Celestia Forums

see http://shatters.net/forum/viewtopic.php?p=70674
and http://sourceforge.net/tracker/index.php?func=detail&aid=1477835&group_id=21302&atid=121302

This is a feature request to get the SPICE library in Celestia.

It would some pretty awesome benefits, like:

• load REAL spacecraft ephemerides (international, not just NASA)
• use the latest, official planet and moon ephemerides
• use the latest astrodynamical constants
• use official IAU coordinate systems
• existing users get the "cool" factor of using *real* NASA/ESA science data (http://www.esa.int/, http://www.jpl.nasa.gov/)
• The Celestia user base will grow to include aerospace engineers and planetary scientists

more info:
ftp://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/ascii/individual_docs/intrdctn.req

please post follow-ups at http://shatters.net/forum/viewtopic.php?p=70674

Hi trgoodson

I believe the SPICE library is part of the ISIS 3 package. I downloaded ISIS 3 to learn how to work with the MRO data and create textures for Celestia. I'm stalled at the moment till I can rebuild my computer and bring it up to date with todays world. For now I am trying to understand the processes by reading the docs.

I'm not sure if the SPICE library can be integrated into Celestia tho. I may be wrong but I think they are miles apart.

cartrite

I think this request is quite a bit more difficult than one might expect. The "standards" for coordinate systems (let alone code standards) are not as "standard" as one might think. They are subject to change every few years. The highly accurate ephemerides from the SPICE library may not be highly accurate at all if the time system's of the IAU are not updated with leap seconds every so often, along with new precession/nutation conventions which may not have been implemented/updated in the original SPICE code. Ultimately, keeping Celestia up to date with SPICE would likely be a losing battle given the mission goals of Celestia as primarily an educational tool.

That said, I for one am working hard on how Celestia might be used as a professional aerospace tool. It's tricky to say the least.

I have a program which has access to the JPL DE405 ephemerides, and I've unfortunately noticed a small difference between the VSOP87 in Celestia and the DE405 data (although there may be an error in converting between equatorial to ecliptical coordinates).

Apollonian wrote:...
given the mission goals of Celestia as primarily an educational tool.

...that's what our sub-community of educators likes to emphasize, but being a longtime Celestia developer and co-author I certainly disagree.

I rather see Celestia as a general, most versatile and precise framework for simulating the Universe, rather than a specialized application.

For example, I have been striving a lot in recent years that Celestia's data base is becoming a 1-1 port of published professional catalogs of celestial objects. Since all catalog extractions are done by PERL scripts, any modifications of the original data (including elimination of typos) are documented in human readable form in the PERL scripts that are part of the official source code.

Being a senior scientist in theoretical particle physics, where most activities these days focus on astro-particle physics and cosmology, I also know what I am talking about in this domain...

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Altogether, my dream is to make Celestia a unique sythesis of precision and stunning 3d graphics, with a reliable asto-physical data base of scientific standards. A most important aspect being Celestia's modular design and the many possibilities of expansion at the user level.
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But I also have my doubts about using SPICE ...For a number of different reasons.

Incidentally, Celestia's accuracy has been tested quite intensively (by me and others) with very favorable results. Notably the very high precision of delicate mutual (eclipsing) events among e.g. Jovian moons, moons of Saturn all the way to precise occultation timings of the Pluto Charon system are most remarkable. The VSOP87 expansions are used as much as possible for calculating planetary orbits. There is certainly room for improvement as to the Moon's ephemeris predictions. But the reasons for this exceptional case are well known and would require something like VSOP2000...

Bye Fridger

Apollonian wrote:... given the mission goals of Celestia as primarily an educational tool.

t00fri wrote:...that's what our sub-community of educators likes to emphasize, but being a longtime Celestia developer and co-author I certainly disagree.

Fridger, even if belong to that underground creeping sub-community ( ), I also agree with you : Celestia's first purpose is not educational. But you have to admit that Celestia can also represent a very powerful educational tool... And I'm quite sure educators who think Celestia is mainly an educative tool are not in the majority...

Vincent wrote:Fridger, even if belong to that underground creeping sub-community ( ), I also agree with you : Celestia's first purpose is not educational. But you have to admit that Celestia can also represent a very powerful educational tool... And I'm quite sure educators who think Celestia is mainly an educative tool are not in the majority...

OK, Vincent,

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Bye Fridger