高超音速的轰鸣( 二 )
这样的滑翔导弹有几个优势。弹道导弹几乎没有灵活性也不是很精准。美国核武库的主力—民兵III型洲际弹道导弹圆概率误差大约是120米，这意味着只有一半的导弹能够落在目标点120米的范围内。这对核弹没有什么问题，但对军舰和跑道等目标就没有意义了。另一方面，现有的巡航导弹打击精度很高，甚至能够穿越窗户攻击目标，但是速度太慢了。而高超音速滑翔导弹综合了弹道导弹的速度优势和巡航导弹的操控性和高精度。美国空军采购主管威尔- 罗珀评价HGV：“可以飞行，可以调整轨迹，可以转向”
The key is their trajectory. An unpowered icbm warhead spends most of its time in the vacuum of space where it cannot duck or dive, but HGVs spend 80% of their time below 100 km, allowing them to manoeuvre for most of their flight. They can also dodge ground-based radar for longer by hiding behind the curvature of the Earth. Whereas American icbms must fly over Russia to hit China—which could lead to dangerous misunderstandings—gliders could take more circuitous routes, avoiding missile defences and leaving adversaries uncertain of the target.
关键在于导弹轨道，无动力洲际弹道导弹弹头大多数时间处于不能进行规避和俯冲的真空中，而高速滑翔导弹80%的飞行时间处于100千米以下，这一高度可以对导弹进行调整。它也可以利用地球曲率躲避地基远程雷达的探测。美国洲际弹道导弹需要穿越俄罗斯才能攻击中国，这很有可能导致危险的误判。与之相比，滑翔导弹能采用更加迂回的路线，避开导弹防御系统，也让对手无法判断攻击目标。
Hypersonic gliders are almost a century in the making. The first rocket-boosted glider flew in Germany in 1928. During the second world war, German engineers tried to extend the range of von Braun’s V-2 by having it glide. After the war, America and the Soviet Union pilfered German rocketry, leading to a series of technological leaps. Alpha Draco, an American HGV, was tested to hypersonic speeds in the 1950s and hypersonic gliding was refined by the space race: the space shuttle was a hypersonic glider, in its way.
高超音速滑翔导弹制造已经差不多一个世纪了。1928年，第一枚火箭推力滑翔导弹在德国升空。在二战期间，德国工程师通过添加滑翔能力来增加布劳恩V-2导弹的射程。战后，美国和苏联窃取了德国的火箭资料，带来了一系列的技术进步。美国高超音速滑翔导弹-阿尔法.德拉科，在1950年进行了高超音速测试。高超音速滑翔技术在太空竞赛中得到改进：从某种意义上讲，宇宙飞船就是一种高超音速滑翔器。
War at Mach 5 （5马赫之战）
Why, then, have hypersonic missiles taken so long to arrive? Extended hypersonic flight presents fiendish scientific and engineering challenges. The lift-to-drag ratio of the space shuttle at hypersonic speeds is around one, notes James Acton of the Carnegie Endowment, a think-tank; an advanced glider would require over twice that. Higher lift-to-drag ratios require sharp leading edges, which, combined with extreme velocities, can generate surface temperatures up to 2,000oC. That can erode a glider’s protective coating, fry its electronics and bend it out of shape. America’s test of one prototype in 2011 failed when the skin blistered and peeled off. The resulting shockwaves overwhelmed control systems in less than two seconds.
为什么过了这么久才出现高超音速导弹呢？涉及高超音速飞行给科学和工程方面带来了恶魔般的挑战。智库卡内基基金会的James Acton指出：高超音速太空飞船的升阻比就是挑战之一，而先进滑翔导弹的升阻比是之两倍。高升阻比需要锐利的前端。在巨大速度作用下，其表面温度能达到2000度以上。这将腐蚀滑翔导弹的保护层，炙烤其中的电子设备，使导弹扭曲变形。2011年，美国的导弹试验原型由于表面起泡剥落而失败。其产生的冲击波在2秒内吞没了控制系统
The only thing that seems to work, says an expert at an arms company that is developing gliders, is to cover the vehicle in cork. But that is vaporised in minutes or less, so does not work for long-range missiles. Dissipating heat as quickly as it is built up is “daunting” and “perhaps impossible” above Mach 10, he says.
“唯一可行的方案”，一家正在研发滑翔导弹的军工公司的专家说：“就是在导弹表面覆盖上软木材料”。但这些材料会在几分钟内蒸发干净，所以并不适用于远程导弹。在10马赫以上的速度时，基本做不到良好的散热。
Great speeds also break up molecules in the atmosphere, creating a field of charged particles (or “plasma”) around the glider, which disrupts GPS and other signals required for guiding the missile to its target. Researchers “still don’t completely understand the physics of hypersonic flight,” wrote Ivett Leyva of America’s Air Force Office of Scientific Research in a 2017 paper.
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