Lightspeed's Nebula Pack
From FreeSpace Wiki
Lightspeed's nebula pack is an extremely popular background pack for FS2. It includes over 20 new nebulae and high-res versions of all planet backgrounds included with the game. You will need Lightspeed's nebulae to play most of the larger user-made campaigns.
Full LS Nebula Pack | Freespacemods.net
Full LS Nebula Pack (ZIP) | Mediafire
The entire Lightspeed pack is included with Turey's installer and Hades Combine's FS2 DVD.
It has also been included in the MediaVPs from version 3.6.10 onward.
-Please include installation instructions here-