空间轨道上制造的光纤质量优于地面产品
Optical fibre made in orbit should be better than the terrestrial sort
It will have fewer flaws and longer lengths
其瑕疵更少，长度更长
IN THE 1970s, when those behind America’s manned space programme were trying to keep it alive as people got bored of moon landings, one fantasy was that there were products which might be made easily in space that were hard to create on Earth—metal foams, for example. Such dreams came to nothing because, however fancy the product, the cost of manufacturing it in orbit was never lower than the price it would have commanded back on Earth.
上世纪70年代，随着大家对月面着陆萌生倦意，美国载人航天计划的幕后推手想着法子继续维持项目。当时提出的一个设想是制造一些在空间环境中比较容易生产，但在地面上却很难做出来的东西，比如金属泡沫。这种梦想最后还是不了了之。产品倒是炫酷，但是在空间轨道上的制造成本之高，绝不亚于将其送回地球的费用。
Two Californian firms, however, think they have cracked this problem. Made in Space and FOMS (Fiber Optic Manufacturing in Space) are both proposing to manufacture optical fibre of the highest quality in the free-falling conditions of the International Space Station. At $1m a kilogram, this is a material that is well worth the trip to and from orbit.
不过，加利福尼亚的空间制造公司和FOMS（空间内光纤制造）公司认为自己已经破解了这个难题。两家公司都提出，能在国际空间站的无重力条件下制造出质量极高的光纤。由于所用的材料价格高达每公斤100万美元，到空间轨道走一遭还是值得的。
Optical fibres are made by pulling glass into strands which have a diameter similar to that of human hair. Cables filled with these fibres have revolutionised telecommunications. When a telephone call, say, is encoded as laser pulses and sent through an optical fibre, it can travel a far greater distance, with a lower loss of signal quality, than if the message involved had been transmitted through a copper wire. As a consequence, except for the last few hundred metres of connection to the customer, copper cabling has almost disappeared.
制造光纤时，是要将玻璃拉成直径相当于人类毛发粗细的纤维丝。采用这种纤维制成的光缆已经让电信事业发生了翻天覆地的变化。比方说，相较于通过铜芯电缆传递信息，如果将电话呼叫转变为激光脉冲信号，通过光纤发送，则呼叫信号传播的距离更远，信号质量损失更小。这样一来，除了接通到客户的最后几百米，其他区段基本已经淘汰铜缆了。
Optical fibre could, though, be better than it is. The glass used contains impurities that both absorb and scatter part of the light passing through it. This can be ameliorated by adding germanium, which reduces absorption and scattering. But that is not a perfect answer.
然而，光纤质量仍然还有上升的空间。由于制造光纤的玻璃含有杂质，会吸收并散射掉一部分从光纤中通过的光。虽然可以通过加入锗减弱吸收和散射作用，但也并非万全之策。
The best solution known in principle was found in 1975, by researchers at the University of Rennes, in France. It is a glass, made from a mixture of the fluorides of zirconium, barium, lanthanum, aluminium and sodium, that is therefore known as ZBLAN (sodium has the chemical symbol Na). Fibre made from ZBLAN has extremely low losses from absorption and scattering, particularly in the part of the spectrum called the mid-infrared, where conventional optical fibre does not work well.
大体上，目前已知最好的解决办法是由法国雷恩大学的研究人员于1975年发现的。制造纤维的玻璃采用氟化锆、氟化钡、氟化镧、氟化铝、氟化钠的混合物制成，称为ZBLAN材料。采用ZBLAN材料制成的纤维，其吸收、散射损失极低，尤其是在常规光纤表现不佳的中红外光谱区。
ZBLAN fibres are, though, fragile. That makes drawing one that is more than about a kilometre long a hard task which, in turn, makes them useless for long-distance work. They also tend to contain tiny crystals that form when the material is cooling. These negate the lack of absorption and scattering that otherwise give ZBLAN its advantages.
不过，ZBLAN光纤很脆，不但很难将其拉制一公里的长度，也无法用于远距离工作。另外，材料在冷却过程中还比较容易产生微小的晶体，使得ZBLAN不再具有吸收和散射方面的优势。
However, in the absence of stresses caused by gravity on the cooling material, much longer fibres could be drawn. Nor would the crystals form. And the one large place under human control where such stresses are absent is the space station.
但是，只要材料在冷却中没有受到重力应力，就能拉制出很长的纤维，也不会有晶体形成。而空间站则是人类可以掌控、又不存在重力应力的一块宽敞之地。
Both firms say they have built apparatus to produce ZBLAN fibres that is small and light enough to send to, and operate in, the space station. Made in Space’s machine has some similarities to the sort of plastic-extrusion 3D printer used by hobbyists. It ingests a preformed pencil of ZBLAN. A furnace melts the tip of this pencil. Thin strands of fibre are then pulled from the molten area. But instead of being used to form an object while still soft, these strands are coated with a second sort of glass for protection and then spooled onto reels for storage.
两家公司均称，已经制造出大小、重量均适于送往空间站进行生产的设备，用于制造ZBLAN纤维。空间制造公司的机器和业余爱好者使用的挤出式塑料3D打印机有些许类似。首先向其投入ZBLAN材料预制棒，待棒材头部在加热炉中熔化后，即可从熔融部位拉制出纤维丝。与3D打印机不同的是，拉出细丝后，并不是趁热做出物体的形状，而是在其外层再包覆一层玻璃保护层，然后盘卷存放。
Made in Space already has a plastic-extrusion printer on board the space station. This is used to make replacements for small items that have got damaged, obviating the delays involved in bringing them from Earth. The company’s managers are therefore reasonably confident that their ZBLAN extruder will also work in free-fall.
空间制造公司已经在空间站安装了一台挤出式塑料打印机，用于替换损坏的小部件，以免耽误将其送回地面。因此，公司管理人员对ZBLAN在失重条件下的工作颇有把握。
They will soon find out. A prototype arrived at the space station in July, and will be tested shortly. An equivalent device built by FOMS will be sent up later this year. Both firms are promising fibre with a performance 100 times better than anything made on Earth, in lengths of several tens of kilometres.
具体结果如何，马上见分晓。今年七月，一台样机已经抵达空间站，很快就会进行调试。FOMS公司制造的类似设备也会在今年晚些时候送达空间站。两家公司都保证，能够生产出几十公里长的光纤，而且性能会百倍于地面制造的任何光纤产品。
To say that this is truly an economic process is cheating slightly, since the ledger fails to account for the trivial matter of the $100bn or so spent to build the space station in the first place. But, given that this is now a sunk cost, it does seem possible that Made in Space and FOMS have actually found a way to fulfil the dreams of the 1970s, and make money by making things in space.
要说这项工艺确实划算的话，还是有些弄虚作假，毕竟之前花费1千亿美元左右的小钱建造空间站的帐还没算呢。不过，鉴于这笔开销已经成为既定成本，空间制造公司和FOMS公司看来确实已经找到了实现昔日梦想的途径，通过在太空生产开辟了一条财路。
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