WEBVTT 00:00.000 --> 00:02.880 Beyond the outer limits of human adventure. 00:02.980 --> 00:05.180 Beyond the barrier of human credibility. 00:15.870 --> 00:17.910 What orbits are most satellites in? 00:17.910 --> 00:24.510 There's a lot of room out there and there are actually an infinite number of orbits that a satellite can be in when orbiting around Earth. 00:24.510 --> 00:28.670 But that doesn't mean all those infinite orbits are actually useful. 00:28.670 --> 00:32.870 There are actually surprisingly few orbits that are targeted for most satellites. 00:32.870 --> 00:38.490 This is because the primary purpose for almost all satellites primarily has to do with the surface of the Earth. 00:38.490 --> 00:41.970 Orbital motion is completely ignorant of Earth's rotation. 00:41.970 --> 00:44.730 But for satellites, Earth is all that matters. 00:44.730 --> 00:49.990 There are only a few orbits that take advantage of both the rotation of the Earth and orbital motion. 00:49.990 --> 00:54.730 So naturally, these orbits are most targeted and getting kind of crowded. 00:54.730 --> 00:59.570 You can see just how crowded it is in space in general through this visualization. 00:59.670 --> 01:03.470 There are over 15,000 objects that we're currently tracking. 01:03.470 --> 01:18.110 This includes all active satellites, all dead satellites that are still orbiting, all rocket bodies that were used to get satellites into their targeted orbits, and all debris from the few satellite collisions that have happened over the years. 01:18.190 --> 01:26.990 Keep in mind that this visualization doesn't show the actual size of these objects, but there are actually several orders of magnitude smaller than the dots represented. 01:26.990 --> 01:30.830 So even though it does look very crowded, there's actually quite a bit of space left over. 01:31.350 --> 01:36.670 Now looking at just the active satellites and ignoring all else, it suddenly looks much less crowded. 01:36.670 --> 01:40.690 There are only about 2,200 active satellites in orbit. 01:40.690 --> 01:45.670 But even just glancing at them, you can already see natural groupings start to arise. 01:45.670 --> 01:49.950 The first of these groupings I'll cover is the most valuable real estate in space. 01:49.950 --> 01:55.850 It's the ring of satellites farther out than anything else, and it's called geostationary orbit, or GEO. 01:55.850 --> 01:58.170 GEO is a very unique spot in Earth's orbit. 01:58.170 --> 02:07.430 It is an orbit that is exactly matched to Earth's rotation, so when a satellite is in geostationary orbit, it doesn't move in relation to the Earth's surface. 02:07.430 --> 02:15.170 So when I select one and speed up the simulator, you can see how Earth is rotating under the ring of the geostationary orbit. 02:15.290 --> 02:19.730 Let's look at the two-dimensional view of Earth with the satellite's orbital motion projected on it. 02:19.730 --> 02:23.490 This is typically referred to as the ground track of the satellite. 02:23.570 --> 02:26.270 In the ground track, you can see it's not moving at all. 02:26.270 --> 02:32.230 The red circle, or satellite's footprint, indicates what the satellite is able to view from its current position. 02:32.230 --> 02:39.190 In this case, since it's a geostationary satellite that's so far out, it can see almost the entire western hemisphere of the Earth. 02:39.190 --> 02:41.610 This is why this orbit is so valuable. 02:41.610 --> 02:49.210 It's the only place where you can put a satellite in orbit and keep it still, and it can access a wide swath of the Earth's surface. 02:49.310 --> 02:56.810 For instance, this satellite that we're showing right now is used to broadcast satellite radio to both North and South America. 02:56.830 --> 03:05.150 Now it's only still in relation to the Earth's surface, so it's still orbiting, but the orbital speed at that distance is exactly matched to the Earth's rotation. 03:05.170 --> 03:09.970 Geostationary satellites have to be on the equator, otherwise they'll still move north and south. 03:09.970 --> 03:12.990 You can see this with an old GOES weather satellite. 03:12.990 --> 03:17.470 Even though it's at the same orbital distance as GEO, it's not exactly on the equator. 03:17.470 --> 03:28.010 It makes a figure eight on the Earth's surface, and at the top and bottom of that figure eight, you can also see it covers more of the northern or more of the southern hemisphere, depending on what position of the figure eight it's in. 03:28.010 --> 03:39.310 All the orbits within that ring of geostationary satellites have an orbital velocity faster than the rotation of the Earth, so it's much harder to maximize their usefulness over certain parts of the Earth's surface. 03:39.730 --> 03:50.350 At a glance, you can tell that geostationary satellites are much farther away than low Earth orbit satellites, but that distance is actually much farther than you might even realize. 03:50.350 --> 03:56.690 It's actually 22,000 miles or 36,000 kilometers away from the Earth's surface. 03:56.690 --> 04:05.750 That distance is so significant, it actually takes light almost a quarter of a second to travel the round trip between the surface of the Earth to the satellite and back. 04:05.750 --> 04:09.710 This can naturally cause issues with the operations of many different satellites. 04:09.710 --> 04:11.930 So now let's move a bit closer to Earth. 04:11.930 --> 04:15.830 The next major group of satellites is in medium Earth orbit, or MEO. 04:15.830 --> 04:22.330 This is a relatively sparse region of space that is loosely defined as below geostationary orbit and above low Earth orbit. 04:22.330 --> 04:31.050 There are far fewer satellites in this regime than either GEO or LEO, but one group of satellites in MEO probably affects your life more than any other. 04:31.050 --> 04:32.470 GPS satellites. 04:32.470 --> 04:33.650 Not only are U.S. 04:33.650 --> 04:39.730 GPS satellites in MEO, but also all the other major GPS constellations are in this region as well. 04:39.730 --> 04:44.970 This includes Galileo for the EU, Baidu for China, and GLONASS for Russia. 04:44.970 --> 04:46.470 Here you can see the U.S. 04:46.470 --> 04:47.890 GPS constellation. 04:47.890 --> 04:56.810 The crisscrossing pattern of the orbits and having multiple satellites in each orbital plane allows them to completely blanket the Earth's surface in GPS coverage. 04:56.810 --> 05:01.250 Medium Earth orbit ends up being the most optimal place to put GPS satellites. 05:01.250 --> 05:14.830 By being in medium Earth orbit, each of the GPS satellites can still see 38% of the Earth's surface at any one time, but they're still moving fast enough to provide complete coverage of the entire Earth's surface as they are moving through their orbit. 05:14.950 --> 05:19.990 Looking at their associated ground tracks, you can easily see that GPS is completely blanketing the Earth. 05:19.990 --> 05:31.130 When we look at the footprint of just one of the GPS satellites, you can see it's still quite large and covers a vast portion of the Earth's surface, but it's still much, much smaller than geostationary satellites. 05:31.190 --> 05:33.650 MEO does have very real trade-offs, though. 05:33.650 --> 05:36.370 The GPS constellations are lonely for a reason . 05:36.450 --> 05:40.050 Let's go down closer to the Earth to the next orbit, low Earth orbit. 05:40.090 --> 05:46.770 Of the 2,200 satellites currently in orbit, about 1,600 of them are all in low Earth orbit, or LEO. 05:46.770 --> 05:52.730 LEO is very close to the Earth's surface and is defined as all orbits that are lower than 2,000 kilometers. 05:53.030 --> 05:57.830 Naturally, because it's so close to the Earth's surface, it requires the lowest amount of energy to reach. 05:57.830 --> 06:09.130 For example, SpaceX's Falcon 9 rocket can lift over 8,000 kilograms to geostationary transfer orbit, which is the orbit that puts satellites on their way to geostationary orbit. 06:09.130 --> 06:15.690 But it can lift more than double that amount to low Earth orbit, or 22,900 kilograms. 06:16.030 --> 06:19.870 This is really the primary reason why most of the satellites are in LEO. 06:19.870 --> 06:21.310 It's the default choice. 06:21.310 --> 06:27.450 Essentially, unless your has some pressing reason to be in a different orbital plane, it goes to LEO. 06:27.450 --> 06:34.390 Since LEO satellites are closest to the Earth, they also move the fastest, completing an orbit in only about 90 minutes. 06:34.390 --> 06:38.210 You can see that with the International Space Station, which is in low Earth orbit. 06:38.210 --> 06:43.470 90 minutes is a lot faster than the 24 hours it takes for geostationary satellites. 06:43.470 --> 06:47.750 This also makes communication a lot harder, as you can see from the satellite's ground track. 06:47.750 --> 06:57.410 Since the satellite is so much closer to the Earth, its red circle is minuscule when compared to the geostationary satellites, and even when compared to the MEO satellites. 06:57.410 --> 07:05.030 Combined with the fact that they're orbiting so fast, they're actually only in view of any single point on the Earth's surface for about 5 to 10 minutes at a time. 07:05.030 --> 07:09.750 That means all communications with these satellites need to happen within that very short pass window. 07:09.830 --> 07:15.870 But it also means that they are able to view large portions of the Earth as they race around it very quickly. 07:16.030 --> 07:21.210 Within LEO, there are orbits that have additional value other than just being close to the Earth's surface. 07:21.210 --> 07:26.070 Sun Synchronous Orbit, or SSO, aligns the orbital motion of the satellite with the Sun. 07:26.070 --> 07:32.930 The Sun provides power for all satellites and provides illumination for satellites trying to image the Earth's surface. 07:32.930 --> 07:42.050 Sinking the orbit with the Sun means that the satellite will pass over the same location at the same time every day, which can be naturally useful, especially for imaging satellites. 07:42.050 --> 07:48.790 That predictability can also be used to predict the power generation of a satellite and really optimize its usefulness. 07:48.790 --> 07:56.250 Between them, LEO and GEO cover the vast majority of satellites, and MEO makes up the majority of the remaining ones. 07:56.250 --> 08:01.470 But there is still a class of orbits that can be useful for unique cases. 08:01.670 --> 08:04.270 This class is called Highly Elliptical Orbits. 08:04.270 --> 08:11.710 These are orbits that are not circular, but rather pass very close to the Earth's surface on one side of the orbit and very far away on the other. 08:11.710 --> 08:21.070 There are a large number of these orbits that are used for very interesting reasons, but the one that I'm going to cover today is called Molnaya, and this is what it looks like. 08:21.070 --> 08:27.850 As you can see, this orbit passes very close to the Earth's surface in the Southern Hemisphere, but then is very far away in the Northern Hemisphere. 08:27.850 --> 08:35.930 Since satellites go faster when they are closer to the Earth's surface, this means that those satellites have vastly more time over the Northern Hemisphere. 08:35.930 --> 08:46.050 It allows these satellites to essentially stay over one location in the Northern Hemisphere for a very long time, and then race around the Southern Hemisphere quickly to reduce the amount of uselessness it has. 08:46.050 --> 08:54.210 One reason this was used was to keep a satellite over the high latitudes of Northern Russia, which would normally be out of view for geostationary satellites. 08:54.210 --> 09:00.310 This is just one example of how Highly Elliptical Orbits can be more useful than their circular counterparts. 09:00.550 --> 09:13.670 There are numerous other orbits that I could cover that are useful for different reasons and in different ways, but the ones that I've covered today are the vast majority of the ones that are used by satellites currently in operation and currently orbiting our world.