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On April 12, 1961, Soviet cosmonaut Yuri Gagarin piloted a 2,400 kilogram spacecraft in humanity's first manned space flight.
1961年4月12日，前苏联宇航员尤里·加加林驾驶着一架2400公斤的宇宙飞船，完成了人类历史上首次载人航天飞行。
One week later, Bell Aerosystems debuted another advancement in aviation: the gas-powered rocket pack.
一周后，贝尔飞行系统公司公布了航天史上另一项进步，即燃气动力的火箭发动机组。
Capable of flying 35 meters in just 13 seconds, the rocket pack thrilled onlookers. But the device's engineers were less enthused.
该发动机组能在13秒内飞行35米，这让观者为之惊叹。但该设备的工程师们却没有那么兴奋。
Despite years of cutting-edge work, they knew this short flight was all the rocket pack could muster.
他们知道，尽管经历了多年的尖端工作，这次短途飞行已经是火箭背包所能支持的所有。
So why was a massive spacecraft easier to send flying than a single pilot?
那么，为什么一艘巨大的飞船会比飞行员更容易起飞呢？
According to Newton's laws of motion, the physics behind flight are actually quite simple.
根据牛顿的运动定律，飞行背后的物理原理其实很简单。
All you need is a powerful enough upward force to counteract the downward force of gravity.
你所需要的只是一股足够强大的向上的力量来抵消向下的重力。
And since objects with more mass experience stronger gravitational forces, lighter objects should be easier to get off the ground.
由于质量更大的物体受到更强的引力，较轻的物体应该更容易离开地面。
However, modern jet engines, our primary tool for flight, actually get more efficient the larger they are.
然而，现代喷气发动机，我们飞行的主要工具，实际上在物体越大时效率越高。
Jet engines work by sucking in huge volumes of air, and then expelling that air as quickly as possible.
喷气发动机的工作原理是吸入大量的空气，然后快速地排出空气。
While most of this actually bypasses the inner machinery, it still contributes to a huge portion of the engine's thrust.
虽然大部分空气都绕过了内部机械，它仍然能为引擎提供大部分的推力。
But the air that does enter the engine's core gets compressed by a series of tightly packed blades.
进入发动机核心的空气被一系列紧密排列的叶片压缩。
That compressed air then enters the combustion chamber, where it is injected with jet fuel and ignited.
压缩空气之后进入燃烧室，被注入喷气燃料并点燃。
The heat causes the compressed air to rapidly expand, bursting out of the exhaust and propelling the engine forward.
热量使压缩空气迅速膨胀，从排气管中喷出，推动引擎前进。
As air leaves the engine it also turns a turbine embedded in the exhaust nozzle.
当空气离开发动机时，它也会转动嵌入在排气管中的涡轮机。
This turbine powers the fan and the compressor blades, creating a cycle that maintains thrust for as long as there's fuel to burn.
这个涡轮机驱动风扇和压缩机叶片，创造了一个循环，只要有燃料可以燃烧，就可以保持推力。
The more air an engine can take in and expel the more thrust it can produce.
发动机吸入的空气越多，排出的推力也就越大。
On a modern jet, the diameter of a frontal fan is larger than a truck.
在现代喷气式飞机上，前部风扇的直径要比卡车大。
And even spinning at relatively low speeds, these engines produce more than enough thrust to maintain the necessary speed for flying a passenger aircraft.
即使以相对较低的速度旋转，这些引擎产生的推力足以维持客机飞行的必要速度。
But smaller engines simply can't take in this much air.
但是小型发动机根本不能吸收这么多的空气。
For most of the 20th century, engineers couldn't produce an engine small and light enough for an individual to wear,
在几乎整个20世纪，工程师们都无法生产出供个人使用、足够小巧轻便，
yet powerful enough to lift itself alongside its pilot and fuel.
同时强大到可以推动自己的发动机。
Designs could only carry enough fuel for 30 seconds of flight,
设计只能携带30秒飞行所需的燃料，
and when airborne, the powerful thrust in a single direction made jetpacks difficult and dangerous to control.
当在空中飞行时，单一方向的强大推力使得喷气背包难以控制，也非常危险。
But the new millennium brought advances in materials, manufacturing, and computing technology,
但是新千年带来了材料、制造和计算技术的进步，
including systems which could manage fuel injection with incredible precision.
包括着可以精确控制燃油喷射的系统。
Together, these dramatically improved the fuel efficiency and power-to-weight ratio of jet engines.
总之，这些因素显著地提高了燃油效率以及喷气式发动机的功率重量比。
By 2016, micro-engines the size of a coffee can and weighing less than 2kg could achieve 220 Newtons of force.
到2016年，咖啡罐大小、重量不到2kg的的微型发动机可以产生220牛顿的力。
This was when an English engineer named Richard Browning saw the opportunity to create a new kind of lightweight jetpack.
当时一位名叫理查德·布朗宁的英国工程师看到了制造一种新型轻型喷气背包的机会。
In addition to a single engine strapped to the back, this so-called Jet Suit involved a pair of micro-engines on each arm to split and balance the thrust.
除了背后绑着一个引擎外，这种喷气式飞行服在每只手臂上都有一对微型引擎来分担和平衡推力。
Working with the back engine, these provided three-points of stability,
与后面的发动机一起工作，它们提供了三个稳定点，
which some pilots describe as being akin to comfortably leaning on crutches while a friend supports your back.
一些飞行员形容这就像是舒服地拄着拐杖，同时有个朋友支撑着你的背。
It may seem complicated to manage all these engines at once,
同时管理所有这些引擎可能看起来很复杂，
but many pilots master it in less than a day with the help of another advanced computer system -- their brain.
但是很多飞行员在不到一天的时间里就掌握了它，在另一个先进的计算机系统--大脑的帮助下。
Various brain regions and multiple sensory systems perfectly calibrate our sense of balance and spatial orientation, helping pilots smoothly direct their flights.
不同的大脑区域和多重感觉系统完美地校准了我们的平衡感和空间方向感，帮助飞行员顺利飞行。
Slight movements of the arms allow operators to increase and decrease lift, quickly turn in mid-air, or glide forward for up to 5 minutes.
手臂轻微的移动可以让操作者增加和减少升力，在半空中快速转弯，或者向前滑行长达5分钟。
This technology is still fairly new, and without major advances in fuel efficiency and engine technology, don't expect to have a jetpack of your own any time soon.
这项技术还是相当新的，没有燃油效率和发动机技术的重大进步，不要指望很快就有自己的喷气飞行器。
But if reaching for the sky already got us this far, who knows where we'll fly next?
但是如果我们已经到达了天空，谁知道我们接下来会飞向哪里？
