英语听力：自然百科 行星旅行指南：火星 Mars—8

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“At this point we know at least as much as the engineers knew at the time that they agreed to land on the moon. And they had only nine years. So I think once the nation decides they really want to land humans on Mars, the system can be designed and developed and built.”

 

Fast forward to the future, after six months’ crossing the blackness of space, things suddenly get a lot more interesting. The combination of a high approach speed, a thin atmosphere and twice the gravity of the moon makes Mars one of the hardest places to land in the solar system, even for robots. 

 

“You hit the top of Martian atmosphere, you are going Mach 27, 27 times the speed of sound. And for our vehicle between when we hit the top of Martian atmosphere and when we were bouncing on the surface with the airbags were six minutes. It’s a hell of a ride. You use a hitch¹ rope to slow you down to a leisurely² Mach 2, twice the speed of sound and then we threw out a super-size parachute.”

 

Everything is complex and everything has to happen precisely³ on time. 

 

“The worst part is when you come into contact with the Martian surface, there is no runway, OK? There’s no nice place to land, and you can’t control very well where you are going to come down, so you are going to come down in a field of rocks like this. How do you guarantee that your $1 billion spacecraft is actually going to survive that? The approach that worked for us with our rovers was great big airbags, bounce, bounce, bounce, bounce, bounce, finally the vehicle comes to rest. 

 

Vikings use the rocket motors, and they just touch down gently on the surface and they were fortunate. It was just good luck. They landed in a field of boulders⁴ like this, but they didn’t land with one that was poking⁵ through the valley and it all worked. You had to be good and you had to be lucky.”

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