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JPL Horizons data automator program (Read 4544 times)
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JPL Horizons data automator program
06/16/07 at 18:09:48
This automator creates *.gsim files from JPL Horizons data.  This is not a polished program.  From time to time a bug pops up, so it's important to carefully check the files it creates for you.
To use, you need to make sure that your e-mail system saves your e-mails on your computer.  Outlook Express saves files as *.eml files, but they're just text files with an eml extension.  I can't do this with my free Yahoo account, as it does not save the e-mails to my computer.  Maybe there's a way, but I don't know it.
Make a new folder and download all these files into the folder
There are 3 tabs:
Tab #1: "Select Items and Create E-Mail"
-pick the objects you want to be included in your simulation
-choose a time and date
-click the "Create E-mails" button
-if there are any objects you would like to include that are not in the list, you can type them in manually into the e-mail.  Put single quotes around them.  Don't put more than 5 per line.  Don't include more than 200 per e-mail.  Usually you will only get data in "E-mail #1".  "E-mail #2" and higher are if you request more than 180 objects, it breaks it into several e-mails.
-copy the e-mails to the clipboard.
-create an e-mail to horizons@ssd.jpl.nasa.gov .  Put the word "job" in the subject line.  Paste the data into the body of the e-mail.
Horizons will respond by sending you an e-mail for each object.  Copy these e-mails into a folder on your computer.  If you are using a free e-mail like Yahoo that does not save the files on your computer, you can always copy the contents of each e-mail into a seperate text files and save it in your folder.
Tab #2:  "Build and Save .gsim file"
-point the directory to the folder where you stored your e-mail files.
-press the "Build" button.
-press the "Save As" button.  Give it a name.
You should now have a .gsim file of your desired objects created with JPL Horizons data.  Open it in Gravity Simulator and inspect it.  Sometimes it puts a nameless object after Earth's moon.  Delete it if it does this or your sim will not run properly.  There may be other bugs, so make sure you inspect your simulation to make sure all the objects are included.  It gives a default color of Red to any object not in the list in tab 3.  You might want to edit the colors to your liking.  It gives a default mass=0 and size=0 to objects not in this list too, so you may want to edit your objects.
Tab #3: "View Extra data"
You shouldn't need to use this one.
For Jupiter, Saturn, Uranus, and Pluto, its best to choose their barycenter (1st 9 objects in the list), unless your simulation deals with that planet it particular.  For example, if you are studying near Earth Asteroids that don't go anywhere near Jupiter, then choose Jupiter barycenter instead of Jupiter.  This creates an object with the mass of Jupiter + all its moons, and places in the position and velocity of the Jupiter system barycenter.  Otherwise, if you selected Jupiter (object 599), you would also need to include Io, Europa, Callisto and Ganymede, and then you would need to use a slower timestep when you run the simulation.  Likewise, if you are studying the outer planets, you may want to choose Earth-Moon Barycenter (object 3) instead of Earth (399) and Moon (301), as this combines Earth and Moon into a single object with their combined masses, and combined position and momentum.  This way the Moon doesn't limit your timestep.  Since Mercury, Venus have no moons and Mars' moons are insignificant, there is no difference between choosing the planet or its barycenter.
The file "moreobjects.dat" contains a list of extra objects to include in the list on the first tab.  So if you find a long list of interesting asteroids, you can copy and paste it into this file so the program includes it.
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