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Old March 18 2013, 09:11 PM   #274
gturner
Admiral
 
Location: Kentucky
Re: SpaceX is a go for April 30th: 1st commercial launch to space stat

Except that in laboratory conditions you know exactly where the missile launched from, exactly what it's trajectory is, and there's no actual risk involved if you intercept it too late or too low, plus there's usually only one target and you know for sure that's the one you're shooting at.
But for an ICBM intercept you don't need the launch location, just the range and vector range rate. You don't need to know the history of the trajectory, even though you'd know more about that than any conventional tactical launch where unknown aircraft are lobbing missiles on multiple incoming vectors, often from below the radar horizon. The problem is much simpler than warship defense where they have to expect a saturation attack from a variety of platforms and incoming angles simultaneously, possibly coming in with heavy jamming support, and where the warning and flight times are shorter. And with an ICBM intercept, you don't have to worry that some of the incoming missiles are friendlies returning to refuel.

That's the actual battlefield environment we're used to. The battlefield environment for space is vastly cleaner, the sensor data is better, the background problems are gone, the targets have almost no ability to maneuver without creating an instantaneous and large IR signature, they follow a purely ballistic path in between maneuvers, and they're very, very fragile compared to conventional targets (a slightly damaged warhead isn't going to survive re-entry, but a flaming Kamikaze can still hit).

It's a much easier targeting environment than the early Sidewinders had to cope with, and they could complete an intercept using just half-a-dozen vaccuum tubes for a control system, yet were able to distinguish targets from bright background clouds, adjust their control sensitivity for differing air-speeds and air-densities, and make off-angle lead intercepts.

The difficulty with ABM intercepts is the massive delta-V required to get the terminal package into the target environment.
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