  Space object identification is vital for operating spacecraft, space traffic
control, and space situational awareness, but initial determination,
maintenance, and recovery of identity are all difficult, expensive, and
error-prone, especially for small objects like CubeSats. Attaching a beacon or
license plate with a unique identification number to a space object before
launch would greatly simplify the task, but radio beacons are power-hungry and
can cause interference. This paper describes a new concept for a satellite
license plate, the Extremely Low Resource Optical Identifier or ELROI. ELROI is
a milliwatt-scale self-powered autonomous optical beacon that can be attached
to any space object to transmit a persistent identification signal to ground
stations. A system appropriate for a LEO CubeSat or other small space object
can fit in a package with the area of a postage stamp and a few millimeters
thick, and requires no power, data, or control from the host object. The
concept has been validated with ground tests, and the first flight test unit is
scheduled for launch in 2018. The unique identification number of a LEO
satellite can be determined unambiguously in a single orbital pass over a
low-cost ground station.
