I only found this thread just now from the 'recent posts' list. 

But wow - that first one is stunning. The hills in the background look a little smooth - no rocky parts, but other than that it's great.  

Do you have higher res versions of any of them? I just tried the asteroid one in a scene, and though it certainly gives a great sense of depth and immersion, the resolution loss kinda kills it. The bright centre sorta just becomes a light blur and the smaller roids become groups of large pixels.
But I reckon if you combine that type of image with a starfield and *maybe* a more expansive nebulae system, you have a 
brilliant mission skybox. 

The nebulae ones look good, (I like the middle one the best) but what are they intended for?