I have a suspicion on what's happening. It may be that the planets aren't disappearing, they're moving! Maybe at that distance from the origin the transformation matrix has lost so much precision that it can only remain stable for a few seconds before it jumps to a new location, close by but out of camera view. Recently I noticed that when I went beyond 16,777,216 units that I completely lost the ability to move in single unit increments and that when I kept going farther out I started to lose the ability to move even in triple digit increments! Maybe loss of precision in the transformation matrix is the little gremlin behind all these kinds of problems. What do you guys think?