Artificial Satellites

Eyes You'll Never See: The Many Uses of Artificial Satellites

Suggested time: one 60-minute class period (about 20 minutes to read, 40 minutes for questions)

1. Talking Across Oceans: Communication Satellites

Before 1962, a phone call between New York and London traveled through a fragile copper cable lying on the floor of the Atlantic Ocean — expensive, low-capacity, and one fishing anchor away from going dead. Communication satellites changed that by parking themselves in a geostationary orbit, a circular path 35,786 kilometers above the equator where a satellite's orbital period exactly matches Earth's 24-hour rotation. Because the satellite turns at the same rate the planet turns, it appears to hang motionlessly over one fixed spot on Earth — which means a dish on the ground can point at exactly one place in the sky, all day, every day, and never lose the signal. That single trick is what makes live international television, satellite radio, and long-distance internet backbones possible.

2. Knowing Exactly Where You Stand: GPS & Navigation

Global Positioning System satellites live in a lower, faster neighborhood: medium Earth orbit, about 20,200 kilometers up, circling the planet roughly twice a day. No single GPS satellite could tell you your location — the trick only works because a constellation of around 30 of them constantly broadcasts the exact time, and a receiver in your phone measures how long each signal took to arrive. Since radio waves travel at the speed of light, a difference of just a few billionths of a second changes the calculated distance to that satellite. By comparing its distance from four or more satellites at once, your phone solves a kind of three-dimensional puzzle and places that blue dot on the map, usually within a few meters. Farmers use the same system to steer tractors in perfectly straight rows; airlines use it to fly the shortest safe path between continents.

3. Watching Storms Before They Arrive: Weather & Earth-Observation Satellites

Tracking a hurricane requires two very different points of view, and meteorologists use two very different orbits to get them. Geostationary weather satellites (like NOAA's GOES series) sit at the same 35,786-kilometer altitude as communication satellites, staring at the same hemisphere every second of every day — perfect for watching a storm's motion build in real time. But that distance costs resolution: fine details blur out. So a second fleet of satellites flies in low Earth orbit, only 700–800 kilometers up, circling the entire planet in about 90 minutes along a path that passes near both poles. These polar-orbiting satellites cannot stare at one storm continuously, but every pass gives a sharper, closer look, and over a single day their paths sweep across the whole surface of the Earth, imaging every square kilometer of it. Combining both views is how a five-day hurricane forecast gets made.

4. Doing Science Above the Sky: Research Satellites

The same low-altitude neighborhood that hosts Earth-observation satellites is also home to orbiting laboratories built to look outward instead of down. The Hubble Space Telescope orbits about 540 kilometers up — close enough to be serviced by astronauts, but, more importantly, high enough to sit above almost all of Earth's atmosphere. That matters because the atmosphere that lets you breathe also blurs starlight, and it blocks entire bands of light (like most ultraviolet and infrared wavelengths) before they ever reach the ground. A telescope above that layer sees a sharper, more complete picture of the universe than any ground-based telescope ever could. The International Space Station, orbiting at a similar altitude, exists for a different kind of science: in continuous free-fall, it gives researchers a true microgravity laboratory for testing how fluids, flames, crystals, and the human body behave when weight is (almost) taken out of the equation.

Three orbital neighborhoods, one underlying rule: closer orbits move faster and see more detail but less area at once; farther orbits move slower (and, at exactly 35,786 km, stay locked over one spot) but see more of the Earth at once, at lower resolution.

5. One Physics Idea, Three Altitudes

Every one of these machines — whether it is relaying a phone call, guiding a tractor, watching a hurricane, or photographing a galaxy — is doing the exact same physics: falling. A satellite in orbit is constantly being pulled straight down by Earth's gravity, and it is also moving forward fast enough that the curve of its fall matches the curve of the Earth itself, so it never gets any closer to the ground. Gravity isn't fighting the orbit; gravity is the orbit — it supplies exactly the centripetal force needed to keep the satellite turning in a circle instead of flying off in a straight line. What changes from mission to mission is only the altitude, and altitude decides everything else: how fast the satellite must travel, how long it takes to circle the planet once, how much of Earth it can see at a given moment, and how much detail it can resolve. Engineers do not choose an orbit at random — they choose the altitude that fits the job.

Part 2: Analysis & Application Questions