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.help pv2ue Jun99 "Slalib Package"
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SUBROUTINE slPVUE (PV, DATE, PMASS, U, JSTAT)
- - - - - -
P V U E
- - - - - -
Construct a universal element set based on an instantaneous position
and velocity.
Given:
PV d(6) heliocentric x,y,z,xdot,ydot,zdot of date,
(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)
Returned:
U d(13) universal orbital elements (Note 3)
(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 PMASS
-2 = too close to Sun
-3 = too slow
Notes
1 The PV 6-vector can be with respect to any chosen inertial frame,
and the resulting universal-element set will be with respect to
the same frame. A common choice will be mean equator and ecliptic
of epoch J2000.
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 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.
Reference: Everhart, E. & Pitkin, E.T., Am.J.Phys. 51, 712, 1983.
P.T.Wallace Starlink 18 March 1999
Copyright (C) 1999 Rutherford Appleton Laboratory
Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
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