The most recent space segment augmentation for Cospas-Sarsat is MEOSAR (Medium Earth Orbiting Search and Rescue). MEOSAR blends the advantages of the LEOSAR and GEOSAR systems, while avoiding the drawbacks. Over time there will be more than 70 MEOSAR satellites, and the MEOSAR system will become the dominant space-segment capability of Cospas-Sarsat. In addition to the large number of satellites, the MEOSAR system benefits from relatively large satellite footprints and sufficient satellite motion relative to a point on the ground to allow the use of Doppler measurements as part of the method of calculating a distress beacon's location. MEOSAR consists of SARR transponders aboard the following navigation-satellite constellations: the European Union's Galileo, Russia's Glonass, and the United States' Global Positioning System (GPS). With respect to GPS, experimental S-band payloads aboard 19 GPS Block IIR and GPS Block IIF satellites are used operationally by the Cospas-Sarsat System. GPS Block IIIA spacecraft with SAR payloads (also S-band) were launched on 23 December 2018, 22 August 2019 and 30 June 2020. The GPS Block IIIA SAR payloads are under test. GPS Block IIIF satellites are planned to have dedicated, operational L-band SAR payloads, with launches beginning around 2025. The GPS SAR system is known as the "Distress Alerting Satellite System" (DASS) by NASA.