I tried to make a new skybox today. the result is so ugly that it is actually making me feel sick. I think the problem is pictures of space are often so cluttered with stars and what not that they are far to complex.
I haven't quite figured out if planets are going to be models, or just part of the skydrop. Perhaps the best think to do would be to compromise and make them "billboards" or something. A billboard would look better than a static picture, while taking less resources than a model, however I would have to add billboard support to the game, which is something i really don't want to bother with at the moment.
I was going to write a program to generate "space backgrounds" but that would take a while, and I've got more relevant things to do at the moment. I bet i can find something like that if i fish around here long enough.. (i seem to remember seeing a space sticky in the game design thread)