Artificial satellites, the thousands of human-made objects orbiting our planet, exist within defined, stacked regions of space known as orbital zones. These zones are precisely calculated distances from Earth where the laws of physics allow an object to maintain a stable path. The distance of any given satellite is determined entirely by its purpose, with different tasks requiring different speeds and altitudes to function effectively. This tiered structure ranges from a mere 160 kilometers to tens of thousands of kilometers into space.
The Closest Zone: Low Earth Orbit
Low Earth Orbit (LEO) is the closest and most densely populated region, ranging from about 160 kilometers up to 2,000 kilometers above the surface. This proximity is appealing because it requires the least energy to reach and allows for the clearest observations of the planet. To avoid being pulled back to Earth by gravity, objects in LEO must travel at high speeds, with orbital velocities around 7.8 kilometers per second.
This high speed results in a short orbital period, meaning a satellite in LEO can circle the globe in as little as 90 to 120 minutes. The International Space Station (ISS), for example, maintains an altitude between 400 and 420 kilometers, completing about 16 orbits every day. Due to the limited view of the Earth, communication and internet services, such as Starlink, require thousands of satellites to ensure continuous global coverage.
LEO is also preferred for Earth observation and reconnaissance, as being closer allows imaging satellites to capture high-resolution photos and collect detailed data. Satellites here encounter traces of the Earth’s atmosphere, which creates atmospheric drag. This drag constantly pulls the satellites downward, meaning they must periodically fire onboard thrusters to boost themselves back into a stable orbit.
The Middle Ground: Medium Earth Orbit
The region between LEO and Geostationary Orbit is Medium Earth Orbit (MEO), extending from 2,000 kilometers up to the GEO altitude of 35,786 kilometers. This intermediate zone balances the low latency of LEO and the wide coverage area of higher orbits. Unlike LEO, satellites in MEO are far enough away to avoid significant atmospheric drag, reducing the need for frequent orbital corrections.
MEO is dominated by global navigation systems, most notably the Global Positioning System (GPS) constellation. GPS satellites operate in a semi-synchronous orbit at approximately 20,200 kilometers above the Earth. At this distance, the satellites complete an orbit in exactly 12 hours, meaning they pass over the same two points on the Earth’s surface every day.
This 12-hour period allows ground receivers to predictably access signals from multiple satellites, which is necessary for accurate location and timing calculations. Other global navigation systems, such as GLONASS and Galileo, utilize similarly specific MEO altitudes. The greater distance compared to LEO means MEO satellites have a larger footprint, allowing fewer satellites to provide comprehensive coverage.
The Farthest Zone: Geostationary Orbit
The farthest orbital path is Geostationary Orbit (GEO), located at a precise altitude of 35,786 kilometers above the Earth’s equator. This distance is unique because it is the only altitude where a satellite’s orbital period exactly matches the 23-hour, 56-minute period of the Earth’s rotation. A satellite placed in GEO thus appears to hover motionless over a fixed point on the planet’s surface.
This stationary appearance makes GEO an ideal location for communication and broadcast satellites, as ground-based dish antennas do not need to move to track them. Television providers and weather monitoring agencies rely on GEO satellites to provide continuous coverage of broad regions, with just three satellites capable of covering nearly the entire globe. However, the immense distance results in a noticeable signal delay, or latency, of a quarter-second or more for a round trip signal.
The GEO belt is considered a finite resource, and international agreements regulate the specific “slots” above the equator to prevent signal interference. Satellites placed at this altitude have a field of view covering about 43% of the Earth’s surface. This fixed position and wide view make them indispensable for long-distance telecommunications and continuous meteorological observation.
Defining the Orbital Sweet Spot
The differences in distance across the orbital zones are governed by a fundamental balance between the Earth’s gravitational pull and the satellite’s forward motion, or inertia. This relationship dictates that the speed required for a stable orbit is inversely proportional to its altitude. The closer a satellite is to Earth, the faster it must travel to resist the planet’s strong gravitational force.
A satellite maintains its orbit because it is continuously falling toward the Earth, but its forward speed is so high that the curvature of its fall matches the curvature of the planet. In the LEO zone, gravity is strongest, necessitating the fastest speeds to ensure the satellite does not fall back into the atmosphere. As a satellite moves farther out, the gravitational pull weakens, allowing the satellite to maintain a stable path at progressively slower speeds.
The GEO altitude of 35,786 kilometers is the point where the gravitational force has weakened just enough that the required orbital speed naturally results in a period of 24 hours. This principle of balancing centripetal force, provided by gravity, with the satellite’s inertial tendency, defines every functional altitude in use. Engineers select a specific orbital distance, or “sweet spot,” based on the speed and coverage area a mission needs.