Celestia Forums

It might be interesting to visualize with Celestia and my Titan texture update, what close-distance views of the Titan surface we can expect from the Feb 15 flyby of Cassini.

Appparently, it looks quite exciting. You may just make out the Huygens landing site close to Titan's upper right rim (about at 1 o'clock ). Plenty of new imaging information lies ahead of us!

Of course Titan's clouds are switched off in the image below

Bye Fridger

Fridger,I'm not sure you should read too much into the cassini trajectories with regards to the moons ,although the cassini trajectory is relatively accurate from the XYZ file, the moons are a little out.The best way to check would be to download xyz orbits for the moons as well.For instance for some of the flybys of Titan ,when I was making xyz for Cassini,Cassini flew straight through Titan (most of those planned for 2006 especially) and so I changed the xyz so as it went around Titan.Jestr

jestr wrote:Fridger,I'm not sure you should read too much into the cassini trajectories with regards to the moons ,although the cassini trajectory is relatively accurate from the XYZ file, the moons are a little out.The best way to check would be to download xyz orbits for the moons as well.For instance for some of the flybys of Titan ,when I was making xyz for Cassini,Cassini flew straight through Titan (most of those planned for 2006 especially) and so I changed the xyz so as it went around Titan.Jestr

Jestr,

I surely agree with you as concerns precision features. Yet all I wanted to know (and illustrate) above was /qualitative/ information about the surface region to be imaged during the flyby. Given that the official arrival time at the minimum distance position agrees pretty well with the Celestia simulation, I would guess that the image above remains qualitatively right. I was also interested in the kind of illumination by the sun we shall encounter. It should also be about realistic in Celestia. The lighting is particularly interesting, since the flyby takes place close to the terminator this time.

Bye Fridger

The lighting is particularly interesting, since the flyby takes place close to the terminator this time.

It doesn't when I look at it in Celestia. Cassini approaches Titan from the sunlight side (I don't know what part of the surface it's looking at when this happens since I don't have your texture), so it'll get lots of good low phase angle images.

I can't even GET the view you showed. At 2005 02 15 06:58.22 UTC, Cassini is 1,323.2 km from Titan, and Titan's phase is gibbous, not half-full and Cassini is still approaching Titan.

I'm using Pre6 and the files that came with that - is there any reason why what I see should be different to what you see?

I have reproduced my above image several times. It is based on Jestr's Cassini add-on (with a somewhat improved/updated xyz orbit I gather?) and my latest Titan texture that perfectly matches the Huygens landing site. Yes, Cassini approaches Titan from the sunlit side. But I rotated the image for convenience, which of course does not modify the intrinsic topology of the Cassini-Titan encounter...

I find the point of minimum distance at 7:04 UTC at 801 KM below the terminator (i.e. in the dark). The official closest approach data are: 6:54 UTC (Saturn time) at 950 km. So it's not so bad.

I do never use a particular PRE version, since I always compile the latest CVS myself (on a daily basis, if things change). Also, I am using Linux not Windows.


Here is the basic key sequence I used:

I set the time to Feb 14 0:00 UTC

CMD cassini
KEY g
CMD titan
KEY shift c
KEY :
(to phase-lock the two!)
and then I merely need to decrease the distance by hitting

KEY L

until the minimum is found.

Bye Fridger

OK, here is the view precisely at minimum distance of 801 km on Feb 15 , 7:04 UTC, as you can see from the printout of the data.

At that time, Cassini is just a little below the terminator in the dark. A few minutes earlier, at ~1300 km distance, the sunlit part of Titan is still visible from Cassini, exactly like in my first image.

Bye Fridger

So which is the most accurate Cassini trajectory?

There's one ssc trajectory file on the motherlode at
http://www.celestiamotherlode.net/catal ... ecraft.php

by Jack Higgins, but you say you're using one by Jestr - but there only a appears to be updated model files availble from there in his section.

Where can I find a more uptodate file? And are we even certain that Jestr's file IS more realistic than the default in the pre-release?

And using an individually compiled file (as well as a modified add-on) isn't all that helpful for those of us who are unable to compile the code for ourselves - we wouldn't necessarily be able to reproduce for ourselves what you show. Still, the difference in OS shouldn't make a difference should it?

http://www.celestiamotherlode.net/catalog/show_addon_details.php?addon_id=627

And using an individually compiled file (as well as a modified add-on) isn't all that helpful for those of us who are unable to compile the code for ourselves - we wouldn't necessarily be able to reproduce for ourselves what you show. Still, the difference in OS shouldn't make a difference should it?

What is this remark again supposed to mean?

If you are discontent with my contributions to this forum, I can as well simply skip them and make use of my time otherwise...Just let me know...

Nobody is in any way obliged to reproduce my flyby preview image above. If YOU want to do it, you have to work a little harder. I have spent enough of my time, I guess. There are very extensive instructions meanwhile, how to compile Celestia (free of charge). My new Titan texture is available for download and so is Jestr's great Cassini-Huygens add-on.
I have carefully checked that Jestr's add-on almost perfectly reproduces the Huygens-Landing location as well as the last Titan flyby. That's a good argument for me at least.

CVS-updating and recompiling Celestia in any supported OS takes less than ONE minute with a modern computer, if you arrange things right and write a few scripts to handle the CVS update. It's equally easy in Win and Linux.

Hence it would really be ridiculous for me to download and run some 15MB PRE version instead . Developers are supposed to work with the CVS code, right?

Bye Fridger

PS: I guess the story about the correction of the Cassini orbit close to Saturn is well known. There is also plenty of reading material in the net about it. The orbit was modified in December as we all know. Most of us know presumably the reasons for that modification (the issue about the forgotten Doppler-shift effect that would almost have made the back communication of the Huygens data impossible...). The adopted solution was to correct the orbit such that landing on Titan was shifted by several weeks and the effect of the Doppler frequency shift diminished by a factor of 2 or so.

t00fri wrote:http://www.celestiamotherlode.net/catalog/show_addon_details.php?addon_id=627

And using an individually compiled file (as well as a modified add-on) isn't all that helpful for those of us who are unable to compile the code for ourselves - we wouldn't necessarily be able to reproduce for ourselves what you show. Still, the difference in OS shouldn't make a difference should it?

What is this remark again supposed to mean?

All it means is that unless you use the standard files, then nobody else will be able to recreate what you see. Or at least, if you don't specify the files you're using then the rest of us will just end up scratching our heads wondering why we're not seeing the same thing when we try, because we don't have the files you have. That's not intended to single you out, that goes for everyone posting things like this.

And surely you should appreciate that not everyone has the time or inclination or knowledge to recompile code.

As to why people want to recreate things that you or others post, did it not occur to you that we may want to see the approach and departure for ourselves in Celestia? There's no "obligation" here, it's just a matter of being helpful.

Hence it would really be ridiculous for me to download and run some 15MB PRE version instead . Developers are supposed to work with the CVS code, right?

Like it or not, most people with 1.4.0 have the PRE versions, not self-compiled versions.

Evil Dr Ganymede wrote:

t00fri wrote:http://www.celestiamotherlode.net/catalog/show_addon_details.php?addon_id=627

And using an individually compiled file (as well as a modified add-on) isn't all that helpful for those of us who are unable to compile the code for ourselves - we wouldn't necessarily be able to reproduce for ourselves what you show. Still, the difference in OS shouldn't make a difference should it?

What is this remark again supposed to mean?

All it means is that unless you use the standard files, then nobody else will be able to recreate what you see. Or at least, if you don't specify the files you're using then the rest of us will just end up scratching our heads wondering why we're not seeing the same thing when we try, because we don't have the files you have. That's not intended to single you out, that goes for everyone posting things like this.

And surely you should appreciate that not everyone has the time or inclination or knowledge to recompile code.

As to why people want to recreate things that you or others post, did it not occur to you that we may want to see the approach and departure for ourselves in Celestia? There's no "obligation" here, it's just a matter of being helpful.

Hence it would really be ridiculous for me to download and run some 15MB PRE version instead . Developers are supposed to work with the CVS code, right?

Like it or not, most people with 1.4.0 have the PRE versions, not self-compiled versions.

The PRE versions only work for Windows. Are you trying to tell me that I should be using Windows instead of Linux to make you "happy"??

You might notice that you are the only one here who is constantly nagging about how I do things, in which board I should make my contributions and how politely I should phrase my sentences and so on...

I AM SICK OF IT!

Oh for god's sake.

I really can't be arsed to argue with you Fridger all the time - it's bloody tiresome.

I just pointed out that it was impossible to duplicate your image in the prerelease of 1.4.0, is all. You then retorted by saying that everyone should find it easy to recompile it, and I pointed out that this wasn't necessarily the case and also not a particularly valid assumption.

If you're just posting this to show what a future version of Celestia will be able to do, then that's different - but certainly the current version can't illustrate this. But there was no indication that this was the reason.

Whatever. If you want to take all that personally, that's your problem.

I don't think there should be any differences concerning titan/cassini, wether you use a pre version or a fresh compiled version. There had been made very few and minor changes to the code in the last weeks.

If you want to keep track, just install 'tortoise' a very comfortable CVS client that integrates into your windows explores context menu - then it's just a single click to update. If you want to know the preference settings, just ask.

maxim

Greetings,

Speaking of mid-February flybys, there is a spectacular Enceladus flyby two days after the Titan one. I ran it on Celestia (1.3.2 Windows) and saw a dramatic low phase angle approach over a different area than was
imaged in mid-January.

To clarify the Titan encounter, will the images taken with low phase angle (helpful in piercing the atmosphere) also be covering some new territory? There is a timeline PDF document (see my homepage "Neat Astronomy Links") that shows the phase angle and distance of all flybys for the mission. It may be a couple of years until we get a really close approach where the closest approach occcurs at a low phase angle for optimum close-in looks. Something to look forward to. Global mapping of course can be better done when one is not quite at the closest distance, better to be over 10000km away for those images.


Steve Albers

Anonymous wrote:Greetings,

Speaking of mid-February flybys, there is a spectacular Enceladus flyby two days after the Titan one. I ran it on Celestia (1.3.2 Windows) and saw a dramatic low phase angle approach over a different area than was
imaged in mid-January.

I'm more looking forward to the Enceladus encounter, to be honest. The long distance images indicate that large tracts of the surface have been seriously resurfaced.

Evil Dr Ganymede wrote:I'm more looking forward to the Enceladus encounter, to be honest. The long distance images indicate that large tracts of the surface have been seriously resurfaced.

I've always been interested in how such a small, icy world could *apparently* be so active geologically. I wonder if we'll be looking at an ongoing process, or the result of an incident that occured long ago (what it might have been, I couldn't say).

...John...

I have now reinstalled the cassini.xyz orbit file that also comes with the recent Celestia PRE's. I checked that this file was commited to CVS by Grant already 8 months ago!

With this file (and my present Linux CVS code!), the Dec 13 flyby is also qualitatively reproduced as I reported elsewhere in the forum and rechecked just now. It happens about at the right time and with a minimum distance of 1800Km instead of the official 1200km.

As to the Feb 15 flyby, it is qualitatively very similar to the flyby with Jestr's orbit file, except that Jestr's orbit gives a significantly better approximation to the closest distance: Instead of the correct 950Km, Jestr's gives 801km while the original cassini.xyz gives only 512km or so.

It is important to switch off the orange clouds (I-key) as I mentioned above, since with the cloud illumination the terminator is less sharply defined.

In any case I now cannot understand the claim that my first flyby image above cannot be qualitatively reproduced with the standard cassini.xyz orbit file.

I think I now did all the "homework" that I can possibly do.

Bye Fridger

Anonymous wrote:Greetings,

Speaking of mid-February flybys, there is a spectacular Enceladus flyby two days after the Titan one. I ran it on Celestia (1.3.2 Windows) and saw a dramatic low phase angle approach over a different area than was
imaged in mid-January.

To clarify the Titan encounter, will the images taken with low phase angle (helpful in piercing the atmosphere) also be covering some new territory? There is a timeline PDF document (see my homepage "Neat Astronomy Links") that shows the phase angle and distance of all flybys for the mission. It may be a couple of years until we get a really close approach where the closest approach occcurs at a low phase angle for optimum close-in looks. Something to look forward to. Global mapping of course can be better done when one is not quite at the closest distance, better to be over 10000km away for those images.


Steve Albers

Hi Steve,

below I checked the accuracy and constellation of the Enceladus flyby of Feb 17, 3:25 UTC.
With the improved orbit file (+beautiful Huygens landing add-on) by Jestr,

http://www.celestiamotherlode.net/catalog/show_addon_details.php?addon_id=627

the encounter turns out to be quite accurately simulated in Celestia:

Time of minimal altitude: 3:25 UTC (official, PDF document) <==> 3:29 UTC Celestia (CVS)

minimal altitude: 1179 Km (official PDF document) <===> 937 Km Celestia (CVS)

The typical view at the minimal altitude is seen here:



Bye Fridger

I took the opportunity today to tidy up my copy of celestia and install and look at a good few addons properly, two of which are t00fris new coloured Titan and Jestrs Cassini. They are both very good and I've had a pleasant evening with them. It's all the excuse I need to put up some nice screen-shots.

I have roughly recreated t00fris view with latest prerelease (1.4.0pre6) and jestrs xyz, I suspect his graphics setup is quite different from the lowly computer I use, but Titan does look the same when paused at the same time.

http://img.photobucket.com/albums/v200/ ... eation.jpg


Another, a different angle

http://img.photobucket.com/albums/v200/ ... nangle.jpg


Closest approach, sunset at Titan from Cassini, 801 km from the surface. Clouds are on in this one, are they set too low in the default setup?

http://img.photobucket.com/albums/v200/ ... pTitan.jpg


Here is something interesting, with jestrs Cassini xyz file. Titan and Saturn, on the 14th January. Huygens was preparing to land on Titan then, so images weren't returned, I do hope Cassini gets to return something like this in the future.

http://img.photobucket.com/albums/v200/ ... saturn.jpg

t00fri wrote:I have now reinstalled the cassini.xyz orbit file that also comes with the recent Celestia PRE's. I checked that this file was commited to CVS by Grant already 8 months ago!

The file in my /data directory is the one that came with 1.4.0pre6, and it's dated 5/15/2004. Sounds like it's probably the same one.

Either way, this is the screenshot I get at the same time as your first one (2005 02 15 06:58:22 UTC) . As you can see, the illumination angle on Titan is rather different.



You'll have to excuse the line going across the atmosphere on the left, my screen capture appears to be buggered.

It is important to switch off the orange clouds (I-key) as I mentioned above, since with the cloud illumination the terminator is less sharply defined.

That shouldn't make a difference though - we SHOULD be seeing the same thing if the default Cassini xyz files are the same. There's a fairly obvious difference in the illumination of what you're seeing and what I'm seeing- regardless of whether you have atmosphere turned on or not.

In any case I now cannot understand the claim that my first flyby image above cannot be qualitatively reproduced with the standard cassini.xyz orbit file.

Was your first image produced with the default cassini.xyz orbit file that comes in the Celestia /data folder? I don't think it was, and evidently there is a difference between the default file and Jestr's that you did use. That being the case it shouldn't be too hard to understand why I can't recreate your first flyby image with the standard cassini.xyz file.

In any case, can anyone else duplicate the image I posted using the default files in Celestia 1.4.0pre6? Or can you duplicate the image that Fridger posted? [/img]

lostfisherman wrote:I have roughly recreated t00fris view with latest prerelease (1.4.0pre6) and jestrs xyz, I suspect his graphics setup is quite different from the lowly computer I use, but Titan does look the same when paused at the same time.

http://img.photobucket.com/albums/v200/ ... eation.jpg

Ah, so he IS using Jestr's xyz file.

But how do we know that Jestr's is more realistic than the one that already comes with Celestia? Why are they different?