How Do Satellites Work?

Podcast Transcript

Somewhere over your head, right this moment is an artificial satellite. Many of them actually.

They beam television and radio signals down to Earth. They can tell us our exact time and location, and they can also help us predict the weather and they are now even providing broadband internet.

But how do they work? How do you get something to wiz around in space without crashing down?

Learn more about how satellites work, as well as some of the misconceptions people have about them, on this episode of Everything Everywhere Daily.

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Once again that is travelsafe.spain.info or just click on the link in the show notes.

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Unless there are some astronauts in the audience, all of us have used the surface of the Earth as our frame of reference our entire lives. For example, if I have a ball, and I want you to have the ball, I would throw the ball directly to you.

Very simple and everyone understand that.

When you start talking about things in orbit, they can often be mind-bending confusing. Things that seem like they would be obvious are in fact not at all obvious.

Let’s start with one of the biggest misconceptions have about how satellites get to orbit. They get there by going really high above the surface of the Earth.

This is in fact, wrong. Yes, satellites are high above the Earth, but that is because is where we have to go to get away from the atmosphere.

Let’s conduct a thought experiment.

Let’s say that you have a really big rocket and it is in your front yard. You are going to launch this rocket straight up in the sky. By straight up, I mean straight up. At every moment the rocket is above you, its initial launch point is directly below it.

Now let’s say we take it all the way up to the same altitude as the International Space Station, which is about 420 kilometers or 260 miles above the Earth.

Now, let’s also say that we have really good timing, and we timed it such that the rocket would be at the same spot as the International Space Station.

Could your rocket dock with the space station? The answer is emphatically: no.

If anything, it would cause a massive disaster because the ISS would smash into your rocket at a speed of 17,000 miles per hour

The problem is your rocket isn’t in orbit. It is just at a very high altitude. Once it runs out of fuel it is going to fall right back down to Earth, even though it is at an altitude where satellites are orbiting.

Getting into orbit isn’t about altitude, it is about velocity.

When we see a rocket launch, it does go straight up, at least at first. However, it will eventually begin to arc and put most of its energy into moving laterally, not vertically. The problem is, by the time it is doing that, it is far enough away that we can’t see it.

The first person to figure out that orbiting a gravitational body was possible was Sir Isaac Newton. He imagined the problem as a giant cannon because he didn’t have rockets.

According to Newton, suppose you had a cannon on the top of a tall hill and you fired it. The cannonball would arc through the air and land.

Now suppose you keep firing progressively more powerful cannonballs. They will be launched from the cannon faster and go farther. Eventually, they will land beyond the horizon as the Earth is curving.

You might even be able to fire a cannon powerful enough to send a cannonball around the Earth which would hit you in the back….assuming you fired in the right direction.

If you fire a cannonball powerful enough, it will keep flying around the Earth and missing. It will literally be falling around the Earth. The speed at which this is achieved for Earth is 11.19 kilometers per second.

The speed at which this happens is known as escape velocity, and that is why astronauts are often said to be in free fall. They aren’t technically in zero gravity. It is the gravity of the Earth that is keeping them in free fall.

Airplanes that do steep dives can experience several seconds of free fall and passengers can have the same sensation that they do in space.

Douglas Adams wrote in the Hitchhikers Guide to the Galaxy that flying was just throwing yourself at the ground and missing. Replace flying with orbiting, and he basically got it right.

So let’s now assume that you are in space and you are working on the space station. You are working outside in your space suit and you are staring at the Earth as it goes past you.

On a whim, you decide to take the wrench you have in your hand and throw it directly at the surface of the Earth. What will happen to the wrench?

The obvious answer is that the wrench will keep going towards the Earth, and it will eventually burn up in the atmosphere as it is headed towards Earth.

This is not what will happen.

All you’ve done is put the wrench into a different orbit. The new orbit will be more elliptical and its closest point will be closer than the space station, but the farthest point in its orbit will actually be farther away from the earth than the space station!.

Even though you threw it towards the Earth, it will eventually be farther from the Earth from where you threw it.

Now, the wrench will eventually enter the Earth’s atmosphere and burn up, and it will do so faster than the space station will. That is because what matters is the perigee in its orbit, that being the closest point in the orbit. The perigee is where you will experience the most atmospheric drag.

This is why maneuvering in orbit is so complicated. It isn’t at all straight forward is going from point A to point B.

When we fly probes to Mars, we don’t just point a rocket at Mars and fire. If you look at the path the probe actually flies, it looks like a very elongated spiral. You can’t just fly in a straight line to Mars for the same reason you can’t fly in a straight line to International Space Station.

One other orbital paradox has to do with the sun. Many people often suggest things like that we should launch all of our nuclear waste into the sun.

To be sure, launching anything into the sun would get rid of it. However, that is very very hard to do.

Believe it or not, it is actually easier to launch something out of the solar system, than it is to launch something into the sun.

That’s because the Earth is moving around the sun at a high velocity. 30 kilometers per second to be precise. To get to the sun, you would have to negate all of the velocity of the orbit of the Earth, and that is almost three times the Earth’s escape velocity.

To make things even more confusing, it would be easier to launch something into the sun from Pluto than it would from the surface of Mercury. It all has to do with the fact that Pluto travels much slower than Mercury.

Whenever a satellite is put into orbit, it has certain properties. Altitude and velocity are two I’ve discussed. Another important one is its inclination. This is just how much the orbit of the satellite is titled with respect to the equator.

Very few satellites travel directly around the equator. Most are inclined somewhat. If you’ve ever seen a world wall map from a mission control room for a space flight, you’ll notice that the lines on the map that follow the spaceship look like sine waves.

This really just is the representation of the inclination of the satellite when put on a flat map.

If you have a 90-degree inclination, then you have what is known as a polar orbit. Polar orbits are usually used for satellites that do Earth observation. This includes spy satellites, mapping satellites, and the satellites that take the photos you see on Google Maps.

Another important orbit are geosynchronous or geostationary orbits. Technically, they are different, but they are often used as synonyms.

The ISS takes about 90 minutes to orbit the Earth. As you go to a higher and higher orbit, that time takes longer. Eventually, if you get high enough in altitude, to be precise 35,786 kilometers, then the time it takes to orbit the Earth is exactly one Earth Day.

A geosynchronous orbit is any orbit of one day, regardless of its inclination. A geostationary orbit is a geosynchronous orbit that has zero inclination. It is directly over the equator.

Geostationary orbit is extremely useful. The idea for them was originally proposed by science fiction writer Arthur C. Clarke. If you have satellite TV, you are getting that signal from a satellite in geostationary orbit 22,236 miles away.

You can actually tell the latitude of wherever you are by looking at the satellite dishes. Satellite dishes in Iceland, for example, are almost pointing at the horizon.

Is there an equivalent to a ??geostationary orbit for polar orbits? The answer is no. Satellite communications for polar areas is very difficult.

One solution the Soviets came up with is called a Molynia Orbit. This is a highly elliptical orbit with the further point from Earth above the arctic, and the closest point over the antarctic.

Most of the time, the satellite will be over the arctic, but it will be out of view briefly as it passes around the south. In order to have continuous converge, you need several satellites to be operating at once.

The final thing I should mention are special points in orbits when you have two large objects.

In the case of the Earth and the Moon, for example, there are five points known as Lagrange Points where the gravity of both bodies is balanced.

These points were named after 18th-century French mathematician Joseph-Louis Lagrange, who came up with the idea.

The five points are known as L1, L2, L3, L4, and L5.

I mention this because the next big space telescope that is scheduled to be launched in November 2021 will not be in orbit around the Earth like the Hubble Telescope is. It will sit at L2, which is the point beyond the Moon. In fact, it will be located 1.5 million kilometers away from Earth at a point where it will always have a view of the dark side of the Moon.

The James Webb Telescope is an incredible piece of equipment and I’ll probably do an episode on it as the launch date gets closer.

If you ever wondered why rocket science is used as a metaphor for something which is really hard, I think you can now see why. Getting to orbit, and moving around in orbit is really challenging, and it doesn’t at all make sense based on what we know from living on Earth.