[Celestia-developers] Galileo update

[Chris L. <cl...@gm...>]

I've created an update to the Galileo mission, partly in response to this
thread:
http://www.shatters.net/forum/viewtopic.php?f=3&t=14308

The updated ssc and trajectories are here:
http://www.shatters.net/~claurel/celestia/files/patches/galileo-update3.zip

This version of Galileo uses Timeline to split the mission into two parts: a
heliocentric cruise phase, and a Jupiter-centric 'orbital' phase. This is
the same thing that was done for the Cassini mission in 1.6.0. Using a
Jupiter-centered coordinate system for the orbital phase keeps moon fly-bys
from turning into 'fly-throughs' due to VSOP87's limited accuracy. The
trajectories themselves are also more accurate. The xyzv files were
generated from SPICE kernels; the interpolated trajectories should diverge
from the SPICE trajectories by no more than 2km (it's easy to adjust
this--2km seemed like a reasonable compromise between trajectory size and
accuracy.)

I've experimented a lot with the new Galileo mission and found it to be
*much* better than the old one. The encounter distances and times are fairly
(within 200km) of the ones listed here:
http://www.dmuller.net/realtime/mission.php?mission=galileo  (A more
official source for this information would be nice...) Differences are due
to inaccuracies in the orbital theories of the Galilean satellites. SPICE
orbits for the Jovian satellites should give an exact match*

--Chris

*Almost. Celestia still calculates the distance to a planet as the distance
between a point and a sphere. We really need a point-to-ellipsoid distance
calculation.