Extreme background-rejection techniques for the ELROI optical satellite license plate

TL;DR

The paper presents advanced background-rejection techniques for the ELROI optical satellite license plate, enabling reliable identification of satellites from space using low-power optical signals and sophisticated data analysis methods.

Contribution

It introduces novel spectral and temporal filtering methods, including phase-recovery algorithms, to decode low-power optical signals from orbit with high background rejection.

Findings

Successful demonstration of background-rejection techniques in ground tests

Effective encoding and decoding of satellite IDs using optical signals

Validation of methods with simulated and experimental data

Abstract

The Extremely Low-Resource Optical Identifier (ELROI) is a concept for an autonomous, low-power optical "license plate" that can be attached to anything that goes into space. ELROI uses short, omnidirectional flashes of laser light to encode a unique ID number which can be read by a small ground telescope using a photon-counting sensor and innovative extreme background-rejection techniques. ELROI is smaller and lighter than a typical radio beacon, low-power enough to run on its own small solar cell, and can safely operate for the entire orbital lifetime of a satellite or debris object. The concept has been validated in ground tests, and orbital prototypes are scheduled for launch in 2018 and beyond. In this paper we focus on the details of the encoding scheme and data analysis that allow a milliwatt optical signal to be read from orbit. We describe the techniques of extreme background-rejection needed to achieve this, including spectral filtering and temporal filtering using a period- and phase-recovery algorithm, and discuss the requirements for an error-correcting code to encode the ID number. Worked examples with both simulated and experimental (long-range ground test) data illustrate the methods used. We present these techniques to describe a new optical communication concept, and to encourage others to consider observing and analyzing our upcoming test flights.