Time of Flight from Optical Communications Signals on the Optical to Orion Demonstration

The Orion Artemis II Optical Communications System (informally, Optical to Orion (O2O)) demonstration will showcase standards-compliant High Photon Efficiency (HPE) optical communications for the first time on a crewed cislunar mission with Artemis II. In addition to the high data rate capability afforded by the optical signal, O2O uses the optical signal to enable a high-precision, synchronous, two-way telemetry ranging system for time of flight (ToF) measurement. In this paper we will describe the ToF system used for O2O, from the system architecture and algorithms, to simulations of predicted performance, and finally laboratory experiments of the system over several kilometers of fiber. We additionally describe a calibration technique in the ground terminal that eliminates the need for the measurement of multiple independent paths and test equipment delays. We show that the system enables high precision (< 100 ps) high accuracy (< 1 ns) ranging estimation over a wide variety of conditions.