Here's a dorky spaceship with some nifty thrust coming from the engines.

Each plume of thrust is a fairly simple object.

The basic shape of the plume is a cone. Transparent Edges is on Luminosity is way up There's a Transparency Texture with Z falloff, so the plume fades away to nothing behind the ship. There's a subtle Fractal Noise Surface Color Texture, which should be done to the individual's taste. There's a big fat lens flare at the base of each plume.

With the lens flares set normally, and Glow Behind Objects off, The thrusters look great from behind the ship.

But look what happens when we turn the ship around:

You can see the lens flares THROUGH the ship! So now we might try turning on Glow Behind Objects.

Here's what happens:

Whoops. The lens flares are too close to the ship, so they cut through it near the back. That's because the flares are rendered on an imaginary polygon that always directly faces the camera.

Fade Behind Objects won't work either, because the flares won't render at all!

So now what? Haven't we tried everything?

Not yet! Let's think about it. What is our goal? We want the ship to render in front of the flares, the thrusters, and the stars.

Here's a hint: If all else fails, use layers.

We can render everything behind the ship first, then composite the ship over top. So, we temporarily set the ship's Object Dissolve to 100%, and turn Glow Behind Objects off.

Then we render the scene:

Now, we remove or dissolve everything in the scene except for the ship. That includes lens flares, so we Disable Lens Flares in the Lights menu.

Then, we load up the image sequence we rendered before, and set it as the Background Image.

Now we render the thing again.

Problem solved.

There's one very big important note - Watch out when the thrusters are near that half-way point, where they're not quite in front of the ship, and not quite behind it. You'll have to split up the scene into smaller chunks and / or use some clever dissolve envelopes.

Good luck! - GLYPH