1 00:00:00,520 --> 00:00:03,560 Speaker 1: Welcome to brain Stuff from house Stuff works dot com 2 00:00:03,560 --> 00:00:14,240 Speaker 1: where smart Happens. Hi Am Marshall Brain with today's question, 3 00:00:14,560 --> 00:00:18,920 Speaker 1: how do satellites orbit the Earth? Satellites are to some 4 00:00:19,000 --> 00:00:24,000 Speaker 1: degree mysterious objects. They travel in space, which feels like 5 00:00:24,040 --> 00:00:26,880 Speaker 1: an exotic place because most of us have never been there. 6 00:00:27,280 --> 00:00:30,360 Speaker 1: They're so far away we can't see them. They usually 7 00:00:30,400 --> 00:00:33,640 Speaker 1: cost millions or billions of dollars, which means none of 8 00:00:33,720 --> 00:00:36,960 Speaker 1: us will ever own one personally, and so on. Orbital 9 00:00:37,040 --> 00:00:41,280 Speaker 1: mechanics can also be mysterious because there's no easy way 10 00:00:41,360 --> 00:00:45,400 Speaker 1: for us to experience orbital mechanics personally. However, with a 11 00:00:45,440 --> 00:00:49,440 Speaker 1: little imagination, you can understand the basic idea behind orbital 12 00:00:49,520 --> 00:00:53,200 Speaker 1: mechanics very easily. Think about what happens when you throw 13 00:00:53,240 --> 00:00:56,200 Speaker 1: a ball. Imagine that you're standing in a big field 14 00:00:56,320 --> 00:00:58,600 Speaker 1: and you throw a baseball as hard as you can, 15 00:00:58,760 --> 00:01:01,680 Speaker 1: like a picture. The ball might go a hundred feet 16 00:01:02,000 --> 00:01:05,440 Speaker 1: and then hit the ground. You put the ball into orbit. 17 00:01:05,560 --> 00:01:09,800 Speaker 1: It's just that the ball's orbit is very very short. Now, 18 00:01:09,880 --> 00:01:12,920 Speaker 1: imagine that you shot a rifle straightened level instead of 19 00:01:12,920 --> 00:01:16,560 Speaker 1: throwing a ball. The bullet might travel a mile before 20 00:01:16,600 --> 00:01:20,120 Speaker 1: succumbing to gravity and hitting the ground. Now, imagine that 21 00:01:20,160 --> 00:01:23,520 Speaker 1: you shoot a very large and powerful cannon that's able 22 00:01:23,520 --> 00:01:27,800 Speaker 1: to give its shell an extremely high initial velocity. Imagine 23 00:01:27,840 --> 00:01:30,880 Speaker 1: that the cannon is shot straight and level. The shell 24 00:01:31,040 --> 00:01:34,520 Speaker 1: is going to go many miles far enough to actually 25 00:01:34,640 --> 00:01:36,800 Speaker 1: follow the curve of the Earth for a period of 26 00:01:36,840 --> 00:01:40,959 Speaker 1: time before hitting the ground. One thing that gums these 27 00:01:40,959 --> 00:01:44,319 Speaker 1: examples up is air resistance. So imagine that you took 28 00:01:44,400 --> 00:01:47,480 Speaker 1: this powerful cannon to the Moon and you mounted it 29 00:01:47,560 --> 00:01:50,760 Speaker 1: on top of the highest mountain. The Moon has no 30 00:01:50,960 --> 00:01:54,840 Speaker 1: real atmosphere and is completely surrounded by the vacuum of space. 31 00:01:55,440 --> 00:01:58,400 Speaker 1: If you adjusted the speed of the shell just right 32 00:01:58,600 --> 00:02:02,160 Speaker 1: and shot the cannon, the shell would follow the curve 33 00:02:02,200 --> 00:02:05,680 Speaker 1: of the Moon perfectly. It would fall at exactly the 34 00:02:05,720 --> 00:02:08,760 Speaker 1: same rate that the curve of the Moon falls away 35 00:02:08,800 --> 00:02:12,960 Speaker 1: from it, so it would never actually hit the ground. Eventually, 36 00:02:13,040 --> 00:02:15,360 Speaker 1: it would curve all the way around the Moon and 37 00:02:15,520 --> 00:02:18,800 Speaker 1: ram right into the back of the cannon. On the Moon. 38 00:02:19,040 --> 00:02:22,840 Speaker 1: You could actually have satellites in extremely low orbits like 39 00:02:22,919 --> 00:02:25,600 Speaker 1: that just a few miles off the ground to avoid 40 00:02:25,639 --> 00:02:29,639 Speaker 1: the mountains, and the satellites could conceivably be launched from 41 00:02:29,680 --> 00:02:34,480 Speaker 1: powerful cannons on Earth. It's not so easy, because satellites 42 00:02:34,520 --> 00:02:37,440 Speaker 1: have to get up above the atmosphere and into the 43 00:02:37,480 --> 00:02:40,239 Speaker 1: vacuum of space to orbit for any length of time. 44 00:02:40,680 --> 00:02:45,360 Speaker 1: Two miles up is about the minimum to avoid atmospheric interference. 45 00:02:45,760 --> 00:02:49,040 Speaker 1: The Hubble Space Telescope orbits at an altitude of three 46 00:02:49,120 --> 00:02:52,639 Speaker 1: hundred eighty miles or so, but the principle is exactly 47 00:02:52,680 --> 00:02:56,400 Speaker 1: the same. The speed of the satellite is adjusted so 48 00:02:56,480 --> 00:02:59,519 Speaker 1: that it falls to Earth at exactly the same rate 49 00:02:59,600 --> 00:03:03,079 Speaker 1: that the curve of the Earth falls away from the satellite. 50 00:03:03,440 --> 00:03:07,360 Speaker 1: The satellite is perpetually falling, but it never hits the ground. 51 00:03:08,520 --> 00:03:11,399 Speaker 1: Do you have any ideas or suggestions for this podcast? 52 00:03:11,800 --> 00:03:14,440 Speaker 1: If so, please send me an email at podcast at 53 00:03:14,440 --> 00:03:17,160 Speaker 1: how stuff works dot com. For more on this and 54 00:03:17,240 --> 00:03:19,639 Speaker 1: thousands of other topics, go to how stuff works dot 55 00:03:19,680 --> 00:03:22,480 Speaker 1: com and be sure to check out the brain stuff 56 00:03:22,520 --> 00:03:25,000 Speaker 1: blog on the how stuff works dot com home page.