How satellite orbits work: low Earth and geostationary orbits

A satellite stays in the sky because gravity is acting, not because gravity has ended. It keeps falling towards Earth while moving sideways fast enough to follow a path around the planet. This continuing fall provides a starting point for understanding low orbits, geostationary rings and constellations containing many satellites.

Algor's In Orbit lets you examine the distribution of objects and isolate different groups. Before interpreting the dots, read the date, category and scale. An orbital visualisation is a model based on a catalogue, rather than a photograph in which every marker retains the physical dimensions of its object.

Gravity continues to act

In an ideal circular orbit, gravity supplies the centripetal acceleration that continually changes the direction of velocity. A satellite can maintain its speed while its direction changes. Acceleration therefore means more than simply speeding up or slowing down.

Astronauts' apparent weightlessness in low orbit also comes from sharing free fall with their spacecraft. It does not demonstrate that gravitational force is zero. Imagine the astronaut and vehicle falling together: the supporting force normally felt through the floor is absent, while gravity still acts. This distinction explains why floating and orbiting are compatible with a substantial gravitational attraction.

Identify what the markers represent

The overview displays objects included in the catalogue being used. Depending on the filter, these can include active satellites, inactive objects and other tracked items. The visible total should not automatically be called the number of working satellites, and it does not necessarily include every fragment in space.

The screenshots reflect a particular data snapshot. A displayed count is not a live measurement at the moment you read this article. Markers are also enlarged to remain visible. A dense-looking band does not mean the objects touch, nor that their real sizes are comparable with Earth's radius. Establish the meaning of the symbols before drawing conclusions from their apparent density.

Altitude and period are connected

Consider an ideal circular orbit at an altitude of 400 km. Approximating Earth's radius as 6,371 km, the satellite's distance from Earth's centre is 6,371 + 400 = 6,771 km. Before opening Algor In Orbit, draw both distances: one starts at the surface, the other at the centre.

Orbital period increases with orbital radius. In a simple gravitational model, the square of the period is proportional to the cube of that radius.

A low orbit takes roughly an hour and a half to complete, with differences depending on altitude. A higher satellite does not necessarily move faster. For circular orbits, orbital speed decreases with distance from Earth's centre. Separating speed from period avoids the misleading assumption that a longer route must be completed more quickly. State which quantity you are comparing before interpreting an animation.

Now assume a rounded period of 90 minutes as a given value for this exercise. There are 1,440 minutes in 24 hours, so the satellite makes approximately 1,440 ÷ 90 = 16 revolutions. This does not mean it passes over the same city sixteen times: Earth rotates meanwhile, changing the orbit's relationship to locations on the ground.

Why a geostationary satellite appears fixed

A geostationary orbit is circular, lies in the equatorial plane and runs in the same direction as Earth's rotation. Its period matches the sidereal day, approximately 23 hours 56 minutes. At roughly 35,786 km above the equator, the satellite appears stationary relative to an observer on the ground.

It is not motionless in space or beyond gravity. It continuously orbits while maintaining the same apparent position relative to Earth's surface. A geosynchronous orbit has the appropriate period; being geostationary additionally requires the right shape and inclination. The two terms are therefore not interchangeable in every case.

Low-orbit constellations solve a different problem

The Starlink view illustrates how many satellites can occupy multiple orbital planes. In low orbit, an individual satellite does not remain above the same place. Maintaining coverage over time requires coordinated passes by different satellites, together with the wider network and ground infrastructure.

The shorter distance reduces signal propagation time compared with a geostationary path, with other factors equal. Actual service latency also depends on routing, network conditions and other factors. An orbital map is not a measurement of internet performance. Likewise, a catalogue count is not an up-to-date number of users receiving a service. Keep physical geometry separate from the additional systems required to provide connectivity.

Nearby dots do not establish a collision

Two markers can appear close because of perspective while occupying different depths. Evaluating a possible conjunction requires positions at the same time, velocities, uncertainties and dedicated analysis. Looking at a cloud of dots is not enough to estimate collision risk.

Instead, ask questions that match the representation: which orbital regions are occupied, how do inclinations differ, and what changes when you isolate a category? This lets the model explain the arrangement of orbital space without treating a single picture as evidence for a calculation it does not perform. If the question requires timing or uncertainty, identify that missing information explicitly.

Revise by comparing two orbits

Create a one-page study guide with altitude, period, apparent position relative to the ground and a possible use. Compare a low Earth orbit with a geostationary one, then explain why gravity is essential in both cases.

Close the map and answer: which satellite has the longer period, what conditions make one appear fixed, and what must you check before quoting a catalogue number? Explaining these answers means you are reading orbits as physical relationships rather than merely recognising coloured paths.

Sources and further reading

• ESA · Types of orbits