WEBVTT 00:00.000 --> 00:05.480 Why do we use satellites like these for long distance communication? 00:15.500 --> 00:24.280 Communicating with a satellite ranges from several buildings worth of highly specialized equipment to a couple hundred dollars worth of handheld amateur radio hardware. 00:24.280 --> 00:29.760 LEOSATs, only about 400 to 2,000 kilometers up, are even close by terrestrial standards. 00:29.760 --> 00:33.020 That means simple ham radios are often used to communicate with them. 00:33.020 --> 00:39.760 There's even one aboard the International Space Station that you can use to talk to the astronauts, if you catch them at the right time and they're not too busy. 00:39.760 --> 00:44.020 The complexity with communicating with LEO satellites is actually their orbital speed. 00:44.060 --> 00:50.320 LEOSATs are moving so quickly that we have to use antennas that track them as they move rapidly across the sky. 00:50.320 --> 00:57.320 This tracking can be really difficult due to the uncertainty of the satellite location and how fast they move in and out of view. 00:57.320 --> 01:01.780 A satellite coming in and out of view from horizon to horizon is called a pass. 01:01.780 --> 01:05.300 Passes are the only times that we can actually communicate with satellites. 01:05.300 --> 01:12.580 Management of LEO satellites especially revolves entirely around these concept of passes and maximizing their effectiveness. 01:12.580 --> 01:21.960 For instance, it doesn't help having an imaging satellite over the target location if you didn't have a pass before it got to that location to tell it to take that photo. 01:21.960 --> 01:27.640 Similarly, you have to wait until the next pass to be able to actually bring that data back down to ground. 01:27.640 --> 01:31.960 Passes are roughly about 5 to 10 minutes for LEO satellites. 01:31.960 --> 01:35.920 This duration changes drastically based on where the ground station is located. 01:35.920 --> 01:42.340 Near the equator, the Earth's rotation actually causes the ground station and the satellite to lose contact with each other faster. 01:42.340 --> 01:49.080 But near the poles, Earth's rotation is negligible and the satellite is actually in view for almost twice as long, if not more. 01:49.080 --> 01:54.620 Essentially, the higher the latitude of your ground station, the more useful your passes actually end up being. 01:54.620 --> 02:00.580 This is the most ground stations are located in the higher latitudes, even in the very hard to reach locations. 02:00.580 --> 02:06.820 One of the best examples of that is Svalbard, a Norwegian archipelago that's extremely close to the North Pole. 02:06.820 --> 02:13.420 It has over 100 commercial ground station antennas, making it the largest commercial ground station in the world.