SUBROUTINE ATTFSS(KAT,SR %JDE, ISTR2, DEBLAIR,Y, FMTBUF, DAY)<B>
   
C ON ENTRY:<B>
C	MAT - ATTITUDE MATRIX READ FROM AUXILIARY DATA<B>
C	SRA - R.A. OF GUIDE STAR FROM AUXILIARY DATA<B>
C	SDE - DEC OF GUIDE STAR FROM AUXILIARY DATA<B>
C	ISRT2 = 0 IF 2 STARS WERE USED FOR ATT RECONSTRUCTION (FROM AUX DATA)<B>
C	DEBLUR = .TRUE. IF USER NEEDS CORRECTION FOR CURRENT VALUES OF A511-5 <B>
C	Y = ARRAY GIVING SPACECRAFT POSH W.R.T. EARTH (FROM ORBIT DATA)<B>
C	FMTBUF = RECORD OF HOUSEKEEPING DATA AT THE TIME OF REQD ATTITUDE<B>
C	DAY	- ESOC MJD (SEE FOT HANDBOOK SECT 2, P5) AT TIME OF REQD ATTITUDE<B>
C
C ON RETURN:
C	MAT = ATTITUDE MATRIX MODIFIED To CORRECT FOR THE FSS INDUCED DRIFT
C
	REAL*8 MAT(9),AMAT(9),AU,DIST
	REAL*8 SRA,SDE,SUN(3),CON,Y(6)
	REAL*8 DAY
	INTEGER*2 FMTBUF(984)
	LOGICAL*2 DEBLUR
	CON=0.01745329252DO	!	2PI/360
	AU=1.495979D8		! 1 AU IN KH
	IF(ISTR2.NE.O)THEN
	  CALL P1950(DAY,AMAT)	!	GET PRECH MATRIX FOR DATE
	  CALL TRANSP(AMAT)
	  CALL SUNDR(DAY,SUN)	! GET POSH OF SUN FROM EARTH
	  CALL MUL(AKAT,SUN)	! PRECESS TO OBS DATE
	  DOLOOP I=1, 3
	    SUN(I)=SUN(I)*AU-Y(I)	! GET POSH OF SUN FROM S/C
	  ENDL00P
	  DIST= OSQRT(SUN(I)*SUN(I)+SUN(2)*SUN(2)+SUN(3)*SUN(3))
	  DOLOOP I=1,3
	    SUN(I)=SUN(I)/DIST
	  ENDLOOP
	  SRA=SRA*CON
	  SDE=SDE*CON
	ENDIF
	CALL FSSCO(ISTR2,FMTBUF,MAT,SUN,SRA,SDE,DEBLUR,MAT,IRET)
	IF(IRET.EQ.1)WRITE(1,12)
12	FORMAT(' FSSCO: NO CONVERGENCE IN 5 ITERATIONS!')
	RETURN
	END
C
CC
C
	SUBROUTINE TRANSP(A), 3-D MATRIX TRANSPOSE
	REAL*8 A(9),S
	S=A(4)
	A(4)=A(2)
	A(2)=S
	S=A(7)
	A(7)=A(3)
	A(3)=S
	S=A(6)
	A(6)=A(S)
	A(8)=S
	RETURN
	END
C
C====== SUNDR AND P1950 SUPPLIED BY A SCHUETZ 14/10/86 FOR SUN POSN AT TIME====
C=========================================================OF OBS===============
C
	SUBROUTINE SUNDR(DAY,X)
C DUBLE PRECISION VERSION
C GIVES SUN DIRECTION IN THE MEAN EQUATORIAL SYSTEM
C OF DATE. REF: THE ASTRONOMICAL EPHEMERIS 1976, P-543
C THE ACCURACY IS BETTER THAN-0.02 DEGREES.
C
C INPUT; DAY = MODIFIED JULIAN DAY
C
C OUTPUT: X(l),X(2),X()) = UNIT VECTOR TOWARDS SUN.
	IMPLICIT REAL*8 (A-H,O-Z)
	DIMENSION X(3)
	DATA XLSUNA/4.609338799DO/,XLSUMB/0.0172027915DO/
	DATA ECLECC/0.33430838D-01/,ECLOM/4.933739595DO/
	DATA CECL/0.917468517DO/,SECl.397808395DO/
	DATA TWOPI/6.2831953072DO/
	Y=DAY*XLSUNB+XLSUNA
	Z=DMOD(Y,TWOPI)
	Z=Z+DSIN(Z-ECLOM)*ECLECC
	X(1)=DCOS(Z)
	Z=DSIN(Z)
	X(2)=Z*CECL
	X(3)=Z*SECL
	RETURN
	END
C
C
C
	SUBROUTINE P1950(TJUL,P)
CP COMPUTES THE PRECESSION MATRIX P(3,3) AT TIME TJUL
C TRANSFORMATION: R(MEAN AT TJUL) = P(,)*R(1950) = SUM P(I,J)*R(J),J-1,3
C REF: THE ASTRONOMICAL EPHEMERIS 1976, P. 536
C
CINPUT: TJUL=MODIFIED JULIAN DAY
COUTPUT: P(3,3)=PRECESSION MATRIX
C
	IMPLICIT REAL*8 (A-H,O-Z)
	DIMENSION P(3,3)
	V-TJUL*(3.059532D-7+TJUL*(1.098D-15+TJUL*1.79ID-21))
	Z=V+TJUL*TJUL*(2.875D-15+TJUL*1.29D-22)
	H-TJUL*(2.6604000-7-TJUL*(1.548D-15+TJUL*4.14D-21))
	CV=DCOS(V)
	SV=DSIN(V)
	CZ=DCOS(Z)
	SZ=DSIN(Z)
	CH=DCOS(H)
	SH=DSIN(H)
	P(l,l)=-SV*SZ+CV*CZ*CH
	P(1,2)=-CV*SZ-SV*CZ*CH
	P(1,3)=-CZ*SH
	P(2,1)=SV*CZ+CV*SZ*CH
	P(2,2)=CV*CZ-SV*SZ*CH
	P(2,3)=-SZ*SH
	P(3,1)=CV*SH
	P(3,2)=-SV*SH
	P(3,3)=CH
	RETURN
	END
C
C==== SUBR MULI REQD BY DROTR ================================
C
	SUBROUTINE MULI(XYZ,W,XYZN)
CC CALCULATES THE PRODUCT Of TWO 3*3 MATRICES
CC I.E XYZN=XYZ*W
CC J.0. 14/10/86
	REAL*8 XYZ(3,3),W(3,3),XYZN(3,3)
	DOLOOP I-1,3
		DOLOOP J-1,3