I've Generated a 6 hours step ephemeris file for Cassini spacecraft with JPL Horizons and I would like to know if someone has already wrote a program to convert it to a .xyz usable in Celestia so I haven't to write it myself !
If you have done it please send it to Kendrix@wanadoo.fr
Thanks !
Precised Sampled Orbits (.xyz) for Cassini
Unfortunately, 6 hour steps are smaller than necessary for the long coasting between planets and are much too big for the flybys. They often need to be 15 minute steps or even smaller.
After manually deleting the junk at the beginning and ending of the message, I use this teco code:
(search for space =, exit if fails, backspace 2 characters, delete from there through the end of the line)
There are equivalent operations available in most editors, but teco's what I find easiest to use when the end-of-line has to be deleted. Sorry.
After manually deleting the junk at the beginning and ending of the message, I use this teco code:
Code: Select all
<s =$;2rk>
(search for space =, exit if fails, backspace 2 characters, delete from there through the end of the line)
There are equivalent operations available in most editors, but teco's what I find easiest to use when the end-of-line has to be deleted. Sorry.
Selden
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Topic authorKendrix
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???
No problem for the step ! I can create a file with 1 day or 2 between interessant parts and 1 or 2 hours when in Saturn orbit...
the major problem for me is the rest of your post ! I think I don't have the good generated ephemeris... Here is a sample :
2450736.91666667 m 22.1148 0.0005 0.9970409229 3.46814
2450737.16666667 * 22.3284 0.0066 0.9974538605 2.56288
2450737.41666667 * 22.5475 0.0119 0.9978089184 2.37808
2450737.66666667 m 22.7676 0.0171 0.9981453230 2.28454
2450737.91666667 m 22.9882 0.0222 0.9984706897 2.22078
2450738.16666667 * 23.2089 0.0272 0.9987879447 2.17066
2450738.41666667 * 23.4297 0.0322 0.9990985517 2.12802
2450738.66666667 m 23.6505 0.0371 0.9994033565 2.08995
2450738.91666667 m 23.8714 0.0420 0.9997028951 2.05488
2450739.16666667 * 24.0921 0.0469 0.9999975296 2.02190
2450739.41666667 * 24.3128 0.0518 1.0002875169 1.99042
I know that the Julian day is ok but I have to convert the coordinates from long-lat-range to x-y-z in kilometers !
Unless Horizons can do this wut then how ?
the major problem for me is the rest of your post ! I think I don't have the good generated ephemeris... Here is a sample :
2450736.91666667 m 22.1148 0.0005 0.9970409229 3.46814
2450737.16666667 * 22.3284 0.0066 0.9974538605 2.56288
2450737.41666667 * 22.5475 0.0119 0.9978089184 2.37808
2450737.66666667 m 22.7676 0.0171 0.9981453230 2.28454
2450737.91666667 m 22.9882 0.0222 0.9984706897 2.22078
2450738.16666667 * 23.2089 0.0272 0.9987879447 2.17066
2450738.41666667 * 23.4297 0.0322 0.9990985517 2.12802
2450738.66666667 m 23.6505 0.0371 0.9994033565 2.08995
2450738.91666667 m 23.8714 0.0420 0.9997028951 2.05488
2450739.16666667 * 24.0921 0.0469 0.9999975296 2.02190
2450739.41666667 * 24.3128 0.0518 1.0002875169 1.99042
I know that the Julian day is ok but I have to convert the coordinates from long-lat-range to x-y-z in kilometers !
Unless Horizons can do this wut then how ?
Except for the Julian date being on a separate line with extraneous information, Horizons will return the xyz positions in a format directly usable by Celestia. A template of the mail request that I use can be found at http://www.lns.cornell.edu/~seb/celestia/horizons-template.txt
Selden
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Topic authorKendrix
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Ok... I have made a 3h step .xyz file for Cassini for all is lifetime...
but even with 3h you're right the precision is insuffisant for flybys (I have Cassini going through Saturn some times...). It's normal with a craft flying at many km/s !
I will remake a 1h step and if it's still not enough 30mn or 15mn....
@+
but even with 3h you're right the precision is insuffisant for flybys (I have Cassini going through Saturn some times...). It's normal with a craft flying at many km/s !
I will remake a 1h step and if it's still not enough 30mn or 15mn....
@+
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chris
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Kendrix wrote:No problem...
I will make a 1 or 2 days step from 1997 until 2005 and the a 30 min or 15 min step until 2008...
That's a 3 mo file approximatly...
I've found the interpolation code and will try to do a spline interpolation instead of the linear one...
I've already got cubic interpolation working in my private version of Celestia. It'll be in the CVS tree in a few hours . . .
In order to compress the data, I'd suggest writing a program that filters out unnecessary data points. A simple error metric is the distance between point n and the line from point n-1 to point n+1.
--Chris
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Topic authorKendrix
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Cool for the cubic interpolation...
And your idea for the error calculation is good...
But since Horizons couldn't generate more than 17000 lines I'm still forced to make 19 requests for my cassini ephemeris (1 with 1 day step and 18 with 30 min step). And then remove the useless points...
If horizons was unlimited in size I could request a 15 min step for the whole timespan and then remove useless points with your method...
If only we live in a perfect world... :)
And your idea for the error calculation is good...
But since Horizons couldn't generate more than 17000 lines I'm still forced to make 19 requests for my cassini ephemeris (1 with 1 day step and 18 with 30 min step). And then remove the useless points...
If horizons was unlimited in size I could request a 15 min step for the whole timespan and then remove useless points with your method...
If only we live in a perfect world... :)