LEO

LEO (low Earth orbit) is the region of orbits up to about 2,000 km above the Earth’s surface, where satellites circle the planet in roughly 90 to 127 minutes. In satellite internet, LEO refers to constellations of hundreds or thousands of satellites that deliver broadband with latency comparable to terrestrial networks, typically operating at altitudes between about 340 and 1,200 km.

LEO stands in contrast to geostationary orbit (GEO) at about 35,786 km, where a single satellite appears fixed in the sky, and to medium Earth orbit (MEO). The short distance to the ground reduces delay and path loss, but each satellite sees only a small area and passes overhead in minutes, so continuous service requires a large constellation and constant handovers.

How LEO satellite internet works

A LEO broadband system connects a user terminal on the ground to a satellite overhead, which relays traffic either down to a ground station (gateway) connected to the internet or across the constellation through inter-satellite links. Because each satellite moves at about 7.5 km/s, the terminal switches to a new satellite every few minutes.

User terminals therefore use electronically steered phased array antennas that track satellites without moving parts and switch beams within milliseconds. The network schedules these handovers centrally, so users experience a continuous connection with occasional brief interruptions.

Routing choices strongly affect latency. A bent-pipe design sends each signal straight back down to a nearby gateway, so gateways must exist within a few hundred kilometers of users. Laser inter-satellite links remove that dependency and can carry traffic across oceans in space, where light travels faster than in glass fiber, which can shorten some long-distance routes.

Real-world latency includes more than the orbital distance. Scheduling, queuing and the path from the gateway to the destination server add delay, so measured round-trip times are usually several times higher than the pure propagation time to the satellite.

Orbital parameters that shape LEO performance

Designers of LEO constellations choose altitude, inclination and the number of orbital planes to balance coverage, latency, capacity and cost. Lower orbits give shorter delay and smaller beam footprints, but satellites experience more atmospheric drag and need more of them to cover the globe.

Inclined orbits concentrate capacity over populated mid-latitudes, while polar or sun-synchronous orbits extend service to high latitudes. Most large constellations mix several orbital shells at different altitudes and inclinations.

LEO compared with MEO and GEO

The choice of orbit defines the basic trade-off between latency, coverage per satellite and system complexity. The table compares the three orbit classes used for communications.

GEO remains efficient for broadcasting and wide-area services, because one satellite covers about a third of the Earth. LEO wins for interactive applications such as video calls, gaming and cloud work, where the delay of a geostationary link is clearly noticeable.

Applications of LEO constellations

LEO broadband serves users that terrestrial networks reach poorly or not at all. The main markets differ in terminal type and in how much capacity each user needs.

Direct-to-cell satellites use larger antennas in orbit to reach unmodified phones, but the link budget is far tighter than with a dish, so data rates per user are much lower. Governments also back constellations such as IRIS² for secure and resilient communications.

Limitations and concerns

LEO broadband is not a universal replacement for fiber. Its capacity is shared within each beam, so performance depends on how many users subscribe in a given area, and operators may limit new sign-ups in congested cells.

• Obstructions: trees and buildings interrupt the moving line of sight and cause short dropouts.
• Weather: heavy rain attenuates Ku and especially Ka band signals.
• Space debris and collision risk: dense shells require active collision avoidance and controlled deorbiting.
• Astronomical interference: reflective satellites and radio emissions affect optical and radio astronomy.
• Spectrum coordination: LEO systems must avoid interfering with GEO networks and with each other.

A positive property of low orbits is natural decay: at the lowest broadband altitudes, a failed satellite reenters the atmosphere within a few years, which limits long-term debris compared with higher orbits.

The idea in brief

LEO means low Earth orbit, the space close to our planet. Satellites there fly only a few hundred kilometers up. That is much closer than traditional satellites that seem to hang still in the sky.

Because they are close, signals travel fast and internet feels quick. But each satellite races past in minutes. So companies launch thousands of satellites that pass the connection along, like runners in a relay.

A practical scenario

A farm 25 km from the nearest town has only a slow copper line. The owners install a LEO satellite terminal on a pole above the barn roof, clear of trees, and connect it to their home router. The app shows a clear view of the sky with no obstructions.

They now get download speeds of roughly 100-200 Mbit/s in the evening and latency of around 30-40 ms, which allows video calls with the farm’s accountant and remote monitoring of animal barns. During a heavy thunderstorm, speeds drop for a short time. Overall, the farm moves from barely usable internet to service close to urban broadband, without waiting years for fiber.