Celestia Forums

Hi everybody,

I am new to this forum and to celestia and I have two questions which, I hope, can be answered by you specialists.

I work on the Mars Express project and I try to use celestia to display the actual orbital position of Mars Express in our control room. Now, with the orbital parameters used by celestia I can only display the orbit ellipse for a specific time. Problem is, the gravitational effects of Mars make the pericenter move from south to North covering 360 degrees in 22 Months. The usual parameters to describe this motion are the so called J2 ( or C20) parameters. Is there any way to integrate these parameters ? If I use a xyz file instead of course it works, but then I get a mesh of orbits, because celestia then displays all future orbits for ( in this case ) one month. ( Not very practical ... )

The second question relates to the view options. When I run the ssc file for Mars Express somehow the orbit is identified as a moon or planet, which means I can only display the MEX orbit, when I activate the planets Orbits, which at times is not very practical either. Is there a trick for this ?

Thanks already for any help offered.

(Congratulations to all that have worked on this , its a magnificent peace of software !!)

Regards,

J?rg

Hello and welcome here. We need more specialists like you.

Until now, Celestia isn't able to change the orbit in time, like you want to do. It's a limitation in Celestia, unfortunately. The orbit precession is a feature I want to see added for a futur release.

About the orbits shown on screen, I think you just need to use the command <Type "spacecraft"> in your ssc code, so you will be able to show the probe's orbit without activating the moons and planets orbits.

Actually, that's

Class "spacecraft"

Unfortunately, I don't think Celestia currently has an option that would cause it to display only a limited section of a trajectory's path, like +/- 24 hours.

However, one might be able to simulate it by defining multiple objects that include Beginning and Ending directives. An external cron job or bash script could invoke CEL scripts at appropriate times to Select the right object. Alternatively a looping CELX (Lua) script or a really long CEL script could do the selection. It's an ugly hack, though.

[EDIT: I'm leaving it to Chris to comment on the feasability of implementing additional types of orbital definitions.]

for the answers, guys. I was fearing that there would be no easy way out.

Is there maybe a chance to play with the colours of the orbits ? Like suppressing them through making them black or so ? But I actuallt do not think that there is an interface to change colours.

Maybe the easiest is to just live with what I got and wait for a possible new release that would solve the problem.

Thanks again,

and if any of you guys needs information about the Mars Express mission, please do not hesitate to ask me.

Keep up the good work !

J?rg

selden wrote:Actually, that's

Class "spacecraft"

Unfortunately, I don't think Celestia currently has an option that would cause it to display only a limited section of a trajectory's path, like +/- 24 hours.

However, one might be able to simulate it by defining multiple objects that include Beginning and Ending directives. An external cron job or bash script could invoke CEL scripts at appropriate times to Select the right object. Alternatively a looping CELX (Lua) script or a really long CEL script could do the selection. It's an ugly hack, though.

[EDIT: I'm leaving it to Chris to comment on the feasability of implementing additional types of orbital definitions.]

Hmm. Celestia does have the ability to perform the kind of display he wants for a natural satellite with a CustomOrbit (such as the Moon). Could there be any way to get a CustomOrbit for Mars Express in there?

I really like Matt's suggestion. Along those lines:

Would it be possible to externalize all custom orbit data into seperate files? This would allow those with the necessary skills to define cutsom orbits for sattellites and share them as add-ons. It would also allow people to include more terms in their VSOP87 series if they are willing to take the performance hit; this assume that they are not all already included. I suppose that these series are stored in the main executable in a manner that is highly efficient for computation but how much of a performance hit would be incurred at startup in converting from an external format into the necessary internal data structure?

cheers,
Walton

Hi there .... I am still confused with this orbit thing.

When I disable Planet orbits, ALL orbits including spacecraft and moons are disabled. Looks like all the orbits are linked to the Planets. Is there any way around this ? Marking the spacecraft as a moon does not help either .... I would really like to get rid of the Planets orbits. It clutters up the screen with blue lines .....


Any ideas ?

Thanks,

J?¶rg