Celestia Forums

I'm trying to use the .ssc files that several people have provided in the add-on forum. One .ssc file provides the orbit of the Cassini spacecraft enroute to Saturn. How does one go to the spacecraft in Celestia? I unzipped the .ssc files to my Celestia folder, however I can't determine how to use the controls on the Celestia screen to make use of the files.

You need to look at the contents of the .ssc files.
Every object has a name. It's the first quoted string.
e.g.
"Cassini-xyz" "Sol"
means that the object is named Cassini-xyz and its orbit is referenced to the Sun.

If there are no bugs in the .ssc file, then you will find that object's name near the bottom of the popup window of the Menu item "Solar System Browser".

You can use the browser to select that object or you can type a "carriage return" to Celestia and it'll prompt you for the name of the object. The Browser includes both "Center" and "Goto" buttons. Other actions are available in the "Navagation" menu. They all have keyboard shortcuts. see the "Help" menu for a list of them. These actions all act with respect to the object that is currently "Selected". "Selecting" an object is whiat makes it the potential object of these commands.

I hope this clarifies things a little.

Thanks Selden. My problem was that I had not distributed the unzipped files properly. I had left the "Extras" folder in my Celestia directory empty. I fixed that and I can now access Cassini in Celesia.

I had one other question. I looked at the JPL "Ephemerides" site that you mentioned earlier, however I couldn't find the orbital elements for Cassini as you were able to do. Where did you find them at that site?

The Horizons Web interface is quite limited. For short outputs, like elliptical orbital elements, I usually use their telnet interface. For long outputs, like xyz trajectories, I usually use their e'mail interface. There's a brief description of both on their Web page. More detailed documentation is available using the telnet interface. It includes commands that will send several different (plain text) explanatory documents to you by e'mail.

The Web page is at http://ssd.jpl.nasa.gov/horizons.html

As they mention, the telnet interface uses a non-standard port. telnet://ssd.jpl.nasa.gov:6775/

To get orbital elements, the first thing you do is just type in the name of the object, in this case CASSINI. Then answer the questions appropriately.

Their telnet program tries to put your terminal into page mode, but the escape sequences cause the default Windows telnet program to get somewhat confused. You just have to type an extra carriage-return to clear the error before typing your first command.

I've created a template mail message for xyz trajectories at http://www.lns.cornell.edu/~seb/celestia/horizons-template.txt
Horizons' trajectories can't be used as-is. The returned messages have to be edited into a format that Celestia will accept, but that's easy to do.

I hope this helps a little.

Oh I see. I was trying to use the WWW interface instead of the Telnet one. I just tried a few samples with Telnet and got it to work for Cassini. If you get a few moments you might want to try simulating Cassini's orbit using the Orbiter space sim. Orbiter appears to offer more navigational data than Celestia during the simulated flight.

One of the people in the Orbiter forum said that the Orbiter.pdf provides instructions and addendums in the Documents folder which explain how to create a new scenario using the orbital elements of a spacecraft. I'm going to try that myself however you might meet with more success since this all fairly new to me.

Thanks for helping me to decipher the JPL web page.

Peter,

Thanks for the suggestion. Unfortunately, Orbiter's user interface takes just a little more learning time than I'm willing to invest these days. Pressing C, G, F and T are about all I can manage

Selden, have you seen the most recent revision of Orbiter? It was released earlier this month. I agree that the interface is not all that user friendly, however there are a number of add on MFDs (Multi Function Displays) that simplify the process. Creating new orbits in Orbiter appears quite similar to Celestia. It requires only a simple text editor revision of the so called "Scenario files". I'll give it a try and tell you how it turns out.