It’s no secret: satellites power our world. Our phones, GPS, TV channels, and other modes of networking and navigation rely almost exclusively on orbiting satellites. But where are these man-made marvels situated? Do they fly slightly above the clouds or as far away as some asteroids?
The National Aeronautics and Space Administration (NASA) categorizes three primary regions of orbit—geostationary, medium earth, and low earth. These three slices of the sky comprise every satellite orbiting Earth, from the Hubble Space Telescope to the world’s first art satellite, ARTSAT.
Perhaps the most impactful haven for satellites is geostationary orbit (GEO), in which spacecraft remain fixed in one spot above Earth. For this to happen, satellites must orbit while traveling precisely as fast as the planet turns. This speed is obtained at a gravitational “sweet spot” exactly 42,164 km from Earth’s center—usually around 36,000 km above Earth’s uneven surface.
Geostationary orbit, illustrated by the European Space Agency.
Another condition must be met for geostationary orbit—satellites must follow the path of the equator, which is the only part of Earth presenting the same geographical locations to outer space as the planet turns. Away from the equator, Earth’s surface would seem to change wildly beneath the satellite. Consequently, there is only one geostationary orbit.
When you open your favorite weather app, you see data from satellites in geostationary orbit. These satellites analyze one segment of Earth to note cloud formation and weather trends over time. Similarly, your dad’s favorite TV channel is fueled by an antenna pointed at a geostationary satellite—an antenna which never has to be adjusted, since the satellite doesn’t seem to move. This makes geostationary satellites perfect for telecommunications.
If geostationary orbit is the first chapter of the book of satellites, other “sweet spots” called Lagrange points are important footnotes—or rather, headnotes, since Lagrange points are actually far above geostationary orbit. Lagrange points are places where satellites are pulled equally by the Earth and Sun, causing them to orbit the Sun in a kind of echo of Earth’s own orbit.
The Solar System’s Lagrange points (NASA illustration by Robert Simmon).
At each of the five Lagrange points, the Earth’s gravitational pull negates that of the Sun, and satellites orbit the Sun like another planet. But only two of these points—L4 and L5—are stable. At Lagrange points one through three, disturbances could send a satellite drifting away from a perfect Sun-centered orbit. This makes some Lagrange points less useful than others. For instance, a satellite at L3 would not even be able to communicate with Earth.
However, the extremely stable fourth and fifth points are like gravitational wells—a satellite will be pulled back to them if displaced.
Currently, L1 houses the Solar and Heliospheric Observatory (SOHO), an international “solar watchdog” designed to monitor the Sun while making slight adjustments to stay in course. Additionally, L2 is an excellent spot for current and future space telescopes. However, because of the fourth and fifth points’ far distance from Earth, no satellites have yet embraced their stable gravitational whirlpools.
On to Chapter Two of our imaginary handbook—medium earth orbit (MEO ), which comprises a large range of altitudes from 600 to over 22,000 miles high. If geostationary orbit is a ring, then medium earth orbit is like a many-layered sphere encompassing the planet. This sounds like a much larger structure, and it is—so many possible pathways fill the broad region of MEO that entire constellations of navigation satellites, such as the Galileo array pictured below, coexist with the Global Positioning System (GPS) fleet and other, more general orbits like the semi-synchronous and Molniya ones.
The Galileo system of European navigation satellites.
Semi-synchronous orbit is tilted enough from the equator to make use of the many pathways available in medium earth orbit, while still being reliable and predictable. Because of this, semi-synchronous orbit is used by GPS satellites. Another example of medium earth orbits is the Molniya orbit, invented by the Russians to examine the north and south poles. Tilted 63.4° from the equator, the Molniya orbit traces an oval far out into the night sky, slingshotting a satellite high above Earth to observe polar regions once every twelve hours.
The Molniya orbit, a displaced oval tilted 63.4° from the equator.
High and medium earth orbits are indeed useful, but most research satellites are parked in low earth orbit (LEO), a relatively thin shell underneath MEO. At 100 to 600 miles high, LEO presents faster orbital velocities due to increased proximity to Earth. This intimacy with ground control lends itself to space stations, which can quickly send and receive resources, and to imaging satellites, which can capture Earth’s surface in detail.
Low earth orbit and its freedom from the equator.
For comparison, the highest-flying commercial airplanes stay more than ten times closer to Earth. But this fact doesn’t prevent LEO satellites from racing their Boeing siblings in streaks across the sky—and winning. The International Space Station travels almost five miles per second, circling Earth about sixteen times each day.
In conclusion, each region of orbit presents unique benefits and challenges. Administrations such as NASA and the European Space Agency have examined solar wind, climate change, geography, and more using these little-known pockets of progress situated far above the clouds. As Earth turns and night bleeds into day, metal constellations follow our planet’s face into the light of the sun, the darkness of space, and back again—faithfully accompanying Earth on its cosmic journey.
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Images courtesy of the European Space Agency, Felix Barthel, and the National Aeronautics and Space Administration (NASA).