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authorJoe Hunkeler <jhunkeler@gmail.com>2015-08-11 16:51:37 -0400
committerJoe Hunkeler <jhunkeler@gmail.com>2015-08-11 16:51:37 -0400
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+.help el2ue Jun99 "Slalib Package"
+.nf
+
+ SUBROUTINE slELUE (DATE, JFORM, EPOCH, ORBINC, ANODE,
+ : PERIH, AORQ, E, AORL, DM,
+ : U, JSTAT)
+
+ - - - - - -
+ E L U E
+ - - - - - -
+
+ Transform conventional osculating orbital elements into "universal" form.
+
+ Given:
+ DATE d epoch (TT MJD) of osculation (Note 3)
+ JFORM i choice of element set (1-3, Note 6)
+ EPOCH d epoch (TT MJD) of the elements
+ ORBINC d inclination (radians)
+ ANODE d longitude of the ascending node (radians)
+ PERIH d longitude or argument of perihelion (radians)
+ AORQ d mean distance or perihelion distance (AU)
+ E d eccentricity
+ AORL d mean anomaly or longitude (radians, JFORM=1,2 only)
+ DM d daily motion (radians, JFORM=1 only)
+
+ Returned:
+ U d(13) universal orbital elements (Note 1)
+
+ (1) combined mass (M+m)
+ (2) total energy of the orbit (alpha)
+ (3) reference (osculating) epoch (t0)
+ (4-6) position at reference epoch (r0)
+ (7-9) velocity at reference epoch (v0)
+ (10) heliocentric distance at reference epoch
+ (11) r0.v0
+ (12) date (t)
+ (13) universal eccentric anomaly (psi) of date, approx
+
+ JSTAT i status: 0 = OK
+ -1 = illegal JFORM
+ -2 = illegal E
+ -3 = illegal AORQ
+ -4 = illegal DM
+ -5 = numerical error
+
+ Called: slUEPV, slPVUE
+
+ Notes
+
+ 1 The "universal" elements are those which define the orbit for the
+ purposes of the method of universal variables (see reference).
+ They consist of the combined mass of the two bodies, an epoch,
+ and the position and velocity vectors (arbitrary reference frame)
+ at that epoch. The parameter set used here includes also various
+ quantities that can, in fact, be derived from the other
+ information. This approach is taken to avoiding unnecessary
+ computation and loss of accuracy. The supplementary quantities
+ are (i) alpha, which is proportional to the total energy of the
+ orbit, (ii) the heliocentric distance at epoch, (iii) the
+ outwards component of the velocity at the given epoch, (iv) an
+ estimate of psi, the "universal eccentric anomaly" at a given
+ date and (v) that date.
+
+ 2 The companion routine is slUEPV. This takes the set of numbers
+ that the present routine outputs and uses them to derive the
+ object's position and velocity. A single prediction requires one
+ call to the present routine followed by one call to slUEPV;
+ for convenience, the two calls are packaged as the routine
+ slPLNE. Multiple predictions may be made by again calling the
+ present routine once, but then calling slUEPV multiple times,
+ which is faster than multiple calls to slPLNE.
+
+ 3 DATE is the epoch of osculation. It is in the TT timescale
+ (formerly Ephemeris Time, ET) and is a Modified Julian Date
+ (JD-2400000.5).
+
+ 4 The supplied orbital elements are with respect to the J2000
+ ecliptic and equinox. The position and velocity parameters
+ returned in the array U are with respect to the mean equator and
+ equinox of epoch J2000, and are for the perihelion prior to the
+ specified epoch.
+
+ 5 The universal elements returned in the array U are in canonical
+ units (solar masses, AU and canonical days).
+
+ 6 Three different element-format options are available:
+
+ Option JFORM=1, suitable for the major planets:
+
+ EPOCH = epoch of elements (TT MJD)
+ ORBINC = inclination i (radians)
+ ANODE = longitude of the ascending node, big omega (radians)
+ PERIH = longitude of perihelion, curly pi (radians)
+ AORQ = mean distance, a (AU)
+ E = eccentricity, e (range 0 to <1)
+ AORL = mean longitude L (radians)
+ DM = daily motion (radians)
+
+ Option JFORM=2, suitable for minor planets:
+
+ EPOCH = epoch of elements (TT MJD)
+ ORBINC = inclination i (radians)
+ ANODE = longitude of the ascending node, big omega (radians)
+ PERIH = argument of perihelion, little omega (radians)
+ AORQ = mean distance, a (AU)
+ E = eccentricity, e (range 0 to <1)
+ AORL = mean anomaly M (radians)
+
+ Option JFORM=3, suitable for comets:
+
+ EPOCH = epoch of perihelion (TT MJD)
+ ORBINC = inclination i (radians)
+ ANODE = longitude of the ascending node, big omega (radians)
+ PERIH = argument of perihelion, little omega (radians)
+ AORQ = perihelion distance, q (AU)
+ E = eccentricity, e (range 0 to 10)
+
+ 7 Unused elements (DM for JFORM=2, AORL and DM for JFORM=3) are
+ not accessed.
+
+ 8 The algorithm was originally adapted from the EPHSLA program of
+ D.H.P.Jones (private communication, 1996). The method is based
+ on Stumpff's Universal Variables.
+
+ Reference: Everhart & Pitkin, Am.J.Phys. 51, 712 (1983).
+
+ P.T.Wallace Starlink 18 February 1999
+
+ Copyright (C) 1999 Rutherford Appleton Laboratory
+ Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
+
+.fi
+.endhelp