ORBITAL SPEED

轨道速度

Q. What if a spacecraft slowed down onreentry to just a few miles per hour using rocket boosters like the Mars skycrane? Would it negate the need for a heat shield?

Q．在宇宙飞船返回再入大气层时，如果用一个像“好奇号”降落火星表面时所用的“天空起重机”，把飞船的速度降到每小时只有几千米，那是不是就可以不用热防护罩了？

Brian

——布赖恩

Q. Is it possible for a spacecraft tocontrol its reentry in such a way that it avoids the atmospheric compressionand thus would not require the expensive (and relatively fragile) heat shieldon the outside?

Q．有没有一种办法可以让飞船在冲入大气层的时候避免压缩大气，这样就不再需要昂贵而又脆弱的外部热防护罩了？

Christopher Mallow

——克里斯托弗•马洛

Q. Could a (small) rocket (with payload) belifted to a high point in the atmosphere where it would only need a smallrocket to get to escape velocity?

Q．可不可以把一个小火箭（载有货物）提升到一个很高的地方，然后在那里只需要很小的火箭就能达到逃逸速度？

Kenny Van de Maele

——肯尼•范德梅勒

A. THE ANSWERS TO THESE questions all hingeon the same idea. It's an idea I've touched on in other answers, but right nowI want to focus on it specifically:

A．这三个问题问的东西本质上是一样的，而且我在其他几篇文章中也讲到过，不过现在我把它们特别拿出来讲一下：

The reason it's hard to get to orbit isn'tthat space is high up.

进入地球轨道之所以困难并不是因为太空太高。

It's hard to get to orbit because you haveto go so fast.

进入轨道很困难是因为你必须达到足够快的速度。

Space isn't like this:

太空并不是像这样：

Not actual size.

未按真实比例绘制

Space is like this:

太空其实是这样的：

You know what, sure, actual size.

你知道的，按真实比例绘制。

Space is about 100 kilometers away. That'sfar away-I wouldn't want to climb a ladder to get there-but it isn't that faraway. If you're in Sacramento, Seattle, Canberra, Kolkata, Hyderabad, PhnomPenh, Cairo, Beijing, central Japan, central Sri Lanka, or Portland, space iscloser than the sea.

太空大约距离我们有100千米远。它确实很遥远——至少我不想爬100千米高的梯子——但它又没有想象中的远。如果你在萨克拉门托、西雅图、堪培拉、加尔各答、海得拉巴、金边、开罗、北京、日本中部、斯里兰卡中部或者波特兰，那么你离大海的距离比你离太空的距离还要远。