I had an idea about spherical terrains as well (like populous 3 but maybe a bit larger), problem is you're not going to get blitz terrains to be spherical.
You will have to deform a high-poly sphere.
Best thing I can think of (off the top of my head), is perhaps a LOD planet, use the low poly version for in space (maybe implement bump mapping once it's all sorted out), switch to the high poly whilst going through the atmosphere.
Or have multiple LOD's which are revealed depending on altitude, only when they are close to the ground could you get away with Blitz terrains.
You will have to deform a high-poly sphere.
Best thing I can think of (off the top of my head), is perhaps a LOD planet, use the low poly version for in space (maybe implement bump mapping once it's all sorted out), switch to the high poly whilst going through the atmosphere.
Or have multiple LOD's which are revealed depending on altitude, only when they are close to the ground could you get away with Blitz terrains.