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SciShow Space is supported by Brilliant.org.
《太空科学秀》由Brilliant.org赞助播出。
While traveling in space, one of the hardest things to do is, stop. Or change direction.
在宇宙航行最困难的一件事就是停下，或者说改变航向。
Without anything to push against or friction to slow things down, spacecraft need to do all the hard work of changing their speed or path.
由于宇宙里没有施加相互作用力的对象，也无法摩擦减速，所以改变速度和航向这种难事儿需要自己想办法。
And sometimes they do that in ways you'd never expect: like by vaporizing Teflon.
有一种实现方法你可能永远也想不到：模仿蒸发聚四氟乙烯的方式。
They're called pulsed plasma thrusters, and they can use the same stuff that's on your frying pan to make spacecraft zoom around the universe.
它们名作脉冲等离子体推力器，它们可以用平日里煎锅上的东西来使宇宙飞船改变航向
And they've been doing it since the 1960s.
上世纪60年代开始，他们就这样做了。
To make basically any move in space, satellites rely on Isaac Newton's famous Third Law of Motion,
卫星要在宇宙里移动，要依靠艾萨克·牛顿著名的第三运动定律，
which is probably on a poster in every high school physics classroom: For every action, there's an equal and opposite reaction.
这个定律在每个高中的物理课上应该都有讲过，宇宙飞船只要动了，就有作用力和反作用力。
Put another way: throw stuff backwards and you'll go forward.
换言之：往后扔东西就会获得向前的推力。
In fact, you can boil down every rocket design, no matter how complicated, to this basic idea.
实际上，无论多么复杂的火箭，其设计都可以归结为这个基本的想法。
When thinking of a rocket, you might normally imagine what's called chemical propulsion.
提到火箭，您可能就会很自然地想到一种叫化学推进的方式。
That's the fire-coming-out-the-end kind, which uses a controlled explosion to hurl material out the back of the rocket.
这是一种火焰从尾部喷射而出的方式，会通过控制爆破来将材料从火箭尾部甩出。
And once in space, another kind, electromagnetic or EM propulsion, also becomes available.
等火箭抵达宇宙空间后，就要用到另一种方式，也即电磁推进。
They aren't strong enough to get rockets off the ground, but they are great once you're past most of Earth's atmosphere.
电磁推进无法将火箭从对面发射到宇宙中，但一旦脱离了地球大气层，这种方式就倍显其效。
These rockets work kind of like railguns, accelerating charged particles, or ions, out the back with electric or magnetic fields.
火箭的工作方式与磁轨炮有点相像，会通过电场或者磁场给带电粒子（也就是离子）加速，让其从火箭尾部喷发出去。
Today, we have all kinds of EM thrusters, but pulsed plasma thrusters, or PPTs, were the first ones ever flown in space.
如今，我们研发出了各种各样的电磁推进器，但脉冲等离子体推力器(PPT)是第一批在宇宙里飞行的。
They were used in 1964 on the Soviet Zond 2 mission to Mars.
1964年，苏联送往火星的探测器2号就使用了脉冲等离子体推力器。
Like some other engines, PPTs specifically use plasma to generate thrust, instead of a random collection of ions.
与其他发动机的相似之处在于：脉冲等离子体推力器尤其要通过等离子体来产生推力，而不是通过随意收集的电子。
Plasma is a super hot substance made of charged ions, and it's the fourth state of matter.
等离子体是由带电离子组成的温度极高的物质，是第四类物质状态。
In some ways, it behaves kind of like a gas, because its atoms are pretty spread out.
从某些角度来说，等离子体的行为方式与气体很像，因为其原子向外延伸度高。
But unlike the other states of matter, plasmas can be shaped and directed by electric and magnetic fields.
但与其他物态不同的是，等离子体的形状和运动方向可以受到电场和磁场的改变。
To generate its plasma, PPTs eat Teflon! Which is pretty awesome.
要产生等离子体，脉冲等离子体推力器就要吸收聚四氟乙烯哦！这就很酷了。
A pulsed plasma thruster places a block of Polytetrafluoroethylene, what we know as Teflon between a pair of metal plates.
脉冲等离子体推力器在一对金属板之间放置一块聚四氟乙烯。
Then, connected wires charge up those plates with electricity until it arcs through the Teflon block, set off by a spark plug.
随后，连通的电线会给金属板充电，电流流通聚四氟乙烯后，火花塞会对其进行引爆。
That arc delivers thousands of volts into the block, vaporizing the nearby Teflon and ionizing it into a plasma.
电弧会给聚四氟乙烯以高压，使附近的聚四氟乙烯蒸发，电离成等离子体。
The sudden burst of plasma effectively creates a circuit connecting the metal plates, which allows electricity to flow like it's traveling through a wire.
等离子体的突然爆发可以形成一个回路，连通金属板，让电流可以流通两个金属板，仿佛有电线存在一样。
One neat side effect of flowing electricity is that it generates a magnetic field.
电流流通的一个副作用是可以产生磁场。
And everything in the thruster is already arranged so that this field pushes the plasma out into space.
而推进器中已经万事俱备，所以这个磁场可以将等离子体推进到太空中。
At this point Newton's third law springs into action, pushing the spacecraft in the opposite direction of the departing particles.
这个时候牛顿的第三定律就开始显现了：会对宇宙飞船产生与等离子体方向相反的推力。
And, huzzah, motion! Well, the tiniest bit of motion.
然后，哇哦，开始动了！虽然只是缓慢移动。
A pulsed plasma thruster deployed by NASA in 2000 produced an amount of force equal to the weight of a single Post-it Note sitting on your hand.
2000年美国宇航局部署的脉冲等离子体推力器产生的力，大小相当于便利贴贴在手上所产生的压力。
Which might not seem that exciting, but it has some big implications.
听起来可能没什么好兴奋的，但这对我们有几点大启示。
Like other forms of electromagnetic propulsion, these engines require a lot of electricity to run,
跟其他形式的电磁推进一样，这类发动机也需要很多电才能运转，
but in exchange they offer incredible efficiency with their fuel.
为此，需要提供超高性能燃料。
Pulsed plasma thrusters can produce up to five times more impulse or change in momentum for every gram of fuel than a typical chemical rocket.
脉冲等离子体推力器每克燃料产生的脉冲（也就是动量的变化量）是传统化学火箭的五倍多。
They do it very, very slowly, but they get the job done. PPTs also offer exceptional simplicity and safety.
虽然速度很慢，但可以保证任务完成，脉冲等离子体推力器集简单与安全于一身。
The only moving part is a spring that constantly pushes the Teflon block forward and,
唯一“动的部分”就是一根弹簧。这根弹簧会不停地将金属板向前推，
without the need to store pressurized liquid or gas fuel, there's no chance of explosion.
正是因为需要储存加压液体或气体燃料，所以不会发生爆炸。
So it makes sense then that pulsed plasma thrusters were so useful back in the 1960s.
所以，上世纪60年代脉冲等离子体推力器会如此有用也就不足为奇了。
Since then, their lack of power has meant that most spacecraft main engines have remained chemical.
那时起，由于缺乏动力，所以大多数宇宙飞船的主发动机都是依靠化学推进的方式。
And when companies really need some kind of EM drive, like for the Dawn mission to the asteroid belt, they'll tend to choose more sophisticated designs.
而当各公司确实需要某种电磁推进驱动的时候，比如曙光号太空探测船和去往小行星带的宇宙飞船，他们都倾向于选择更为成熟的设计。
But that doesn't mean we're done with these thrusters just yet.
但这并不意味着这种推进器我们就彻底不用了。
Recently, their extreme simplicity has made them a natural fit for the most up-and-coming field of exploration: CubeSats.
近日，电磁推进器的极简风格使其当之无愧地成为未来探索领域最合适的选择，也就是立方体卫星。
CubeSats are tiny, shoebox-sized satellites designed for simple missions and built on the smallest of budgets often by research labs or universities.
立方体卫星体型很小，跟鞋盒子差不多大，这样设计是为了让它完成一些简单的任务，当时研制这种卫星的经费也极少，一般只有一些研究实验室或者大学才做这个。
Earth-orbiting CubeSats seem almost tailor-made for the strengths of pulsed plasma thrusters.
围绕地球运转的立方体卫星，其大小跟脉冲等离子体推力器适配度极高。
Lots of sunlight gives them ample electric power, but since they're so small, space and weight are at an absolute minimum.
由于日光重组，所以它们可以获得充足的电能，但由于它们体型很小，所以其所占空间和重量也是小到不能再小了。
And right now, most CubeSats typically don't have any kind of propulsion system of their own.
而且现在的情况是，大多数立方体卫星并没有任何特有的推进系统。
So one solution is micro pulsed plasma thrusters, which can weigh just a few hundred grams and measure under 10 centimeters on a side.
所以一个解决方案就是使用只有几百克重、单面只有10cm的微型脉冲等离子体推力器。
That might not sound like much, but even a tiny amount of thrust could double the useful life of some kinds of CubeSats.
听起来好像动力不足，但即便一小点儿推力都足以让一些立方体卫星动力十足地运转。
They'll likely need to undergo more testing and development before they're ready for primetime,
它们很可能需要接受更多的研发测试才能达到巅峰，
but someday, we could have a whole fleet of Teflon-eating satellites. Not bad for the same stuff that coats our kitchen pans!
但有朝一日，我们会有一整套以聚四氟乙烯材料为动力来源的卫星，厨房的平底锅外层材料听了也高兴！
So I joked about Newton's third law of motion being etched into our brains earlier,
刚才呢，我开了牛顿第三定律的玩笑。而虽然第三定律已经深入人心，
but when's the last time you really thought about good ole' Newton critically?
但你上一次像今天这样认真思考它是什么时候呢？
Brilliant.org has a whole section on Newton's Laws as part of their Classical Mechanics course.
Brilliant.org上的经典力学课程中有部分内容与牛顿三大定律有关。
And learning about pulsed plasma thrusters made me want to test how well I remember using Newton's third law.
而今天了解了脉冲等离子体推力器后，我也想测试一下我对牛顿第三运动定律的识记程度。
So, imagine you're on a beautiful, frictionless lake. In your own little boat.
那么，想象你在一片美丽而又平滑的湖面上，在自己的小船上。
The sun is shining, there are birds in the air, there might be lilly pads around you.
阳光明媚，鸟儿在空中飞翔，你周围可能还有百合花。
And then you spot another boat, just like yours, a little bit bigger across the lake, 30 meters away.
然后，你又看到了另一艘船，跟你的这艘很像，只是比你的大一点，离你有30米远。
And you know that your boat is 60 kilograms and actually that's your friend, so you know that that boat weighs 90 kilograms.
此时的你知道你的船有60公斤重，而另一艘船是90公斤重。
And you want to bring the boats together so you can have a picnic. Luckily they're connected by a string.
你想让两艘船聚在一起，这样就可以聚餐了，所幸这两艘船用绳子连接在一起了。
So if your string is pulled with a constant force and your two boats meet up after 20 seconds, how far did your boat move?
那么，如果以恒定的力拉这根绳子，直到20秒后这两艘船聚在一起，这期间，你的船移动了多远呢？
You probably don't even need to get into a boat to solve this problem. I believe in you.
你们应该不需要亲身试验一下就能解这道题，我想你们哦！
You can go to Brilliant.org to check out this quiz and a bunch of others like it and the first 777 people to sign up at brilliant.org/scishowspace
大家可以登录Brilliant.org来进行类似的测验，前777名注册brilliant.org/scishowspace的用户
will get 20% off of their annual Premium subscription AND support SciShow Space so thank you!
可以减免20%的订阅年费，这也是对我们节目的一种支持，所以在此谢谢大家啦！
