New Horizons with SPICE kernels

[chris]

http://www.celestiaproject.net/~claurel/celest ... cjl-v1.zip


IMPORTANT
This add-on requires a very recent version Celestia, built from SVN revision 4239 or later. It uses some features of Celestia that are not available in the 1.5.1 release, including Timelines and support for xyzv sampled trajectories. Additionally, you must use a version of Celestia that was built with SPICE support.


To install it, unzip it into your Celestia extras folder.

This add-on uses SPICE ephemerides for the orbits of Pluto and its satellites, and a trajectory from HORIZONS for the New Horizons spacecraft (because no SPICE kernel seems to be available.) The New Horizons model was created by Joseph Firestine (website-www.be3d.org) and textured by Jestr (jestr@ntlworld.com)

For reference, images from Celestia can be compared with output from the New Horizons Geometry Viewer, found here: http://soc.boulder.swri.edu/nhgv

The current version of this add-on does a good job of reproducing the encounter except that the time of closest approach is off by about 15 minutes, likely because the NHGV is using an updated version of the New Horizons trajectory that wasn't available on HORIZONS as of 4 Apr 2008.

Information on the ephemerides used:

New Horizons spacecraft
Position and velocity data from HORIZONS.
HORIZONS gives the source for the trajector as nh_pred_20060119_2010010
The trajectory is sampled at 1 day intervals throughout, except for a window
of a few days around the 14 Jul 2015 Pluto encounter where 5-minute intervals
are used.

Pluto, Pluto system barycenter, and satellites:
The DE421 ephemeris is used for the Pluto system barycenter, and plu017
is used for orbits of Pluto, Charon, Nix, and Hydra relative to the
barycenter. Outside of the time window covered by the ephemeris, simple
elliptical orbits are used for all objects other than the barycenter. The
ellipses are reasonable approximations for Pluto and Charon, but
not for Nix and Hydra, which are significantly perturbed by each
other and the larger moons.

[volcanopele]

Great Job! I've been working on one of my own and just got it up and running.

Here are a few screenies that I did yesterday with version using Spice kernels. Chris' public add-on may differ by bit from what is seen here.

PlutoCharonOccultation01-fix.jpg

PlutoClosestApproach-fix.jpg

PlutoClosestApproach-fix-grid.jpg

[chris]

Great Job! I've been working on one of my own and just got it up and running.

Here are a few screenies that I did yesterday with version using Spice kernels. Chris' public add-on may differ by bit from what is seen here.

Very nice! Is the SPICE kernel that you're using public? I couldn't find anything other than the trajectory from HORIZONS.

I'm working on a couple of extra reference marks that should be useful for encounters: a terminator circle and observer sub-point. Eventually, I'd like to add support for instrument FOV overlays, but I won't get to that for a bit.

--Chris

[volcanopele]

I am using spice kernel files that are not public, which is why I can't release my add-on publicly. But I can say that it seems to work perfectly, with the only difference in time/distance of C/A for the moons being due to the NH public tool using older kernels for the Pluto system (plu013.bsp instead of plu017.bsp). The files generated from Horizons should be the same as the nominal mission spice kernel, so you aren't missing much. One suggestion I would make is to generate an XYZV file that is with respect to Pluto, not SSB, for the time near C/A. Should be more accurate, and will maintain the flyby despite changes to the pluto spice kernel.

Those are great ideas for future features! The only two features I can think of at the moment that would be nice to add to Celestia would be dark side/sun-lit differences for rings (compare for instance http://photojournal.jpl.nasa.gov/catalog/PIA09851 (dark-side) and http://photojournal.jpl.nasa.gov/catalog/PIA06193 (sun-lit), in Celestia, both look the same) and a keypress that would rotate the view so that north (on the selected target) is up.

[fsgregs]

Nice job, everyone. New Horizons flyby looks great.

The orientation of the model is a bit off for the flyby in that the main camera never really points at Pluto-Charon, even from a distance. I edited the ssc file to swing the camera toward the planets during close approach. the edit is:

Orientation [30 1 1 1]
RotationOffset 40

Substitute the above for the original Orientation statement, and you're good to go!

Here is a screenshot:

Frank

[symaski62]

new Horizons <= 178270km => MOON

new horizons <= 223310km => JUpiter

new horizons <= 10213 km => Pluton