Celestia Forums

Hey all!

Yes, here it is at last- the final version of the Huge Galileo xyz trajectory! If you haven't heard about this before, read the "Feedback needed Re: Huge Galileo xyz" topic to find out how it was produced. First mentioned on the 11th August, here, it now contains- wait for it... 369,952 lines of xyz coordinates!! (And that's 16,092,912 characters, if you're interested!)

It's only a 4.83MB download, but when unzipped it's a whopping 15.7MB!!

You can download it from #19 on the spacecraft page of my website, http://homepage.eircom.net/~jackcelestia/ (make sure you follow the instructions on the page!!) But first you can check out a couple of screenshots. For the full set of pictures, view this page!

The full trajectory:


Earth-1 gravity Assist:


Gaspra Flyby:


Earth-2 Gravity Assist:



Earth & Moon together, after the Earth-2 Flyby:

(Compare that to this picture, from JPL's planetary photojournal!)

Ida & Dactyl Flyby:


Io:


Europa:


Ganymede:


Callisto:


Amalthea:


Enjoy!!

Jack

I've downloaded the full mission xyz data file and the patch for the SSC and I couldn't get it to work. But on closer inspection of the SSC, I found a wrong description for the 'sampled orbit'......'galileo.xyz' instead of 'galileo_highdetail.xyz'. Here's the code for anyone who needs a quick fix



I haven't had time to run this through in it's entirity yet, but I have looked at the end of the mission and I assume we now no longer need our 'galileo dies' SSC and xyz file, as this will now replace it!

regards
TERRIER

PS Will there be still be crashes into the moons of Jupiter when we are viewing this, while using Celestia, up to and including version 1.3.1pre11?

TERRIER

You didn't follow the instructions...!!

On my site, I wrote:Ignore what it says in the readme (for now) and just rename the file in the data folder to "galileo.xyz", replacing the original.

Eventually, once i've got the animated galileo working, I'll change the ssc patch (or maybe i'll do it tomorrow- who knows..!)

You can get rid of any other Galileo xyz's you have, if you're using this one.

PS Will there be still be crashes into the moons of Jupiter when we are viewing this, while using Celestia, up to and including version 1.3.1pre11?

Until the final 1.3.1 comes out, yes. But only a few! There's not much point putting up the jupiter xyz I have at the moment, because callisto's orbit is wrong in pre11. It's only fixed in the CVS version, which relatively few people have.

You didn't follow the instructions...!!

True

It's interesting to watch two spacecraft following the old and new Galileo trajectories simultaneously, to see how far the old trajectory deviates from the new (more accurate) one.

I think Jack admitted in the previous thread that the new trajectory file probably includes more samples than necessary for some time periods. I wonder how much it could be reduced without sacrificing too much accuracy at the critical times?

I suppose that depends mostly on how you define "too much". But it would be nice to have some kind of reasonable heuristic for choosing an efficient sampling interval.

- Hank

Hank

It's been suggested before, but i reckon the best way to find out how many points you need would be to work out the angle between 3 of them.
If the angle is greater than (say) one degree, then you need more points to fill in this space. If not, then you can reduce the number of points in this time scale.

I probably went a bit overkill by putting in extra points for the Gaspra and Ida flybys, since their gravitational effects on galileo were negligable, on some (maybe one or two) of the Jupiter orbit pericenters, there wasn't need for the 4000 points, and I probably didn't need so many points for the times leading up to the VEEGA flybys.

Apart from that though, I feel that most of the points were necessary!

On the other hand, if someone is willing to take apart the file and analyse it, feel free...!!

JackHiggins wrote:Hank

It's been suggested before, but i reckon the best way to find out how many points you need would be to work out the angle between 3 of them.
If the angle is greater than (say) one degree, then you need more points to fill in this space. If not, then you can reduce the number of points in this time scale.

It's possible to make Horizons do something similar to that, if you don't use the Web interface. When setting the step size (interval between coords) you can enter 'VAR ####' with #### being the number of arcseconds across the observer's sky.

For close-approach periods, doing that from the POV of the major body would give an approximate time step for your eliocentric coords.

if you don't use the Web interface.

I only ever use the web interface if I want to quickly check if any new large bodies have been added- 99% of the time it's telnet, but I must have missed this partcular bit in the documentation!

However, it would be kinda hard to get xyz's from the POV of lots of different bodies, and then merge them all into one heliocentric xyz file, wouldn't it...? Maybe there's something else on Horizons that does this...?!!

No, as far as I know Horizon's won't do that, but it wasn't what I meant. I guess I was unclear.

What I meant was that for a particular encounter, say the first Europa flyby, you could generate a Europa-centric empheris with, say, 60 arcsecond resolution (that's the smallest interval), look at that empheris to see what the smallest time step for that encounter is, and then generate a heliocentric empheris for that time period with that time step.

Yeah, it's pretty jerry-rigged, but it'd accomplish what you want, right?

Yes, I know I can't spell ephemeris.

(it's in the manual under the heading 'Output Stepping'...fourth paragraph.)