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6050	11310	Hello, welcome to Satellite Orbits 101. I'm Matthew Murray, your presenter, and today I'll
11310	16170	be walking you through some of the fundamental terminology surrounding satellite orbits.
20610	25950	Now, as the title implies, this presentation isn't intended to turn you into a rocket scientist.
26230	30830	It's meant to peel away some of the mysticism surrounding the terms involved in the journey
30830	35690	of satellites or space vehicles and give a better understanding of the meaning behind them.
35690	40410	To that end, I've intentionally stayed away from any intense math or physics and
40410	44210	just focused on scratching at the upper layer of this topic.
50510	55490	Before we jump into what the word orbit really involves, it's worth mentioning a few things and
55490	60030	covering a few terms to help inform you and calibrate your understanding. The first matter
60030	66330	worth discussing is launch locations. They aren't random. Ever notice how the ones in the U.S. always
66330	72970	seem to happen in Florida? Clear sunny days really do matter. A strong enough wind can adversely
72970	78410	affect the trajectory of a launched craft, and lightning doesn't happen just down here on Earth,
78410	83110	it happens in the sky too, and a lightning strike as a craft moves through the atmosphere could
83110	89590	cause huge problems. Launch locations aren't just about weather either. Depending on where you intend
89590	95730	to place a satellite in terms of orbital distance and location, oftentimes the rotation of the Earth,
95730	102030	which is fast as at the equator, is used to give a vehicle an extra push in launch.
110530	115770	Once you achieve orbit, you have to keep it. Fuel on board the vehicle is used periodically to
115770	120790	maintain or augment the orbit. The surface of the Earth isn't flat and smooth, so the changes in the
120790	125470	surface or the topology of the Earth, all those mountains and valleys, can affect how the Earth
125470	130870	pulls on the satellite over time. The other bodies in our solar system, like the Sun and the Moon,
130870	136990	can also have a gravitational effect. Depending on where the vehicle is in relation to the atmosphere,
136990	142110	even a very thin layer of air and particles up there can produce enough drag and resistance
142110	149730	to affect an orbit. This can even increase when the Sun comes around. Just like heat makes air
149730	156190	expand down here, the warming of the atmosphere can make drag even worse up there. And let's not
156190	161030	forget all the junk that satellites and the people who fly those satellites have to dodge
161030	166550	in order to make a journey around the Earth. There's more than 128 million separate pieces,
166550	176080	parts, and objects roaming around our planet right now. All right, so let's start to dig a little bit
176080	182560	deeper. All orbit means, in its most generic terms, is one body or object moving around another.
182960	188840	So when that body, the object is moving around, is the Earth, the orbit is called geocentric.
188840	193820	There are several types of geocentric orbits, and each of those types plays a part in what
193820	200240	the satellite is up there to do. The shape of the orbits can come in different eccentricities,
200240	205920	and all that refers to is the type of curve the orbit has. Is it circular, or is it more of an
205920	214990	oval or an ellipse? Once we begin to consider the type of curve an orbit might have, then we can
214990	220410	begin to lump them into categories. Periodic orbits repeat in some consistent fashion, and they're
220410	225250	either elliptical or circular in nature. Because there's not a break in the pattern, these are
225250	230250	sometimes referred to as closed orbits. There is another class of orbit under the topic of
230250	235290	eccentricity that's not meant to stay in a repeating pattern around the Earth. These are
235290	239670	called escape or open orbits, and they're used to move vehicles away from the Earth in particular
239670	246230	ways. Parabolic orbits are used to complete minimum energy escapes if they're moving away
246230	251630	from the Earth, and captures if they're moving towards a planet. Hyperbolic orbits can send a
251630	257170	vehicle off at a much higher speed. These orbits are factors in gravitational slingshots, where a
257170	268120	vehicle flies by a planet and uses its gravitational pull to pick up speed. There are also terms for the
268320	272660	direction a satellite is moving in around the Earth. Prograde orbits move in the same direction
272660	277560	as the Earth's rotation, and to us here below, if we were to see a satellite in prograde, it would
277560	284000	appear to us as if the satellite was moving to the east. Retrograde means the opposite. A satellite
284000	288660	in this type of orbit is moving against the rotation of the Earth, and if we were to see a
288660	294760	satellite in retrograde, it would appear to us to be moving to the west. This type of orbit is rare,
294760	300080	and it's because of the cost. Remember what we talked about earlier, about using the planet's
300080	304180	rotation to help in launches? Well, that doesn't really work very well when you're trying to
304180	313390	achieve retrograde. Inclinations describe the position of a satellite in relation to the equator
313390	318770	of the Earth, as though it were an angle. So a satellite with an inclination of zero would be
318770	325970	right above the equator, and one with an inclination of 90 or negative 90 is over the north or south
325970	336250	pole, respectively. All right, so there's four types of orbits to talk about with all this in mind.
336250	343490	LEO, or Low Earth Orbit, is an orbit that happens at 1,240 miles or less above the Earth's surface.
343530	349250	It can be circular or elliptical, as can all the other types, and a vehicle at this type of orbit
349250	356790	would take 128 minutes or less to make a trip around the Earth. There's a lot of stuff in LEO
356790	367330	orbit right now around the Earth, including the International Space Station. Let's take a look at
367330	373030	what a LEO orbit would look like using some SDK software visualizations. Notice how close those
373030	396950	satellites and orbital paths are to the Earth. MEO, or Medium Earth Orbits, happen above that
396950	407110	1,240 mile LEO threshold, but below 22,236 miles. These orbits can take between 2 and 24 hours to
407110	412370	get around the Earth. The coverage, or amount of surface, the satellite can see at this distance
412370	416770	gives us things like GPS and other navigation satellite constellations.
416990	421330	Constellations just means there's way more than one satellite doing that job.
426400	430760	Now let's take a look at what a MEO orbit looks like in comparison to LEO.
446060	451640	Geosynchronous orbits happen at that upper MEO threshold and match the planet's rotation in a
451640	456720	journey around the Earth at about 24 hours. Geostationary orbits are a kind of geosynchronous
456720	462060	orbit where it would look to us from below as if the satellite's not moving and that it's fixed
462060	468500	in one place. This is useful in communications between Earth antenna and satellites. It's how
468500	476960	you get satellite TV and radio. So what's a geosynchronous orbit look like in comparison
476960	512950	to the others? Lastly, there's HEO, or High Earth Orbit. This is anything beyond the geosynchronous
512950	518630	MEO threshold. Naturally, these orbits take longer than 24 hours, and a vehicle in one of
518630	523770	these is actually moving slower than the Earth's rotation. This is another situation where it would
523770	528050	look to us, because it's moving slower than the Earth's rotation, as though the satellite were
528050	534190	moving to the west. But it's not retrograde. This type of orbit is where we park space telescopes
534190	569730	and long-range monitoring satellites. Now let's put it all together. Here's another interesting
569730	574350	view where you can see both circular and elliptical orbits at varying distances.
605540	610900	Sadly, all satellites don't go to heaven. In the end, when a satellite has come to the end of its
610900	615420	usefulness, the satellites in lower orbits that we've discussed will be put into a controlled
615420	621340	fuel burn and put on a course to burn up in the atmosphere. The ones in orbits further out will
621340	628920	be guided away from Earth into the expanse. And that's it. Hopefully this discussion has scratched
628920	634520	the surface of orbital terminology for you, and you've learned a couple of new things.
634900	637760	Thanks for your time, and enjoy the rest of the conference.