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.help pv2el Jun99 "Slalib Package"
.nf
SUBROUTINE slPVEL (PV, DATE, PMASS, JFORMR,
: JFORM, EPOCH, ORBINC, ANODE, PERIH,
: AORQ, E, AORL, DM, JSTAT)
- - - - - -
P V E L
- - - - - -
Heliocentric osculating elements obtained from instantaneous position
and velocity.
Given:
PV d(6) heliocentric x,y,z,xdot,ydot,zdot of date,
J2000 equatorial triad (AU,AU/s; Note 1)
DATE d date (TT Modified Julian Date = JD-2400000.5)
PMASS d mass of the planet (Sun=1; Note 2)
JFORMR i requested element set (1-3; Note 3)
Returned:
JFORM d element set actually returned (1-3; Note 4)
EPOCH d epoch of elements (TT MJD)
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)
JSTAT i status: 0 = OK
-1 = illegal PMASS
-2 = illegal JFORMR
-3 = position/velocity out of range
Notes
1 The PV 6-vector is with respect to the mean equator and equinox of
epoch J2000. The orbital elements produced are with respect to
the J2000 ecliptic and mean equinox.
2 The mass, PMASS, is important only for the larger planets. For
most purposes (e.g. asteroids) use 0D0. Values less than zero
are illegal.
3 Three different element-format options are supported:
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
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
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
4 It may not be possible to generate elements in the form
requested through JFORMR. The caller is notified of the form
of elements actually returned by means of the JFORM argument:
JFORMR JFORM meaning
1 1 OK - elements are in the requested format
1 2 never happens
1 3 orbit not elliptical
2 1 never happens
2 2 OK - elements are in the requested format
2 3 orbit not elliptical
3 1 never happens
3 2 never happens
3 3 OK - elements are in the requested format
5 The arguments returned for each value of JFORM (cf Note 5: JFORM
may not be the same as JFORMR) are as follows:
JFORM 1 2 3
EPOCH t0 t0 T
ORBINC i i i
ANODE Omega Omega Omega
PERIH curly pi omega omega
AORQ a a q
E e e e
AORL L M -
DM n - -
where:
t0 is the epoch of the elements (MJD, TT)
T " epoch of perihelion (MJD, TT)
i " inclination (radians)
Omega " longitude of the ascending node (radians)
curly pi " longitude of perihelion (radians)
omega " argument of perihelion (radians)
a " mean distance (AU)
q " perihelion distance (AU)
e " eccentricity
L " longitude (radians, 0-2pi)
M " mean anomaly (radians, 0-2pi)
n " daily motion (radians)
- means no value is set
6 At very small inclinations, the longitude of the ascending node
ANODE becomes indeterminate and under some circumstances may be
set arbitrarily to zero. Similarly, if the orbit is close to
circular, the true anomaly becomes indeterminate and under some
circumstances may be set arbitrarily to zero. In such cases,
the other elements are automatically adjusted to compensate,
and so the elements remain a valid description of the orbit.
Reference: Sterne, Theodore E., "An Introduction to Celestial
Mechanics", Interscience Publishers, 1960
Called: slDA2P
P.T.Wallace Starlink 13 February 1999
Copyright (C) 1999 Rutherford Appleton Laboratory
Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
.fi
.endhelp
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