Long story short -- I had to make my own Celestia ".ssc" files to describe the spacecraft. Using the JPL HORIZONS web interfaceyou can get recent orbital elements, but you have to convert these to something Celestia will understand (an "EllipticalOrbit" stanza in the ".ssc" file).
The perl script below does the conversion; just run it and paste in a single block of Ephemeris data like this:
2456621.500000000 = A.D. 2013-Nov-25 00:00:00.0000 (CT) EC= 4.143129880700237E-02 QR= 9.996672652291025E-01 IN= 2.936558964716465E-01 OM= 3.363978705358475E+02 W = 1.469845587993808E+02 Tp= 2456458.185749091208 N = 9.254559117051611E-01 MA= 1.511401389693867E+02 TA= 1.533315740323342E+02 A = 1.042874927988944E+00 AD= 1.086082590748784E+00 PR= 3.889974610856358E+02And you'll get output line this:
EllipticalOrbit
{
Epoch 2456621.500000000
Period 1.06499689086802
SemiMajorAxis 1.04287492798894
Eccentricity 0.041431298807
Inclination 0.293655896472
AscendingNode 336.397870535848
ArgOfPericenter 146.984558799381
MeanAnomaly 151.140138969387
}
The perl script is below, or you can download it here.
#!/usr/bin/perl -w
# input an ephem set like this:
#2456621.500000000 = A.D. 2013-Nov-25 00:00:00.0000 (CT)
# EC= 4.143129880700237E-02 QR= 9.996672652291025E-01 IN= 2.936558964716465E-01
# OM= 3.363978705358475E+02 W = 1.469845587993808E+02 Tp= 2456458.185749091208
# N = 9.254559117051611E-01 MA= 1.511401389693867E+02 TA= 1.533315740323342E+02
# A = 1.042874927988944E+00 AD= 1.086082590748784E+00 PR= 3.889974610856358E+02
# output like this:
# EllipticalOrbit
# {
# Epoch 2456621.500000000 # = A.D. 2013-Nov-25 00:00:00.0000 (CT)
# # reference http://www.lepp.cornell.edu/~seb/celestia/transforming_ephemeris.html
# Period 1.06499689086801936 # P = (q/(1-e))^1.5 for a closed, elliptical orbit (q = QR, e = ER)
# SemiMajorAxis 1.04287492798894325 # a = (q+Q)/2, where Q is Apoapsis distance (AD in horizons ELEMENTS)
# Eccentricity 0.04143129880700237 # (EC)
# Inclination 0.2936558964716465 # (IN)
# AscendingNode 336.3978705358475 # (OM)
# ArgOfPericenter 146.9845587993808 # (W)
# MeanAnomaly 151.1401389693867 # (MA)
# }
my ($Epoch, $EC, $QR, $IN, $OM, $W, $Tp, $N, $MA, $TA, $A, $AD, $PR);
my ($Period, $SemiMajorAxis);
print "Input a single block of ephem data\n";
while () {
if ( /^((\w|\.)+)/ ) {
$Epoch = $1;
}
if ( /EC=/ ) {
($EC, $QR, $IN) = (split())[1,3,5];
}
if ( /OM= / ) {
#$_ = readline; chomp;
($OM, $W, $Tp) = (split())[1,4,6];
}
if ( /N = / ) {
#$_ = readline; chomp;
($N, $MA, $TA) = (split())[2,4,6];
}
if ( /AD= / ) {
#$_ = readline; chomp;
($A, $AD, $PR) = (split())[2,4,6];
last;
}
}
$Period = ( $QR / (1 - $EC) )**1.5 ;
$SemiMajorAxis = ( $QR + $AD ) / 2 ;
print "EllipticalOrbit\n";
print "{\n";
print "\tEpoch $Epoch\n";
print "\tPeriod $Period\n";
print "\tSemiMajorAxis $SemiMajorAxis\n";
print "\tEccentricity " . sprintf("%12.12f\n",$EC);
print "\tInclination " . sprintf("%12.12f\n",$IN);
print "\tAscendingNode " . sprintf("%12.12f\n",$OM);
print "\tArgOfPericenter " . sprintf("%12.12f\n",$W);
print "\tMeanAnomaly " . sprintf("%12.12f\n",$MA);
print "}\n";
