Jittery movement far from origin

Sound like a floating precision issue. The only thing to really resolve this is using double precision, but that's not supported by opcode or gimpact (trimesh collision for ODE), so I didn't have a look at porting jME Physics 2 or ODEJava to double. As a workaround you can translate your scene near to the origin (e.g. make the players ship the origin) - I had to do that for my space shooter as well.

Ok. I was thinking of that as a work around. I'm just not sure how to go about it. Any tips?

Your only chance (if you really need the high distances and can't just have a tiny universe) is to use double precision in your entities (application model) and map to floating point only for rendering and physics.

I'm sorry, but I'm a little lost. Are you talking about two different workarounds? I was thinking that a solution was to keep the camera and player ship at the origin and move the game world. I presume this is done by applying reverse physics inputs (that would normally be applied to the player ship) to the world rather than the player ship. Although I'm a little hazy on the technical details, I assume it should work?

I'm not quite sure what you mean by setting up a map with doubles and floats (I assume for world translations). How would that solve the issue?