Quasar-12 (USA-137) (NROL-5)

The second-generation Quasar satellites, also known as SDS-2, continue the legacy of the Satellite Data System (SDS) developed by the United States Air Force. Serving as communication relays, these satellites transmit real-time data from US reconnaissance satellites and support communication needs for USAF aircraft and ground stations. Operating in similar elliptical orbits for polar coverage, they maintain communication with KH-11 satellites using a 60 GHz frequency payload. Launched after the first-generation satellites, the SDS-2 series likely incorporates advancements in technology and may feature enhancements in capabilities such as improved data transmission rates or additional onboard systems.