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. All right, 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, is 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
eccentricity 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 a
vehicle off at a much higher speed. These orbits are factors in gravitational slingshots, 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 planet's
rotation to help in launches? Well, 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 1,240 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. MEO, or Medium Earth Orbits, happen above that
1,240 mile LEO threshold, but below 22,236 miles. These orbits can take between 2 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 MEO orbit looks like in comparison to LEO.
Geosynchronous orbits happen at that upper MEO 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
MEO 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.