# Realistic Missile Flight Paths

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I'm writing a small strategy game that involves launching missiles from silos and mobile launchers over moderate distances (i.e. shooting across the entire map). These launches will also be shown like cinematics from the side and if I can manage, with the camera following a missile salvo.

I guess there won't be some kind of convenient library like there is for physics in driving games that I could just use to take care of everything?

[b]My trouble already begins with the launch.[/b][list]
[*]I'm assuming small missiles achieve aerodynamic flight right out of the launcher (their acceleration is huge), so these can go right over to the targeting phase.
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[*]Manned rockets seem to be launched vertically and have an acceleration phase during which they are unstable (being prevented from falling over by thrust vectoring) - is that the case with larger missiles like ICBMs, too? Are there any big missiles that are launched at an angle?
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[b]Next is targeting:[/b][list]
[*]How does a missile hit a certain position on the ground? Probably, there is a cruise phase where the missile climbs to and holds a certain height, but at some point, it has to dive to the target. If the missile was capable of instantaneous direction changes, I could calculate the point where the dive begins given the desired angle of impact, but the direction change will hardly be that abrupt.
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[*]It gets even more difficult for missiles designed to intercept other missiles. If I have an object's position, direction & velocity, it's probably possible to calculate the direction a missile needs to travel in order to hit the target given an initial position and constant velocity. Any got such a formula or links to it?
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I'm not aiming for total realism, I just want it to look good ;) Edited by Cygon

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Intercepting is an active research topic I think.

For cruise missiles, they should have sufficient thrust to weight ratio to make fairly tight turns, if they're going to be doing the "drop down the chimney" thing, though I believe most of those cases are more guided bombs dropped from height rather than cruise missiles.

For the really big ones, they don't really have a cruise phase, they go up, then they come down. That's what the B part of Inter-continental Ballistic Missile is. They don't really have to decide when to start descending, as gravity has a bit of a monopoly on that.

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Interesting! I totally ignored the "ballistic" in ICBM. Doing some YouTube research I've even fond a very good animation with time stamps detailing the launch of an ICBM: [url="http://www.youtube.com/watch?v=2aHpqqhaHJ0"]Minuteman III ICBM Launch and Flight[/url]. If I believe that animation, an ICBM is basically a guided (or perhaps even unguided) bomb strapped to an orbital launch vehicle.

I discovered a library which I believe does exactly what I'm looking for: [url="http://opensteer.sourceforge.net/"]OpenSteer[/url]. It contains several predefined behaviors including "seek" and "arrival" which sound like they at least contain the math I need, if not outright solving my problem.

There's also a very well illustrated post that explains the topic here: [url="http://forums.tigsource.com/index.php?topic=10130.0"]Basic PID controllers: Missiles, Robots and Cars[/url] - maybe I'll just use the technique explained there as it's really simple to understand (though I have past nightmares about tuning a PID controller for a precision motor ).