Hi @Zudo, that looks like an interesting project!
You may need to adjust viewer.camera.frustum.far to a larger value. See Interplenatary visualization settings problems - #15 by jumpjack.
Let us know if you run into any problems. One user had trouble with depth testing if the far plane was set to a very large value–see Not enough depth precision to render solar view? · Issue #8686 · CesiumGS/cesium · GitHub. But I haven’t been able to reproduce that problem in the latest version of CesiumJS.