1) dsc.xls: For creators of deep-sky objects. Enter the right ascension and declination of your deep sky object, and the spreadsheet produces the corresponding Axis and Angle definition, ready to copy-and-paste into your dsc file, which will automatically position one of Selden's billboard object facing precisely towards the Sun, with the top of the original image facing towards celestial north.
2) tle.xls: For Earth-satellite modellers. Since Celestia doesn't support (at present!) NORAD's two-line element dataset for Earth satellites, this spreadsheet automatically converts them to a Celestia object definition. Paste the original TLE into the spreadsheet, and it generates a complete object definition for you, ready to copy-and-paste into your ssc. You just need to supply a mesh object, modify the radius, and perhaps tweak Orientation and RotationOffset for the final orientation - but the object is already set up for you with its principal axes properly aligned with Celestia's.
3) starorbs.xls: For anyone wanting to model real-world binary star orbits as realistically as possible. The most commonly available format for binary orbital elements refers them to the plane of the sky, incompatible with Celestia's frame of reference, the ecliptic plane. So this spreadsheet takes the plane-of-sky orbital elements together with the right ascension, declination and distance of the star system, and outputs a Celestia elliptical orbit definition ready to copy-and-paste into your star system ssc.
Each of the above is available on Selden's website at http://www.lepp.cornell.edu/~seb/celestia/hutchison/spreadsheets.html. Thanks as ever go to Selden for hosting my stuff, as well as for testing out the dsc file. Thanks, too, to Jack for casting his eye over the tle file. Selden tells me the dsc spreadsheet also works well under OpenOffice - I have no idea if the others are Linux compatible, I'm afraid.
Feedback gratefully received.
Grant