From d54fe7c1f704a63824c5bfa0ece65245572e9b27 Mon Sep 17 00:00:00 2001 From: Joseph Hunkeler Date: Wed, 4 Mar 2015 21:21:30 -0500 Subject: Initial commit --- src/slalib/sun67.htx/node188.html | 220 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 220 insertions(+) create mode 100644 src/slalib/sun67.htx/node188.html (limited to 'src/slalib/sun67.htx/node188.html') diff --git a/src/slalib/sun67.htx/node188.html b/src/slalib/sun67.htx/node188.html new file mode 100644 index 0000000..bc0c8bd --- /dev/null +++ b/src/slalib/sun67.htx/node188.html @@ -0,0 +1,220 @@ + + + + +SLA_UE2PV - Pos/Vel from Universal Elements + + + + + + + + + + + + +
+ +next + +up + +previous +
+ Next: SLA_UNPCD - Remove Radial Distortion +
+Up: SUBPROGRAM SPECIFICATIONS +
+ Previous: SLA_UE2EL - Universal to Conventional Elements +

+

+

SLA_UE2PV - Pos/Vel from Universal Elements +   +

+
+
ACTION: +
Heliocentric position and velocity of a planet, asteroid or comet, +starting from orbital elements in the ``universal variables'' form. +

CALL: +
CALL sla_UE2PV (DATE, U, PV, JSTAT) +

+

+
GIVEN: +
+
+ + + + + +
DATEDdate (TT Modified Julian Date = JD-2400000.5)
+

+
GIVEN and RETURNED: +
+
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
UD(13)universal orbital elements (updated; 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 (${\rm \bf r}_0$)
(7-9)velocity at reference epoch (${\rm \bf v}_0$)
(10)heliocentric distance at reference epoch
(11)${\rm \bf r}_0.{\rm \bf v}_0$
(12)date (t)
(13)universal eccentric anomaly ($\psi$) of date, approx
+

+
RETURNED: +
+
+ + + + + + + + + + + + + + + + + + + + + + + + + +
PVD(6)heliocentric $[\,x,y,z,\dot{x},\dot{y},\dot{z}\,]$, equatorial, J2000
(AU, AU/s; Note 1)
JSTATIstatus:
0 = OK
-1 = radius vector zero
-2 = failed to converge
+

+
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 sla_EL2UE. This takes the conventional + orbital elements and transforms them into the set of numbers + needed by the present routine. A single prediction requires one + one call to sla_EL2UE followed by one call to the present routine; + for convenience, the two calls are packaged as the routine + sla_PLANEL. Multiple predictions may be made by again + calling sla_EL2UE once, but then calling the present routine + multiple times, which is faster than multiple calls to sla_PLANEL. +

+It is not obligatory to use sla_EL2UE to obtain the parameters. + However, it should be noted that because sla_EL2UE performs its + own validation, no checks on the contents of the array U are made + by the present routine. +

3. +
DATE is the instant for which the prediction is required. It is + in the TT timescale (formerly Ephemeris Time, ET) and is a + Modified Julian Date (JD-2400000.5). +
4. +
The universal elements supplied in the array U are in canonical + units (solar masses, AU and canonical days). The position and + velocity are not sensitive to the choice of reference frame. The + sla_EL2UE routine in fact produces coordinates with respect to the + J2000 equator and equinox. +
5. +
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, E. & Pitkin, E.T., Am. J. Phys. 51, 712, 1983. +
+
+ +next + +up + +previous +
+ Next: SLA_UNPCD - Remove Radial Distortion +
+Up: SUBPROGRAM SPECIFICATIONS +
+ Previous: SLA_UE2EL - Universal to Conventional Elements +

+

+

+SLALIB --- Positional Astronomy Library
Starlink User Note 67
P. T. Wallace
12 October 1999
E-mail:ptw@star.rl.ac.uk +
+ + -- cgit