What is a satellite constellation?
A satellite constellation is a group of artificial satellites placed in complementary orbits so that, collectively, they provide uninterrupted coverage of a defined area — whether global, polar, or regional. Unlike a standalone satellite, a constellation is designed so that at least one satellite is always above the local horizon from any point within the service area.
Design principles
Constellation architects select orbital altitude, inclination, number of planes, and number of satellites per plane to balance coverage, revisit time, latency, and cost. Walker patterns — Walker-Star (polar planes) or Walker-Delta (inclined planes) — are the standard symmetric configurations. The number of satellites required scales inversely with altitude: a GEO-equivalent footprint at 550 km requires hundreds of satellites.
Types of constellations
Communications constellations (Starlink, OneWeb, Iridium) prioritise continuous coverage and low latency. Navigation constellations (GPS, Galileo, GLONASS) prioritise geometric diversity for accurate positioning. Earth observation constellations (Planet Labs, ICEYE, Spire) prioritise revisit rate — how often a satellite passes over the same point.
Handoff and inter-satellite links
As a LEO satellite moves out of range (~10 minutes per pass), service must transfer seamlessly to the next satellite in view. Modern constellations like Starlink achieve this through ground-network handoffs or, increasingly, through inter-satellite laser links (ISL) that route traffic across the constellation backbone without touching the ground.