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0	5480	Why do we use satellites like these for long distance communication?
15500	19860	Communicating with a satellite ranges from several buildings worth of highly specialized
19860	24280	equipment to a couple hundred dollars worth of handheld amateur radio hardware.
24280	29760	LEOSATs, only about 400 to 2,000 kilometers up, are even close by terrestrial standards.
29760	33600	That means simple ham radios are often used to communicate with them. There's even one
33600	37260	aboard the International Space Station that you can use to talk to the astronauts,
37260	39760	if you catch them at the right time and they're not too busy.
39760	44020	The complexity with communicating with LEO satellites is actually their orbital speed.
44060	48740	LEOSATs are moving so quickly that we have to use antennas that track them as they move
48740	53020	rapidly across the sky. This tracking can be really difficult due to the uncertainty
53020	57320	of the satellite location and how fast they move in and out of view.
57320	62100	A satellite coming in and out of view from horizon to horizon is called a pass. Passes
62100	66900	are the only times that we can actually communicate with satellites. Management of LEO satellites
66900	72580	especially revolves entirely around these concept of passes and maximizing their effectiveness.
72580	77960	For instance, it doesn't help having an imaging satellite over the target location if you didn't
77960	82560	have a pass before it got to that location to tell it to take that photo. Similarly,
82560	87640	you have to wait until the next pass to be able to actually bring that data back down to ground.
87640	93040	Passes are roughly about 5 to 10 minutes for LEO satellites. This duration changes
93040	97260	drastically based on where the ground station is located. Near the equator, the Earth's
97260	101500	rotation actually causes the ground station and the satellite to lose contact with each
101500	105700	other faster. But near the poles, Earth's rotation is negligible and the satellite is
105700	110700	actually in view for almost twice as long, if not more. Essentially, the higher the latitude
110700	115120	of your ground station, the more useful your passes actually end up being. This is the
115120	119700	most ground stations are located in the higher latitudes, even in the very hard to reach
119700	125000	locations. One of the best examples of that is Svalbard, a Norwegian archipelago that's
125000	130380	extremely close to the North Pole. It has over 100 commercial ground station antennas,
130380	133420	making it the largest commercial ground station in the world.