这主意可不是异想天开

SCWalter

动汽车企业家及火星私人殖民的拥护者埃隆·马斯克现在打算重塑铁路运输。马斯克提出重现一种叫做真空列车的老式科幻概念，列车将以超过1 200千米的时速带着旅客横穿加州——比喷气客机还要快。他的想法至少在理论上是可行的，如果付诸实践会如何呢？

California is home to many clever people. One of them is Elon Musk， the hyperactive boss of Tesla Motors， an electric-car company， and SpaceX， a rocketry business （he also sits on the board of a solar-energy firm）. There is nothing Mr. Musk likes more than revolutionizing high-tech industries. And he thinks he has come up with a better way to get California moving than a standard high-speedtrain—Hyperloop， prompting excited speculation about what he might have had in mind.

Mr. Musks Atmospheric Caper

Essentially， Mr. Musk proposes to revive an old science-fiction idea called the vac-train （short for “vacuum train”）， albeit with a few important tweaks. The Hyperloop would carry passengers across California at more than 1，200 kph—faster than a jet airliner—allowing them to zoom between San Francisco and Los Angeles in little over half an hour， compared with more than two-and-a-half hours for California High Speed Rail project. Mr. Musks notional budget is around $6 billion， less than a tenth of what the high-speed train is supposed to cost.

Vac-trains， as first described in the 1910s by Robert Goddard， would send rolling stock （or hovering stock， perhaps） hurtling through hermetically sealed tubes from which the air has been evacuated. The trains would thus encounter no drag， and be able to reach immense speeds. Goddard reckoned his design—which also proposed magnetic levitation instead of wheels—was good for about 1，600 kph.

This and other designs for transporter tubes inspired much futuristic art， but none was ever built because maintaining a vacuum in a long tunnel is difficult. Even a small leak would scupper a full-fledged vac-train， which relies on no air at all being able to build up in front of it， and thus slow it down. For that reason， the Hyperloop is not actually a true vac-train. Instead， Mr. Musk plans to remove sufficient air from the tubes to give them a pressure roughly a sixth of that on the surface of his beloved Mars， or a thousandth of that on earth at sea level. This would keep the air resistance low enough to deal with in other ways.

The chief of these would be to suck up the air that did accumulate in front of the tubes rolling stock using a fan， and then expel most of it from the pods rear end. Some of this air， though， would be diverted out of the sides through special skis， to create a cushion that would stop the pod touching the tunnel walls.endprint

Each pod would be launched by a linear-induction motor （such motors are also being tested for use as catapults on aircraft carriers）， and booster motors every 110 km would keep its speed up. On reaching its destination， the pod would pass through a motor that works in reverse， converting its kinetic energy back into electricity for storage in batteries or use in motors up the line. And， this being California， the whole thing would naturally be powered by solar panels mounted on the roof of the tube.

Loop the Loop

Its breathtaking audacity aside， the thing does look feasible as an engineering project.

The tube would be held above ground， on pylons， reducing the amount of land it consumed， and would follow existing roads， which should simplify construction and make maintenance easier. And the air cushion surrounding each pod should ensure that the ride is smooth. Moreover， although unexpected engineering problems would be bound to crop up， Mr. Musks experience—and that of his engineers—with space flight and car design would bode well for overcoming them.

With projects like this， though， good engineering is never enough. Politics and economics are more forbidding obstacles. Being new， the Hyperloop is risky.

In the past Mr. Musk has said that， given his other commitments， he lacked the time to try to build the Hyperloop himself. The reason for putting it into the public domain was therefore to give someone else the chance to take it up. “I think it might help if I built a demonstration article，” he mused. “So I think I probably will do that， actually.”

美国加州有许多聪明人，埃隆·马斯克就是其中之一。他精力旺盛，身兼一家电动汽车公司——特斯拉汽车公司和一家做火箭生意的“太空探索技术公司”（SpaceX）的老板（他还在一家太阳能公司的董事会中任职）。马斯克最喜欢的就是革命性的高科技产业。他认为他已经想出了一个比标准高速列车更好的方法来让加州动起来——超旋，这激起了人们的踊跃猜测：他脑子里在想些什么？

马斯克的空气把戏

大体上说，马斯克提出重现一种叫做真空列车的老式科幻概念，但有一些重要的调整。超旋将以超过1 200千米的时速带着旅客横穿加州——比喷气客机还要快。旅客乘坐超旋在旧金山和洛杉矶之间奔驰只需要半个小时多一点，而加州高铁则需要超过两个半小时。马斯克的理论预算约为60亿美元，不到高速列车假想成本的十分之一。

真空列车最早由罗伯特·戈达德于1910～1920年间提出，它通过密闭排气的管道高速运送轮车（也可能是悬浮车）。因此，列车不会遇到阻力，能够达到极高的速度。戈达德的设计中也提出了用磁悬浮替代车轮，他计算后认为自己的设计可以达到约1 600千米的时速。

戈达德描述的真空列车和其他有关运输管的设计为许多未来艺术带来了灵感，但是，从来没有一项设计付诸建造，因为在一条长长的隧道中保持真空状态很困难。真空列车依靠的就是前方没有一点儿空气聚集，因此不会减速，即使很小的泄漏也会彻底破坏一列整装待“飞”的真空列车。正因如此，超旋实际上不是一辆真正的真空列车。马斯克计划从管道中抽出足够的空气，使得列车承受的气压大约是他心爱的火星表面气压的六分之一，或者说是地球海平面气压的千分之一。这将让空气阻力降低到可以用其他方式应对。

这一设计的重点是用风扇吸走管道中车辆前方聚积起来的空气，然后把大部分空气从运输舱的后面排出。不过，一部分空气将通过特殊的导风板从侧面导出，形成缓冲气垫，防止运输舱碰到隧道壁。

每个运输舱用一台直线感应电机发射出去（这种电机也正在进行作为航母弹射器的测试），而且每110千米有助推电机给运输舱加速。到达目的地后，运输舱将通过一台反向工作的电机，将动能转化回电能储存在电池里，或者用在返程线路的电机上。此外，这是在加州，整个系统自然会由安装在管道顶部的太阳能电池板供电。

付诸实践

抛开它那惊人的大胆不谈，这一方案看起来的确是一个切实可行的工程项目。

管道将会建设在地上的塔架之上，减少土地占用，而且会沿着现有的道路修建。这样一来应该可以简化建设，使维护工作更容易。同时，每个运输舱周围的气垫应该可以确保行驶平稳。此外，虽然意料之外的工程问题势必会出现，但马斯克和他的工程师们在太空飞行和汽车设计上的经验将会成为克服这些问题的好兆头。

不过，对于这样的项目来说，掌握好工程学是远远不够的。政治和经济问题是更令人生畏的障碍。作为一项新技术，超旋是有风险的。

马斯克曾说过，考虑到他承担的其他工作，他自己没有时间来试着建设超旋。因此，他将这一方案公之于众的原因就在于把机会留给其他人去把握。“我想如果我造出一个演示品可能会有所帮助。”他若有所思地说，“所以我可能真的会这么做。”endprint