Alternative PNT from low-Earth orbit (LEO) satellites is being developed or proposed by various entities. Satelles delivers a fully operational Satellite Time and Location (STL) service to back up or augment GNSS, strengthening the resilience of critical infrastructure. This article details STL’s timing synchronization performance with different types of user equipment. PETE JOHNSON, TREVOR LANDON AND JEREMY SOMMER, SATELLES, INC. STL is a time-of-arrival (TOA) multilateration system offering three-dimensional (3D) positioning and timing using dedicated satellite signals, designed by Satelles for the Iridium satellite communication system. The STL signals are broadcast in the L band by Iridium’s 66-satellite LEO constellation at an orbital altitude of 780 km.