I got one for blender under Linux (Fedora 8 onwards).
Instead of using the driver issued by 3dconnexions, I use a daemon written by John Tsiombikas, spacenavd
Guys, he did a great work, even provided an SDK for open source development.
Also, you can find many snippets of example code that should make supporting it a very small task.
I guess, you only need one of these, which considering that it is cheaper than my mouse (logitech MX518 lol, got it for 50 euros), I'm surprised you did not have one already to play with it.
Obviously you'll go for the PERSONAL edition.
They did some BS with their proprietary drivers, apparently enough to piss off everyone in FL/OSS, but disregard them and just get it done to play in celestia. I don't play with celestia as much as I used to with ... redshift in my Amiga (remember this), but with a Space Navigator, I'd use it more. Besides, were it along with blender and maya (2k€ program) to be the ONLY Linux programs to use space navigator, well, expect your user base to rise exponentially. I started using drawing programs like gimp, after I got wacom. Some times, you use a software to play with a hardware you fancy.
Needless to say that a space navigating program with a SPACE navigator should go hand by hand. Who knows, they might even advertise Celestia for their space navigator. I would