{
   # Time in Julian days since Jan 1 2000 12:00 GMT
   my $T = (time() - 946728000) / (24 * 60 * 60);

   my ($xm, $ym, $zm) = calc_position($T, 6439.5, 6443.5,
      [-0.2576477260382208e6, -0.1244143318652203e6, 0.1571494964303338e5,
      0.1128910971393731e4, -0.1026042752851206e3, -0.3344243625567091e1,
      0.5108570281514203, 0.7273850253892471e-2, -0.2976495487727882e-2,
      -0.1508820799631562e-4, 0.1988387208061850e-4, -0.9944829575544334e-7,
      -0.1420192252858349e-6],
      [0.2161347296153234e6, -0.1235954423872278e6, -0.1336330642763758e5,
      0.1347907704333395e4, 0.6144497680180469e2, -0.6876023550099470e1,
      -0.1365228336729124, 0.3626374756466881e-1, 0.2847434884414048e-3,
      -0.2277001670510105e-3, 0.2675604082417520e-6, 0.1582321480640805e-5,
      -0.1939924674109133e-7],
      [0.8988317387937439e5, -0.3579858449186091e5, -0.5547166174276667e4,
      0.4032955946240293e3, 0.2725379907222771e2, -0.2195153465571546e1,
      -0.7682906296761302e-1, 0.1217607039333434e-1, 0.2702389308507909e-3,
      -0.7822887028838594e-4, -0.1051459145053017e-5, 0.5554057086131247e-6,
      0.1433643809289891e-8]);
}

sub calc_position {
   # Evaluate Chebyshev polynomials to get x,y,z position
   my ($T, $Tstart, $Tend, $xpoly, $ypoly, $zpoly) = @_;
   die 'time out of range' if $T < $Tstart || $T > $Tend;
   my $t = ($T - $Tstart) / ($Tend - $Tstart) * 2 - 1;
   my $x = $xpoly->[0] + $xpoly->[1] * $t;
   my $y = $ypoly->[0] + $ypoly->[1] * $t;
   my $z = $zpoly->[0] + $zpoly->[1] * $t;
   my $T0 = 1;
   my $T1 = $t;
   $t *= 2;
   for my $i (2 .. $#$xpoly) {
      ($T1, $T0) = ($t*$T1 - $T0, $T1);
      $x += $T1 * $xpoly->[$i];
      $y += $T1 * $ypoly->[$i];
      $z += $T1 * $zpoly->[$i];
   }
   return ($x, $y, $z);
}