which specific addon is it?
can you provide me with a link?
---------- Post added at 07:00 PM ---------- Previous post was at 06:48 PM ----------
As for the explanation, its not particularly hard if you know how to use photoshop or some other image editing program.
Orbiter uses DDS (Direct Draw) files for all it's surface tiles and textures.
DDS files usually have 4 channels; Red, Blue, Green, and Alpha.
Red, Blue, and Green (as thier titles imply) determine the actual color and shape of the texture, and function in much the same way as any tradional "three-color" photo.
Alpha determines any special effects such as tranparency or luminosity(glowing) that should be applied to the image in game.
I'm guessing that the black area in the screenshot you postsed is supposed to be transparent, allowing you to see the surface tile under it. If you have a program that can edit *.DDS files (as I said, I use GIMP) open up the Baikonuer surface tiles and check to see if the alpha channel was set to make the black area transperant. If not, change it.
There are plenty of online tutorials explaining exactly how to go about doing this. Just run a search for "editing alpha channels" or something similar.
