I'm not 100% sure what people want in a planetery mod (everything! of course...), but here are some possible scenarios...
1. Flying in orbit around a planet, dunno the altitude, let's assume about the same as the Space Shuttle, maybe a little lower.
Gravity would be negligible, as would any atmospheric effects, etc. The only thing different from current FS missions would be the
BIG planet on one side of the screen. This could be implemented with a fairly low number of polys - at this distance, it's pretty flat, it could be represented as an inverted shallow bowl.
What would make it more realistic would be to animate the textures. The poly itself would stay put, relative to the player (just like nebulae/planets do now -- when you fly towards them, they remain at a constant distance) But it would be neat to have the planet rotating underneath you, the cloud patterns and/or continents would be shifting. Again, because of the scale, the player's movements in-game would not affect this rotation. (150 m/sec plus or minus won't make a difference if orbital velocity is 10,000 m/sec)
The only things missing from the current engine to implement this are the odd shaped backgrounds (convex vs concave surface) and the animation. Probably not too tough to do...
BTW this would not be a realistic orbital simulation, as odd things happen... you have to "slow down to speed up" in orbital mechanics... but it's a
game...2. Atmospheric flight more like a flight simulator package. Big engine changes, such as allowing for the physics of atmospheric flight (lift, gravity, etc). Adding features like weather, nightime flight, etc. makes it even more complicated. Maybe we should wait for Microsoft to open-source their Flight Simulator
3. Landing/Ground warfare get real.

Once again. a totally different type of engine. Has nothing in common (controls, HUD, etc.) with FS2, except the storyline. Hell, why not throw in submarine warfare while we're at it (after all, we know what those Vasudans wuv...)
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I might be misinterpreting what people are requesting (or fantasizing about

) It
would be neat to tie it all together -- space, air, and surface -- but really, we're talking about three different engines... If that's what we want, we need to get two more engines, the FS2 is pretty much a space simulator exclusively...