Sensor Picket

A sensor picket is a satellite designed to track spacecraft traffic within a volume, such as a solar system, and report this back to its controllers.

Designed to be small and cheap, for easy mass production and deployment, pickets are often given black, radar-absorbent coating to make them hard to detect once placed in their orbits. They usually run off solar power, and have small thrusters for maneuvering.

Pickets provide one of the linchpins behind the common aphorism that "there ain't no stealth in space". By seeding picket satellites evenly around its solar system(s), a nation can track all spacecraft traffic occurring within—try as they might, engineers have never been able to hide million-degree fusion exhaust, and reactionless propulsion is nonforthcoming. While simple picket sensors are not enough to give detailed readings about the ships they track, they are sufficient for general traffic control and basic military intelligence on fleet movements. Data supplied from pickets is used to target more detailed sensors.

Sensor pickets were used extensively during the Second Interstellar Period, constituting star nations' front-line warning system against attack, and in the modern day are used by the Star Patrol and national law enforcement for traffic control.