Transcription
Chuck, you know what I think needs some explaining. Okay. Just where satellites orbit Earth in space.
I thought you were going to say where satellites come from when a mommy satellite and a daddy satellite really love each other. You know the very first satellite. Yes. Yes. Yes. Um Sputnik. Sputnik. Right. And what's interesting is we didn't really have words for satellites. If you looked at newspaper articles of the day, it says Russia launches a moon around the Earth. The word moon was a common word cuz nothing else was artificial in space except you got the moon, right? So you add another thing going around Earth just like the moon does. It's a second moon. It's a second moon, right?
So Isaac Newton figured out how to make a satellite. Get out. Yes. It goes back to him. We talked about Isaac Newton's diagram before where he's got Earth. Even drew a little continent on it just in case you you were had any doubt right that he was drawing Mars. Exactly. And you can drop an object such as an apple falling straight down. Well, you can give an object sideways speed. Right. Okay. And if you give it sideways speed, it falls to Earth, just a little farther down range. He just kept doing this. And he reasoned that at a high enough speed, I can shoot myself in the head. In the back of the head. But wait a minute. If you've done that, duck, first of all, if you duck, what does it do at that point? Does it just fall out of the out of the sky? No. It'll keep going with no rockets, no anything, right? It's just freely falling towards Earth the whole way. You can time that. How long does it take to go completely around the Earth? Okay. And that takes 90 minutes. Going around the Earth. You are in orbit. And the only way you can come out of orbit is if something tries to stop it. Either the atmosphere or a retro rocket or something. Something has to act upon you. Act upon you. And that is orbit. And it's close to Earth. And we call that low Earth orbit. Low Earth orbit. Low Earth orbit. Acronyms to LEO. LEO.
One issue with LEO orbits, the atmosphere still has some particles that reach up that high. Oh, just a little bit. Just Just enough. Give you a little It's a speed bump. It's a speed bump. However, it drops you to a slightly lower orbit every time where there's more of these. Now, the speed bump becomes a speed drag. Okay. And then it goes to lower where there's even more. It's a runaway process. Yeah. So, I don't know if you knew this. Every now and then we got to boost the International Space Station up from its otherwise it would just decay out of and what is the fuel source for that? Because you certainly don't want to be running out of gas. Mom, I'm coming home early. When you 300 miles above the Earth, so I'm I'm told I can only know what I that the astronauts tell me that when they dock with their rockets, if it's a mission where they're going to readjust the space station, they will do it with those rockets. Oh, that's brilliant. Yeah. And so everyone has to strap in when that happens because you don't you got to make sure. So you just use and you do it really slowly because you don't want to b break off a piece. It's a big old gangly thing, right? If you push it on one side, it could break off or start you rotating in ways you don't want. So, a very slow, steady process. Great. Right. To to just boost it back into an orbit that can serve its needs. Thrusters at half.
So, the space station, the Hubble telescope, all the rockets where we've ever sent humans in orbit around Earth have been to low Earth orbit. Low Earth orbit. Okay. Right. And within a few minutes variation on a 90 minute journey and at 90 minutes you see 16 sunrises and sunsets a day. What? I know. Oh my god. That must be awful or beautiful. It can't be beautiful 16 times a day. It can be beautiful and awful. Okay, that's true. It's awfully beautiful.
Go back to the 1940s. Arthur C. Clark, author of 2001, A Space Odyssey and countless sci-fi novels. So Arthur C. Clark saw what was already known. Clearly, there's an orbit out there where it would take you as long to go around Earth as Earth takes to rotate. His brilliance was to realize that that might be where you put a satellite for communications. He correctly reasoned that if you're going to send radio communication between one continent and another, let's say just United States and Europe, you might want to park a satellite in the middle of the Atlantic, right? So that we send a satellite signal up and then it comes back down and that because otherwise the radio signals only go in straight lines and they would not reach Europe because Earth is round. What a terrible inconvenience that is. Some of the earliest satellites launched were communication satellites, right? One of the more famous ones was called Telstar. Telstar. Telstar. There was even a car model. Okay. Just just cuz people were just like, "Oh, I'm driving a Tel Star." I know. It was very My car came from space. No, the space connection was very strong and culturally real. What happened to us? What the hell happened to us?
So when you're on that orbit, you are basically geostationary. Mhm. You're moving in space, but not relative to the surface of the Earth that's turning with you, right? Geostationary, right? Yeah. Yes. How high up is geocynchronous? Thank. I thought you'd never ask. Uh 22,000 miles above Earth's surface. Oh, wow. That's pretty That's That's a lot compared to a couple hundred. Yeah, that's I mean, they're far away. Far away. Yeah, far away.
We talked about low Earth orbit and geo. And now we got geo, right? We got Leo and Geo. Leo and Geo. Okay. So now, how about the space in between? You know what we put in middle of orbit? GPS satellites. Okay. All right. So now they are moving. They're not hovering above your head. No. Yet there's always one talking to your phone. Yes. How is it possible that they're orbiting the Earth, yet there's always one talking to your phone? Just put enough of them up there. That's all there is. So the GPS satellites which are now we depend on for so much. It was it was a military operation. It was the air force. Always is. You got to give it to the military. We might kill people and break stuff. We get a lot of good stuff out of it. Lots of good stuff. I wrote a whole book on that. The titled was accessory to war. The unspoken alliance between astrophysics and the military. Yeah. It's it's 600 pages. So, it's your fault. Don't shoot the messenger here. All right. So, you put enough of them up there. There's always one over your head in order to to take the signal. Yeah. And by the way, if the satellite is higher up, it sees more of Earth's surface. Correct. Right. Okay. And therefore, you don't need them every 100 miles or so. Just they can be more spread out. Now, a feature of the system is that well, most people live within a certain range of the Earth's equator, right? Okay. Latitude range, like between 0 and 50° or so. You know, we're all in a band. We're in a band. So, you can very nicely serve that region with satellites that sort of cover those zones. Yeah. But suppose you're Santa Claus. Suppose you're you're in a latitude either north or south. you don't have the satellite coverage. So if anyone cares about you, they will send satellites also going nearly polar as well as equatorial so that you can cover the folks that are there. Gotcha. Okay. So we call that middle earth orbit. Neo, nothing to do with uh I was about to say middleear orcs. Or that's not what I said. Middle earth orcs. That's even better. My my satellite is my my phone is glowing blue. So we have Leo, Mio, and Gio. Wow. And there there's the trinity. That's the trinity. The trinity of orbit of satellite orbits. Yeah.
So now the reason why ideally you want many many satellites in low earth orbit for communication. If you rely on just the geo, that's 23,000 mi up, 23,000 mi down, you're talking 50,000 mi. The speed of light is 186,000 m per second, right? So this is 50,000 mi one way and then you want to send a signal back to me, it's another 50,000 miles. Light can cover that distance. And so the speed of radio waves can cover that distance in about a half a second. So it's going you're going to get a little laggy. There's a little laggy. You going to have a little laggy a half a second and plus there's the processing. So it might be up to a second delay. Yeah. And what we learned is we don't have patience for that. No, we don't. You can't have witty reparte, right? When that's happening. So the way to do that is to put up many many many more satellites in lower earth orbit because they don't have as much coverage because they're not they're not high enough. They're not high. They're not high up, right? I still can't get good coverage with Sprint. Mm-m.
Oh, by the way, in the early days of the communication satellites parked over the oceans, it's just a one-way TV signal. Oh, they're just broadcasting to you. They're broadcasting to you. You're not talking back to the the correspondent. Well, that makes sense. So, that delay, you didn't even notice and you didn't even You don't even care about that delay. Yes. Yeah, there it was. That makes sense. Those are avatars. I was a geek enough kid to time that because TV shows would begin exactly on the hour and on the and and when they began a show in Europe for the Olympics typically uh I've noticed there was like a fractional delay because it was going up to satellite and back then I'm old enough to remember it would say live via satellite via satellite live via satellite. Okay, now no one cares. No. So there it is and and Newton started it all and Newton and our boy Arthur C. Clark. All right, that's another explainer from Star Talk from my office here at the Hayden Planetarium. Till next time, keep looking up. [Music]