第277集：轨道

本集《天文小讲》由斯威本大学在线天文学项目赞助，这是全球历史最悠久的在线天文学学位课程。

This episode of Astronomy Cast is brought to you by Swinburne Astronomy Online, the world's longest running online astronomy degree program.

欲了解更多信息，请访问 astronomy.swin.edu.au。

Visit astronomy.swin.edu.au for more information.

《天文小讲》第277期，2012年10月22日星期一，主题：轨道。

Astronomy Cast episode two seventy seven for Monday, 10/22/2012, Orbit.

欢迎收听《天文小讲》，这是我们每周基于事实的宇宙探索之旅。

Welcome to Astronomy Cast, our weekly facts based journey through the cosmos.

我们帮助您不仅了解我们知道了什么，更了解我们是如何知道这些的。

We help you understand not only what we know, but how we know what we know.

我是弗雷泽·凯恩，《今日宇宙》的出版人，和我一起的是帕梅拉·盖伊博士。

My name is Fraser Cain, I'm the publisher of Universe Today, and with me is Doctor.

帕梅拉·盖伊，南伊利诺伊大学埃弗茨维尔分校的教授。

Pamela Gay, a professor at Southern Illinois University, Evertzville.

嗨，帕梅拉，你最近怎么样

Hi Pamela, how are

你怎么样？

you doing?

我很好，弗雷泽，你呢？

I'm doing well, how are you doing Fraser?

很好。

Good.

很多人问我有没有受到最近发生在王子港外海地震的影响，我完全没事。

So a bunch of people asked me if I had gotten hit by this recent earthquake that happened off the coast of Prince Rupert, and I'm totally fine.

连一点感觉都没有。

Didn't even feel it.

没有引发海啸。

No tsunami was generated.

所以我认为没有人员伤亡，也没有造成破坏。

So I don't think there was any injuries, no damage.

这是一次相当温和的7.7级地震，这相当令人惊讶。

It was a pretty tame 7.7 magnitude earthquake, which is quite surprising.

当地震发生在加拿大这样人口稀少的地区时，总是好事。

It's always good when they're in largely unpopulated areas like Canada.

就像加拿大，人口稀少。

Like Canada, which is largely unpopulated.

你之前有几件事想提一下，顺便宣传一下吗？

Now you had a couple of things that you wanted to mention and kind of shamelessly promote?

嗯，有。

Well, did.

根据我当地的百货商店说，圣诞节马上就要到了，店里全都堆满了圣诞商品，吓人极了。

So Christmas season is fast approaching according to my local department stores, which are all terrifyingly filled with Christmas stuff.

我们想提醒大家，我们支付账单的方式之一就是卖T恤。

And we would like to remind all of you that one of the ways that we pay our bills is we sell t shirts.

所以，拜托，拜托，拜托，拜托，去买件T恤吧。

And if you can please, please, please, please go buy t shirts.

这能帮我们支付所有的服务器费用。

This will help us pay all of our server bills.

我们目前的服务器费用资金已经不足了。

And we're actually running short on funding for our server bills right now.

所以，如果你想要专门捐赠用于服务器费用，请不要捐给《天文之声》。

So and if you wanna if you wanna donate specifically for server bills, don't donate to Astronomy Cast.

去Astrasphere网站吧。

Go to Astrasphere Yeah.

因为Astrasphere负责支付服务器费用。

Because Astrasphere pays for the servers.

所以，请购买T恤，捐赠给astrasphere.org，这样我们就能 hopefully 让服务器继续运行，这始终是一个好目标。

So buy t shirts, donate to astrasphere.org, and, we will hopefully keep our servers turned on, and, that's always a good goal.

这是一个涵盖《天文之声》、《365天天文》、《宇宙探索》以及所有其他精彩内容的 umbrella 组织，所以我们

That is the umbrella organization that holds Astronomy Cast and three sixty five Days of Astronomy and Cosmo Quest and all of the fun stuff that So we

《天文之声》是由Astrasphere新媒、南伊利诺伊大学爱德华兹维尔分校和《今日宇宙》联合制作的。

Astronomy Cast is a joint production of Astrasphere New Media, Southern Illinois University Edwardsville, and Universe Today.

当你捐赠给《天文之声》时，款项会通过南伊利诺伊大学爱德华兹维尔分校处理，用于支付我们的节目笔记、帮助Preston完成所有剪辑工作，但这些资金并不用于支付服务器费用。

And when you donate to Astronomy Cast that goes through Southern Illinois University Edwardsville, that goes to help pay for our show notes, it goes to, help pay for Preston to do all of our editing, but that does not pay for the servers.

Astrasphere 正在支付服务器费用。

Astrasphere is paying for the servers.

明白了。

Got it.

所以如果你想资助服务器，请捐给 Astrasphere，我们真的很需要这笔钱。

So if you wanna donate to servers, donate to Astrasphere, and we really need money for that.

好的。

Okay.

好吧。

Alright.

那么，我们开始吧。

Well, let's, well, let's get rolling then.

本集《天文casts》由 Eighth Light 公司赞助。

This episode of Astronomy Cast is brought to you by Eighth Light Inc.

Eighth Light 是一家敏捷软件开发公司。

Eighth Light is an agile software development company.

他们打造美观、耐用且可靠的应用程序。

They craft beautiful applications that are durable and reliable.

Eighth Light 按需提供严谨的软件领导力，并分享其专业知识，以提升您的项目。

Eighth Light provides disciplined software leadership on demand and shares its expertise to make your project better.

如需了解更多信息，请访问他们的网站：www.eighthlight.com。

For more information, visit them online at www.eighthlight.com.

请记住，网址是 www.thedigiteight,thlight.com。

Just remember, that's www.thedigiteight,thlight.com.

给他们发个消息吧。

Drop them a note.

Eighth Light，软件是他们的技艺。

Eighth Light, software is their craft.

当一个物体绕地球运行时，它实际上是在下落。

So when an object is orbiting the Earth, it's really falling.

诀窍，正如《银河系漫游指南》中所描述的，是如何朝地面投掷自己却偏偏错过。

The trick, as described in the Hitchhiker's Guide to the Galaxy, is how to throw yourself at the ground and miss.

有几种不同类型的轨道，它们各有优势，从亚轨道跳跃到地球静止轨道。

There are several different kinds of orbits, they're good for different reasons, from suborbital jumps to geostationary orbit.

是时候学习所有关于绕圈飞行的知识了。

Time to learn everything there is to know about going around and around and around.

我从来没见过我们开始前你的开场白。

I never get to see your intros before we start.

我喜欢那句《银河系漫游指南》里的引言。

And I love that quote from Hitchhiker.

我知道。

I know.

我知道。

I know.

这很棒，我有点剽窃了它，对吧？

That's a great I sort of stole it, right?

因为这是关于飞行的这句话：飞行的诀窍就是直接朝地面坠落，但偏偏错过。

Because it's this, it's this quote about flying that the trick to flying is to just fall at the ground but miss.

而书中的主角在某个时刻终于明白了如何做到这一点，并开始飞行。

And, and the lead character in the books, at one point finally figures out how to do this and flies around.

但那正是轨道的真正含义。

But but that's really what orbit is.

对吧？

Right?

轨道就是不断下落却避开了地面。

Orbit is falling and missing the ground.

从较高的高度开始会更有帮助。

It helps to start from a large altitude.

你知道吗？

So you know what?

我想稍微回溯一下，我们之前做过好几期关于牛顿的节目。

I wanna go back a bit and like we we did a bunch of shows on Newton.

我觉得我们对牛顿关于轨道的观点有些忽视了。

I don't I don't think we kinda gave Newton Newton's thoughts on orbit, kinda short shrift.

那么，我们能不能简单聊聊牛顿是如何弄清楚轨道是什么，以及他是如何推断出月球在做什么的？

So so can we kind of have a quick conversation about about how Newton figured out what orbit is and sort of piece together what the moon is doing?

好吧，用炮弹来解释，对吧？

Well, so With cannonballs and Right?

与其说是牛顿发现了轨道，不如说是开普勒先发现了轨道，而牛顿则解释了轨道背后的原因。

It it wasn't so much Newton that figured out orbits as Kepler and then Newton figured out the why of the orbit.

开普勒发现的是，轨道是椭圆形的，而牛顿则发现了有一种叫做引力的诡异力量，它让苹果落地，也让月球朝地球下落却始终错过。

So so what what Kepler had figured out was, orbital periods that orbits our ellipses And then Newton figured out that there's this crazy force called gravity that causes keys to fall to the ground and causes moons to fall towards the earth and miss.

关键是，如果你只是把一串钥匙直接往下扔，不施加任何力，只是松开它们，它们会直接朝地球的质心坠落。

And and the trick is if you simply drop a set of keys straight down, applying no force on them, just releasing them, they're gonna fall straight towards the center of mass of the earth.

钥匙的质心会被地球的质心吸引。

The center of mass of the keys is attracted towards the center of mass of the planet.

但如果你把钥匙扔出去，它们就会获得一定的水平速度，在忽略空气阻力和摩擦等因素的情况下，它们会保持恒定的水平速度，同时垂直方向朝地球中心下落。

Now, if you instead toss the keys, they're going to move with a certain amount of horizontal velocity, and ignoring air resistance, ignoring friction, things like that, they're going to maintain a constant horizontal velocity while falling towards the center of the earth vertically.

关键在于，如果你把钥匙扔得足够快，它们就会越飞越远，绕着我们这个弯曲的星球转得越来越远。

Now the catch is if you throw those keys hard enough, they're gonna keep going further and further and further, getting further around our curved planet.

你可以想象用某种枪把钥匙射出去

You can imagine like shooting those keys out of some kind of gun that shoots

没错。

Exactly.

一

A

钥匙枪。

key gun.

从某种意义上说，这比大炮还危险。

Which in some ways seems more dangerous than cannonballs.

是啊。

Yeah.

但如果你给钥匙足够的速度，它们会绕一圈后击中你的后脑勺。

But if you get enough velocity on those keys, they're gonna come all the way back around and hit you in the back of the head.

关键在于，它们下落的速度与地球的曲率一致。

And so the catch is they're falling at the same rate that the Earth is curving.

如果你在水平方向上获得恰到好处的速度，它们就会一直围绕地球下落，最终回到起点。

And if you get the velocity horizontally just right, they're gonna keep falling all the way around the planet and come back to where they started.

对。

Right.

我其实正打算深入探讨这个问题，对吧？

And so I was actually just gonna go into that exact question, right?

也就是说，如果你施加的力不够，它们就会螺旋式向内坠落。

Which is that if you don't add quite enough force, they're gonna spiral inward.

但如果你施加的力超过了这种完美平衡，它们就会螺旋式向外飞去，对吧？

But if you add add more force than what that perfect balance, then they spiral outward, right?

没错。

Exactly.

所以，这就区分了弹道轨迹——这种轨迹会再次击中地球的其他地方，

So you you have this is the difference between a ballistic trajectory, which is one that hits the planet again somewhere else.

以及轨道速度——这种速度会产生从圆形到椭圆形轨道，再到逃逸轨道的各种情况，就像旅行者号或其他那些脱离地球、持续飞行的星际探测器。

Orbital velocity, which is one where you end up with anything from a circular to an elliptical orbit, to an escape orbit, which is kind of like Voyager or any other of those interplanetary space probes that got away from the Earth and kept going.

对，对。

Right, right.

当然，所有这些轨道都有不同的类型，科学家们使用它们是因为有不同的目的。

And of course, are all, you know, all of these are different kinds of orbits that scientists are, you know, they have use different reasons.

所以我们来谈谈其中一些。

So we'll talk about some of those.

让我们回到最初的问题。

So let's sort of go back to the beginning.

那么，牛顿在月球和重力方面最大的突破是什么呢？

So what was the big leap maybe that Newton made about the moon and gravity, right?

牛顿的重大突破是，月球正在围绕地球下落。

Well, Newton's big leap was the moon is falling around the planet.

在此之前，我们知道天体会绕行。

Up until then, we knew things orbited.

但我们完全不明白为什么它们会绕行。

We had no clue why they orbited.

我们完全不知道是什么让行星围绕太阳运行。

We had no clue what held the planets around the sun.

也不知道是什么让月球围绕地球运行。

No clue what held the moon around the earth.

这一切都极其神秘。

This was all highly mysterious.

直到牛顿出现，他说：哇，是引力。

And and it was Newton coming along and saying, woah, gravity.

他把力的概念整合起来，认为每一个作用都是由力引起的。

And and putting this idea of forces together and every action is due to a force.

每一个作用力都有一个大小相等、方向相反的反作用力。

For every action there's an equal and opposite reaction.

把这些要素整合在一起，这就是牛顿的重大突破。

Putting all those pieces together, that was what Newton's big breakthrough was.

对，对。

Right, right.

所以你面临的情况是，月球正在向地球下落，同时又在围绕地球‘下落’，这是一种完美的平衡。

And so you've got the situation where the moon is falling towards the earth and at the same time it's sort of falling around the Earth and it's this perfect balance.

它总是在不断错过，但并没有向内螺旋，也没有向外缓慢螺旋。

It's always continuously missing but it's not spiraling inward and it's not I guess it's slowly spiraling outward.

它确实在缓慢地向外螺旋，是的，

It's slowly spiraling Yeah,

但那是一种不同的力在起作用。

but that's sort of a different force that's going on.

好的，太棒了。

Okay, great.

那么，让我们谈谈我们可能会使用的轨道类型，先从近地轨道开始吧。

So then, so let's talk about the kinds of orbits that maybe we'll use and, you know, let's let's get low to Earth first.

我认为实际上并不在轨道上的飞行，比如费利克斯·鲍姆加特纳刚刚完成的那种飞行。

And I think something that's actually not in orbit at all is the kind of flight that for for example, you know, Felix Baumgartner just did.

对吧？

Right?

他并没有进入轨道，但他到达了太空的边缘。

Didn't order But it at he traveled to the edge of space.

我正握着，所以我的空气

Am holding So my air

那是什么？

what's that?

基本上，当你足够高地进入大气层，或者足够高地离开大气层——这取决于你如何界定大气层的层级。

So basically there's a certain point where you get high enough above the atmosphere or high enough into the atmosphere depending on how you want to mince your atmospheric levels.

我觉得你说的是‘精简宇航员’，不过好吧，你继续。

I think you said mince your astronauts, but yeah, go ahead.

嗯。

Yeah.

我们别精简宇航员了。

Let's not mince astronauts.

不。

No.

不。

No.

把大气层切碎。

Mince your atmosphere.

是啊，把大气层切碎。

Yeah, mince your atmosphere.

当然，是的。

Sure, yeah.

所以当你在大气层中越来越高时，大气的密度会下降。

So as as you get higher and higher up into the atmosphere, the the density of the atmosphere drops.

这一点你只要去丹佛市就能感受到。

This is something you start to experience just by going to the city of Denver.

当你像攀登珠穆朗玛峰时，情况会更糟。

It gets worse as you do things like climb climb Mount Everest.

随着你继续上升，你会开始缺氧。

As you keep going up, begin to run out of air.

而缺氧的一个副作用是，你失去了散射阳光、形成头顶美丽蓝天的物质。

And one of the side effects of running out of air is you run out of stuff to scatter the sunlight and create the pretty blue sky above you.

因此，当你上升到足够高的高度，比如气象气球的海拔50公里及以上时，基本上就能看到蓝天的尽头与太空的黑暗开始交界。

So as you get sufficiently high up at weather balloon altitudes 50 kilometers and higher, basically, you start to reach the point where you can see where the blue sky ends and the blackness of space begins.

但当你看到这一过渡时，你实际上并不一定已经进入太空。

And and you aren't actually necessarily in space at the point that you can see that transition.

这是一件很有趣的事：你该如何定义什么是太空？

That's one of the funky things is how do you define what space is?

它并不是由你头顶从蔚蓝天空变为繁星点点的那一刻来定义的。

And it's not defined by where you go from pretty blue sky above you to stars above you.

它实际上是根据能量来定义的，因为那样更符合数学原理。

It's it's actually defined based on energies because that's much more mathematical.

所以当我们最初讨论太空从哪里开始时，我们会先想到：我们何时开始看到太空的繁星黑暗？

So when we first start talking about where does space begin, we start with thinking about, well, where do we start to see the starry blackness of space?

而当你达到气象气球或疯狂人士从胶囊跳下的高度时，大约50公里及以上，就能看到这种景象。

And that's once you start getting to weather balloon or crazy dude jumping out of capsule altitudes, which is roughly 50 kilometers and higher.

所以，如果你没机会亲眼看到直播或了解当时的情况，他从胶囊中翻滚而出，前大约一分钟完全失控。

And so, you you can see that, you know, I if don't anyone actually got a chance to watch this live or see what happened, but he tumbled out of the capsule and was totally out of control for the first probably minute or so.

然后

Then

那真是吓人极了。

That was used terrifying.

是啊，真的太吓人了。

I know, was really scary.

然后你可以看到他设法利用了空气阻力。

Then you could see he sort of cap he was able to sort of get some air wind resistance.

他成功控制住了身体，进入了相对平稳的飞行状态。

He was able to get under control until he was in sort of nicely controlled flight.

你能清楚地看到，当他处于无大气环境时，随后进入足够稠密的大气层，从而能够调整姿态并消除旋转。

You could really see where he had no atmosphere and then he had enough atmosphere to to start to orient himself and and remove that that spin.

但没错。

But Yeah.

是的。

Yeah.

听起来他真的被吓坏了。

It sounds like it really scared the pants off of him.

好吧。

So okay.

所以，这是你遇到的第一种情况。

So that's so that's your first situation.

下一个，对，就是太空船一号和即将推出的太空船二号，不过again

The the next one, right, is the is that you have like spaceship one and the upcoming spaceship two, which is Well, again

但在你开始涉及那么复杂的情况之前，实际上还有更多层次。

there there's actually many more layers to go before you start getting that complicated.

所以太空船一号和太空船二号，这仅仅是亚轨道飞行。

So spaceship one and spaceship two, that's just suborbital flight.

但你还需要考虑其他事情，比如——我会把这个词念错，因为每期节目至少得有一个词念错。

But then you also have to look at things like, I'm gonna mispronounce this because really there has to be at least one mispronounced word per show.

这是卡门线。

It's the Karmayan line.

它位于海平面以上100公里的高度。

It's it's at an altitude of a 100 kilometers above sea level.

这是另一个我们开始定义什么是太空飞行的地方。

And and this is another one of those places where we start defining what is spaceflight.

在这种情况下，我们关注的是许多能量边界。

And in this case, it's where we're looking at a lot of energy boundaries.

我们开始思考：你如何旅行？

We're starting to look at, so how do you travel?

你是依靠机翼产生的升力飞行吗？

Do you travel using the lift generated by your wings?

还是依靠推进器和轨道速度飞行？

Do you travel using thrusters and orbital velocities?

正是在这条线上，大气变得足够稀薄，使你从飞机变成了火箭。

And it's at this line that the atmosphere gets sufficiently thin that you are now a rocket and not an airplane.

对。

Right.

但我觉得人们真正需要理解的是，像太空船一号那样，它们只是上升到这条100公里的界线，然后就返回地面。

And but I think what's really important for people to understand is that with, like with Spaceship One, they just go up to this line, the 100 kilometer line, and then come back down.

这需要大量能量，但相比进入轨道所需的能量，这仍然只是一小部分。

And that is, it requires, a lot of energy but it still uses a fraction of the energy to actually go into orbit.

我的意思是，这真的算是亚轨道飞行吗？

I mean is that really suborbital?

我的意思是，它

I mean it's

嗯，亚轨道飞行是指任何达到太空国际边界——即100公里高度的情况。

Well suborbital is any time you hit international the boundary for space, which is 100 kilometers.

好的，没错。

Okay, yeah.

所以根据定义，既然它们达到了100公里，超过了飞机不再能依靠空气动力飞行的高度。

So by definition, since they hit the 100 kilometers, since they get past the altitude at which you are no longer traveling as a plane.

是的。

Yes.

它们确实属于亚轨道飞行。

They do count as suborbital.

之所以有“亚”这个字，是因为没有涉及绕轨道运行。

And the reason that the sub word is there is because there's no orbiting involved.

只是单纯的上升和下降过程。

There's simply the going up and the coming back down part.

这是弹道式的。

It's ballistic.

对，是弹道式的，而且只用了很少的能量。

Right, ballistic and it's using a fraction of the energy.

那么科学家们，我知道科学家们喜欢用，比如探空火箭之类的东西，对吧？

Now what would sort of scientists, I know scientists like to use, they'll use like sounding rockets and things like that, right?

即使是直上直下的亚轨道飞行，有没有什么价值呢？

Is some value to going into a suborbital flight, even like straight up and down, right?

没错，当你只需要快速获取数据时，这有很多优势。

Right, so there's lots of different advantages for when you need just quick data.

你可以测量辐射水平，测量不同高度的大气厚度，还可以进行快速的X射线测量。

You can do things to measure radiation levels, you can do things to measure, thicknesses of the atmosphere at different altitudes, you can take quick x-ray measurements.

因此，你不必发射一颗环绕轨道的X射线卫星，只需将自己送入大气层，就能获得基本的X射线数据，也能获得基本的微波数据。

So instead of having to launch an orbiting x-ray satellite, you can get basic x-ray, you can also get basic microwave data by launching yourself up into the atmosphere.

现在，除了使用探空火箭，另一种更便宜的方法是使用类似气象气球的装置。

Now instead of using sounding rockets, another cheaper way to go is to actually use the equivalent of weather balloons.

只需更换传感器设备，升到足够高的高度并漂浮，探空火箭只能提供几分钟的数据，而气象气球却能持续数小时。

Just swap out the sensor package, get high enough up and float around and whereas you have a few minutes with a sounding rocket, you can get many hours out of a weather balloon.

没错，直到你的气球爆掉为止。

Right, until your balloon pops.

嗯，是的，这确实是个问题。

Well, yes, that is a problem.

嗯，好的，太棒了。

Yeah, okay, cool.

所以这是垂直上升和下降，我认为这一点非常重要，人们需要理解这个区别：进入轨道所需的能量，远大于仅仅上升后再返回所需的能量。

So that's straight up and down and I think that's, know, and it's really important I think for people to understand this distinction that you know, the energies required to go up and then come back down or a fraction of the energy actually go into into orbit.

那么，让我们来谈谈一些更典型的弹道飞行。

So so let's talk about some, you know, more ballistic flight now.

我觉得一个很好的例子是美国第一位宇航员艾伦·谢泼德，他当时就是沿着弹道轨迹飞行的。

You know, I think a great example was like the first American man in space, Alan Shepard, he went on a ballistic trajectory.

对。

Right.

事实上，他和我们下一期节目将要谈到的许多动物都是如此。

And in fact, he and many animals that we'll be talking about in the next show.

在节目里，是的，是的。

In the show, yeah, yeah.

他们所做的就是把人送得足够高，让他能体验到失重状态；他们不会在太空中待太久，所以不用操心食物和水的问题，因为最初人们还不确定人在太空中能不能进食。

So what they did was they basically went up high enough that they could experience zero g, that, they wouldn't be up there long enough that they had to worry about food and water because they didn't know if people could eat in space initially.

然后直接把他们送回地面。

And then just bring them straight back down.

这就是我们对太空船二号的设想，也是许多XCOR商业项目的蓝图。

And this is what we're looking at for spaceship two, this is what we're looking at, for a lot of the XCOR commercial stuff.

这些不同的太空旅游飞行大多将是亚轨道飞行，只需上升到足够高度，让你能看见繁星夜空，体验失重，并在地面上飞行一段距离——幸运的是，地球还在你下方自转，但你不需要像进入轨道那样飞完全程绕地球一圈。

Many of these different tourist flights are all going to be these suborbital flights that go up just long enough that you can see the starry night, that you can experience zero g, that you can make some distance across the ground, luckily the planet's also rotating beneath you, but you don't have to get all the way up and all the way around the planet as you do with an orbit.

对。

Right.

而且我认为你可以把这个概念进一步延伸。

And then I think you can take that concept even further.

比如那些可怕的洲际弹道导弹，或者，你知道的，未来的……

I mean, you've got like the horrible intercontinental ballistic missiles, or or, you know, futuristic You

你说‘可怕’，但我很期待有一天我们能拥有太空船三号，可以进行亚轨道飞行去澳大利亚。

say horrible and I'm looking forward to the day that we have, I don't know, spaceship three and we can fly to Australia suborbital.

我想去澳大利亚进行弹道飞行。

I want to be ballistic to Australia.

当然。

Of course.

当然。

Of course.

而这正是关键所在。

Well, and that's the whole point.

对吧？

Right?

让我们移除核弹头，换成一个漂亮的高超音速冲压发动机或冲压发动机。

Is, let's remove the nuclear payload and let's replace that with a, you know, with a nice scram jet or ramjet.

并且降低再入速度。

And and decrease the velocity of reentry.

是的。

Yes.

是的。

Yes.

所以，我想知道，在这些情况下，洲际弹道导弹会采取什么样的飞行轨迹？

So, you know, I mean, in these situations, like, what kind of trajectory will will an ICBM take?

你知道，如果你想要摧毁俄罗斯，虽然我们并不想摧毁俄罗斯，但假设美国人真的计划这么做的话。

You know, if you wanna destroy Russia, which we don't wanna destroy Russia, but let's say the Americans did plan to do that.

那么，让我们假设，我不知道。

Well, so so let's Let let's say, I don't know.

我们不要摧毁任何东西。

Let's not destroy anything.

让我们假设

Let's let's say that

我们用导弹给俄罗斯送花吧。

we Let's send flowers to Russia on a missile.

不行。

No.

我想连夜派新闻记者去澳大利亚。

I wanna send, like, news reporters overnight to Australia.

这才是我想做的事。

This is what I wanna do.

不。

No.

你选择的与其说是现在的轨道，不如说是扔橄榄球。

You pick the it's it's not so much an orbit this at this point as throwing a football.

所以你需要考虑三件不同的事情，每一件都扮演着不同的角色。

So so you have three different things that you need to take into consideration, and each of them play a different role.

在最简单的层面上，你试图投掷它，让它上升后再落回，上升时间大致等于下降时间。

At the most simplistic level, you're you're trying to pitch it so that it it goes up and then comes back down, and time up is roughly equal to time down.

就是整个橄榄球的抛物线。

It's that whole football arc.

通常有两种不同的角度可以选择，都能到达同一个地点。

There's usually two different angles that you can pick to get to the same location.

所以你可以选择很高的角度，让它优雅地向上然后越过。

So you can go really high and have this nice gentle arc up and over.

你也可以选择低角度，但必须获得更大的水平速度，才能在撞地前到达目的地。

You can go low and you have to get much more horizontal velocity to be able to get there before you crash into the ground if you take the lower angle.

这两种情况的计算都相当直接。

Both of these are fairly straightforward to calculate.

这是我们用来折磨大一物理学生的典型问题之一。

It's one of those things we torture freshman physics students with.

在计算这些轨迹时，你必须考虑的第二件事是我们的地球在自转。

The second thing you have to take into consideration as you're calculating these trajectories is our planet is rotating.

所以你现在瞄准的点，到时已经不在那里了。

So the point that you aim at now is not going to be there later.

因此，你需要计算出随着地球自转，你所瞄准的点将移动到哪里。

So you have to figure out where the point you're aiming at is going to be as the planet rotates.

而在解决这个问题的过程中，你必须考虑的第三件事是：你自己也在移动。

And in the process of figuring this out, the third thing that you have to take into consideration is you're moving as well.

当你的火箭从地面发射时，地面也在移动，为你提供了初始速度。

So as your rocket is getting taken off from the ground, the ground is moving giving you initial velocity.

这正是我们喜欢在法属圭亚那、卡纳维拉尔角等靠近赤道的地区发射的原因——因为这些地方的地球表面绕地心旋转的速度最快。

This is part of why we like to launch from places like, French New Guinea, from Cape Canaveral, from near equatorial regions is because those parts of the planet are rotating about the center of mass of the earth the fastest.

如果你从卡纳维拉尔角或新墨西哥州瞄准，目标是南非，那么南非的旋转速度是不同的。

If you're aiming from Cape Canaveral or New Mexico, and you're trying to land in South Africa, well, South Africa's going around at a different rate.

在试图计算如何从这里到达那里时，你必须考虑所有这些因素，而科里奥利力正是由于这些旋转速度的差异而发挥作用的。

And you have to take all of these things into consideration in trying to figure out how to get from here to there, and Coriolis forces end up playing a role in all of this because of those differences in rotation rates.

而这确实是最大的前沿领域。

Well, and this really is the big frontier.

我的意思是，人们正在研究各种这类技术，比如冲压发动机、超燃冲压发动机，如果他们能开发出一种时速可达马赫20左右并能应对大气再入的飞行器，我们就能实现从洛杉矶到澳大利亚悉尼仅需几个小时的飞行。

I mean, the people are working on different kinds of this technologies, ramjets, scramjets, you know, they can come up with something that can go like, oh, Mach 20 or so and be able to handle the atmospheric reentry, then we will be able to do flights from say, you know, from Los Angeles to Sydney, Australia in just a couple of hours.

这将是一场巨大的变革。

It'll be a dramatic change.

至于超燃冲压发动机之类的技术，它们目前仍是在比亚轨道飞行低得多的海拔高度进行测试的。

Well the things with the scramjets and stuff is they're still doing those at at fairly low altitudes compared to to the suborbital flights.

所以我认为，亚轨道飞行在某些方面反而更容易实现。

So I think the suborbital flights in some ways have a much easier way to go.

唯一的难题是，如果你想从美国飞往澳大利亚，而地球的自转方向恰好与你这次航行所需的方向相反。

The only trick is if you wanna America to Australia, well, that and trying to get from America to Australia, the planet's rotating in the opposite direction that you want it to be for that particular journey.

你可以想象一个未来，从新墨西哥州前往南非再到澳大利亚变得更容易，或者从新墨西哥州经摩洛哥到澳大利亚可能更糟。

You can almost imagine a future where it's easier to go from New Mexico to South Africa to Australia, or that's probably bad from New Mexico to Morocco to Australia.

对，把速度变化分段进行。

Right, break up the velocity changes a bit.

当你这样做的时候，你实际上是沿着地球自转的正确方向前进。

Well, and you're going in the correct direction around the planet when you do it that way.

所以只要所有人都朝同一个方向前进，能量消耗就会少得多。

So as long as everyone's going in the same direction, it becomes a lot energetically easy.

好的，那我们接下来提升到下一个层次，真正进入轨道。

Alright, so we're gonna kick things up to the next level then and actually go into orbit.

所以你知道，现在我们有了火箭，我认为这里真正重要的是，这并不是关于向上的速度，而是横向的速度，对吧？

So you know, this now we've got a rocket and I think what's really important here is that you know, it's not about velocity upwards, it's velocity sideways, right?

是的，这正是难点所在：你必须足够高，比如在低地球轨道上，你的速度大约是每秒8000米。

Yes, and this is the tricky part, is so you have to get high enough up that, well, low Earth orbit, you're traveling at about 8,000 meters per second.

把这个速度和最快的飞机——每秒仅1500到2000米——相比一下。

So that's, compare that to an airplane that goes maybe 1,500, 2,000 meters a second for the fastest ones we build.

因此，为了达到比我们最快飞机快四倍的速度，两次将速度翻倍比你想象的要难得多。

So you're looking at four times faster than our fastest airplanes in order to It's harder than you would think to double your speed twice.

对。

Right.

所以你需要达到大约每小时20,000到25,000公里的速度才能进入轨道。

And so you're looking at, yeah, what 20,000, 25,000 kilometers an hour to get

大约是每小时30,000公里，也就是大约每小时20,000英里。

in It's about more of 30,000 kilometers an About 20,000 miles per hour.

是的。

Yeah.

正如你所说，这比仅仅垂直上升再返回所需的能量多出近一个数量级。

And that's as you say many almost an order of magnitude more than to try and just go up and come back down.

这需要巨大的能量。

It's a phenomenal amount of energy.

因此，只有火箭才能提供如此巨大的能量输出，而且在许多情况下，火箭几乎全部都是燃料。

So really only rockets have the energy output to be able to do this and in many cases a rocket is just all fuel.

必须消耗掉这么多燃料，几乎所有的质量都变成了燃料，才能达到这种速度。

It's having to just burn up all this fuel, almost all its mass is just fuel to get it into this velocity.

是的。

Yeah.

这是我们正在努力解决的问题之一：在没有太空电梯的情况下，如何以最节能的方式发射物体，这是一个巨大的挑战。

And this is one of those things we're trying to figure out, what is the most energy efficient way to launch things is such a difficult challenge without a space elevator.

有人正在尝试使用磁轨炮，本质上是利用磁场沿着轨道加速物体。

You have people that are trying to use magnetic cannons, where essentially use magnetic fields to accelerate things along rails.

还有人考虑用各种甩投方式，但这种方法在《月球是个严酷的主人》中描述得更好，而非基于科学现实。

You have people who are considering various slingshotting things, although really this is best expressed in Moon is a Harsh Mistress rather than in Science Reality.

然后就是各种不同的火箭。

You you then have all the different rockets.

你还有系绳系统。

You've got tethers

系绳系统并不是从行星表面出发的好方法。

Tethers isn't so much a good way to get off the surface of a planet.

太空电梯。

Space elevators.

是的。

Yeah.

太空电梯可以提升你的轨道。

Space elevators boost your orbit.

是的。

Yeah.

然后还有一个问题，你是从地面开始，还是从飞机上开始？

And then there's the matter of do you start from the ground or do you start from an airplane?

因此，看待这个问题有各种不同的方式。

And so there's all different ways to look at doing this.

当我们回顾早期的亚轨道测试时，是把东西从一架燃料占三分之二、假装是飞机的飞行器底部投放，看看它能飞多高。

And when you look at our early suborbital testing, it was drop something off the bottom of an aircraft that's two thirds fuel and pretends to be an airplane and see how high it can go.

是的。

Yeah.

那么，有哪些不同类型的轨道呢？

So then what are the different kinds of orbit?

我的意思是，第一个应该是低地球轨道，对吧？

So I mean like what's the low, I guess the first one is the low Earth orbit, right?

对。

Right.

在这种轨道上，你距离地面几百英里，大约每一个半小时绕地球一圈。

So here you're looking at a few 100 miles up orbiting the Earth every hour and a half or so.

在这些低地球轨道上，你需要担心的一件事是，你仍然处于足够稠密的大气层中——直到你上升到大约700公里的高度，你仍处于热层内，因此你必须定期进行轨道提升，因为即使这层大气极其稀薄，其阻力仍足以减缓你的轨道速度，最终会像对天空实验室那样把你拉回地球。

And in these low earth orbits one of the things that you have to worry about is you're still in a thick enough part of the atmosphere, you're still in the thermosphere up until you get to about 700 kilometers up, that you have to not constantly, but on a regular basis boost yourself back up because there's sufficient drag from this very, very thin diffused part of the atmosphere that it's still pushing on you enough to slow down your orbit and will eventually like it did with Skylab pull you out of space.

当你想留在太空时，这可不是好事。

And that's a bad thing when you're trying to stay in space.

对。

Right.

我知道空间站一直在不断被提升轨道。

So you know, I know that the space station is constantly being having its orbit boosted back up.

而且它还在不断躲避太空碎片。

And it's constantly also doing things like dodging space debris.

太空碎片，没错。

Space debris, yeah.

对。

Yeah.

所以他们实际上在频繁地移动这个巨大的航天器，远超你的想象。

So they're they're moving that giant spacecraft way more than than you would think about.

所以这本质上是一个不稳定的轨道，任何被放置在低地球轨道上的物体，都只是时间问题，最终会自行脱离轨道并坠落到某处。

So it's really an inherently unstable orbit that that any object placed in low Earth orbit really is just on a, you know, it's just a matter of time before it just deorbits itself and crashes somewhere.

是的。

Yeah.

是的。

Yeah.

所以，没错，就是这样的。

And and so, yeah, it's just Yeah, just

那么，什么是更稳定的轨道呢？

so then what's a more stable orbit, right?

它们接下来会去哪里？

Where do they go next?

一旦你上升到大约一万公里的高度，就会达到大气残留物足够稀薄的程度，那时你基本上就可以稳定地停留在那个高度了。

Once you start getting about 10,000 kilometers up, then you start hitting the point where there's sufficiently little atmospheric leftover bits that you're pretty much good to go up that high.

但那已经很高了。

But that's pretty high up.

你还没有达到地球同步轨道，但已经开始接近了。

You're still not geosynchronous, but you're starting to get there.

那么，将航天器置于这种轨道上有什么优势呢？

Now, and so what are some, what are the advantages of placing a spacecraft into that kind of an orbit?

在一定高度上，维持轨道所需的燃料更少。

Well, at a certain level, there's, you need less fuel to stay put.

对，这样更稳定。

Right, there's stability.

但再往上，在那个高度上，时间点有点奇怪。

But beyond that, at at that sort of altitude, it's it's a kinda weird timing.

你并不是地球同步的。

You're not geosynchronous.

所以你只是在行星上方缓慢漂移。

So you're just slowly drifting over the planet.

你和阴影不同步。

You're not synchronous with shadows.

它很稳定，但我不知道你究竟想用这个轨道做什么。

It's it's stable, but it it's kind of I don't know what you're trying to do with that orbit.

我知道在某些情况下，有一种奇怪的轨道，让你每天能同时处于多个地球静止点。

I know that in some cases there's like a funny orbit where you can be sort of geostationary several at the same time every day.

是的。

Yeah.

对吧？

Right?

因此，有一种特殊的轨道，到达地球静止轨道所需的能量较少，但仍能提供相当稳定的轨道。

And so there's a special kind of orbit you can do that it doesn't require as much energy to get to geostationary, but it still gives you a fairly stable orbit.

我知道还存在更椭圆的轨道。

And I know there's also more elliptical orbits.

所以有很多轨道并不完全是圆形的，它们呈椭圆形，会远离地球很远。

So there's lots of orbits that aren't necessarily perfectly circular, they go in these elliptical orbits where they go way far out.

我们上周其实就讨论过这个，就是XMM卫星的情况，对吧？

We actually talked about this last week, right, with the XMM satellite.

对，你刚才提到的莫尼亚轨道，是一种用于与极高纬度和极低纬度地区通信的轨道。

Right, and the orbit that you were talking about a moment ago, the Molninha orbit, it's an orbit that gets used for communications with very northern and very southern latitudes.

它在轨道的一部分靠近地球，而在轨道的另一侧则远离地球足够远，使得其运行速度与地球自转速度大致相同。

It comes close to the earth on one part of its orbit, and then goes sufficiently far out on the other side of its orbit that it's moving at roughly the same rate that the planet is rotating.

因此，这种高度椭圆的轨道使其在位于地球极端北纬或南纬地区上空时，能像通信卫星一样工作，然后快速飞越到地球的另一侧。

And so this highly elliptical orbit allows it to act like a communications satellite when it's, over extreme northern or extreme southern latitudes on the planet, zip around, the other side of the planet.

我们使用普通地球同步卫星时遇到的一个问题是，它们始终位于赤道正上方。

And one of the problems we run into with normal geosynchronous satellites is they're happily straight above the equator.

如果你想从阿拉斯加的朱诺，或者西伯利亚的某个地方观看电视，这就没用了，因为卫星靠近地平线，你需要穿过大量的大气层。

And if you wanna watch television from Juneau, Alaska, or, I don't know, somewhere in Siberia, that's not going to help you because the satellite is so close to the horizon, you're looking through so much atmosphere.

正是这些高度椭圆的轨道，让你能够将电视信号或其他服务覆盖到这些极端的南北纬地区。

So it's with these highly elliptical orbits that you're able to get some sort of a television station or something up over these extreme northern and southern latitudes.

正如你提到的，还有围绕赤道运行的椭圆轨道，但你也有极地轨道，卫星从极点到极点运行，这样可以实现对整个地球的全面覆盖。

And also as you mentioned, right, there's the elliptical orbit where the satellite is orbiting around the equator, but you've also got these polar orbits, right, where the satellite is going pole to pole and that gives you a chance to sort of get complete coverage of the whole planet.

使用极地轨道的一个巧妙之处在于，你可以精确调整时间，使你总是在相同的光照角度下观测地球。

And one of the neat things that you can do with the polar orbits is you can time them just right so that you're always seeing the planet at the exact same illumination angle.

这尤其对间谍卫星有利，因为它能让你轻松地从一次轨道到下一次轨道之间，分辨出地球表面的变化。

So that has the benefit, especially if you're a spy satellite, of allowing you to very easily make out differences from orbit to orbit in what you're seeing on the planet below you.

因此，许多间谍卫星都发射到极地轨道。

So a lot of spy satellites are launching to polar orbits.

是的，没错，它们确实如此。

Yes, yes they are.

知道了，很好。

Good to know.