A laser inter-satellite link is an optical communications connection between two satellites, routing data through space at up to hundreds of gigabits per second without touching the ground. Mega-constellations use them to carry traffic across regions with no gateway coverage — oceans, poles and remote land.
Understanding Laser Inter-Satellite Link
Why lasers instead of radio
Three reasons: bandwidth, beamwidth and licensing. An optical carrier at ~1550 nm offers vastly more usable bandwidth than any radio band. The transmitted beam is extremely narrow, so links are hard to intercept or jam and cause no interference — which is also why no ITU spectrum coordination is needed. The cost is pointing difficulty: hitting a dinner-plate-sized receiver on a spacecraft thousands of kilometres away requires microradian-class pointing, maintained continuously as both satellites move.
From demonstration to backbone
Optical crosslinks were demonstrated experimentally for decades — including NASA's Laser Communications Relay Demonstration and ESA's European Data Relay System, which routes imagery from LEO satellites to geostationary relays at 1.8 Gbps — before Starlink made them a mass-produced commodity, flying thousands of terminals. The technology has become a defining feature of second-generation constellation design, turning fleets of individual satellites into orbiting mesh networks.