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When you picture a spaceship, you probably think of something like this, or this, or maybe this.
当你想象一架宇宙飞船时，你的脑海中可能会出现它，或者它，又或者它。
What do they all have in common?
它们有什么共同之处呢？
Among other things, they're huge because they have to carry people, fuel,
总的来说，它们十分巨大，因为它们需要载人，需要装载燃料，
and all sorts of supplies, scientific instruments, and, in rare cases, planet-killing lasers.
还需要装载各种各样的补给品和科学仪器，甚至，在非常时期装载毁灭星球的镭射激光。
But the next real-world generation of spacecraft may be much, much smaller.
但是从现实世界的角度来说，下一代的宇宙飞船可能会变得非常非常小。
We're talking fit-inside-your-pocket tiny.
我所说的小，是指小到可以直接放进你的口袋的程度。
Imagine sending a swarm of these microspacecraft out into the galaxy.
想象把一大群这样的微小型航天器发射到宇宙的星系中去。
They could explore distant stars and planets
它们可以探索遥远的恒星和行星，
by carrying sophisticated electronic sensors that would measure everything from temperature to cosmic rays.
通过自身携带的复杂的点子感应器。它们能测量任何东西，从温度到宇宙射线。
You could deploy thousands of them for the cost of a single space shuttle mission,
仅仅需要发射一次航天器，你就能够操控数以万计的微小型航天器飞向太空，
exponentially increasing the amount of data we could collect about the universe.
这极大地增加了我们能够在宇宙中采集的数据量。
And they're individually expendable,
而且，作为单个个体来说，他们可以算是消耗品，
meaning that we could send them into environments that are too risky for a billion dollar rocket or probe.
也就是说，我们可以把它们送到那些造价高昂的火箭或者探测器不能冒险探测的环境中去。
Several hundred small spacecraft are already orbiting the Earth,
几百个小型航天器其实已经在绕地球轨道飞行了，
taking pictures of outer space, and collecting data on things,
它们拍下外太空的照片，收集各类数据，
like the behavior of bacteria in the Earth's atmosphere and magnetic signals that could help predict earthquakes.
比如地球大气层中细菌的行为特征，还有发射磁信号来帮助预测地震。
But imagine how much more we could learn if they could fly beyond Earth's orbit.
但是设想一下，如果它们可以飞出地球轨道，那我们将会收获多少东西呀！
That's exactly what organizations, like NASA, want to do:
这就是许多组织，比如说NASA（美国国家航空航天局）想做的事情：
send microspacecraft to scout habitable planets and describe astronomical phenomena we can't study from Earth.
发射微小型航天器去探索适合居住的星球或者描述在地球上无法研究的天文现象。
But something so small can't carry a large engine or tons of fuel, so how would such a vessel propel itself?
但是这么小的航天器难以装载大引擎或者数以吨计的燃料，那它要以什么动力向前推进呢？
For microspacecraft, it turns out, you need micropropulsion.
原来，对于微小型航天器来说，它需要的是微推进。
On really small scales, some of the familiar rules of physics don't apply,
有些人们熟知的物理学知识并不能应用在它们身上，
in particular, everyday Newtonian mechanics break down, and forces that are normally negligible become powerful.
举例来说，每天牛顿力学体系都在崩塌，许多平常被我们忽视的力变得无比强大。
Those forces include surface tension and capillary action, the phenomena that govern other small things.
这些力之中就包括表面张力和毛细引力，还有那些其他小事上体现出来的现象。
Micropropulsion systems can harness these forces to power spacecraft.
微推进系统可以利用这些力量来供微小型航天器使用。
One example of how this might work is called microfluidic electrospray propulsion.
关于这方面，我们可以举个例子，叫做微射电流喷射推进。
It's a type of ion thruster, which means that it shoots out charged particles to generate momentum.
这是一种离子推进器，它可以通过喷射带电离子来产生动能。
One model being developed at NASA's jet propulsion laboratory is only a couple centimeters on each side.
NASA喷气推进实验室设计的一个模型只有几厘米大小。
Here's how it works.
让我们来看看它的工作原理。
That postage-stamp sized metal plate is studded with a hundred skinny needles
那张邮票大小的金属板上覆盖着一百根纤细的针，
and coated with a metal that has a low melting point, like indium.
并且由一层低熔点的金属覆盖着，比如说铟。
A metal grid sits above the needles, and an electric field is set up between the grid and the plate.
一张金属网将位于这些针的上方，并且在金属网和金属板之间将会建立一个电场。
When the plate is heated, the indium melts and capillary action draws the liquid metal up the needles.
当金属板被加热的时候，铟就会融化，随后毛细引力将液态的铟吸到针尖。
The electric field tugs the molten metal upwards,
电场将融化的金属向上拖，
while surface tension pulls it back, causing the indium to deform into a cone.
而表面张力则将融化的金属向下拉，使铟变形成为圆锥状。
The small radius of the tips of the needles makes it possible for the electric field to overcome the surface tension,
针尖极小的半径让电场力得以克服表面张力，
and when that happens, positively charged ions shoot off at speeds of tens of kilometers per second.
而当电场力克服表面张力时，带正电的离子将以数万公里每秒的速度喷射而出。
That stream of ions propels the spacecraft in the opposite direction, thanks to Newton's third law.
由牛顿第三定律可知，这束离子流将推进航天器向相反的方向前进。
And while each ion is an extremely small particle,
尽管每一个离子都是极其小的粒子，
the combined force of so many of them pushing away from the craft is enough to generate significant acceleration.
但是无数个离子联合起来推动航天器的力量足以形成强有力的加速。
And unlike the exhaust that pours out of a rocket engine,
比起那些火箭引擎排出的大量气体，
this stream is much smaller and far more fuel efficient, which makes it better suited for long deep-space missions.
这股离子流要小得多，而且也更省燃料，这也让微小型航天器更加适合长时间的外太空任务。
These micropropulsion systems haven't been fully tested yet,
这些微小型航天器目前还没有完全测试完毕，
but some scientists think that they will provide enough thrust to break small craft out of Earth's orbit.
但是很多科学家认为他们能够提供足够的推力，来让小型飞船飞出地球轨道。
In fact, they're predicting that thousands of microspacecraft will be launched in the next ten years
事实上，他们预计，数以千计的微小型宇宙飞船会在十年内被发射出去，
to gather data that today we can only dream about.
用以收集那些我们现在看来难以企及的数据。
And that is micro-rocket science.
这就是微型火箭科学。
