If it's cold and dense,
若空气寒冷稠密
you slow down faster,
减速会更快
you end up shorter.
降落轨道就较短
If it's hot and low density,
若空气炎热稀薄
you end up flying farther.
那就会飞得更远
The dangers of this unpredictable atmosphere
大气不可预知
are heightened by the speed the spacecraft
而航天器驶向火星的速度极高
has to travel at to get to Mars.
这使着陆更加危险
It will arrive
抵达火星时
at 13,000 miles per hour.
航天器的速度高达每秒5.8公里
We have enough energy
航天器高速飞行
of motion in the spacecraft
具有极高的动能
that we could vaporise the spacecraft in the atmosphere of Mars
使得只要它进入火星 与大气摩擦
just by slamming into that atmosphere
产生的巨大热量
and developing so much friction that the vehicle would burn up.
就足以将航天器汽化并烧毁火星车
So it's a challenge.
所以这是一个挑战
The rover will be tucked inside a spacecraft
当进入危险的火星大气层时
when it reaches the dangerous Martian atmosphere.
火星车将藏在航天器内部
Its first line of defence
它的第一道防线
will be the world's biggest heat shield.
是世界上最大的防热罩
Next, the team have to stop it
接下来 还要让它减速
from crashing head-on into the Red Planet.
以防火星车一头撞上地面
So they have designed
所以他们设计了
the biggest supersonic parachute ever made.
一张有史以来最大的超音速降落伞

重点解释：

1.slow down 减速

例句：You must slow down your car.
你必须把车子开慢。

2.end up 结束

例句：If he carries on driving like that, he'll end up dead.
他照这样开车,早晚得死于非命。

3.burn up 烧起来； 烧尽

例句：All the wood has been burnt up.
木柴全部烧光了。