This derived product set consists of Global Navigation Satellite System Ultra-Rapid Earth Rotation Product (ERP) from the NASA Crustal Dynamics Data Information System (CDDIS). GNSS provide autonomous geo-spatial positioning with global coverage. GNSS data sets from ground receivers at the CDDIS consist primarily of the data from the U.S. Global Positioning System (GPS) and the Russian GLObal NAvigation Satellite System (GLONASS). Since 2011, the CDDIS GNSS archive includes data from other GNSS (Europe’s Galileo, China’s Beidou, Japan’s Quasi-Zenith Satellite System/QZSS, the Indian Regional Navigation Satellite System/IRNSS, and worldwide Satellite Based Augmentation Systems/SBASs), which are similar to the U.S. GPS in terms of the satellite constellation, orbits, and signal structure. Analysis Centers (ACs) of the International GNSS Service (IGS) retrieve GNSS data on regular schedules to produce GNSS Earth Rotation products. The IGS Analysis Center Coordinator (ACC) uses these individual AC solutions to generate the official IGS ultra-rapid combined ERP products. The ultra-rapid ERP combination is a sub-daily solution, released four times per day, at 03:00, 09:00, 15:00, and 21:00 UTC (prior to GPS week 1267 they were released twice daily). IGS ultra-rapid ERP files are to be used with the IGS ultra-rapid orbit solution files. All ERP solution files utilize the IGS ERP format.