Here's something in the same gendre... how about a comet? Make a large asteroid (again, this would be for individual use, not for an asteroid field), say the size of a Deimos. Make sure that the comet's surface is a rotating subsystem that tumbles forward (or even on more axes if possible, but at different rates) around a submodel in the center, that also has an engine, though not as a targetable subsystem (like on an escape pod). I'm not sure if this is possible without making the engine subsystem targettable, but an engine wash would be cool in its wake. Then, use lots and lots of particles combined with a massive missile trail. For the particles, I'm not sure how they work exactly and what control we have over its properties, but if they could be altered for this model to have a longer lifespan, it would ensure a dynamic tail for it. Then, all we need is to give the model a reasonable speed in its table file, place it in FRED, and give it ai-waypoints-once orders to have it pass through the field of battle. Idealy, it would have the same grey appearance on radar as an asteroid, by using the "navbuoy" flag, but I'm not sure if this flag will accept waypoint orders. I'd also recommend "big_dammage" to keep it from being destroyed by small arms.
Now obviously, this comet is not designed to be scientifically accurate, since comets tails do not always follow them, n'or do they always HAVE a tail, but FS has never been about strict scientific adherence... more like a very classy and intelligent shoot-em up.
This may be outside the possiblities for FS2, but it could also be a chance for some of our experienced moders to show their stuff and take on such a challange.... hint, hint.
Later!
