Getting to space is easy. It 8217;s not, like,something you could do in your car, but it 8217;s not a huge challenge. You couldget a person to space with a rocket the size of a telephone pole. The X-15aircraft reached space just by going fast and then steering up.
进入太空很简单。虽然你确实没法开车进入太空，但这并不是一个大问题。仅靠一个电话线杆大小的探空火箭就能把一个人送入太空。要知道美国的X-15飞机就是因为飞得非常快，然后机头往上一拉进入太空的。
You will go to space today, and then youwill quickly come back.
你这是来也匆匆，去也匆匆。
But getting to space is easy. The problemis staying there.
进入太空容易，要留在太空中就没那么简单了。
Gravity in low Earth orbit is almost asstrong as gravity on the surface. The Space Station hasn 8217;t escaped Earth 8217;sgravity at all; it 8217;s experiencing about 90 percent the pull that we feel on thesurface.
近地轨道处的地球引力几乎和在地面上一样强。即使是空间站也没能逃离地球引力的魔爪，它受到的引力大小约是在地面上的90％。
To avoid falling back into the atmosphere,you have to go sideways really, really fast.
要想不从太空掉回来，你必须要绕地球飞得足够快。
The speed you need to stay in orbit is about8 kilometers per second. Only a fraction of a rocket 8217;s energy is used to liftup out of the atmosphere; the vast majority of it is used to gain orbital(sideways) speed.
要想保持在绕地轨道的高度你需要达到每秒8千米的速度。火箭的能量只有很少一部分用来将负载带到大气层外，大部分的能量都被用于加速到轨道上侧着走的速度。
This leads us to the central problem ofgetting into orbit: Reaching orbital speed takes much more fuel than reachingorbital height. Getting a ship up to 8 km/s takes a lot of booster rockets.Reaching orbital speed is hard enough; reaching orbital speed while carryingenough fuel to slow back down would be completely impractical.
于是我们就看到了入轨的重点：达到轨道速度要比进入轨道高度花费多得多的燃料。要想把一艘飞船加速到每秒8千米需要许许多多的助推器。达到轨道速度已经很难了，还要携带足够的燃料把速度再降下来根本就是不切实际的。
These outrageous fuel requirements are whyevery spacecraft entering an atmosphere has braked using a heat shield insteadof rockets-slamming into the air is the most practical way to slow down. (Andto answer Brian 8217;s question, the Curiosity rover was no exception to this;although it used small rockets to hover when it was near the surface, it firstused air-braking to shed the majority of its speed.)
如此惊人的燃料需求也是为什么飞船在再入大气层时都用热防护罩而不是反推火箭来减速——一头栽入大气层是最可行的减速方式。（至于布赖恩问的那个问题，“好奇号”也是这么减速的，它携带的反推火箭只是在接近地面时才启动，之前已经通过火星大气制动降低了一大部分的速度了。）
How fast is 8 km/s, anyway?
那么，每秒8千米有多快呢？
I think the reason for a lot of confusionabout these issues is that when astronauts are in orbit, it doesn 8217;t seem likethey 8217;re moving that fast; they look like they 8217;re drifting slowly over a bluemarble.
我觉得人们之所以会有开头的那些迷惑，是因为在太空中的航天员看起来移动得并不快，他们看起来就像在慢慢飘过一颗蓝色星球。