大道至简-看动画了解弹道导弹的突防措施

视频是用动画的形式用简单的语言介绍弹道导弹突防的一些措施，主要介绍的是气球轻诱饵、诱饵加热以及多弹头等突防措施，是由美Union of Concerned Scientists编辑发布的。

英文配音:

The United States proposes to build a national missile defense system to intercept long-range missiles attacking the US.Here's how it's supposed to work.

After launch the attacking missiles， warhead is released early in flight before any interceptors can reach it. The defense uses ground-based radars and satellite based heat sensors to detect the incoming warhead. It then launches interceptor missiles each carrying a kill vehicle. As a kill vehicle approaches the warhead it relies on its own detectors to locate the warhead guiding itself to smash into it. 

That's the theory. Unfortunately if the US were attacked, things probably wouldn't look quite so simple. Any country that can build a long-range missile could also build far simpler devices called countermeasures to confuse the defense. For example the attacker could use balloons made out of shiny mylar plastic just like children's balloons. Dozens of uninflated balloons could be packed around the nuclear warhead each to be inflated with a small gas generator like a car airbag. Only slower after launch, the missile releases dozens of balloons all empty except for the one containing the warhead.Because there is no air resistance in space,the lightweight balloons and the heavy warhead all travel at the same speed. The defense radars can't tell which balloon contains the warhead. The shiny metallic coating of the mylar prevents the radars from seeing what's inside each balloon. Furthermore ,the balloons can be made to tumble, so the radar can't identify the warhead from its motion either. 

What about heat detection?A warhead gives off heat, however a small battery-powered heater can be used to heat the balloons to different temperatures. As a result the defense's infrared sensors have no way to determine which balloon contains the warhead. So now the defense has to shoot at all the balloons to intercept the warhead. The u.s. plans to build 100 to 250 interceptors and will fire up to 4 interceptors at each target if the attacker launches several missiles each with dozens of balloons. The defense would quickly run out of interceptors. 

Another easy countermeasure is using bomblets instead of a single large warhead. The attack is made with many small warheads called bomblets or submunitions. The missile releases a hundred or more bomblets early in flight before the interceptors can reach them. The cloud of bomblets arcs through space growing up to fifteen miles across by the time it reaches the target. Because of this using bomblets is the most effective way to disperse chemical and biological agents from a missile. Now every object the defense sees is a real warhead but there are simply too many for the defense to intercept them. All countermeasures like these would defeat the planned missile defense system and a defense that won't work is no defense at all.

参考中文译文： 

 美国要建立一个国家导弹防御系统来拦截攻击美国的远程导弹。这是它应该如何工作的。导弹发射后，攻击导弹弹头在任何***到达之前、在飞行早期释放。导弹防御系统使用地面雷达和卫星热传感器来探测进入的弹头。然后发射***导弹，每个导弹携带一个杀伤***。当一个杀伤***接近弹头时，它依靠自己的探测器来定位弹头，引导自己撞向弹头。

当然这是理论上的。不幸的是，如果美国遭到弹道导弹攻击，事情看起来可能不会那么简单。任何一个能制造远程导弹的国家也可以制造一种更简单的装置，用于导弹突防。例如，攻击者可以使用由闪亮的聚酯薄膜塑料制成的气球，就像儿童的气球一样。在核弹头周围可以装上几十个未充气的气球，每个气球都用一个小型的气体发生器充气，就像汽车安全气囊。在导弹发射后不久，除装有弹头的气球外，数十个气球都是空的，因为太空中没有空气阻力，所以轻型气球和重型弹头都以相同的速度飞行。导弹防御雷达无法分辨哪个气球含有弹头。聚酯薄膜闪亮的金属涂层防止雷达看到每个气球内的东西。此外，气球可以翻滚，因此雷达也不能从弹头的运动中识别弹头。

热检测怎么样？弹头释放热量，但是一个小的电池驱动的加热器可以用来把气球加热到不同的温度。因此，导弹防御的系统中的红外传感器无法确定哪个气球含有弹头。所以导弹防御系统必须向所有气球射击来拦截弹头。美国计划建造100到250个***，如果攻击者发射数枚导弹，每枚导弹都有几十个气球，那么每个目标将发射多达4个***。防御系统很快就会耗尽***。另一个简单的对策是使用多弹头炸弹而不是单一的大型弹头。这种攻击是用许多被称为炸弹或子母弹的小弹头进行的。在***到达之前，导弹在飞行初期释放了100多枚子弹头。当炸弹云到达目标时，它会在长达15英里的空间中形成攻击云。因此，使用多弹头是进行化学武器攻击的最为有效的方法。现在，弹道防御系统看到的每一个物体都是一个真正的弹头，但是来袭目标实在太多了，无法拦截它们。像这样的突防对抗措施都将击败导弹防御系统，而一个不起作用的防御系统根本就不是什么防御系统。