However, if our species wants to have a long term future, we have to escape our prison.

被宇宙以廣闊但又無法觸及的空間嘲諷著

But what is keeping us here in the first place?

然而 如果人類這種物種想要有長久的未來

Turns out, we owe the universe a debt that is 4.5 billion years old.

我們必須逃脫地球這個監獄

*Intro*

但是什麼把我們困在這裡?

Everything with mass in the universe attracts every other thing with mass.

原來是因為我們在45億年前欠了宇宙一點債

We call this phenomenon 'gravity'.

(一個能量形成的監獄)

The closer you are to a big chunk of mass, the stronger the attraction or the more you're pulled

宇宙中的任何東西都具有質量

in.

同時也因為質量而相互吸引著

This effect traps us on earth.

我們稱這個現象為「萬有引力」

We can imagine this as being prisoners in a gravity prison, or a gravity well.

當你越靠近一個具有巨大質量的物體 就會有越強的引力

It's not a literal well, but a handy concept to understand how this works.

也等於你被拉的越緊

Being in a gravity prison means that you owe gravity energy.

這個現象將我們侷限在地球上

But how can you owe energy?

我們可以想像我們是囚犯

Because in our universe, things don't want to change their speed or direction.

被囚禁在監獄 也就是所謂重力穴

To convince them to move, you have to expend energy.

他並非字面上穴的概念

Billions of years ago, the gravitational attraction of trillions of trillions of dust particles

但是可以讓我們輕鬆的理解它的原理

orbiting our sun caught them together until they formed a planet.

被困在引力的監獄中 意指你欠引力能量

This process used energy and created the gravity well we're now a part of.

但我們是如何欠引力能量的?

The deeper you are inside the gravity well, the more energy you owe gravity.

因為在宇宙中

If you don't find a way to get enough energy, then you aren't able to leave no matter what you do.

物體不會想要改變他們的速度或方向

Because your atoms were once part of the dust that the universe expended energy on to get to this place.

為了要說服他們移動

Ok. Hmm...Let's summarise all of that again.

你必須消耗能量

Objects in the universe don't like to move. You have to convince them to do so with energy.

數十億年前 引力吸引了無數的塵埃粒子圍繞在太陽的軌道上

Gravity used energy to convince the parts of our planet to move together.

將他們吸引在一起 直到行星的行成

This created a gravity prison in the process, trapping us .

這個過程中消耗能量

To escape, it we need to repay it with energy.

並且建立了我們現今被困在其中的重力穴

Ok. How do we do that?

當你陷在越深處的重力穴 也就代表你欠引力越多能量

To get into space, we need to go through a complicated process of exchanging energy.

如果你沒辦法找到足夠的能量

For this purpose, we build a negative potential energy repaying machine.

你將無論如何永遠無法離開引力

Known By their more boring name 'rockets'

因為你身上所有的原子都屬於宇宙膨脹能量的其中一點塵埃

Rockets work by using some of the most energetic chemical reactions humans know about

以達到現在的狀況

to basically explode fuel in a controlled way.

好的 讓我們來統整一下

This converts chemical energy into kinetic energy.

宇宙中的物體不喜歡移動

The exhaust of the reaction is directed outwards,

你必須以能量說服他們移動

and pushes the rocket away from Earth.

引力以能量說服粒子聚集在一起以形成行星

By expanding a lot of energy, we are increasing our gravitational potential energy.

同時建立起了囚禁我們的重力監獄

Which is a complicated way to say that we are paying back our energy debt to gravity.

為了要逃脫 我們需要用能量回饋他

But it's actually a lot trickier than that.

但是 我們要如何做到?

When you burn fuel to get into orbit, you lose lots of energy to heat, exhaust and atmospheric drag

(逃離重力監獄)

,so you actually need much more.

為了要進入宇宙 我們必須透過複雜的能量交換程序

And you can't just pile a huge amount of radioactive, really explosive, dangerous fuel close to your

因此 我們發明了一種反能量回饋裝置

payload and detonate it.

或者有個比較無趣的名稱－火箭

You need a controlled burn which is complicated and makes your rocket very heavy

火箭目前以某些人類已知最劇烈的化學反應為動力

...which means it has more mass.

為的就是燃燒燃料以達到控制火箭的目的

The more mass something has, the more energy you need to convince it to move,

這個過程將化學能轉換成動能

so you need more fuel to lift up your rocket.

將燃燒的產物排出火箭 使火箭脫離地球的重力

But,if you need more fuel, that means you need more rocket to carry that fuel!

當我們消耗大量能量的同時 也增加了自身引力的能量

But, this makes your rocket heavier thus requiring more fuel which requires more rocket to carry that

簡單來說 就是我們正在償還我們欠重力的能量

new fuel and so on.

但事實上這比我們想像的還要棘手

At the end of this madness, you need closer to a 100x the weight of your payload to launch

當你燃燒能量已進入地球的軌道時

Ariane 6, for example (the european rocket) will weigh 800 tons and should be able to

你會失去大量的能量轉換成熱量 廢氣以及空氣阻力

transport 10 tons into geostationary transfer orbit or, 20 tons into medium earth orbit.

所以事實上你需要更多能量

But a rocket can only produce so much thrust, so there is a maximum weight, after which it just won't

而且你不能只是在你身邊堆一大堆具有輻射 高爆性又危險的燃料

take off.

然後引爆他

If you add too much weight, it won't lift off. So, you can't just build bigger and bigger fuel tanks

你需要穩定控制的燃燒

This is the tyranny of the rocket equation and it means space flight will never become easy.

但會使你的火箭非常複雜又很笨重

But wait, it gets worse.

也代表著會有更多的質量

Getting to space is still not good enough- you're still inside the gravity prison at the edge of space and

物體的質量越重 你就需要越多能量以說服其移動

will crash back to Earth.

所以你需要更多燃料來讓火箭起飛

Staying in space is much harder than getting there.

但是當你需要越多燃料 也就表示你需要更多火箭來裝這些燃料

To get to a stable position, where it can stay for a while, a rocket has to reach low Earth orbit.

但這讓你整個火箭更重 因此也就需要更多燃料也就需要更多火箭來裝那些新的燃料

To do this, you need a lot of kinetic energy which means going extremely fast

依此類推

at an altitude of about 100 km, this is 8 km/s

在這惱人的過程的結果 你需要將近一百倍的重量以推動欲載的東西

28,000 km/h is fast enough to travel around Earth in 90 minutes.

以亞利安6號運載火箭(歐洲火箭)為例 將會重達800噸重

Here, we can use a trick.

以將10噸重的物體送上地球靜止軌道

Instead of flying straight up, we can go sideways!

或者是20噸重的物體送上中地球軌道

Earth is a sphere.

但是火箭的推力有限 也就是說他有重量的上限 超過了就無法起飛

So, if you're going sideways, fast enough (even though you're falling towards Earth) the ground will curve

如果火箭太重 他就無法起飛 所以我們不能單單製造更重的燃料槽

away beneath you.

這個問題對於火箭工程而言十分嚴苛 因此太空旅行會如此困難

So, as long as you're above the atmosphere (about 100 km up) you'll be able to stay up there in orbit.

但等等 有件事情讓這變得更糟糕

This is what the ISS does (falling around Earth, expending energy form time to time) to stay

不是進入宇宙就已經夠了 你還是會被困在宇宙邊緣的重力監獄

fast enough.

最終還是會墜毀回地球

If we look at orbits in scale, we see that near Earth orbit is laughably close to Earth.

待在太空遠比進入太空還要困難

To deploy, for eg Satellites, on leave for other planets, requires another round of energy debt repayment.

要達到穩定並且可以待一段時間的狀態 火箭必須要達到低地球軌道

Getting to orbit is the most difficult part of space flight for us right now.

為了進入軌道 你需要大量的動能 也就是要非常的快

For example: If we want to send a rocket to Mars, half the energy is necessary just to get into orbit

為了達到100公里的高度 必須要有每秒8公里的初速度

and the other half for the 55 million km to Mars.

時速28000公里則可以在90分鐘內繞地球一圈

Therefore, to be as effective as possible, rockets aren't built in one giant piece.

在此 我們可以用一些小技巧

Instead, we use multistage rockets. We don't need to carry an empty fuel tank, so rockets drop it.

比起直接往上飛 我們可以往旁邊飛

Rockets today, shed their boosters and main stage as they ascend with each successive stage being it's own

地球是圓的

fully contained rocket, complete with its own engine and fuel.

所以如果我們往旁邊飛 如果速度快到就算你正在往下墜落 地面還是會對你有利

Ok. So this is why getting to space is hard.

所以 當你在大氣層外(約100公里) 你就可以維持在地球的軌道上

If you feel all of this seems really complicated, don't worry. It's literally rocket science!

國際太空站(ISS)就是這樣運作的 不斷的墜落並且不斷的花費能量以維持速度

This video was made possible in part by a sponsorship by Airbus Safran Launchers

如果我們在遠一點的地方看軌道會發現我們的軌道十分可笑的接近地球

and Arianespace.

為了部屬像是衛星的人造天體到其他星球上 需要更多能量的償還

Who are getting their new Ariane 6 rocket ready to launch into space in 2020.

進入軌道是目前太空旅行最困難的部分

You can learn more about the rocket here.

舉例來說 如果我們要去火星 一半的能量會被消耗掉為了要進入軌道

And as always, if you like what we do please consider supporting us on Patreon.com.

另外一半用來穿越5500萬公里到達火星

It really helps us out a lot!

因此 考量到效率 火箭並不會是一體成形的巨大物件

If you're craving more space stuff now: here's a playlist for you.

取而代之的是 我們會打造一個多個結構的火箭