### FILE="Main.annotation"
## Copyright:   Public domain.
## Filename:    LEM_GEOMETRY.agc
## Purpose:     A section of LUM69 revision 2.
##              It is part of the reconstructed source code for the flown
##              version of the flight software for the Lunar Module's (LM)
##              Apollo Guidance Computer (AGC) for Apollo 10. The code has
##              been recreated from a copy of Luminary revsion 069, using
##              changes present in Luminary 099 which were described in
##              Luminary memos 75 and 78. The code has been adapted such
##              that the resulting bugger words exactly match those specified
##              for LUM69 revision 2 in NASA drawing 2021152B, which gives
##              relatively high confidence that the reconstruction is correct.
## Reference:   pp. 334-338
## Assembler:   yaYUL
## Contact:     Ron Burkey <info@sandroid.org>.
## Website:     www.ibiblio.org/apollo/index.html
## Mod history: 2019-07-27 MAS  Created from Luminary 69.
##              2021-05-30 ABS  Replaced use of ANTENBIT with BIT12 to match
##                              Luminary 69.

## Page 334
		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 335
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 336
#          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*SMNG 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 GIVING 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 337
		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	BIT12
		CCS	A
		TCF	+4
		
		DXCH	MODEA
		DXCH	MODEB
		DXCH	MODEA
		
		TC	INTPRET
		GOTO
			S2
## Page 338
# 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
		PUSH	COS		# SHAFT ANGLE TO 2
		DMP	SL1
			0
		STODL	36D		# Z COMPONENT
		
		SIN	DMP
		SL1
		STOVL	32D
			32D
		RVQ