Hypersonic boom
高超音速发展
Long range, gliding missiles that fly at more than five times the speed of sound are coming 远程滑翔导弹正以超五倍音速的速度“飞来”
“‘Once the rockets are up, who cares where they come down?/ That’s not my department!’ says Wernher von Braun.”Tom Lehrer’s satirical ditty on the Nazi-turned-American rocketeer was faithful to the essence of early missile development, whose principal challenge was hoisting the weapons into the sky. Gravity did most of the rest. The first warheads capable of steering on descent did not arrive until the 1980s. Even they were limited in how much they could move around, making it pretty easy to predict their target area.
“‘一旦火箭升空，谁会在意它们落在哪里? / 那不是我的事！’沃纳·冯·布劳恩说。”汤姆·莱勒(Tom Lehrer)对这位纳粹出身的美国火箭专家的讽刺小调，如实反映了早期导弹研发的要义——其主要挑战是将武器升上天空，剩下的大部分都决定于重力作用。直到20世纪80年代，第一批能够在下降过程中加以操纵的弹头才问世。此前，它们的活动范围甚至也受到限制，这使得预测它们的目标区域变得相当容易。
A new generation of hypersonic missiles is changing all that. Some might be capable of gliding across continents at great speed, their target unpredictable until seconds before impact. Russia claims to have a hypersonic glider on the cusp of deployment; others are redoubling their efforts. Many are likely to start entering service in the 2020s. All this opens up new military possibilities—and problems.
新一代高超音速导弹正在改变这一切。有的导弹有可能以极快的速度滑过大陆，其目标在撞击前几秒钟是无法预知的。俄罗斯声称即将部署一枚高超音速滑翔导弹；有的国家则在加倍努力。许多导弹可能到21世纪20年代开始服役。所有这些都带来了新的军事可能性，也会引发诸多问题。
Missiles that travel at speeds greater than Mach 5 (five times the speed of sound, or about 1.5km per second), have existed for some time. Intercontinental ballistic missiles (ICBMs) re-enter the atmosphere at up to 8km per second. What is different about the hypersonic weapons in the pipeline is that they are designed to sustain such speeds over long distances, manoeuvre as they do so and, in some cases, hit targets with pinpoint accuracy.
速度超过5马赫(音速的5倍，约每秒1.5公里)的导弹已经存在一段时间了。洲际弹道导弹(ICBMS)以每秒8公里的速度重新进入大气层。弹道高超音速武器的不同之处在于，其设计目的是长距离保持这样的速度，同时可以进行操控，在某些情况下，还能精确命中目标。
“Manoeuvrable missiles travelling at many times the speed of sound barely leave time for considered human responses,” warned Heiko Maas, Germany’s foreign minister, in March. Such weapons may also elude today’s arms-control agreements, which were written for an earlier generation of weapons.
德国外交部长海科·马斯(Heiko Maas)今年3月警告称：“以多倍音速飞行的可操纵导弹让人几乎没有时间去深思熟虑。”这类武器也可能规避当今军备控制协议，因为这些协议是针对上一代武器制定的。
There are two basic designs: cruise missiles and gliders. Hypersonic cruise missiles are essentially faster versions of existing ones but powered by very different jet engines. Gliders are pricier and harder to build, but can travel faster and farther, and so are receiving more attention. Like ICBMs and von Braun’s V-2s, they are lofted into space and fall to earth unpowered. But unlike the old-fashioned projectiles, they do not follow a predictable, parabolic arc through the sky. Instead, a hypersonic glide vehicle (HGV) detaches from the rocket while it is still ascending and either skips along the upper atmosphere or, having re-entered, glides through it for hundreds or thousands of kilometres.
基本设计包括两类：巡航导弹与滑翔导弹。高超音速巡航导弹本质上是现有导弹的更快版本，但由非常不同的喷气发动机提供动力。滑翔导弹造价更高、制造难度更大，但飞行速度更快、距离更远，因此正受到越来越多的关注。就像洲际弹道导弹和冯·布劳恩的V2火箭一样，它们被送入太空，在没有动力的情况下坠落到地球。但与老式发射物不同的是，它们在空中并不沿着可预知的弧形抛物线运动。相反，高超音速滑翔飞行器(HGV)在火箭仍在上升时脱离火箭，要么沿高层大气跃进，要么在重新进入大气层后滑翔数百或数千公里。
Such gliders have several advantages. Ballistic missiles are less agile and tend not to be very accurate. A Minuteman III ICBM, the backbone of America’s nuclear arsenal, has a “circular error probable” of roughly 120m, meaning only half the missiles fired are expected to land within 120m of the impact point. That is fine for nuclear bombs but useless for hitting a ship or runway. Today’s cruise missiles, on the other hand, are very accurate—one could be sent through a window—but much slower. HGVs combine the speed of ballistic missiles with the manoeuvrability and accuracy of cruise missiles. “You can fly, you can shape your trajectory, you can turn,” says Will Roper, the US Air Force acquisitions chief.
这种滑翔机有几个优点。弹道导弹不太灵活，而且往往不是很精确。“民兵3”洲际弹道导弹是美国核武库的支柱，其“圆概率误差”约为120米，也就是说导弹发射后只有一半预计会落在距弹着点120米以内。这对于核弹来说算好的了，但要是打击一艘船或者一条跑道就没用了。另一方面，现今的巡航导弹非常精确——可以通过一扇窗户发射——但速度要慢得多。HGV融合了弹道导弹的速度与巡航导弹的机动性和精确性。美国空军首席采购官威尔•罗珀(Will Roper)表示：“你能飞，你能改变轨迹，你能转弯。”
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 100km, 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.
运行轨迹是关键。一枚无动力洲际弹道导弹弹头的大部分时间都在真空中运动，无法闪避或俯冲，但HGV80%的时间都在100公里以下，这使得它们在飞行大部分过程中具有机动性。它们还可以利用地球曲度将自己隐藏起来，从而避开地面雷达更长时间。美国洲际弹道导弹必须飞越俄罗斯才能击中中国——这可能造成危险的误解——而滑翔导弹可以采取更迂回的路线，避开导弹防御系统，让对手无法确定目标。
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.
高超音速滑翔导弹的研制已历时近一个世纪。1928年，第一枚火箭助推滑翔导弹在德国飞行。二战期间，德国工程师试图通过让冯·布劳恩的V-2火箭滑翔来增加其射程。战后，美国和苏联盗用德国的火箭技术，引领了一系列的技术飞跃。阿尔法·德拉科(Alpha Draco)是美国的一种HGV，在上世纪50年代接受了高超音速速度的测试，后来在太空竞赛中其高超音速滑翔功能又得以改进：航天飞机在某种程度上是一种高超音速滑翔机。
War at Mach 5
5马赫速度的战争
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 2,000℃. 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.
那么，高超音速导弹的发展之路为何如此漫长呢？延长高超音速航程面临极为复杂的科技和工程难题。智库卡内基基金会的詹姆斯·阿克顿（James Acton）指出，航天飞机在高超音速下的升阻比约为1；一架先进的滑翔机则需要两倍以上。升阻比增高，滑翔机前缘就需要十分锋利，再加上极快的速度，可以产生高达2000℃的表面温度。这会腐蚀滑翔机的保护层，烧坏电子设备，使其变形。2011年，美国对一款原型机的测试无功而返，因为它的外壳产生气泡并最终脱落，由此产生的冲击波在不到两秒钟的时间里就摧毁了控制系统。
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.
一家正在开发滑翔导弹的武器公司的专家说，唯一可行的办法是用栓皮覆盖飞行器。但这在几分钟或更短的时间内就会蒸发掉，因此不适用于远程导弹。他说，速度超过10马赫时，要想迅速散热，“让人望而却步”，而且“估计是不可能的”。
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.
高速飞行还会分解大气中的分子，在滑翔导弹周围形成一个带电粒子(或“等离子体”)场，从而干扰GPS和其他引导导弹到达目标所需的信号。美国空军科学研究办公室的伊维特·莱瓦(Ivett Leyva)在2017年的一篇论文中写道，研究人员“仍然不完全理解高超音速飞行的物理原理”。
The big powers have all made some progress in surmounting these challenges. Thomas Bussing, who heads missile development for Raytheon, an arms company, says there has been a “step change” over the past decade, thanks to advances in computational fluid dynamics, new materials and electronic and guidance systems. America, which set aside $2.6bn for hypersonic weapons in the Pentagon’s 2020 budget, is probably farthest ahead. It tested a wedge-shaped glider in 2010 and 2011, a more successful cone-shaped design in 2011, 2014 and 2017 (the Alternate Re-entry System) and is working on tactical systems that use smaller, cheaper rockets and could be launched from ships and aircraft.
大国在应对这些挑战方面都取得了一些进展。托马斯·巴辛(Thomas Bussing)是雷神武器公司导弹研发部门的负责人，他说，由于计算流体动力学、新材料、电子和制导系统的发展，在过去的十年里已经发生了“阶跃变化”。美国在五角大楼2020年预算中为高超音速武器安排了26亿美元，可能遥遥领先。该公司在2010年和2011年测试了一种楔形滑翔导弹，在2011年、2014年和2017年测试了一种更成功的锥形滑翔导弹(交替式再入系统)，目前正在研发一套战术系统，所用的火箭更小也更便宜，而且可以从舰船和飞机上发射。
Russia has been working on hypersonics for decades, haltingly. Its flagship Avangard glider was flaunted publicly by President Vladimir Putin in March 2018 and tested to greatfanfarein December, after which it was declared ready for service this year—somewhat implausibly, say experts. Pavel Podvig of the United Nations Institute for Disarmament Research points out that very few of the glider’s tests were successful and that the programme was nearly shut down four years ago.
几十年来，俄罗斯在高超音速研究方面一直步履蹒跚。2018年3月，俄罗斯总统弗拉基米尔·普京(Vladimir Putin) 公开炫耀了其旗舰级滑翔导弹——“先锋(Avangard)”，并在12月进行了大张旗鼓的测试，之后宣布该导弹拟于今年服役——专家认为，这有点令人难以置信。联合国裁军研究所的帕维尔·波德维格 (Pavel Podvig) 指出，滑翔导弹的试验很少取得成功，而且四年前该项目就差点被关停了。
China has tested its own DF-ZF HGV at least nine times since 2014. Almost nothing is publicly known about its nimbleness or accuracy. Australia, India, France and Japan are all chasing the pack. “We have lost our technical advantage in hypersonics,” warned General Paul Selva, America’s highest-ranking air-force officer in January. China has built two to three times as many hypersonics-related facilities as America, including the world’s fastest wind tunnel for testing, and pumped out the most public research on the technology (716 publications in 2017, compared with 207 from America and 76 from Russia).
自2014年以来，中国已经至少9次测试了自己的DF-ZF高超音速滑翔飞行器。公众对其灵活性和准确性几乎一无所知。澳大利亚、印度、法国和日本都在“跟跑”。今年1月，美国空军最高级官员保罗·塞尔瓦(Paul Selva，译注：美国参谋长联席会议副主席、美国空军上将暨美国国防部二号人物)将军警告说：“我们已经失去了超音速上的技术优势。”中国建造的高超音速相关设施是美国的两到三倍，其中包括世界上最快的风洞测试，并对该技术进行了公开面最广的研究(2017年发表716篇论文，相比之下，美国发表207篇，俄罗斯发表76篇)。
Even so, Mr Acton suggests that the Chinese programme is probably less advanced than America’s. For one thing, America is testing its gliders over significantly longer ranges than China is. It is also solving a different, harder, problem. America wants the ability to deliver conventional warheads over continental distances. It is because ICBMs are not accurate enough for this that it wants HGVS. Russia and China are keener on nuclear-tipped ones, partly because they fear their existing nukes might one day be stopped by improvements in America’s missile-defence shield. Their own gliders need not be so precise.
尽管如此，阿克顿先生认为中国的项目可能不如美国的先进。首先，美国正在比中国更远的射程上测试滑翔导弹，并且在解决一个不同的、更难的问题。美国希望有能力在洲际范围内运载常规弹头。由于洲际弹道导弹在这方面不够精确，因此需要用HGV。俄罗斯和中国更热衷于拥有带有核弹头的滑翔导弹，部分是因为他们担心他们现有的核武器有一天会遭到改进后的美国导弹防御系统拦截。他们自己的滑翔导弹不需要特别精确。
Douglas Barrie, an expert at the International Institute for Strategic Studies, a think-tank, forecasts that hypersonic gliders are likely to start entering service in the early 2020s. The result might be twitchier decision-makers and a more frenzied battlefield.
智库国际战略研究所(International Institute for Strategic Studies)专家道格拉斯·巴里(Douglas Barrie)预测，高超音速滑翔导弹可能在本世纪20年代初开始服役。其结果可能是，决策者更加紧张，战场更加疯狂。
Area defences, which guard broad swathes of territory like continental America, rely on shooting down missiles mid-course and on a straightforward trajectory. Gliders do not go as high and are less predictable, hence Mr Putin’s boast that the Avangard is “invulnerable to interception” (some reckon that interceptors placed in space might have a shot as super-hot gliders should stand out to infra-red sensors).
区域防御系统(area defences)守卫着广袤领土，比如美国大陆，它依靠的是在中途击落导弹和一条明确的轨道。滑翔导弹飞得没那么高，也不那么容易预测，因此普京夸口说“先锋”是“不会被拦截的”(一些人认为，放置在太空的拦截器可能有机会击中它，因为超热滑翔导弹应该会在红外线传感器面前“现出原形”)。
Point defences, which guard individual sites against shorter-range missiles, might have more luck. Gliders must slow down as they approach their targets. Systems like America’s THAAD have a proven ability to shoot down ballistic missiles, which close in more quickly.
点防御系统(point defences)可以保护单个地点免受短程导弹的攻击，或许运气更好。滑翔导弹在接近目标时必须减速。美国萨德之类的系统已经被证明有能力击落弹道导弹，这种导弹接近目标时速度更快。
“The world has changed dramatically,” says Mr Bussing. “These systems are very, very difficult to counter and fundamentally give the holder a tremendous advantage over the states that don’t have them. The sense of urgency to develop ways to counter them is an imperative.”
“世界飞速变化，”巴辛说，“这些系统非常、非常难以对付，从根本上说，拥有这些系统的国家因此会比没有的国家有着巨大的优势。当务之急就是要有一种紧迫感，努力找到对付它们的方法。”
One American military official suggests that humans will have to hand ever more control to defences that are already semi-autonomous: “There will be no time at all for a man in the loop.” The uncertain payload of gliders is another problem. If targets could not tell the difference between conventional and nuclear gliders, or feared that conventional ones, through accuracy and kinetic energy alone, could threaten important targets, they might choose to launch their own nuclear forces to avoid losing them.
一位美国军方官员表示，人类将不得不把更多的控制权交给已经处于半自治状态的防御系统：“一个人根本没有时间参与其中。” 还有一个问题是滑翔导弹的有效载荷不确定。如果目标不能分辨出常规滑翔导弹和核滑翔导弹的区别，或者担心常规滑翔导弹仅通过精度和动能就可对重要目标构成威胁，他们可能会选择发射自己的核力量，以避免失去它们。
There are also wider implications for arms control. The impending collapse of the Intermediate-Range Nuclear Forces (INF) Treaty, which barred America and Russia from possessing land-based missiles of 500km-5,500km ranges, clears the way for both countries to develop and deploy new ground-launched hypersonic missiles. A separate treaty, New START, caps the number of longer-range weapons, but is up for renewal in 2021 and looking shaky. When it was negotiated in 2010, America and Russia implicitly agreed that gliders would not be covered. Former officials say that was a mistake.
军备控制还有更广泛的含义。正面临瓦解的《中程核力量条约》(INF)禁止美国和俄罗斯拥有500公里至5500公里射程的陆基导弹，为两国开发和部署新的地面发射高超音速导弹扫清了道路。另一份名为《新削减战略武器条约》(New START)的条约为远程武器的数量设定了上限，但该条约到2021年就将失效，而且看起来并不可靠。2010年谈判时，美国和俄罗斯含糊其辞地同意该条约不包括滑翔导弹。前官员称这是一个错误。
Germany convened an arms-control conference in Berlin on March 15th to kick- start a discussion on taming the risks posed by futuristic weapons, including hypersonic missiles, through diplomacy. Mr Maas called for an “international missiles dialogue” to discuss the challenge.
3月15日，德国在柏林召开了一场军备控制会议，开始讨论通过外交手段遏制包括高超音速导弹在内的未来武器带来的风险。马斯呼吁开展“国际导弹对话”来商讨这一挑战。
The UN’s disarmament office has proposed that rivals could swap information on test flights and take other confidence-building measures. Corentin Brustlein of IFRI, a French think-tank, suggests capping glider numbers. Yet America and Russia are enmeshed in worsening disputes over today’s weapons, let alone tomorrow’s, and China shows little interest in tying its hands. Gliders are likely to enjoy a fair geopolitical wind.
联合国裁军办公室提议，竞争对手可以交换试飞信息，并采取其他建立信任的措施。法国智库IFRI（法国国际关系研究所）的科朗坦·布拉斯特莱恩(Corentin Brustlein)建议限制滑翔导弹的数量。然而，对于现在的武器，美国和俄罗斯之间的争端已经日益恶化，更不用说未来的武器了，而且中国也基本没有流露出要“收手”的意思。滑翔导弹可能会乘着一股公平的“地缘政治风”飞翔。
（陈继龙译自《经济学人》杂志2019年4月6日刊）