FUNCTION HOSOrbit, T, hos=HosIn, degrees=Degrees, quick=quick

;+
; NAME:
;	HOSOrbit
; PURPOSE:
;	Calculates the position of a Helios spacecraft at a given time
; CATEGORY:
;	smei/gen/idl/ephem
; CALLING SEQUENCE:
;	R = HOSOrbit(T,hos=Hos [,/degrees])
; INPUTS:
;	T			array; type: integer or standard time structure
;					times (UT)
;	hos=Hos		scalar; type: integer; default: 1
;					spacecraft (1=Helios A; 2=Helios B)
; OPTIONAL INPUT PARAMETERS:
;	/degrees	if set all angles are returned in degrees	
; OUTPUTS:
;	R			array[3,*]; type: float
;					longitude, latitude, distance
;					(longitude and latitude for Equinox 1975.0 ???)
; INCLUDE:
	@compile_opt.pro		; On error, return to caller
; CALLS:
;	KeplerOrbit, SuperArray, SyncArgs, TimeGet, ToDegrees
; PROCEDURE:
;	The spacecraft orbit is assumed to lie in the ecliptic
;	See O. Montenbruck, Practical Ephemeris Calculations, p. 42-45
;	Perihelion passages for Helios A:
;
;	year       doy           JD               ecl long perih
;
;	1975      74.38411   2442486.8841             257.8521    !
;	1975     264.5102       2677.0102                .8493    !
;	1976      89.6610       2867.1610                .8570    !
;	1976     279.7965       3057.2965                .8478    !
;	1977     103.9367       3247.4367                .8448    !
;	1977     294.0973       3437.5973                .8496    !
;	1978     119.2591       3627.7591                .8517    !
;	1978     309.4239       3817.9239                .8518    !
;	1979     134.5879       4008.0879                .8530    !
;	1979
;	1980     149.9095       4388.4095                .8465    !
;	1980     340.2279       4578.7279                .8542    !
;	1981     164.978        4768.729              257.978
;	1981
;	1982
;	1982
;	1983
;	1983
;
;	Perihelion passages for Helios B:
;
;	1976     108.1035    2442885.6035             294.2079     !
;	1976     293.7552       3071.2552             294.2007     !
;	1977     113.5434       3257.0434             294.2332     !
;	1977     299.3565       3442.8565             294.2353     !
;	1978     120.2137       3628.7137             294.2470     !
;	1978     306.0831       3814.5831             294.2528     !
;	1979     126.9678       4000.4678             294.2577     !
;	1979     312.8478       4186.3478             294.2553     !
; MODIFICATION HISTORY:
;	1990, Paul Hick (UCSD)
;	1997, Paul Hick (UCSD), replaced explicit orbit calculation by call to KeplerOrbit
;	SEP-1999, Paul Hick (UCSD/CASS; pphick@ucsd.edu)
;		added option to set the first argument Yr to a standard time structure
;-

dpm	= ToDegrees(degrees=Degrees)
Hos	= HosIn-1

aa	= [0.6471445,0.6372573]				; Semi-major axes (AU)
ee	= [0.521757 ,0.543814 ]				; Eccentricities
pl	= [  257.85 ,   294.23]/dpm
pt	= [3247.4367d0,3442.8565d0]-11545L

if keyword_set(Quick) then		$
	return, KeplerOrbit(T, degrees=Degrees, elements=[aa[Hos], ee[Hos], pl[Hos], pt[Hos]])
										; Perihelion longitudes
pl	= [ [ 257.8521d0, 257.8493d0, 257.8570d0, 257.8478d0, 257.8448d0, 257.8496d0,	$
			  257.8517d0, 257.8518d0, 257.8530d0, 257.8465d0, 257.8542d0, 257.9780d0],	$
			[ 294.2079d0, 294.2007d0, 294.2332d0, 294.2353d0, 294.2470d0, 294.2528d0,	$
			  294.2577d0, 294.2553d0, 0d0,0d0,0d0,0d0] ]/dpm
										; Times of perihelion passage
pt	= [ [2486.8841d0,2677.0120d0,2867.1610d0,3057.2965d0,3247.4367d0,3437.5973d0,	$
			 3627.7591d0,3817.9239d0,4008.0879d0,4388.4095d0,4578.7279d0,4768.7290d0],	$
			[2885.6035d0,3071.2552d0,3257.0434d0,3442.8565d0,3628.7137d0,3814.5831d0,	$
			 4000.4678d0,4186.3478d0, 0d0,0d0,0d0,0d0] ]
pt	= pt-11545L							; Days since 2000 Jan 1.5
										; 11545 = 2451545-2440000
nP	= n_elements( where( pt[*,Hos] ne 0d0 ) )

JD = TimeGet(T, /njd, /scalar)

Out = 0.
iPP = 0
SyncArgs, JD, Out, iPP
Out = SuperArray(Out,3,/lead)

FOR i=0,n_elements(JD)-1 DO BEGIN			; Find nearest perihelion for all times
	A = min(abs(JD[i]-pt[0:nP-1,Hos]),n)
	iPP[i] = n
ENDFOR

FOR i=0,nP-1 DO BEGIN						; Loop over all perihelia
	A = where(iPP eq i)
	IF A[0] NE -1 THEN Out[*,A] = KeplerOrbit(T[A], elements=[aa[Hos],ee[Hos],pl[i,Hos],pt[i,Hos]], degrees=Degrees)
ENDFOR

RETURN, Out  &  END