 Hello. Welcome to Satellite Orbits 101. I'm Matthew Murray, your presenter, and today I'll be walking you through some of the fundamental terminology surrounding satellite orbits. Now as the title implies, this presentation isn't intended to turn you into a rocket scientist. It's meant to peel away some of the mysticism surrounding the terms involved in the journey of satellites or space vehicles and give a better understanding of the meaning behind them. To that end, I've intentionally stayed away from any intense math or physics and just focused on scratching at the upper layer of this topic. Before we jump into what the word orbit really involves, it's worth mentioning a few things and covering a few terms to help inform you and calibrate your understanding. The first matter worth discussing is launch locations. They aren't random. Ever notice how the ones in the U.S. always seem to happen in Florida? Clear sunny days really do matter. A strong enough wind can adversely affect the trajectory of a launched craft, and lightning doesn't happen just down here on Earth, it happens in the sky too, and a lightning strike as a craft moves through the atmosphere could cause huge problems. Launch locations aren't just about weather either. Depending on where you intend to place a satellite in terms of orbital distance and location, oftentimes the rotation of the Earth, which is fast as at the equator, is used to give a vehicle an extra push in launch. Once you achieve orbit, you have to keep it. Fuel on board the vehicle is used periodically to maintain or augment the orbit. The surface of the Earth isn't flat and smooth, so the changes in the surface, or the topology of the Earth, all those mountains and valleys can affect how the Earth pulls on the satellite over time. The other bodies in our solar system, like the Sun and the Moon, can also have a gravitational effect. Depending on where the vehicle is in relation to the atmosphere, even a very thin layer of air and particles up there can produce enough drag and resistance to affect an orbit. This can even increase when the Sun comes around, just like heat makes air expand down here, the warming of the atmosphere can make drag even worse up there. And let's not forget all the junk that satellites and the people who fly those satellites have to dodge in order to make a journey around the Earth. There's more than 128 million separate pieces, parts, and objects roaming around our planet right now. Alright, so let's start to dig a little bit deeper. All orbit means in its most generic terms is one body or object moving around another. So when that body, the object, is moving around as the Earth, the orbit is called geocentric. There are several types of geocentric orbits and each of those types plays a part in what the satellite is up there to do. The shape of the orbits can come in different eccentricities, and all that refers to is the type of curve the orbit has. Is it circular or is it more of an oval or an ellipse? Once we begin to consider the type of curve an orbit might have, then we can begin to lump them into categories. Periodic orbits repeat in some consistent fashion and they're either elliptical or circular in nature. Because there's not a break in the pattern, these are sometimes referred to as closed orbits. There is another class of orbit under the topic of eccentricities that's not meant to stay in a repeating pattern around the Earth. These are called escape or open orbits and they're used to move vehicles away from the Earth in particular ways. Parabolic orbits are used to complete minimum energy escapes if they're moving away from the Earth and captures if they're moving towards a planet. Hyperbolic orbits can send the vehicle off at a much higher speed. These orbits are factors in gravitational sling shots where a vehicle flies by a planet and uses its gravitational pull to pick up speed. There are also terms for the direction a satellite is moving in around the Earth. Prograde orbits move in the same direction as the Earth's rotation and to us here below, if we were to see a satellite in prograde, it would appear to us as if the satellite was moving to the East. Retrograde means the opposite. A satellite in this type of orbit is moving against the rotation of the Earth and if we were to see a satellite in retrograde, it would appear to us to be moving to the West. This type of orbit is rare and it's because of the cost. Remember what we talked about earlier about using the planets rotation to help in launches? That doesn't really work very well when you're trying to achieve retrograde. Inclinations describe the position of a satellite in relation to the equator of the Earth as though it were an angle. So a satellite with an inclination of zero would be right above the equator. And one with an inclination of 90 or negative 90 is over the North or South Pole respectively. All right. So there's four types of orbits to talk about with all this in mind. Leo or low Earth orbit is an orbit that happens at 1240 miles or less above the Earth's surface. It can be circular or elliptical as can all the other types. And a vehicle at this type of orbit would take 128 minutes or less to make a trip around the Earth. There's a lot of stuff in Leo orbit right now around the Earth including the International Space Station. Let's take a look at what a Leo orbit would look like using some SDK software visualizations. Notice how close those satellites and orbital paths are to the Earth. Leo or medium Earth orbits happen above that 1240 mile Leo threshold but below 22,236 miles. These orbits can take between two and 24 hours to get around the Earth. The coverage or amount of surface the satellite can see at this distance gives us things like GPS and other navigation satellite constellations. Constellations just means there's way more than one satellite doing that job. Now let's take a look at what a meal orbit looks like in comparison to Leo. Geosynchronous orbits happen at that upper meal threshold and match the planet's rotation in a journey around the Earth at about 24 hours. Geostationary orbits are a kind of geosynchronous orbit where it would look to us from below as if the satellite's not moving and that it's fixed in one place. This is useful in communications between Earth antenna and satellites. It's how you get satellite TV and radio. So what's a geosynchronous orbit look like in comparison to the others? Lastly there's HEO or high Earth orbit. This is anything beyond the geosynchronous meal threshold. Naturally these orbits take longer than 24 hours and a vehicle in one of these is actually moving slower than the Earth's rotation. This is another situation where it would look to us because it's moving slower than the Earth's rotation as though the satellite were moving to the west but it's not retrograde. This type of orbit is where we park space telescopes and long range monitoring satellites. Now let's put it all together. Here's another interesting view where you can see both circular and elliptical orbits at varying distances. Sadly all satellites don't go to heaven. In the end when a satellite has come to the end of its usefulness the satellites in lower orbits that we've discussed will be put into a controlled fuel burn and put on a course to burn up in the atmosphere. The ones in orbits further out will be guided away from Earth into the expanse. And that's it. Hopefully this discussion has scratched the surface of orbital terminology for you and you've learned a couple of new things. Thanks for your time and enjoy the rest of the conference.