《那些古怪又讓人憂心的問題》第85期:軌道速度(1)

ORBITAL SPEED

軌道速度

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．在宇宙飛船返回再入大氣層時，如果用一個像“好奇號”降落火星表面時所用的“天空起重機”，把飛船的速度降到每小時只有幾千米，那是不是就可以不用熱防護罩了？

Brian

——布賴恩

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．有沒有一種辦法可以讓飛船在衝入大氣層的時候避免壓縮大氣，這樣就不再需要昂貴而又脆弱的外部熱防護罩了？

Christopher Mallow

——克里斯托弗•馬洛

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．可不可以把一個小火箭（載有貨物）提升到一個很高的地方，然後在那裏只需要很小的火箭就能達到逃逸速度？

Kenny Van de Maele

——肯尼•範德梅勒

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．這三個問題問的東西本質上是一樣的，而且我在其他幾篇文章中也講到過，不過現在我把它們特別拿出來講一下：

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

進入地球軌道之所以困難並不是因爲太空太高。

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

進入軌道很困難是因爲你必須達到足夠快的速度。

Space isn't like this:

太空並不是像這樣：

Not actual size.

未按真實比例繪製

Space is like this:

太空其實是這樣的：

You know what, sure, actual size.

你知道的，按真實比例繪製。

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.

太空大約距離我們有100千米遠。它確實很遙遠——至少我不想爬100千米高的梯子——但它又沒有想象中的遠。如果你在薩克拉門託、西雅圖、堪培拉、加爾各答、海得拉巴、金邊、開羅、北京、日本中部、斯里蘭卡中部或者波特蘭，那麼你離大海的距離比你離太空的距離還要遠。