Quasar-21 (USA-279) (NROL-52)

The fourth generation of Quasar satellites, also known as SDS-4, represents the latest evolution in the Satellite Data System (SDS) developed by the United States Air Force. Building upon the capabilities of previous generations, SDS-4 continues to serve as a critical communication relay for real-time data from US reconnaissance satellites and supports communication needs for USAF aircraft and ground stations. While specific details about SDS-4 remain classified, it likely incorporates state-of-the-art technology advancements to further improve data transmission rates, communication reliability, and overall performance.