eleven v-ray Fog node
I had a low poly version of the object so I could position it within the fog, then apply my fog layer to the initial render. Fog Density is a multiplier to the Fog Distance; the larger this distance number, the more transparent the fog. If you have a distance of 750 and density of 0.5 your actual value will be 375. In the spaceship composition I’ve used this node to give it the look of moving through the atmosphere.