMP
		STODL	34D		# Y COMPONENT

		COS	PUSH		# .5 COS(T) TO 0
		SLOAD	RTB
			TANGNB +1
			CDULOGIC
RRNB1		PUSH	COS		# SHAFT ANGLE TO 2
		DMP	SL1
			0
		STODL	36D		# Z COMPONENT

		SIN	DMP
		SL1
		STOVL	32D
			32D
		RVQ

# THIS ENTRY TO RRNB REQUIRES THE TRUNNION AND SHAFT ANGLES IN MPAC AND MPAC +1 RESPECTIVELY

RRNBMPAC	STODL	20D		# SAVE SHAFT CDU IN 21.
			MPAC		# SET MODE TO DP.  (THE PRECEEDING STORE
					# MAY BE DP. TP OR VECTOR.)
		RTB	SETPD
			CDULOGIC
			0
		PUSH	SIN		# TRUNNION ANGLE TO 0
		DCOMP
		STODL	34D		# Y COMPONENT
		COS	PUSH		# .5COS(T) TO 0
		SLOAD	RTB		# PICK UP CDU'S.
			21D
			CDULOGIC
		GOTO
			RRNB1
# Page 325 (empty page)