WEBVTT - TechStuff Tidbits: Satellite Orbits 101 0:00:04.400 --> 0:00:07.760 Welcome to tech Stuff, a production from I Heart Radio. 0:00:12.000 --> 0:00:14.800 Hey there, and welcome to tech Stuff. I'm your host, 0:00:14.920 --> 0:00:18.040 Jonathan Strickland. I'm an executive producer with I Heart Radio. 0:00:18.079 --> 0:00:21.640 And how the tech are you? You know? Ever since 0:00:21.720 --> 0:00:25.720 the then Soviet Union sent ups foot Nick way back 0:00:25.760 --> 0:00:29.720 in nineteen fifties, seven man made satellites have played a 0:00:29.760 --> 0:00:34.120 really important role in our world in multiple contexts. You know, 0:00:34.159 --> 0:00:37.680 in the early days, at least from a political standpoint, 0:00:37.720 --> 0:00:41.960 it was a lot about demonstrating scientific and engineering superiority. 0:00:42.560 --> 0:00:45.760 That was kind of what was driving the space race, 0:00:45.800 --> 0:00:49.440 at least from a financial and political standpoint, back when 0:00:49.520 --> 0:00:54.200 the US and USS are we're racing to achieve first 0:00:54.480 --> 0:00:58.520 in space. But I mean, obviously they're also important to 0:00:58.680 --> 0:01:02.000 further our scientific under standing of our world and beyond, 0:01:02.600 --> 0:01:06.440 and also to do stuff like layout communications infrastructure that 0:01:06.480 --> 0:01:09.600 would allow for global communication. And of course there are 0:01:09.640 --> 0:01:12.840 thousands of other applications and satellites are really out of 0:01:12.880 --> 0:01:16.200 this world. And yes, I also hate me for saying that, 0:01:16.920 --> 0:01:18.920 And I thought it could be a little beneficial to 0:01:18.959 --> 0:01:22.800 talk about the various orbits that satellites can inhabit and 0:01:22.840 --> 0:01:26.560 then explain the differences between those orbits and the purposes 0:01:26.600 --> 0:01:29.000 of them. And I think that's really helpful in order 0:01:29.040 --> 0:01:31.839 to understand stuff like why is the James Webb Space 0:01:31.880 --> 0:01:34.920 Telescope in an orbit that's so far out that we 0:01:35.040 --> 0:01:38.720 cannot reach it with a human crew? Right? Why is that? 0:01:39.280 --> 0:01:43.440 Or why scientists warn us about the dangers of space chunk. 0:01:43.480 --> 0:01:46.200 I mean, space is huge, so you would think the 0:01:46.240 --> 0:01:49.880 odds of any two objects colliding with one another out 0:01:49.960 --> 0:01:54.240 in space would be astronomical. Man, I'm gonna have a 0:01:54.240 --> 0:01:57.760 lot of puns in this episode. So we're gonna go 0:01:57.840 --> 0:02:01.160 through the various orbits and explain we would send certain 0:02:01.200 --> 0:02:06.440 types of satellites to one orbit versus another. And first 0:02:06.440 --> 0:02:09.239 of all, let's let's actually just talk about the word orbit. 0:02:09.320 --> 0:02:12.600 And I'm sure everyone out there has a grasp on this, 0:02:12.840 --> 0:02:16.440 but technically, what we're talking about is a curved path 0:02:17.200 --> 0:02:21.160 that causes one object to move around a second object, 0:02:21.600 --> 0:02:24.360 or two objects to move around each other due to 0:02:24.840 --> 0:02:28.240 the poll of gravity. And gravity is one of the 0:02:28.320 --> 0:02:32.040 fundamental forces of the universe. It's also the weakest one, 0:02:32.120 --> 0:02:35.720 by the way, it has practically no effect once you 0:02:35.720 --> 0:02:40.000 get down to the molecular or atomic level. Gravity is 0:02:40.040 --> 0:02:43.640 a force of attraction that exists between stuff in our universe. 0:02:43.919 --> 0:02:49.440 What has mass, right, anything that has mass experiences the 0:02:49.560 --> 0:02:53.760 effects of gravity. So technically you could say there's a 0:02:53.800 --> 0:02:58.919 gravitational attraction between every object that has mass and every 0:02:58.960 --> 0:03:03.240 other object that has mass. However, the magnitude of that 0:03:03.360 --> 0:03:10.200 attractive force is dependent upon two really important factors. One 0:03:10.600 --> 0:03:14.160 is the actual mass of the objects in question. The 0:03:14.280 --> 0:03:18.040 more mass, the greater the attraction, So to truly massive 0:03:18.080 --> 0:03:21.600 objects will have a greater attraction to one another than 0:03:21.720 --> 0:03:24.280 two very small objects. This is why when we get 0:03:24.280 --> 0:03:28.960 down to the molecular and atomic levels, gravity is is negligible. 0:03:29.000 --> 0:03:31.799 We can just ignore it. Uh. This, by the way, 0:03:31.840 --> 0:03:34.200 is also why the gravity on the Moon is so 0:03:34.280 --> 0:03:37.839 much less than the gravity on Earth. The acceleration due 0:03:37.840 --> 0:03:40.560 to gravity on the Moon is a little less than 0:03:40.640 --> 0:03:44.200 sevent of that what we'd experienced here on Earth, So 0:03:44.640 --> 0:03:48.480 the gravitational pull between say the Moon and an astronaut 0:03:49.520 --> 0:03:53.160 is much less than what that astronaut would experience while 0:03:53.160 --> 0:03:56.240 walking around on Earth. Because the Moon is less massive 0:03:56.360 --> 0:03:59.320 than the Earth, the astronaut is probably about the same. 0:03:59.680 --> 0:04:03.440 But the other factor is the distance that's between those 0:04:03.440 --> 0:04:06.480 two objects if they are really far apart, the gravitational 0:04:06.520 --> 0:04:10.440 force between them, while technically still being present, will be 0:04:10.520 --> 0:04:15.040 extremely weak. Again, if it's really really far apart, you 0:04:15.040 --> 0:04:17.359 can ignore it because it's so weak as to be 0:04:17.960 --> 0:04:21.760 you know, almost nothing. I should also add the Einstein's 0:04:21.800 --> 0:04:25.360 theory of general relativity actually dismissed the idea of gravity 0:04:25.400 --> 0:04:30.200 being an actual force. Rather, gravity is the consequence of 0:04:30.279 --> 0:04:34.880 objects with mass bending spacetime, and that gets a little 0:04:35.520 --> 0:04:39.839 difficult to envision, so let's simplify it. Imagine that you 0:04:39.920 --> 0:04:43.719 have a trampoline and then you put a pretty heavy 0:04:43.760 --> 0:04:47.120 bowling ball in the middle of that trampoline. Well, the 0:04:47.120 --> 0:04:49.760 weight of the bowling ball will cause the trampoline's surface 0:04:49.800 --> 0:04:53.440 to deform right, it will dip downward because the weight 0:04:53.480 --> 0:04:55.880 of the bowling ball. And if you were to try 0:04:55.880 --> 0:05:00.200 and roll a marble across the trampoline, then it's stead 0:05:00.240 --> 0:05:03.680 of traveling in a straight line, the marble's path would 0:05:03.680 --> 0:05:07.120 be affected by that bend in the trampoline. It would 0:05:07.120 --> 0:05:11.040 actually turn towards the dip and thus towards the bowling ball. Well, 0:05:11.040 --> 0:05:14.520 Einstein's theory stated that we're seeing that exact same effect 0:05:14.800 --> 0:05:17.839 out in the universe, except while we could describe the 0:05:17.839 --> 0:05:21.640 surface of a trampoline effectively as a two dimensional object, 0:05:21.880 --> 0:05:24.720 you know, an object that doesn't have depth to it. 0:05:25.480 --> 0:05:28.479 In space, we have to deal with three dimensions, that 0:05:28.560 --> 0:05:31.760 being spatial dimensions. I mean we also have time, which 0:05:31.800 --> 0:05:34.920 is the fourth dimension. And this gets are a bit 0:05:34.960 --> 0:05:37.680 tricky for us to visualize, or at least I find 0:05:37.680 --> 0:05:41.360 it tricky. Maybe you can do it. I can't. But yeah, 0:05:41.480 --> 0:05:44.320 when we often refer to gravity as a force, Einstein 0:05:44.360 --> 0:05:46.320 would correct us on that one and say it's not 0:05:46.400 --> 0:05:50.320 really a force. Now, with that bowling ball and marble 0:05:50.480 --> 0:05:55.039 trampoline example, we can actually understand why satellites have to 0:05:55.120 --> 0:05:58.160 work in the way that they do. So let's say 0:05:58.320 --> 0:06:01.200 you roll the marble hard enough to reach the point 0:06:01.240 --> 0:06:04.520 where the bowling ball's presence is going to cause the 0:06:04.560 --> 0:06:08.360 marble's pathway to change, But you're not rolling it so 0:06:08.440 --> 0:06:11.160 hard that the marble can make it out the other 0:06:11.240 --> 0:06:14.040 side to the opposite, you know, into the trampoline. So, 0:06:14.080 --> 0:06:17.320 in other words, the marble is unable to escape the 0:06:17.320 --> 0:06:21.640 bowling balls gravitational pull. The marble will roll down and 0:06:21.760 --> 0:06:23.640 hit the bowling ball and come to a stop it 0:06:23.720 --> 0:06:27.400 at some point. Now, if you rolled the marble really hard. 0:06:27.520 --> 0:06:30.880 It might be able to get through the deformed area 0:06:30.920 --> 0:06:34.600 of the trampoline's surface like it might have enough momentum 0:06:34.839 --> 0:06:40.320 too to navigate through the dip. But its path is 0:06:40.320 --> 0:06:42.560 still going to change, right. It's not a flat surface. 0:06:42.560 --> 0:06:44.840 It's not going to travel in a straight line. It 0:06:44.960 --> 0:06:47.479 will have a bend in its pathway. But maybe it 0:06:47.480 --> 0:06:50.599 will get all the way across the trampoline. Uh, it 0:06:50.720 --> 0:06:54.000 just won't be directly across. However, if you wanted to 0:06:54.080 --> 0:06:59.400 keep the marble so that it's constantly circling the bowling ball, well, 0:06:59.480 --> 0:07:01.040 we would have to have some way to keep the 0:07:01.080 --> 0:07:04.000 marble at just the right speed. It would need to 0:07:04.040 --> 0:07:07.800 be fast enough to counteract the marble's tendency to fall 0:07:07.880 --> 0:07:11.560 toward the bowling ball, but not be so fast as 0:07:11.600 --> 0:07:15.520 to cause the marble to continue off the pathway and 0:07:15.640 --> 0:07:18.800 eventually off the edge of the trampoline. If we could 0:07:18.880 --> 0:07:22.960 add energy to the marble consistently, we would be all set, 0:07:23.000 --> 0:07:26.400 because otherwise, the friction that the marble would encounter as 0:07:26.400 --> 0:07:28.600 it rolled across the trampoline would be enough to slow 0:07:28.600 --> 0:07:31.600 it down and it would fall towards the bowling ball. 0:07:32.040 --> 0:07:33.960 So we'd have to find a way to give the 0:07:34.000 --> 0:07:37.560 marble a little boost now and then in order for 0:07:37.640 --> 0:07:41.360 it to maintain its circular pathway around the bowling ball. 0:07:42.560 --> 0:07:46.240 So satellites in orbit around something else, whether it's our 0:07:46.320 --> 0:07:50.000 planet or some other celestial body, need to move at 0:07:50.000 --> 0:07:53.480 a speed that's fast enough to avoid falling toward whatever 0:07:53.520 --> 0:07:57.040 it is orbiting around. So out in space there aren't 0:07:57.080 --> 0:08:00.000 nearly as many factors that would slow down a satellite 0:08:00.120 --> 0:08:03.920 speed as we find here on Earth. There's very little 0:08:03.960 --> 0:08:07.280 friction or air resistance out there, So once you get 0:08:07.280 --> 0:08:11.160 a satellite in orbit, the speed the satellite has courtesy 0:08:11.240 --> 0:08:14.280 of the launch vehicle is sufficient to keep most satellites 0:08:14.280 --> 0:08:18.360 in an orbit for many years. Satellites have thrusters, and 0:08:18.400 --> 0:08:21.160 they have fuel, but those thrusters are not meant to 0:08:21.240 --> 0:08:25.040 accelerate the satellite in order for it to maintain orbital speed. 0:08:25.560 --> 0:08:28.400 Those thrusters are really used to maneuver the satellite so 0:08:28.920 --> 0:08:33.240 it can either transition from one orbit to another, go 0:08:33.360 --> 0:08:36.840 through a transfer orbit in other words, or used to 0:08:36.960 --> 0:08:39.800 move the satellite out of the pathway of potential space 0:08:39.880 --> 0:08:44.720 junk or other debris. Now, satellites and lower orbits can 0:08:44.920 --> 0:08:49.520 and do experience drag from the Earth's atmosphere, so there's 0:08:49.520 --> 0:08:54.400 actually no hard boundary for where our planet's atmosphere ends. 0:08:55.120 --> 0:08:58.760 We do have the Carmen line, which is sort of 0:08:58.800 --> 0:09:02.480 a convenient definite mission of the edge of space, but 0:09:02.840 --> 0:09:06.160 it's mainly there as a way to define it for 0:09:06.200 --> 0:09:10.200 political purposes and just to have a practical definition, because 0:09:10.360 --> 0:09:16.040 it's so nebulous again to use another pun and so 0:09:16.200 --> 0:09:20.480 vague that it's very difficult to say this is uh 0:09:20.520 --> 0:09:24.480 categorically where space begins, and the common line is at 0:09:24.480 --> 0:09:28.760 a hundred kilometers above sea level here on Earth. Now, 0:09:29.400 --> 0:09:32.880 that does not mean that there is no atmosphere beyond 0:09:32.960 --> 0:09:37.560 one kilometers in altitude. There is atmosphere beyond that limit, 0:09:37.679 --> 0:09:43.320 but it's extremely thin. Individual particles can be very far 0:09:43.360 --> 0:09:46.079 apart from each other, so it doesn't resemble the atmosphere 0:09:46.120 --> 0:09:51.240 we have here on the surface. UH. And these few 0:09:51.320 --> 0:09:56.480 particles are still enough to cause drag on lower altitude satellites, 0:09:57.200 --> 0:10:02.560 so gradually those satellite speeds will slow down enough that, um, 0:10:02.600 --> 0:10:06.040 you know, it will eventually de orbit. It will lose 0:10:06.240 --> 0:10:10.240 enough velocity and fall back to Earth unless we were 0:10:10.280 --> 0:10:13.360 to do something like if we were to move it 0:10:13.400 --> 0:10:16.360 to a different orbit than that could be enough to 0:10:17.160 --> 0:10:19.720 extend the life of the satellite, or we might even 0:10:19.800 --> 0:10:23.559 use thrusters to push the satellite out into an orbit 0:10:23.559 --> 0:10:28.600 where it'll just be dead out there in space. Now 0:10:28.640 --> 0:10:32.640 we can classify Earth satellite orbits in different ways, including 0:10:32.720 --> 0:10:36.520 their altitude. Now, we can classify Earth satellite orbits in 0:10:36.559 --> 0:10:40.680 several different ways, and I'll explain some of those ways 0:10:40.880 --> 0:10:51.240 when we come back from this break. Okay, before the break, 0:10:51.280 --> 0:10:54.680 I mentioned we can classify Earth orbits in several different ways. 0:10:55.000 --> 0:10:58.199 One of those ways is the altitude of those orbits. 0:10:58.600 --> 0:11:02.480 Generally speaking, we can split altitudes into low Earth orbit, 0:11:02.640 --> 0:11:06.280 mid Earth orbit, and high Earth orbit. The low orbit 0:11:06.400 --> 0:11:10.679 range is around one to two thousand kilometers above sea level, 0:11:10.960 --> 0:11:14.040 so these are well above the Carmen line. Obviously, remember 0:11:14.080 --> 0:11:16.680 the carbon lines at a hundred kilometers above sea level. 0:11:17.559 --> 0:11:22.120 These satellites move really wicked fast. Uh. These are satellites 0:11:22.160 --> 0:11:26.160 that orbit the Earth several times each day, so they're 0:11:26.160 --> 0:11:29.000 not orbiting the Earth in time with the Earth's rotation. 0:11:29.000 --> 0:11:32.959 They're actually going faster than the Earth's rotation. The lowest 0:11:33.120 --> 0:11:38.280 orbiting satellites are completing in orbit somewhere around minutes per orbit. 0:11:38.800 --> 0:11:40.960 That means a satellite like that could orbit the Earth 0:11:41.000 --> 0:11:45.959 around sixteen times each day. However, lower satellites are going 0:11:46.000 --> 0:11:49.720 to encounter more drag because they're gonna be hitting the 0:11:49.760 --> 0:11:55.120 occasional particle of atmosphere and their orbits will deteriorate faster 0:11:55.320 --> 0:11:59.000 than those satellites that are at a higher orbit. And 0:11:59.040 --> 0:12:01.720 these lower satellites and only be useful for a few years. 0:12:01.760 --> 0:12:05.200 So you wouldn't want anything designed for a long term 0:12:05.280 --> 0:12:08.640 mission to be in that orbit. Uh, it would it 0:12:08.679 --> 0:12:11.679 would not be able to maintain that orbit for longer 0:12:11.720 --> 0:12:15.480 than a few years. In the low Earth orbit range, 0:12:15.520 --> 0:12:18.480 we have a lot of satellites that do Earth observations, 0:12:18.520 --> 0:12:22.360 so satellites meant for Earth sciences often occupy this space. 0:12:23.040 --> 0:12:28.440 In addition, satellites like space x is Starlink network, they 0:12:28.440 --> 0:12:32.600 occupy the low Earth orbit range. There around five kilometers 0:12:32.679 --> 0:12:36.760 above sea level, so not quite in the middle of 0:12:36.840 --> 0:12:39.640 low Earth orbit range. They're actually on the lower end. 0:12:40.559 --> 0:12:43.880 And part of SpaceX's strategy for Starlink is to launch 0:12:44.040 --> 0:12:48.680 tens of thousands of satellites into that general orbit to 0:12:48.760 --> 0:12:54.000 provide global consistent coverage for Internet service and to essentially 0:12:54.480 --> 0:12:57.959 resupply those satellites as older ones are decommissioned, which is 0:12:58.040 --> 0:12:59.880 kind of a fancy way of saying, they either get 0:13:00.040 --> 0:13:03.360 e orbited as then they fall back to Earth or 0:13:03.400 --> 0:13:05.679 they're pushed into an orbit that no one is using, 0:13:06.000 --> 0:13:10.200 kind of a graveyard orbit. Now, the mid Earth orbit 0:13:10.400 --> 0:13:13.520 that ranges from two thousand kilometers above sea level up 0:13:13.520 --> 0:13:18.079 to thirty five thousand, seven hundred eighty kilometers, so a 0:13:18.120 --> 0:13:21.760 big big range here, and a lot of navigational satellites 0:13:21.760 --> 0:13:26.160 and spy satellites occupy this space. Um As out here, 0:13:26.240 --> 0:13:30.800 you can put satellites in an orbit where they stay 0:13:30.880 --> 0:13:34.960 above particular regions for a good amount of time each day. 0:13:35.080 --> 0:13:39.000 And in fact, now we need to talk about a 0:13:39.080 --> 0:13:43.160 special subset of orbits that are kind of between Mid 0:13:43.200 --> 0:13:46.760 Earth and High Earth orbits. And you probably heard terms 0:13:46.760 --> 0:13:52.280 like geosynchronous and geo stationary orbits. These orbits are just 0:13:52.559 --> 0:13:55.760 a touch further out from the mid orbits, and sometimes 0:13:55.760 --> 0:13:58.080 they even get grouped with High Earth orbits. It really 0:13:58.120 --> 0:14:01.000 just depends on whom you're talking to, UH, and it's 0:14:01.080 --> 0:14:07.520 very easy to confuse geosynchronous with geostationary. Technically, geostationary orbits 0:14:07.559 --> 0:14:12.760 are a subset of geosynchronous orbits. So at this altitude, 0:14:13.000 --> 0:14:17.600 this far out from the Earth, the satellites orbit is 0:14:17.640 --> 0:14:20.720 the same as the rotational speed of the Earth. So, 0:14:20.760 --> 0:14:25.400 in other words, the satellite maintains its relative position to 0:14:25.520 --> 0:14:29.600 the Earth throughout the full day. The satellite remains over 0:14:29.600 --> 0:14:33.360 the same general region of the Earth throughout the entirety 0:14:33.400 --> 0:14:36.160 of the day. Now we have to remember that the 0:14:36.200 --> 0:14:39.640 Earth also has a tilt to its axis, and this 0:14:39.720 --> 0:14:42.800 means that if a satellite is at this altitude but 0:14:42.920 --> 0:14:47.000 not directly over the equator, the satellite's position with reference 0:14:47.040 --> 0:14:50.160 to the Earth's surface will actually move north and south 0:14:50.200 --> 0:14:53.560 throughout the day. So it will still maintain its position 0:14:53.600 --> 0:14:56.480 with regard to longitude, that is, east and west. It's 0:14:56.480 --> 0:15:00.200 gonna remain in its same location east versus west, but 0:15:00.240 --> 0:15:05.720 it's latitudinal position north versus south that'll vary throughout the day. 0:15:05.920 --> 0:15:10.120 A geo stationary orbit is an orbit above the equator. 0:15:10.600 --> 0:15:14.440 That means there's a zero degree inclination with reference to 0:15:14.520 --> 0:15:18.120 the equator, and the satellite will remain over the same 0:15:18.120 --> 0:15:21.720 spot on the Earth's surface. But again, this only works 0:15:22.040 --> 0:15:25.280 if you are along the equator. This can get pretty 0:15:25.320 --> 0:15:28.000 congested like there's a There are a lot of reasons 0:15:28.000 --> 0:15:31.560 why you might want to put a satellite there so 0:15:31.600 --> 0:15:35.960 that it's over the same reference point on Earth throughout 0:15:36.040 --> 0:15:39.840 the day. But obviously there's a limited number of of 0:15:40.040 --> 0:15:43.280 orbits that you can put satellites in above the equator 0:15:43.440 --> 0:15:45.680 for one thing, you know, just to avoid things like 0:15:46.200 --> 0:15:51.960 communication interference, so it gets pretty tricky. Also, you you 0:15:52.120 --> 0:15:58.280 often will find countries that do have space programs getting 0:15:58.720 --> 0:16:03.160 treaties and agreement with countries that don't but are equatorial 0:16:03.280 --> 0:16:07.520 countries so that they can essentially get the rights to 0:16:07.640 --> 0:16:10.800 place a satellite above those countries. This is one of 0:16:10.800 --> 0:16:13.960 those cases where it's not just science and technology but 0:16:14.040 --> 0:16:18.880 politics that become important. And then you also have high 0:16:19.040 --> 0:16:22.040 Earth orbit was where we start to go beyond the 0:16:22.080 --> 0:16:26.480 geo stationary and geosynchronous orbits. We're talking about altitudes greater 0:16:26.520 --> 0:16:30.200 than thirty five thousand seven kilometers now way out here, 0:16:30.880 --> 0:16:34.680 you typically are talking about things like communications, satellites, um 0:16:34.720 --> 0:16:37.880 it can be other things too, but you know, you 0:16:37.920 --> 0:16:41.480 start to get limited in what useful stuff you can 0:16:41.520 --> 0:16:45.120 put out in this orbit. Oddly enough, when you go 0:16:45.240 --> 0:16:49.720 much further out you can find uh other really interesting 0:16:49.800 --> 0:16:52.240 uses like the James Webb Space Telescope. But we'll get 0:16:52.240 --> 0:16:56.360 there now. I mentioned geo stationary orbits, which requires the 0:16:56.360 --> 0:17:00.240 satellite to not only be above the mid Earth orbital age, 0:17:00.240 --> 0:17:04.679 but also over the equator ak zero inclination with reference 0:17:04.720 --> 0:17:08.320 to the equatorial plane. But we can classify other orbits 0:17:08.320 --> 0:17:14.080 by referencing inclination. For example, a polar orbit is one 0:17:14.119 --> 0:17:17.479 that passes over the North and South Pole over the 0:17:17.520 --> 0:17:21.639 course of its orbit, and this requires an inclination of 0:17:21.720 --> 0:17:24.560 ninety degrees. That is, it needs to be at a 0:17:24.680 --> 0:17:28.800 right angle with reference to the equator. And then you 0:17:28.880 --> 0:17:35.000 have sun synchronous orbits. Okay, so this gets really complicated, 0:17:35.000 --> 0:17:38.720 but I'll try and give you a very very high 0:17:38.800 --> 0:17:42.720 level view. Again. Another pun and you might want a 0:17:42.760 --> 0:17:46.440 satellite in a sun synchronous orbit to observe certain regions 0:17:46.480 --> 0:17:49.200 of the Earth, and you want the lighting of those 0:17:49.240 --> 0:17:53.440 regions to be consistent from one day to the next. Well, 0:17:53.480 --> 0:17:55.840 if you want to do that, you put a satellite 0:17:55.840 --> 0:18:00.520 in a polar sun synchronous orbit. This is an glinnation 0:18:00.680 --> 0:18:03.440 of about ninety eight degrees, so it's a little bit 0:18:03.480 --> 0:18:07.439 further out from a right angle, and a satellite in 0:18:07.480 --> 0:18:11.680 this orbit will orbit north south or depending upon your 0:18:11.680 --> 0:18:15.400 point of reference, south north around the Earth, and meanwhile 0:18:15.400 --> 0:18:21.280 the Earth is continuing to rotate east west below the satellite. Now, interestingly, 0:18:21.960 --> 0:18:26.200 the satellite's orbital path will also begin to rotate. In fact, 0:18:26.240 --> 0:18:30.439 that's actually crucial because if the orbital path did not rotate, 0:18:30.560 --> 0:18:31.960 you know, you can think of it like a hula 0:18:32.000 --> 0:18:35.960 hoop around a globe, where the hula hoop is going 0:18:36.080 --> 0:18:38.560 over the north and south pole, so it's vertical with 0:18:38.600 --> 0:18:42.960 respect to the globe. Then imagine that you would slowly 0:18:43.160 --> 0:18:47.360 twist the hula hoops so that it is actually orbiting 0:18:47.400 --> 0:18:50.719 the Earth that way as well. It's important because you 0:18:50.760 --> 0:18:53.120 have to remember the Earth is an orbit around the Sun. 0:18:53.280 --> 0:18:57.200 So in order for you to have a consistent satellite 0:18:57.240 --> 0:19:02.240 view with the same lighting over the same region each day, 0:19:02.680 --> 0:19:05.879 the orbit has to rotate, right, because the Earth is 0:19:05.880 --> 0:19:07.879 going around a circular path of the Sun. If the 0:19:08.000 --> 0:19:12.240 orbit didn't rotate, then you wouldn't have that effect of 0:19:12.320 --> 0:19:15.760 passing over the same region um at the same time 0:19:15.800 --> 0:19:19.760 of day each day. Now, the rotation of the orbit 0:19:19.880 --> 0:19:22.880 happens because the Earth is not a perfect sphere. It's 0:19:22.960 --> 0:19:26.280 a bit bigger around the equator and holy cats, I 0:19:26.280 --> 0:19:29.600 can totally relate to that. And so the equator region 0:19:29.960 --> 0:19:33.080 exerts the gravitational pull on the satellite that if no 0:19:33.160 --> 0:19:37.479 other physics were involved, would ultimately cause the satellite's orbit 0:19:37.880 --> 0:19:42.000 to drift into one that's over the equator. But due 0:19:42.000 --> 0:19:47.000 to the satellite's angular momentum, the satellites orbit doesn't tilt 0:19:47.160 --> 0:19:52.360 down to become equatorial. Instead, the whole orbit rotates. If 0:19:52.400 --> 0:19:55.000 you if you were to ever use a coin, and 0:19:55.160 --> 0:19:58.439 you've seen a coin start to do that that cool 0:19:58.640 --> 0:20:02.120 rotate thing on a table, like it's it's starting to fall, 0:20:02.119 --> 0:20:05.080 but it hasn't actually clattered flat on the table, but 0:20:05.160 --> 0:20:08.360 it's doing that thing where it's kind of rotating around, 0:20:08.680 --> 0:20:11.359 almost like a top. That's kind of what the orbit 0:20:11.440 --> 0:20:14.080 is doing. And the rotational speed of the Earth, the 0:20:14.160 --> 0:20:16.520 rotational speed of the orbit, and the period of the 0:20:16.640 --> 0:20:20.600 orbit line up so that the satellite will always pass 0:20:20.680 --> 0:20:23.320 over a specific spot on the Equator at the same 0:20:23.359 --> 0:20:26.840 time of day each day. So let's say it passes 0:20:27.040 --> 0:20:31.440 over Bogatam at three pm. Well that's gonna happen from 0:20:31.480 --> 0:20:34.920 there on out, So tomorrow it'll be overhead of Bogata 0:20:34.920 --> 0:20:36.960 at three pm, and the next day, and the next 0:20:37.040 --> 0:20:40.800 day and so on. Subsequent orbits throughout the day will 0:20:40.800 --> 0:20:44.000 have the satellite pass over different equatorial cities, like say 0:20:44.080 --> 0:20:48.640 Singapore or Nairobi, and it will always pass over those 0:20:49.040 --> 0:20:53.000 respective cities at the same time of day each day 0:20:53.080 --> 0:20:56.640 for that city. I'm not saying it will pass over Bogata, 0:20:56.760 --> 0:20:59.399 Singapore and Nairobi at three pm. That would be impossible, 0:20:59.440 --> 0:21:03.840 but that they will pass over uh those respective cities 0:21:03.880 --> 0:21:07.480 at the same time per day. And I realized that 0:21:07.480 --> 0:21:10.480 this gets really tricky to imagine. It's hard to explain 0:21:11.119 --> 0:21:15.679 without visual aids. So if you're having trouble getting a 0:21:15.720 --> 0:21:19.280 handle on polar Sun synchronous orbits, I recommend searching for 0:21:19.440 --> 0:21:23.840 videos that illustrate how they work. Also, I'm not even 0:21:23.880 --> 0:21:27.920 scratching the surface here as far as how complicated these get. 0:21:28.359 --> 0:21:30.919 If you really want to learn more, I recommend a 0:21:30.960 --> 0:21:35.119 paper by Ronald J. Bowaine, and it's titled A B 0:21:35.400 --> 0:21:40.280 C's of Sun Synchronous Orbit Mission Design. It is a 0:21:40.400 --> 0:21:45.200 really good paper that goes into the technical details. Anyway, 0:21:45.200 --> 0:21:47.679 you might wonder why we would even worry about getting 0:21:47.720 --> 0:21:49.760 that kind of information in the first place, Like what's 0:21:49.800 --> 0:21:52.080 the big deal. Why do we even care about getting 0:21:52.080 --> 0:21:55.560 a satellite out there to pass over the same part 0:21:55.640 --> 0:21:58.360 of the Earth at the same time of day each day. Well, 0:21:58.400 --> 0:22:01.280 one reason is that it helps us track changes in 0:22:01.320 --> 0:22:04.800 a region over time. This is particularly important as we 0:22:04.840 --> 0:22:08.239 examine the effects of climate change in that region. So 0:22:08.320 --> 0:22:11.399 you want as many factors to be the same in 0:22:11.440 --> 0:22:16.000 your observation so that any differences you see you can say, well, 0:22:16.040 --> 0:22:18.880 this clearly didn't show up because the satellite is passing 0:22:18.880 --> 0:22:21.240 over at a different time of day, so the lightings 0:22:21.280 --> 0:22:25.800 at a different angle instead, Uh, really reflective of actual 0:22:25.920 --> 0:22:29.080 changes that are happening on the ground. So keeping as 0:22:29.200 --> 0:22:34.360 much of your other factors consistent as possible is really important. 0:22:34.560 --> 0:22:37.280 Keeping in mind that obviously, like angles of light are 0:22:37.280 --> 0:22:41.080 going to change as the seasons change, but you know 0:22:41.200 --> 0:22:44.000 that's something you can you can factor in. Whereas like 0:22:44.200 --> 0:22:45.760 you want to be able to say, like, from one 0:22:45.800 --> 0:22:49.439 summer to the next, Oh, we've seen that, say the 0:22:49.480 --> 0:22:55.280 coastline of this region has changed dramatically, and potentially that's 0:22:55.320 --> 0:22:58.919 due to climate change. That's why you would need to 0:22:59.359 --> 0:23:01.840 have something like this so that you could draw those 0:23:01.920 --> 0:23:05.320 kind of conclusions. All Right, we've got more to say 0:23:05.359 --> 0:23:08.760 about orbits. I know it's just gonna keep on going 0:23:08.800 --> 0:23:11.440 around and around, because that's what orbits do. But before 0:23:11.440 --> 0:23:22.240 we get to that, let's take another quick break. Okay, 0:23:22.320 --> 0:23:26.959 so far, what I've described are you could essentially call 0:23:27.040 --> 0:23:30.520 them circular orbits. They don't have to be, but that's 0:23:30.520 --> 0:23:32.760 the way we typically imagine orbits, or at least the 0:23:32.760 --> 0:23:35.239 way I typically imagine an orbit is kind of like 0:23:35.280 --> 0:23:40.760 a circle around whatever body it's orbiting, so they more 0:23:40.840 --> 0:23:45.240 or less keep a a consistent distance from the the 0:23:45.400 --> 0:23:49.760 orbiting uh center, so Earth. In other words, like they 0:23:49.760 --> 0:23:52.480 would just keep a pretty consistent distance from the Earth. 0:23:52.480 --> 0:23:55.320 But orbits do not have to be perfectly circular, or 0:23:55.359 --> 0:24:00.440 even circular at all. You can have elliptical orbits, and 0:24:00.600 --> 0:24:04.480 an elliptical orbit is oval in shape, and this means 0:24:04.520 --> 0:24:09.440 that the satellite's distance from the Earth varies throughout its 0:24:09.520 --> 0:24:14.120 orbital path. That also means that the satellite's velocity will 0:24:14.240 --> 0:24:17.760 change as it orbits the Earth. So as the satellite 0:24:17.800 --> 0:24:21.320 is moving toward the Earth, its velocity will start to 0:24:21.359 --> 0:24:24.920 increase due to the Earth's gravitational pull, and as it 0:24:25.280 --> 0:24:29.119 moves away from the Earth, its velocity begins to slow 0:24:29.160 --> 0:24:32.359 down again because the Earth's gravity is pulling back on it. 0:24:32.920 --> 0:24:35.800 Now the low point of the orbit, so the part 0:24:35.840 --> 0:24:39.520 where the satellite is closest to the Earth is called 0:24:39.560 --> 0:24:44.600 the parage, the furthest point from the Earth is the apogee. 0:24:44.760 --> 0:24:47.680 That's the high point of the orbit. And a lot 0:24:47.680 --> 0:24:51.640 of communication satellites have an elliptical orbit. And you might 0:24:51.640 --> 0:24:55.200 wonder why, Well, because an elliptical orbit means that a 0:24:55.280 --> 0:24:58.560 satellite is going to travel over a specific region for 0:24:58.640 --> 0:25:03.840 a really long time as it moves through its apogee, right, 0:25:03.840 --> 0:25:05.960 because it's slow, and this is the part where it's 0:25:05.960 --> 0:25:08.600 for this from the Earth, So you can provide a 0:25:08.800 --> 0:25:13.840 long period of coverage UH using this kind of orbit. 0:25:14.119 --> 0:25:16.600 And then when it moves out of sight, when it's 0:25:16.640 --> 0:25:18.760 out of the line of sight, it's actually starting to 0:25:19.240 --> 0:25:22.680 approach its parage, so it speeds up, so it zips 0:25:22.720 --> 0:25:24.600 around the back of the Earth. So this way you 0:25:24.680 --> 0:25:30.679 have UH limited interruptions of coverage. And if you have 0:25:30.880 --> 0:25:33.760