Temperature is a measure of the average kinetic energy of a collection of particles. In space, individual molecules have a high average kinetic energy, but there are so few of them that they don 8217;t affect you.
温度描述的是一堆粒子的平均动能的大小。在太空中，一个个分子都有着很高的分子平均动能，只是它们数量太少影响不到你。
When I was a kid, my dad had a machine shop in our basement, and I remember watching him use a metal grinder. Whenever metal touched the grinding wheel, sparks flew everywhere, showering his hands and clothes. I couldn 8217;t understand why they didn 8217;t hurt him-after all, the glowing sparks were several thousand degrees.
在我还小的时候，我家地下室里有一个机械小作坊。我记得我曾经看着我爸使用一台金属研磨机，每当金属接触砂轮时都会有四散飞溅的火花，许多火花飞到了他的手上或衣服上。我当时不能理解为什么我爸不会受伤，因为那毕竟都是几千摄氏度的火花。
I later learned that the reason the sparks didn 8217;t hurt him was that they were tiny; the heat they carried could be absorbed into the body without warming anything more than a tiny patch of skin.
后来我才知道火花不会伤人的原因是它太小了，它所携带的那一丁点儿的热量会被人体吸收，只影响到极小一部分皮肤。
The hot molecules in space are like the sparks in my dad 8217;s machine shop; they might be hot or cold, but they 8217;re so small that touching them doesn 8217;t change your temperature much.1 Instead, your heating and cooling is dominated by how much heat you produce and how quickly it pours out of you into the void.
太空中那些“热”分子就像我爸作坊里的火花，它们可能很热也可能很冷，但它们的体形过于微小，就算碰到了也不会对你产生多大影响。1相反，潜艇里是变热还是变冷则取决于产生多少热量，以及你能多快地把这些热量排出去。
Without a warm environment around you radiating heat back to you, you lose heat by radiation much faster than normal. But without air around you to carry heat from your surface, you also don 8217;t lose much heat by convection.2 For most human-carrying spacecraft, the latter effect is more important; the big problem isn 8217;t staying warm, it 8217;s keeping cool.
现在你的周围没有一个温暖的环境能把热量辐射回来，因此你通过辐射流失的热量会比在正常情况下快许多。不过没有了周围的空气从你体表带走热量，你因对流而流失的热量也同时减少了。2对于大多数载人飞船来说，后者更值得关注。他们要面临的最大问题不是保持温暖，而是保持凉爽。
A nuclear submarine is clearly able to maintain a livable temperature inside when the outer hull is cooled to 4°C by the ocean. However, if the submarine 8217;s hull needed to hold this temperature while in space, it would lose heat at a rate of about 6 megawatts while in the shadow of the Earth. This is more than the 20 kilowatts supplied by the crew-and the few hundred kilowatts of apricity3 when in direct sunlight-so they 8217;d need to run the reactor just to stay warm.4
在水温为4℃的海洋中，核潜艇显然有能力在舱内维持一个可供生存的温度。不过要想在太空中维持这个温度，处于地球的阴影中时，潜艇流失热量的功率约为6兆瓦，而艇员们散发热量的功率只有20千瓦，就算加上太阳直射时的几百千瓦日暖3也不够，所以他们必须打开反应堆来供暖。
To get out of orbit, a submarine would need to slow down enough that it hit the atmosphere. Without rockets, it has no way to do this.
为了脱离地球轨道，潜艇需要把速度降到足够低的程度，这样才能重返大气层。但没有火箭，它无法完成。