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The Pioneer 10 and 11 probes, launched in 1972 and 73, were named after the pioneers who settled the western United States, because these probes were also explorers:
先锋10号和11号探测器分别于1972年和1973年发射，它们的名字是根据在美国西部落脚的先锋来命名的，因为这些探测器相当于探索者：
Pioneer 10 was the first spacecraft to pass through the asteroid belt, and both probes explored the outer planets before continuing on their path out of the solar system.
先锋10号是第一个飞过小行星带的航天器。先锋10号和11号会先探索外部行星，然后才会飞出太阳系。
But in the early 1980s, a NASA analysis team discovered something strange: Pioneer 10 and 11 were both slowing down and veering off course.
但在上世纪80年代的时候，美国宇航局的某个分析团队发现了奇怪的事情：先锋10号和11号都有减速以及偏离轨道的现象。
The deceleration became known as the Pioneer Anomaly, and for a long time, it had scientists and engineers totally stumped.
这种减速现象又称先驱者号异常。很长一段时间里，这种现象让科学家摸不着头脑。
It took an intense data hunt, a computer simulation, and more than 3 decades to figure out what was going on.
要想弄清楚是怎么回事，不仅需要高强度数据搜索、计算机模拟，在时间上也需要30多年。
The team first noticed the anomaly because of the Doppler effect, which describes how the frequency of light admitting from an object changes if the object is moving.
该小组第一次发现这种异常现象是因为多普勒效应。所谓多普勒效应就是某个物体发出的光的频率会随着物体的移动而改变。
The engineers working on Pioneer expected the light coming from the probes to be shifted by a certain amount, based on the probes' speed.
先锋号的工程师们原本以为探测器发出的光频会随着探测器的速度而做出一定的改变。
But when they measured the actual frequency of the light, it was slightly higher than they'd predicted.
但他们测量光频后发现，光频只比他们预想的高了一丢丢。
They already knew that the probes would be slowing down at least a little, because of things like the pull of the Sun's gravity.
他们已经知道：探测器会稍许减速的，因为有太阳引力这样的存在。
But the frequency of the light showed that Pioneer 10 and 11 were both slowing down more than they should have been, and no one knew why.
但光频表明先锋10号和11号的减速幅度都异常大，让人摸不着头脑。
Each year they were a few hundred kilometers from where they were expected to be.
每年，探测器距离本来应该到的地方都有几百公里的距离。
Two other probes seemed to have some trajectory issues too, though there was less data on them:
还有两个探测器似乎也有相同的轨道问题，只不过数据量少一些：
Galileo, which launched in 1989 to study Jupiter and its moons; and the Ulysses spacecraft, a Sun probe that launched in 1990.
1989年用以研究木星及其卫星的伽利略号；1990年用以研究太阳的探测器尤利西斯号。
If you're going to launch something into space, you really do want to know where it's going.
如果向宇宙里发射什么物体，就会很想知道它去了哪里。
So in 1994, a team of scientists decided to try to identify the source of the Pioneer anomaly.
于是，1994年，一组科学家决定尝试确认先锋号异常现象的原因。
The most likely culprit seemed to be thermal radiation.
最有可能的罪魁祸首似乎是热辐射。
If the different components of the spacecraft were emitting heat unevenly, the extra radiation coming from one side could be enough to slow them down a tiny bit.
如果航天器不同部分放出的热量不均的话，那么某一面的额外辐射就可以让航天器稍微减速。
And when I say tiny, I mean tiny — each Pioneer probe was being slowed by a force that was about 10 billion times weaker than Earth's gravitational pull.
我说稍微是因为真的只是稍微——每个先锋号探测器都会因为某种力的作用而减速。而这种力大概是地球引力十亿分之一。
But over time, and in the microgravity environment of outer space, this tiny force was enough to knock the probes off-course.
但是随着时间的流逝，外太空微重力环境中的微弱力量也足以让探测器偏离轨迹。
The thing is, the researchers didn't know for sure that thermal radiation was the problem.
关键是：研究人员不确定热辐射是否就是症结所在。
That amount of force also happened to work out really well for some cosmological theories that were being developed at the time.
这种力的大小恰好十分符合当时一些宇宙学理论的内容。
The team announced the Pioneer anomaly to the public in a paper published in 1998.
该研究组在1998年的一篇论文中向公众介绍了先锋号异常。
In response, theorists published hundreds of papers about what could be causing it.
此后，一些理论学家发布了数百篇论文研究先锋号异常的原因。
They thought it might have come from things like an undiscovered planet, dark matter, or even the expansion of spacetime itself.
他们认为这可能是因为某个尚未发现的恒星、暗物质甚至是时空本身的延伸。
If some of the papers turned out to be correct, they'd prove that a lot of what we knew about our universe was just plain wrong.
如果其中的一些论文所述为真，那么就表明我们对宇宙的很多认知都是错误的。
Around 2005, another team of researchers — including one of the authors of the 1998 paper — decided to try and simulate the missions, to see what kind of thermal radiation they were emitting and whether that could account for the anomaly.
2005年左右，又有一组研究人员——包括1998年论文的几位作者——决定尝试模拟探测器的任务，旨在验证它们放射了何种热辐射，以及这种热辐射是否可以解释异常现象的原因。
All they needed were 3D models of the spacecraft, and as much data they could get their hands on.
他们只需要探测器的3D模型以及手头尽可能多的数据便能完成验证。
Except, they ran into two problems: First, the Pioneer spacecraft were designed on paper.
不过，他们遇到了2个难题：首先是先锋号探测器是论文设计的内容。
Computer-aided design just didn't exist at the time.
但那时候还没有机辅设计。
So, they had to create their 3D models from scratch.
所以他们要从0开始设计3D模型。
Second, NASA didn't require mission records to be archived, so there was no telling where the data was.
第二个难题是：美国宇航局之前的任务并没有进行记录，所以也不知道数据在哪儿。
They did eventually get the data they needed, though it took some digging:
但他们最终还是得到了所需的数据，虽然费了一番周折。
They found the Doppler data on a navigator's computer hard drives, and at the National Space Science Data Center.
他们在导航器的电脑硬驱和国家太空科学资料中心里发现了多普勒数据。
They managed to get the other science and housekeeping data from one of the other engineers who worked on the Pioneer missions —
他们通过努力，成功从另一位研究先锋号的工程师那里获取了其他科学数据和内务处理数据——
he'd decided to save a copy, even though NASA destroyed the original files.
他决定保存副本，虽然美国宇航局毁掉了原始文件。
Then there were the 400 magnetic tapes of navigational data inside some moldy cardboard boxes under a staircase at the Jet Propulsion Laboratory in California.
随后，他们在加州喷气推进实验室楼梯下发霉的纸箱里发现了400个航行资料的磁带。
By combining all this data with old blueprints, and consulting some of the engineers that built the Pioneers, the team created a 3D model and used it to analyze how heat radiated from each probe.
在用蓝图整合了所有数据并咨询了建造先锋号的一些工程师后，该研究组创建了一个3D模型，并用这个模型分析了热量是如何从每个探测器中辐射出来的。
In 2012, they published their results: they finally had enough evidence to conclude that the Pioneer anomaly was caused by a force coming from the probes' thermal radiation.
2012年，他们发布了研究结果：他们终于有充足的证据证明先锋号异常是由探测器热辐射产生的力引起的。
Over thirty years, this tiny force pushed both probes off-course a combined distance of 400,000 kilometers — farther than the Moon is from Earth.
在30年的时间里，这股并不大的力量将先锋号推离轨道40万千米远——这距离超过了月球和地球之间的距离。
The main heat sources were the electrical heat from spacecraft components and waste heat from their nuclear power sources – the Radioisotope Thermoelectric Generators.
主要热源是来自航天器组件的电热以及来自核能源（放射性同位素热电发生器）的废热。
The Pioneer probes were especially affected by this problem because they rotated to stabilize themselves.
先锋号探测器尤其受到了这个问题的影响，因为它们要靠旋转来稳定自己。
But that technique didn't fix the push from thermal radiation.
但旋转并不能抵消热辐射带来的推力。
Ulysses and Galileo were also spin-stabilized, so it made sense that they would be affected, too.
尤利西斯号和伽利略号也都是旋转稳定型探测器，所以它们受到影响也就不奇怪了。
Other NASA designs are stabilized by control thrusters that do compensate for small disturbances like thermal recoil.
还有一些美国宇航局的设计是靠控制推进器来实现稳定，因为控制推进器确实可以抵消一些热反冲产生的微弱干扰。
The Pioneer probes were retired in the 1990s, and we've lost communications with both of them.
上世纪90年代，先锋号功成身退——它们跟地球失去了联络。
But it turns out that they had more in common with pioneers in the Wild West than we thought:
但我们发现，它们跟西大荒的共通性比我们以为的还要多：
They were packing heat!
它们可以囤积热量！
Thanks for watching this episode of SciShow Space, and thanks especially to our patrons on Patreon who help make this show possible.
感谢收看本期的《太空科学秀》，尤其要感谢我们的忠实粉丝。
And for the last four month of 2016, we're going to be collecting all the money we raise and putting in toward a brand new project.
2016年的最后4个月里，我们会收集募集到的所有资金，研发新的项目。
It's gonna be a new channel, here on YouTube, and it will either be SciShow Health, SciShow Life, or SciShow Psychology.
这个项目就是YouTube上一个新的频道，可能会叫《健康科学秀》、《生活科学秀》或者《心理科学秀》。
And who was going to be picking which of these great ideas we will be executing on – it's our patrons on Patreon.
那么，谁会最终决定我们会采用哪个名字呢？就是我们的观众啦。
So if you wanna have a voice in that process, and also help us keep making cool stuff, You can go to patreon.com/scishow.
如果大家想建言献策并帮助我们选出好听的名字的话，就请登录patreon.com/scishow吧。
