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

宇宙の見えない鎖に縛られている

But what is keeping us here in the first place?

しかし種を存続させたいなら

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

脱獄が必要だ

*Intro*

でも その鎖とは何だろう？

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

話は45億年前になされた

We call this phenomenon 'gravity'.

ある借金にまでさかのぼる

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

エネルギーの刑務所

in.

すべての物体はお互いに引き合う

This effect traps us on earth.

この現象を"重力"と言う

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

大きな物体に近づけば

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

物体は より大きな力で引っ張られる

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

これが見えない鎖だ

But how can you owe energy?

私たちは重力刑務所の囚人と言える

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

単純だが 仕組みの説明として有効だ

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

囚人にはエネルギーの借金がある

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

どういうことだろう？

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

物体は速度や方向を変えたがらず

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

動かすにはエネルギーが必要だ

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

何億年前 大量のちりが重力に引かれ

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

太陽の周りで固まり 惑星ができた

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

ここでエネルギーが使われ

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

重力のくぼみができた

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

この分が重力からの

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

エネルギーの借金だ

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

エネルギーがなければ

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

ここからは出られない

Ok. How do we do that?

あなたを形作っている原子は

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

宇宙が集めたちりだからだ

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

OK　もう一度整理しよう

Known By their more boring name 'rockets'

物は動きたくない

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

動かすにはエネルギーが必要

to basically explode fuel in a controlled way.

重力はエネルギーを使い

This converts chemical energy into kinetic energy.

地球を作った

The exhaust of the reaction is directed outwards,

これが重力の刑務所になっていて

and pushes the rocket away from Earth.

出るには エネルギーの返済が必要

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

では どう返済するのか？

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

重力刑務所の脱出

But it's actually a lot trickier than that.

宇宙に行くには

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

エネルギーのやり取りが必要だ

,so you actually need much more.

そのために

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

このエネルギー返済マシーンを使う

payload and detonate it.

普通に言うなら"ロケット"だ

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

ロケットは 化学反応よる爆発力を

...which means it has more mass.

うまく制御して使っている

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

ここではエネルギーの変換が起きる

so you need more fuel to lift up your rocket.

化学反応物を一方向に出し

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

進む物理力にする

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

そして上に行くと

new fuel and so on.

位置エネルギーが増大する

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

簡単に言うと

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

重力にエネルギーを返している

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

実際はもっと複雑だ

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

宇宙までには他に

take off.

熱 排気ガス 空気抵抗などがあり

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

払う分はもっと多い

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

そして大量の燃料を人と一緒に乗せ

But wait, it gets worse.

爆発させるので

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

その制御のため

will crash back to Earth.

ロケットは頑丈でなければならない

Staying in space is much harder than getting there.

つまり 重くなる

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

重いと さらにエネルギーが要るので

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

載せる燃料の量が増える

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

燃料が増えれば また重くなり

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

そのための燃料もまた増え

Here, we can use a trick.

そうして むしろ燃料の方が多くなる

Instead of flying straight up, we can go sideways!

結果 ロケットの重さは100倍になる

Earth is a sphere.

例えば アリアン６という

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

ヨーロッパのロケットは

away beneath you.

10トンのものを宇宙に運ぶために

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

800トンの重さになっている

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

そして推進力しかないため

fast enough.

ロケットの重さ自体には上限がある

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

重すぎると発射できず

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

燃料タンクは大きくできない

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

ここが悩みの種であり

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

宇宙飛行が困難な理由だ

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

それだけではない

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

宇宙に出たとしても

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

重力圏から出なければ

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

地球に戻される

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

行くより 留まる方が難しい

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

留まるというのは

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

低軌道に入るということだ

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

大量の運動エネルギーが必要で

and Arianespace.

とてつもない速度になる

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

高度100kmだとすると

You can learn more about the rocket here.

秒速８km

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

時速２万8000km必要で

It really helps us out a lot!

90分で地球を一周できる速さだ

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

ここで技を使う