Here's something that may help. This isn't free but I'm using this program to make space, Planet and natural enviroment backgrounds for my films. Vue 6 Esprit. I started with Vue 6 Easel and did a side grade to esprit. If you have enough computing power, time and skills one can make fantastic animations. I've made some fantastic static backdrops.http://www.e-onsoftware.com/
The software company has a few YouTube videos showing its capabilities.
It can also make some fantastic titles for films. Its only limited to your creativity and imagination.
I plan to use it for my next film - The Robot Planet & The Robosapien.