Why don’t satellites fall?

If you throw a stone straight ahead, it will fall to the ground. But if you could throw it fast enough that, as it falls, the Earth curves away beneath it, the stone would never fall. It would enter orbit. That’s the entire mechanism of satellites: a continuous fall that never ends.

In general relativity, bodies are not pulled by a “gravitational force” as Newton imagined — we’ve already explained that such a force doesn’t really exist. Instead, they move along geodesic paths — the “straight” (or not so straight…) lines of curved spacetime.

For the satellite itself, motion is uniform and straight: it feels no acceleration and moves at constant speed (that’s why astronauts on the ISS experience “microgravity”). For us on Earth, observing spacetime bending around our planet, the geodesic path appears circular or elliptical. It’s the same logic as with airplanes: when they fly, we think they move straight over the planet, but since the planet is spherical, the plane actually follows an arc.

The “work” is done during launch. The initial horizontal velocity at a specific altitude is what counterbalances the constant fall. In the vacuum of space there’s no friction to slow it down, so it can maintain its orbit for decades. Only satellites in very low altitudes (~300–400 km) need periodic adjustments, because there’s still a trace of atmospheric drag that gradually reduces their speed and eventually causes them to “fall” (orbital decay).

Orbital architecture is divided into three categories:

• Low Earth Orbit (LEO) – for observation and communication satellites.

• Medium Earth Orbit (MEO) – for GPS satellites.

• Geostationary Orbit (GEO) – for the “steady sentinels” that always watch the same point.

• 
  

Space up there is so vast that the odds of collision are incredibly small. Yet millions of pieces of space debris travel through that region and must be constantly tracked. If one comes too close, the satellite performs a small maneuver to correct its path.

The real risk is not that orbits will collapse on their own, but that debris will accumulate. In 1978, NASA’s Donald Kessler described a chain-reaction scenario: if two large objects collide, their fragments could strike others, triggering an exponential increase in debris. The result could render certain orbits practically unusable for decades.

The practical verification of general relativity

It’s seen most clearly in precision phenomena:

The clocks on GPS satellites run faster because of weaker gravity, yet slightly slower due to their high velocity (special relativity). The net difference is about 38 microseconds per day — without correction, positional accuracy would drift within minutes, and vehicles on Earth would deviate by several meters or even kilometers.

Satellites follow geodesic, not necessarily “perfectly circular,” orbits: they can be elliptical or exhibit perihelion precession, a purely relativistic effect.

Maybe our satellites are a bit like us: they remain in orbit not because they have endless fuel, but because once — long ago — they were given the right push. Since then, they’ve simply followed the invisible curve shaped by the pull of a distant center. Years may pass, they may encounter countless particles along their path, and yet they keep going.

And if you look up at the sky one night, you might wonder: perhaps we, too, in this invisible web of spacetime, do nothing more than search for the curve that keeps us in orbit around what we love.