[00:06.050 --> 00:11.310]  Hello, welcome to Satellite Orbits 101. I'm Matthew Murray, your presenter, and today I'll
[00:11.310 --> 00:16.170]  be walking you through some of the fundamental terminology surrounding satellite orbits.
[00:20.610 --> 00:25.950]  Now, as the title implies, this presentation isn't intended to turn you into a rocket scientist.
[00:26.230 --> 00:30.830]  It's meant to peel away some of the mysticism surrounding the terms involved in the journey
[00:30.830 --> 00:35.690]  of satellites or space vehicles and give a better understanding of the meaning behind them.
[00:35.690 --> 00:40.410]  To that end, I've intentionally stayed away from any intense math or physics and
[00:40.410 --> 00:44.210]  just focused on scratching at the upper layer of this topic.
[00:50.510 --> 00:55.490]  Before we jump into what the word orbit really involves, it's worth mentioning a few things and
[00:55.490 --> 01:00.030]  covering a few terms to help inform you and calibrate your understanding. The first matter
[01:00.030 --> 01:06.330]  worth discussing is launch locations. They aren't random. Ever notice how the ones in the U.S. always
[01:06.330 --> 01:12.970]  seem to happen in Florida? Clear sunny days really do matter. A strong enough wind can adversely
[01:12.970 --> 01:18.410]  affect the trajectory of a launched craft, and lightning doesn't happen just down here on Earth,
[01:18.410 --> 01:23.110]  it happens in the sky too, and a lightning strike as a craft moves through the atmosphere could
[01:23.110 --> 01:29.590]  cause huge problems. Launch locations aren't just about weather either. Depending on where you intend
[01:29.590 --> 01:35.730]  to place a satellite in terms of orbital distance and location, oftentimes the rotation of the Earth,
[01:35.730 --> 01:42.030]  which is fast as at the equator, is used to give a vehicle an extra push in launch.
[01:50.530 --> 01:55.770]  Once you achieve orbit, you have to keep it. Fuel on board the vehicle is used periodically to
[01:55.770 --> 02:00.790]  maintain or augment the orbit. The surface of the Earth isn't flat and smooth, so the changes in the
[02:00.790 --> 02:05.470]  surface or the topology of the Earth, all those mountains and valleys, can affect how the Earth
[02:05.470 --> 02:10.870]  pulls on the satellite over time. The other bodies in our solar system, like the Sun and the Moon,
[02:10.870 --> 02:16.990]  can also have a gravitational effect. Depending on where the vehicle is in relation to the atmosphere,
[02:16.990 --> 02:22.110]  even a very thin layer of air and particles up there can produce enough drag and resistance
[02:22.110 --> 02:29.730]  to affect an orbit. This can even increase when the Sun comes around. Just like heat makes air
[02:29.730 --> 02:36.190]  expand down here, the warming of the atmosphere can make drag even worse up there. And let's not
[02:36.190 --> 02:41.030]  forget all the junk that satellites and the people who fly those satellites have to dodge
[02:41.030 --> 02:46.550]  in order to make a journey around the Earth. There's more than 128 million separate pieces,
[02:46.550 --> 02:56.080]  parts, and objects roaming around our planet right now. All right, so let's start to dig a little bit
[02:56.080 --> 03:02.560]  deeper. All orbit means, in its most generic terms, is one body or object moving around another.
[03:02.960 --> 03:08.840]  So when that body, the object is moving around, is the Earth, the orbit is called geocentric.
[03:08.840 --> 03:13.820]  There are several types of geocentric orbits, and each of those types plays a part in what
[03:13.820 --> 03:20.240]  the satellite is up there to do. The shape of the orbits can come in different eccentricities,
[03:20.240 --> 03:25.920]  and all that refers to is the type of curve the orbit has. Is it circular, or is it more of an
[03:25.920 --> 03:34.990]  oval or an ellipse? Once we begin to consider the type of curve an orbit might have, then we can
[03:34.990 --> 03:40.410]  begin to lump them into categories. Periodic orbits repeat in some consistent fashion, and they're
[03:40.410 --> 03:45.250]  either elliptical or circular in nature. Because there's not a break in the pattern, these are
[03:45.250 --> 03:50.250]  sometimes referred to as closed orbits. There is another class of orbit under the topic of
[03:50.250 --> 03:55.290]  eccentricity that's not meant to stay in a repeating pattern around the Earth. These are
[03:55.290 --> 03:59.670]  called escape or open orbits, and they're used to move vehicles away from the Earth in particular
[03:59.670 --> 04:06.230]  ways. Parabolic orbits are used to complete minimum energy escapes if they're moving away
[04:06.230 --> 04:11.630]  from the Earth, and captures if they're moving towards a planet. Hyperbolic orbits can send a
[04:11.630 --> 04:17.170]  vehicle off at a much higher speed. These orbits are factors in gravitational slingshots, where a
[04:17.170 --> 04:28.120]  vehicle flies by a planet and uses its gravitational pull to pick up speed. There are also terms for the
[04:28.320 --> 04:32.660]  direction a satellite is moving in around the Earth. Prograde orbits move in the same direction
[04:32.660 --> 04:37.560]  as the Earth's rotation, and to us here below, if we were to see a satellite in prograde, it would
[04:37.560 --> 04:44.000]  appear to us as if the satellite was moving to the east. Retrograde means the opposite. A satellite
[04:44.000 --> 04:48.660]  in this type of orbit is moving against the rotation of the Earth, and if we were to see a
[04:48.660 --> 04:54.760]  satellite in retrograde, it would appear to us to be moving to the west. This type of orbit is rare,
[04:54.760 --> 05:00.080]  and it's because of the cost. Remember what we talked about earlier, about using the planet's
[05:00.080 --> 05:04.180]  rotation to help in launches? Well, that doesn't really work very well when you're trying to
[05:04.180 --> 05:13.390]  achieve retrograde. Inclinations describe the position of a satellite in relation to the equator
[05:13.390 --> 05:18.770]  of the Earth, as though it were an angle. So a satellite with an inclination of zero would be
[05:18.770 --> 05:25.970]  right above the equator, and one with an inclination of 90 or negative 90 is over the north or south
[05:25.970 --> 05:36.250]  pole, respectively. All right, so there's four types of orbits to talk about with all this in mind.
[05:36.250 --> 05:43.490]  LEO, or Low Earth Orbit, is an orbit that happens at 1,240 miles or less above the Earth's surface.
[05:43.530 --> 05:49.250]  It can be circular or elliptical, as can all the other types, and a vehicle at this type of orbit
[05:49.250 --> 05:56.790]  would take 128 minutes or less to make a trip around the Earth. There's a lot of stuff in LEO
[05:56.790 --> 06:07.330]  orbit right now around the Earth, including the International Space Station. Let's take a look at
[06:07.330 --> 06:13.030]  what a LEO orbit would look like using some SDK software visualizations. Notice how close those
[06:13.030 --> 06:36.950]  satellites and orbital paths are to the Earth. MEO, or Medium Earth Orbits, happen above that
[06:36.950 --> 06:47.110]  1,240 mile LEO threshold, but below 22,236 miles. These orbits can take between 2 and 24 hours to
[06:47.110 --> 06:52.370]  get around the Earth. The coverage, or amount of surface, the satellite can see at this distance
[06:52.370 --> 06:56.770]  gives us things like GPS and other navigation satellite constellations.
[06:56.990 --> 07:01.330]  Constellations just means there's way more than one satellite doing that job.
[07:06.400 --> 07:10.760]  Now let's take a look at what a MEO orbit looks like in comparison to LEO.
[07:26.060 --> 07:31.640]  Geosynchronous orbits happen at that upper MEO threshold and match the planet's rotation in a
[07:31.640 --> 07:36.720]  journey around the Earth at about 24 hours. Geostationary orbits are a kind of geosynchronous
[07:36.720 --> 07:42.060]  orbit where it would look to us from below as if the satellite's not moving and that it's fixed
[07:42.060 --> 07:48.500]  in one place. This is useful in communications between Earth antenna and satellites. It's how
[07:48.500 --> 07:56.960]  you get satellite TV and radio. So what's a geosynchronous orbit look like in comparison
[07:56.960 --> 08:32.950]  to the others? Lastly, there's HEO, or High Earth Orbit. This is anything beyond the geosynchronous
[08:32.950 --> 08:38.630]  MEO threshold. Naturally, these orbits take longer than 24 hours, and a vehicle in one of
[08:38.630 --> 08:43.770]  these is actually moving slower than the Earth's rotation. This is another situation where it would
[08:43.770 --> 08:48.050]  look to us, because it's moving slower than the Earth's rotation, as though the satellite were
[08:48.050 --> 08:54.190]  moving to the west. But it's not retrograde. This type of orbit is where we park space telescopes
[08:54.190 --> 09:29.730]  and long-range monitoring satellites. Now let's put it all together. Here's another interesting
[09:29.730 --> 09:34.350]  view where you can see both circular and elliptical orbits at varying distances.
[10:05.540 --> 10:10.900]  Sadly, all satellites don't go to heaven. In the end, when a satellite has come to the end of its
[10:10.900 --> 10:15.420]  usefulness, the satellites in lower orbits that we've discussed will be put into a controlled
[10:15.420 --> 10:21.340]  fuel burn and put on a course to burn up in the atmosphere. The ones in orbits further out will
[10:21.340 --> 10:28.920]  be guided away from Earth into the expanse. And that's it. Hopefully this discussion has scratched
[10:28.920 --> 10:34.520]  the surface of orbital terminology for you, and you've learned a couple of new things.
[10:34.900 --> 10:37.760]  Thanks for your time, and enjoy the rest of the conference.