Saturn System - Cassini Mission with Spice Kernels

[volcanopele]

I have uploaded my current version of my Saturn/Cassini addon (with SPICE kernels!). This Add-on requires the latest SVN build of Celestia (build 4241 or greater) since this add-on makes use of features not available in the release version of Celestia such as CustomRotation and Timeline.

The addon can be downloaded from http://pirlwww.lpl.arizona.edu/~perry/C ... nSpice.zip [file size ~ 10 MB]. To keep the file size down, this file does not include the spice kernels. The readme file in the zip file includes the URLs for all the kernels that needed to be downloaded to the addon's data directory. Without these files, the Saturn system and Cassini will not appear correctly!

chris, please note a major issue I have had. While I can get Saturn, Cassini, and the major satellites to appear correctly, trying to view the small satellites as anything more than a bright point causes Celestia to crash. To prevent this for now, these moons have been removed from this add-on. So their appearance in Celestia after the installation of this addon comes from the built-in numberedmoons.ssc and minormoons.ssc files. The code I used to implement these moons in my addon is included in the extrastuff,txt file if you would like to test it to find out why Celestia is crashing when I try to view them up-close. A good way to test this is to attempt to view Telesto from Cassini on Oct. 11, 2005 at 20:35 UTC.

Textures by Steve Albers except for Titan (my own), Phoebe (NASA/JPL/SSI), and Saturn (Bjorn Jonsson). Cassini.xyz file and Cassini model by Jestr.

[volcanopele]

Here are some screenies:

Enceladus_Rev131_2.jpg

Dione_04072010_054537.jpg

Rhea_03022010_181100.jpg

[volcanopele]

More Screenies:

Titan_T42flyby.jpg

Saturn_04112009.jpg

Saturn_04072010.jpg

[chris]

Thank you for creating this! I'm in the process of downloading the SPICE kernels right now. As soon as I've got them all, I'll try and figure out what's going on with the small satellites. Outright crashes are usually pretty easy to track down and fix.

--Chris

[volcanopele]

Thanks!

Additional screenshots at http://ciclops.org/view.php?id=4884

[chris]

The crash is a Celestia bug with Replace. I think I've got a fix for it, but I'm still testing it. But, you can easily modify the add-on so that you don't hit this bug. The source of the problem is that extrastuff.ssc is getting loaded /after/ spice-saturn.ssc. This means that when extrastuff.ssc is loaded, Saturn_bary isn't defined yet, and thus the timelines of all the bodies in that file are invalid. The simple workaround is to rename extrastuff.ssc so that it's loaded after spice-saturn.ssc. Call it zzsmallmoons.ssc or something.

I realize that the alphabetical loading order of add-ons is far from an ideal. What's needed is some sort of package file that defines a loading order for files in the add-on. This file could give other information about the add-on: author, version, description, and a list of other required add-ons.

--Chris

[volcanopele]

I've updated the file so that the SPICE kernel coverage for the Cassini mission is pushed back to the day after the Earth flyby. Again the file is located at http://pirlwww.lpl.arizona.edu/~perry/C ... nSpice.zip . If you have already downloaded the file and all the spice kernels listed in the README.txt file, you will need to download 041014R_SCPSE_01066_04199.bsp and place it in the data directory of the addon.

[volcanopele]

Actually, extrastuff is a text file, extrastuff.txt and shouldn't be loaded by Celestia, and as far as I can tell, isn't. It is just there for testing purposes and would be included in the spice-saturn.ssc file when you want to test it.

The crash occurs when the data in extrastuff.txt is in spice-saturn.ssc.

[chris]

Actually, extrastuff is a text file, extrastuff.txt and shouldn't be loaded by Celestia, and as far as I can tell, isn't. It is just there for testing purposes and would be included in the spice-saturn.ssc file when you want to test it.

The crash occurs when the data in extrastuff.txt is in spice-saturn.ssc.

OK. I see what's going on: some of the Spice orbits in extrastuff.txt have two Endings instead of a Beginning and Ending. Celestia (correctly) reports that as an error. Then, the same bug is triggered: when you try to Replace an object, and the replacement has a bad timeline, Celestia will crash. If you change the Endings to Beginnings, everything will work fine. In the mean time, I'm working on a fix for the crash.

You can use the console log to help debug ssc errors. Press ~ to see the console, then use the up and down arrow keys to scroll and look at errors and warnings from ssc files.

--Chris

[chris]

I also noticed that the wrong kernel is used for Polydeuces and Pallene: they're in sat281.bsp (as the comment suggests) and not sat252s.bsp. Looks like a simple copy-and-paste error.

I've got a fix for the crash bug--I'll be checking it in after some further testing.

--Chris

[volcanopele]

When I implemented the fixes you mentioned (I knew it was something stupid like that I wasn't seeing), Celestia stopped crashing when I looked at Telesto or any of the other small moons.

I will update the zip file in a few minutes. here are a few more screenshots:

Telesto-10112005_202557.jpg

Helene-03032010_134043.jpg

[chris]

The 9 Oct 2008 Enceladus flyby is a great one. I never realized just how fast Cassini is moving--no wonder the images at close approach can be a little blurry.

I found The Planetary Society's Cassini-Huygens tour page to be very useful:

http://www.planetary.org/explore/topics ... .html#2008

--Chris

[volcanopele]

I've uploaded the new version and that should work fine for all of Saturn's satellites.

[chris]

It seems that SPICE is quite good at only loading the required sections of an ephemeris. Even though the Cassini add-on has about 400M of SPICE kernels, Celestia never uses more than about 60 megabytes of memory. This is encouraging: it should be possible to make a large interplanetary exploration package for Celestia with SPICE kernels for Galileo, Cassini, New Horizons, the Voyagers, the Pioneers, Dawn, etc. The entire thing could be loaded at once. And with object timelines, it's still possible to view the planets beyond the timespan covered by SPICE kernels.

I've got some new code that makes it possible to control the orientation of objects with SPICE frames. But, it looks like a huge amount of data required to get the orientation of a spacecraft over a long timespan.

--Chris

[CAP-Team]

This is great! I just noticed that for spacecraft, when the orbits are drawn, they are drawn for the entire mission, which clutters the screen, when looking at a spacecraft orbiting a planet, or when using spice kernels for moons.

Is it possible for moons, spacecraft, and so on to draw just a part of the orbit, so you can specify the amount of days ahead and behind the object.

For example, for the Cassini mission, 15 days ahead is just fine, while during interplanetary cruise the trajectory to Saturn is interesting to see, so maybe this can be implemented in the object's timeline?

[CAP-Team]

Volcanopele,

I also notice you use AP kernels, which are predicted kernels, while there are also R(econstructed) kernels available which should be the actual paths instead of predicted paths.

Having great fun playing with this addon

[CAP-Team]

After looking at the .ssc for this addon, I think there are used a lot of .bsp files that would be useful for permanent use for planet and moon positions.
E.g. why not "build" the entire solar system with .bsp spice kernels (solarsys.ssc), and then just add the various spacecraft, asteroids etc.

This could be done for the period 1900 to 2050 at least.

[volcanopele]

The difference between predict and reconstructed paths tend to be pretty small, usually less than a couple of kilometers or so. I didn't think that small difference was worth the order of magnitude difference in the number of kernels needed to cover the entire mission.

To have only a small part of Cassini's path shown in Cassini, set the period value to 15 in the spice-saturn.ssc file. For example:

Code: Select all

      # 2008-2010
      {
         OrbitFrame { EclipticJ2000 { Center "Sol/Saturn_bary"}}
   
         Ending    "2010 06 30 23:59"   # End of Extended Mission

         Orientation     [ 90 0 1 0 ]
         FixedRotation { }
         BodyFrame { EquatorJ2000 { Center "Sol/Saturn" } }
         SpiceOrbit
         {
            Kernel "070918AP_SCPSE_07261_10191.bsp"
                        Target "-82"
                      Origin "6"
            Period 15
            BoundingRadius 1e10
         }
      }


You can use spice kernels for all planets and satellites. I decided to create addons for the outer solar system only because those are the worlds I would be looking at 99% of the time in Celestia. You can use my Cassini and Galileo addons as working examples to build addons for other spacecraft, like Dawn or Messenger.

[CAP-Team]

Setting the period for the specific parts of the mission works perfectly, it's a pity though that Celestia always fills the two endings of a part of an orbit.

Also I've been looking what the value BoundingRadius means, I've tried various values but I have no clue what it means (I don't even know what culling means )

[volcanopele]

I have uploaded Version 2 of my SPICEy Saturn System addon. These provide improved accuracy for the position of Saturn, its various satellites (though the outer irregulars (except Phoebe) are not included in this addon so the default Celestia versions are used), and the Cassini Spacecraft. Please read the instructions thoroughly before running. Most of the spice files are not included in order to reduce the file size of the add-on package. The file FILES TO DOWNLOAD.txt includes a list of all the files you need to download to the add-on's data directory.

There are two editions of this add-on. For Saturn and the satellites, the two editions are identical. For the standard version, Saturn_spice.zip, the position and orientation of the Cassini spacecraft are accurately simulated. This would be useful for those who want to watch Cassini perform its various observations, but this DRASTICALLY increases the number of files you need to download to get this add-on up and running. The total size of all the files that need to be downloaded with the standard version is 2.73 GB. If you don't need Cassini's orientation to be simulated, then download the Fixed Rotation version, Saturn_Spice_fixed.zip. Cassini's orientation remains fixed but the position accuracy is still just as good. The total file size of the SPICE kernels to be downloaded is 892 MB.

Saturn System and Cassini SPICE addon - Standard Version
http://pirlwww.lpl.arizona.edu/~perry/C ... _Spice.zip

Saturn System and Cassini SPICE addon - Fixed Cassini Rotation Version
http://pirlwww.lpl.arizona.edu/~perry/C ... _fixed.zip

Positions for Cassini run from Launch through the end of the Extended mission. However, the kernels for orientation run out on July 22, 2009.

This add-on requires Celestia Version 1.6, currently in development, but nearing completion. Compiled versions can be downloaded from the Development sub-forum.

Among the features added in Version 2 of this add-on include:

* SPICE rotation support for Cassini and several of Saturn's small satellites
* Rotation for other small satellites improved
* Updated Spice kernels used for Saturn and its satellites, extended the coverage for the major satellites back to 1900 and forward to 2053. All satellites included in this add-on, except Pan and Daphnis have coverage that at least goes back to 1950 and forward to 2050.
* Reverted back to tri-axial ellipsoids for most satellites, though CMS models are still included in the add-on
* Textures updated

For screenshots, see http://ciclops.org/view/5470/Rev_102 and http://ciclops.org/view/5505/Rev_104 .

A quick primer on Cassini's orientation, the cameras on Cassini are pointed in the -Y direction. To see what Cassini might be looking at with the cameras, look down the "barrel" of the yellow Magnetometer boom. The antenna is at -Z. Look down the "barrel" of the thrusters to see what the HGA might be looking at (Earth during downlinks, Titan during RADAR instrument observations).