這主意可不是異想天開

SCWalter

動汽車企業家及火星私人殖民的擁護者埃隆·馬斯克現在打算重塑鐵路運輸。馬斯克提出重現一種叫做真空列車的老式科幻概念，列車將以超過1 200千米的時速帶著旅客橫穿加州——比噴氣客機還要快。他的想法至少在理論上是可行的，如果付諸實踐會如何呢？

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.”

美國加州有許多聰明人，埃隆·馬斯克就是其中之一。他精力旺盛，身兼一家電動汽車公司——特斯拉汽車公司和一家做火箭生意的“太空探索技術公司”（SpaceX）的老板（他還在一家太陽能公司的董事會中任職）。馬斯克最喜歡的就是革命性的高科技產業。他認為他已經想出了一個比標準高速列車更好的方法來讓加州動起來——超旋，這激起了人們的踴躍猜測：他腦子里在想些什么？

馬斯克的空氣把戲

大體上說，馬斯克提出重現一種叫做真空列車的老式科幻概念，但有一些重要的調整。超旋將以超過1 200千米的時速帶著旅客橫穿加州——比噴氣客機還要快。旅客乘坐超旋在舊金山和洛杉磯之間奔馳只需要半個小時多一點，而加州高鐵則需要超過兩個半小時。馬斯克的理論預算約為60億美元，不到高速列車假想成本的十分之一。

真空列車最早由羅伯特·戈達德于1910～1920年間提出，它通過密閉排氣的管道高速運送輪車（也可能是懸浮車）。因此，列車不會遇到阻力，能夠達到極高的速度。戈達德的設計中也提出了用磁懸浮替代車輪，他計算后認為自己的設計可以達到約1 600千米的時速。

戈達德描述的真空列車和其他有關運輸管的設計為許多未來藝術帶來了靈感，但是，從來沒有一項設計付諸建造，因為在一條長長的隧道中保持真空狀態很困難。真空列車依靠的就是前方沒有一點兒空氣聚集，因此不會減速，即使很小的泄漏也會徹底破壞一列整裝待“飛”的真空列車。正因如此，超旋實際上不是一輛真正的真空列車。馬斯克計劃從管道中抽出足夠的空氣，使得列車承受的氣壓大約是他心愛的火星表面氣壓的六分之一，或者說是地球海平面氣壓的千分之一。這將讓空氣阻力降低到可以用其他方式應對。

這一設計的重點是用風扇吸走管道中車輛前方聚積起來的空氣，然后把大部分空氣從運輸艙的后面排出。不過，一部分空氣將通過特殊的導風板從側面導出，形成緩沖氣墊，防止運輸艙碰到隧道壁。

每個運輸艙用一臺直線感應電機發射出去（這種電機也正在進行作為航母彈射器的測試），而且每110千米有助推電機給運輸艙加速。到達目的地后，運輸艙將通過一臺反向工作的電機，將動能轉化回電能儲存在電池里，或者用在返程線路的電機上。此外，這是在加州，整個系統自然會由安裝在管道頂部的太陽能電池板供電。

付諸實踐

拋開它那驚人的大膽不談，這一方案看起來的確是一個切實可行的工程項目。

管道將會建設在地上的塔架之上，減少土地占用，而且會沿著現有的道路修建。這樣一來應該可以簡化建設，使維護工作更容易。同時，每個運輸艙周圍的氣墊應該可以確保行駛平穩。此外，雖然意料之外的工程問題勢必會出現，但馬斯克和他的工程師們在太空飛行和汽車設計上的經驗將會成為克服這些問題的好兆頭。

不過，對于這樣的項目來說，掌握好工程學是遠遠不夠的。政治和經濟問題是更令人生畏的障礙。作為一項新技術，超旋是有風險的。

馬斯克曾說過，考慮到他承擔的其他工作，他自己沒有時間來試著建設超旋。因此，他將這一方案公之于眾的原因就在于把機會留給其他人去把握。“我想如果我造出一個演示品可能會有所幫助。”他若有所思地說，“所以我可能真的會這么做。”endprint