I have worked up several awk scripts to convert various database formats
files into ephem format. Contact the author if you need one or have one.
This distribution kit contains three examples.

tle2edb.awk is for converting the NASA "2-line" earth satellite format into
xephem format; see the Help on Credits from the Main menu for how to get timely
shuttle elements in this format emailed to you.

jost2edb.nawk is for converting the elements that are included near the end of
occasional comets ephemerides posted to sci.astro by Jost Jahn.

encke2edb.nawk is for converting the elements that are at the WWW site
http://encke.jpl.nasa.gov. The script has not been tested, that is, I have not
checked xephem's results with any ephemerides posted by Jahn.