Satellites Part I: What do they do?

And why you should care.

Mar 04, 2021

Satellites are an integral part of our daily life. Internet, GPS, TV, cell service, and so many other commonplace technologies are solely reliant on satellites and them working properly. With the exception of the International Space Station, almost none of these are visible to the naked eye, and they’re traveling over the Earth at speeds of up to 20,000 mph – 10 times faster than a bullet. Some satellites are close to Earth, some are far away, and some even travel to the outer reaches of our solar system. All of them, however, have one thing in common: they’re all looking for something. But what are they looking for and why are they looking for it? Now that’s the interesting part. This will be the first of four installments in a series completely devoted to satellites, thanks for coming along for the ride.

We’ll start with satellites that look outward. The most famous example of this type of satellite is the Hubble Space Telescope. [1]

Telescopes are some of the most common outward facing satellites. They scan different parts of the sky in search of a whole bunch of things that interest astronomers: other stars similar to our Sun, the characteristics of the Black Hole in the center of our galaxy, even signs of alien life. Satellites have a clear view of these things because they fly outside Earth’s atmosphere, which scatters light, thus making things on the other side harder to see. When you’re outside of it, you have a much better view.

Now not all of these outward facing satellites look for stuff humans can see. We have satellites that scan the sky for radio waves, gamma rays, and other forms of radiation energy that aren’t on the visible spectrum. This is helpful because not all of the things we’re looking for present themselves in visible light. If we wanted to, for example, search for a technologically advanced alien planet, we could look for artificial radio signals coming from distant stars. Humans emit plenty of our own radio signals into space – some on purpose and some as a harmless consequence of our communications network. All of these, however, could be received by someone else if they’re looking in the right direction.

A cool byproduct of the speed of light is that an alien’s distance from us will determine what they see. If they’re 100 light years away, and happen to train their eyes on us, they’ll only now be receiving information that we emitted in 1921. If they were, say, 65 million light years away (which is entirely possible given the size of the universe) and could zoom in enough, they would see a planet full of dinosaurs. Maybe that’s what’s deterring them from visiting…

The last group of outward looking satellites we’ll talk about are the ones that actually go where they’re looking. We have sent satellites to every planet in our solar system, and 49 just to Mars alone. These missions can take place over decades. The Cassini probe took 7 years to reach Saturn and spent another 10 years orbiting and sending back data. The farthest one we have to date, by a long shot, is the Voyager 1 probe. This satellite launched in 1977 and passed by almost every single planet in the outer solar system on its way to interstellar space. Currently, Voyager 1 is 13 billion miles away from Earth—that’s 4 times further away than Pluto, the outer reach of our solar system.

These satellites are cool. Very cool. They are the ones that will teach us about our place among the stars. But to you and me, on a daily basis, they aren’t that helpful. Let’s take a look at the ones that look inward.

All satellites can be categorized based on their orbit: how far from Earth they are and what their path around it looks like. Outward facing satellites fall into these categories too, but for our purposes, these inward facing satellites’ jobs entirely define their orbits. Satellites that are in Low Earth Orbit (LEO) are the ones that you usually think of when you think “satellite”. The ISS, communications satellites, spy satellites, Earth imaging satellites, and many others reside in this orbit – around 200 to 500 miles above Earth’s surface. These satellites travel the fastest (~17,000 mph) and complete a full orbit around the Earth in the least amount of time (~90 minutes). This is why astronauts on the ISS typically experience 16 sunrises and sunsets per day. The upside of this orbit is that it’s relatively easy to get to, but the downside is how fast they’re moving. If you have a GPS satellite in Low Earth Orbit, it’s on the other side of the planet more than half the time. As a result, we need a lot of satellites that constantly transfer responsibility to each other as one passes below the horizon and the next rises above it. Another huge issue is space debris. As humanity becomes more present in space, we leave a lot of things behind. Left over debris in orbit around Earth has the potential to hit other satellites and severely damage if not destroy them. There is a lot of empty space up there, but it’s getting more and more crowded with every launch. The figure below shows all of the stuff in space near Earth that we are able to track. [2]

I’m with you now, let’s get away from all of this noise and take a vacation. Somewhere quiet where we can relax. Enter Geosynchronous Orbit (GEO). Out here we are >20,000 miles from Earth, about 80 times farther than we were in Low Earth Orbit. As a result, we’re moving more slowly, and our orbit is much longer. This distance from Earth was selected for a very specific reason. At this distance (22,236 miles to be exact), the time it takes to complete one full orbit is exactly the time it takes for Earth to make one full rotation. As a result, to us the satellite always appears in the same spot in the sky. This is incredibly helpful when you need to be in constant communication with just one satellite, need more reliable GPS, or are communicating with a single part of the globe. AT&T has dozens of communications satellites in Geosynchronous Orbit to serve different countries. These orbits are helpful, but they require satellites to have stronger antennas and more fuel to get up there. [3]

Let’s recap. Satellites are important. They monitor weather, give us NFL Red Zone, look for aliens, and most importantly they tell us where the nearest Taco Bell is at 1 am. But now that we know some of the types of satellites, how do we get them where they need to go? What can they actually do when they’re there? And what happens to them when they die? We’ll take a look at the full life cycle of satellites in our next three newsletters. For now, take a look up to the stars and say a quick thank you. Thanks for reading and subscribe for more!

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