How Satellites Stay in Orbit

There are roughly 11,000 active satellites circling Earth right now, and another 3,000 that have stopped working but are still up there. Every one of them is falling. The difference between a falling satellite and a falling rock is that the satellite is moving sideways so fast that it keeps missing the ground. Understanding how that works is the key to understanding modern civilization’s infrastructure in the sky.

The short answer

A satellite stays in orbit because it has achieved a precise balance between two forces: Earth’s gravitational pull and its own forward velocity. Gravity tugs the satellite inward, while its momentum carries it forward. At the right speed, the satellite falls toward Earth at the same rate that the ground curves away beneath it. The result is an endless, self-perpetuating fall around the planet. As NASA explains, this balance is what defines an orbit, and it applies to every body in space, not just satellites.

The full picture

Gravity and forward velocity

Isaac Newton imagined firing a cannon from a mountaintop. Fire it slowly and the ball arcs up and comes back down. Fire it faster and it travels farther before landing. Fire it fast enough, and the ball would travel so far that the curvature of Earth becomes the limiting factor. The ball would still be falling toward the ground, but the ground would be curving away beneath it at the same rate. That is exactly what an orbit is.

For low Earth orbit, that required speed is roughly 28,000 kilometers per hour. At that velocity, a satellite completes one lap around the planet in about 90 minutes. No engine sustains this motion, once the satellite is released at the right speed and altitude. It simply keeps going because there is almost no air resistance to slow it down.

The higher the orbit, the slower the required speed. At geostationary altitude, about 35,786 kilometers above the equator, satellites travel at roughly 11,000 kilometers per hour. At that speed, they match Earth’s rotation exactly, so from the ground they appear to hang motionless in one spot. This is why geostationary satellites are the workhorses of weather forecasting, television broadcasting, and communications. Their fixed position means ground antennas do not need to track them across the sky.

Types of orbits

Not all orbits are the same. Different altitudes and inclinations, the angle relative to the equator, serve different purposes.

Low Earth orbit (LEO): Sitting roughly 200 to 2,000 kilometers up, LEO is the most crowded neighborhood in space. The International Space Station orbits here, as do many Earth observation satellites and, increasingly, large broadband constellations like SpaceX’s Starlink. The proximity to Earth means these satellites can take high-resolution images and transmit signals with minimal delay. The tradeoff is that at these altitudes, there is still enough atmosphere to cause gradual orbital decay. Satellites in very low LEO need occasional reboosting to stay aloft.

Medium Earth orbit (MEO): Between 2,000 and 35,786 kilometers, MEO is home primarily to navigation satellites, including the GPS constellation. At these altitudes, signals cover a wider area and fewer satellites are needed for global coverage compared to LEO.

Geostationary orbit (GEO): At exactly 35,786 kilometers above the equator, objects orbit at the same angular speed as Earth rotates. This synchronous relationship makes GEO invaluable for communications and weather monitoring. The main drawback is distance. Signals take about a quarter of a second to make the round trip, which matters for real-time applications, and the high altitude requires large, sensitive antennas on the ground.

Polar and Sun-synchronous orbits: Many Earth observation satellites use polar orbits, which pass over the poles as the planet rotates beneath them, enabling global coverage. Sun-synchronous orbits are a specific type of polar orbit timed so the satellite passes the same latitude at the same local solar time every orbit, which is essential for consistent lighting conditions in imagery.

Orbital mechanics and station-keeping

An orbit is not a perfect, immutable path. Several forces act on satellites over time, and left unchecked, they would gradually destabilize.

The atmosphere does not simply stop at a fixed altitude. The exosphere, the outermost layer of Earth’s atmosphere, extends hundreds of kilometers into space. Even at typical LEO altitudes, individual molecules are sparse but present. Over time, this drag saps a satellite’s velocity, causing the orbit to decay and the satellite to spiral inward. At LEO, most satellites experience enough drag to require reboosting every few weeks or months without active management.

Earth itself is not a perfect sphere. It bulges slightly at the equator and has uneven mass distribution beneath the surface. This causes gravitational variations that tug satellites out of their ideal paths. The European Space Agency details how these perturbations accumulate and why ground controllers must regularly calculate and execute correction maneuvers.

Solar radiation pressure, the gentle push from sunlight, also affects orbits, especially on satellites with large solar panels or irregular shapes. Over months and years, this pressure can change a satellite’s eccentricity, making its orbit more or less elliptical than intended.

To counter these effects, satellites carry small thrusters for station-keeping maneuvers. These are not engines for acceleration in the everyday sense. They fire briefly, perhaps once every few weeks or months, to nudge the satellite back to its correct orbit. A geostationary satellite might need one or two such corrections per month to stay within its allocated orbital slot, which is typically a box a few tens of kilometers wide. Letting it drift would eventually put it in conflict with neighboring satellites or take it outside its service footprint.

Why objects stay up for decades

The Moon is a satellite too, albeit an natural one, and it has been orbiting for over four billion years with no thrusters at all. The reason is that at sufficient altitude, perturbations become negligible. Geostationary orbit sits well above most atmospheric effects. Satellites there might require station-keeping only to counter the combined gravitational influence of the Sun, Moon, and Earth’s own bulge, which slowly pushes geostationary satellites toward one of two stable points above the equator.

At LEO, the situation is more urgent. The International Space Station, for example, orbits at roughly 420 kilometers and loses about two kilometers of altitude per month due to drag. Without regular reboosts from visiting cargo vehicles and its own engines, it would gradually descend and eventually reenter the atmosphere. In 2030, when the ISS is retired, it will be deliberately deorbited in a controlled maneuver to splash down in a remote stretch of the Pacific Ocean.

For defunct satellites that run out of fuel or fail electrically, there is no choice but to let orbital decay take its course. Most objects in LEO will naturally reenter within 25 years, due to an international guideline requiring operators to clear LEO within that timeframe after mission end. Large satellites in LEO that cannot be controlled are sometimes maneuvered to a slightly higher graveyard orbit rather than left to drift dangerously among active assets.

Why it matters

Satellites are not abstract scientific instruments. They underpin infrastructure that billions of people use every day without thinking about it.

GPS navigation, weather forecasts, television signals, internet connectivity for remote regions, phone calls that cross oceans: all depend on satellites maintaining their orbits precisely. When a satellite drifts from its assigned position, services degrade. When it fails entirely, replacements can take years and hundreds of millions of dollars to build and launch.

The growing population of orbital debris makes this more urgent. There are estimated to be over 27,000 pieces of debris larger than 10 centimeters currently tracked in Earth orbit, plus millions more too small to track but large enough to disable a satellite on impact. Each satellite that stays in orbit longer than intended, or that fails without a plan for disposal, adds to the collision risk. The Kessler syndrome, a cascading chain of collisions described in NASA’s orbital debris program, is a scenario where debris density becomes high enough that collisions trigger further collisions, rendering entire orbital regions unusable for generations.

Modern satellite design increasingly incorporates end-of-life planning, including onboard fuel reserves for final deorbit maneuvers and designs that allow for capture and removal. Regulatory pressure is building in the United States and internationally to make this the norm rather than the exception.

Common misconceptions

“Satellites hover in a fixed spot above a city.” Only geostationary satellites do this, and they must sit above the equator at 35,786 kilometers. LEO satellites pass overhead in minutes and do not stay still relative to any point on the ground. Your phone GPS does not track a fixed object in the sky; it triangulates position from a constellation of dozens of satellites moving overhead continuously.

“There is no gravity in space, so satellites float.” There is gravity everywhere in Earth orbit, roughly 90 percent of what it is at the surface. Astronauts on the ISS experience weightlessness not because gravity disappears, but because they and the station are in freefall together. They are falling around the planet, not floating without gravity.

“Once in orbit, a satellite stays there forever.” Orbits decay. Without occasional corrections, drag and gravitational perturbations will eventually bring any satellite back down. For satellites in LEO this can happen within years. For geostationary satellites it takes centuries, but without station-keeping they still drift from their assigned positions long before natural decay becomes an issue.

Key terms

Orbit: The curved path an object takes around a larger body, resulting from the balance between forward velocity and gravitational pull.

Low Earth orbit (LEO): The region roughly 200 to 2,000 kilometers above Earth, where most active satellites and the ISS operate, characterized by fast orbital periods and significant atmospheric drag.

Geostationary orbit (GEO): The circular orbit 35,786 kilometers above the equator where satellites match Earth’s rotation and appear stationary in the sky, used primarily for communications and weather monitoring.

Station-keeping: The small thruster burns used to correct a satellite’s orbit against decay from atmospheric drag, solar radiation pressure, and gravitational perturbations.

Orbital decay: The gradual loss of altitude and orbital energy caused primarily by atmospheric drag, eventually leading a satellite to reenter the atmosphere and burn up.