Name: 為什麼登陸火星這麼難？ (Why It's So Hard to Land on Mars)
Uploaded: 2021-01-14T10:28:40.000Z
Duration: 6 min 43 s
Description: 【看影片學英語】數萬部 YouTube 影片，搭配英漢字典即點即查，輕鬆掌握單字發音與用法，長久累積看電影不必再看字幕。

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Thanks to its watery history and potential for past life,

Mars has been fascinating people for decades.

So it's no surprise that we've sent more spacecraft there than any other planet.

Most other worlds have had just a small handful.

The problem is, around half of the probes that have ever attempted to explore Mars

So as much as we want to understand the planet, getting to its surface is no easy feat.

Mars's unique atmosphere often gets the better of us,

and it's taken some creative engineering to get to the ground.

Before Mars, the only places we'd ever landed spacecraft were the Moon and Earth.

And while that did come with challenges, we had strategies nailed down pretty well for both.

The hard thing about landing on Earth is that our thick atmosphere creates extreme friction

But we've solved that problem with heat shields, and besides, that thick atmosphere

It has virtually no atmosphere, which gets rid of the heat problem,

We have to use retro-rockets to land, little rockets that fire underneath a spacecraft

Mars, meanwhile, is a whole different beast.

It comes with all the challenges of landing on Earth and the Moon,

Its atmosphere is 100 times thinner than Earth's, meaning parachutes can't grab onto enough

air to completely slow down the spacecraft.

But unlike the Moon, there's also just enough atmosphere to create problems.

Just like friction causes space rocks and old satellites to burn up in Earth's atmosphere,

a space probe entering Mars's atmosphere can get hotter than 2000 degrees Celsius.

That's hot enough to melt iron, and just about every other metal.

So the millions of dollars' worth of machinery we send to Mars

needs serious protection to keep from being fried.

So, how do you get an expensive, heavy chunk of metal, traveling tens of thousands of kilometers

an hour, to come gently to a stop on the surface of another world?

A whole lot of creativity. And probably a good amount of coffee.

Every mission to land on Mars starts with something called an aeroshell:

a special capsule that protects its cargo against the heat.

Its outer layer is filled with a material, called an ablator, that was invented in the

1970s for the first Mars landers: the Viking missions.

It reacts with the Martian atmosphere in a way that removes the heat

It gets so hot that it glows red, but inside the capsule,

cargo stays a little cooler than room temperature.

Next, once friction has slowed things to about 1600 kilometers per hour,

a parachute opens, and part of the aeroshell is cast off.

Amazingly, engineers are still using a parachute pretty similar to the one

designed for the Viking landers more than 40 years ago.

It's made of nylon and polyester, with tethers made of the same material as bulletproof vests.

That makes it super strong and light, which is really important, considering the craft

is still moving at supersonic speeds when it deploys.

And while it isn't enough to slow down a spacecraft all the way, it does help.

After a few minutes, the parachute brings the craft down to a few hundred kilometers

per hour, and it gets discarded along with the rest of the aeroshell.

Now, this is where things get really creative, and no type of mission has been exactly the same.

Engineers have had to come up with special solutions to get each spacecraft on the ground.

For example, those 1970s Viking landers used retro-rockets like on the Moon.

But there was always the possibility that they'd botch a landing on uneven ground.

And while they were fine for landers, carrying around a bunch of rockets would be a pointless

burden on the rovers we started sending to Mars in the '90s.

So for the Pathfinder mission that landed in 1997, which included the first experimental

rover, engineers tried a new method: a cluster of airbags.

After slamming into the ground, this robotic explorer bounced along for hundreds of meters.

And by bounced, I mean it shot several stories into the air

and moved as fast as cars on the freeway before rolling to a stop.

In fact, it worked so well that scientists used the same system to land

the more recent Spirit and Opportunity rovers.

Then, in 2012, things had to change again,

because airbags were out of the question for the Curiosity rover.

It was nearly five times the mass of Spirit and Opportunity,

so engineers came up with their most epic solution yet.

Basically, it was a stage that used retro-rockets to hover above the surface.

From there, it slowly lowered the rover on a tether,

then cut itself free and flew off to crash-land nearby.

NASA's next Mars mission, Mars 2020, will use a similar strategy.

But who knows what kind of unique designs we'll see after that.

Oh, and in case this all isn't complicated enough, every single step of these landings

also has to happen completely automatically.

That's because radio signals travel at the speed of light, so they take at least eight

minutes to go from Earth to Mars and back, which is longer than it takes to land.

And it's not exactly easy to put a spacecraft on autopilot in a world that's still

The good news is, all these years of work have been well worth it.

Besides preparing us for future exploration,

these landers have brought us closer to knowing what Mars was like in the past.

That could help us figure out whether or not it ever hosted life, and what it would take

to support human life one day in the future.

And it's all thanks to some brilliant engineers and organizations.

If you've ever dreamed of becoming an engineer who lands spacecraft on other planets, you'll

want to make sure you're an expert on orbital mechanics.

And conveniently, Brilliant has some courses that can really help you out.

you can even try their quiz about how to send a spacecraft to Mars.

I like how Brilliant makes the physics easy to understand,

and their visuals and diagrams are super helpful.

You can check it out at Brilliant.org/SciShowSpace, and right now, the first 200 people to sign

up at the link will get 20% off of an annual premium subscription to Brilliant.

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為什麼登陸火星這麼難？ (Why It's So Hard to Land on Mars)

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