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Why getting BACK from space is harder than getting there - Video học tiếng Anh

Why getting BACK from space is harder than getting there

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0:00When a spaceship or meteor enters our

0:02atmosphere, it becomes a fireball. But

0:04that heat doesn't come from friction

0:07with the atmosphere like most people

0:08think. There's actually something way

0:10more interesting going on. It takes so

0:12much kinetic energy to get a spacecraft

0:14to the moon. I mean, that's why the

0:16rockets are so huge. But when you slow

0:18down, all of that kinetic energy has to

0:20go away somewhere, right? Well, you

0:22could fire giant rockets to slow you

0:24down and shave off some kinetic energy,

0:26but you'd also have to carry all that

0:27fuel up with you, too. That's why

0:29spacecraft use the atmosphere as a break

0:31instead. It's a genius way to take all

0:34that kinetic energy and just convert it

0:36to heat. Here's why friction isn't

0:38what's happening. A spacecraft like

0:40Orion slams into the atmosphere at

0:4225,000 mph. That's something like 40

0:45times faster than a passenger jet. At

0:48that velocity, the air in front of the

0:50spacecraft can't get out of the way. So,

0:52it just gets squeezed and compressed

0:55really violently. That heat is not from

0:58air molecules rubbing against each

0:59other. It's because the spacecraft acts

1:02like a giant piston, compressing the air

1:04into this impossibly thin layer. And

1:06when you compress a gas, it heats up.

1:08The air gets so hot as it gets squeezed,

1:11it stops being air and becomes a

1:13superheated plasma. It's a whole other

1:15state of matter. That plasma can reach

1:1810,000°,

1:19hotter than the surface of the sun. And

1:21it works really well. squishing the

1:24atmosphere into a hot plasma removes

1:26more than 99.9%

1:28of Orion's kinetic energy before it

1:30deploys those parachutes. And this is

1:32why it's so important that space

1:34capsules are the opposite of pointy

1:36because that blunt shape creates a shock

1:38wave that's pushed out away from the

1:40surface. So almost all of that heat

1:42stays out in front of the heat shield

1:44and not touching the ship and the inside

1:47of the spacecraft stays a comfortable

1:48room temperature. Sharp, streamlined

1:51shapes, which works basically everywhere

1:52else in aerodynamics, actually makes

1:54re-entry worse. And that's why every

1:56crude capsule ever built is shaped like

1:58a pudgy little cone. Follow me for more

2:01cool science videos.