Satellite Data System (SDS) spacecraft are communication relay satellites for transmitting real-time data from US reconnaissance satellites (e.g. KH-11, Onyx, Topaz). They are also used for communications to USAF aircraft and connect the various ground stations of the Air Force Satellite Control Network (AFSCN). The spacecraft relay the downlinked data to a ground station at Fort Belvoir, Virginia.
These satellites are the fourth generation of the system, the SDS-4, which appears to use only the geostationary orbit and no longer the highly elliptical Molniya orbits of the earlier generations.
The code-name QUASAR has been confirmed by leaked budgets in 2013 to be associated with these satellites.
Note: The numbering is not sure, as it is not confirmed, how many first generation Quasar were launched.
Note: The NROL designations refer to the launch, not to the payload.
|Type / Application:||Comsat / Relay|
|Quasar 20 (SDS-4 1, USA 269, NROL 61) ?||2016-047A||28.07.2016||CC SLC-41||Atlas-5(421)¹|
|Quasar 21 (SDS-4 2, USA 279, NROL 52) ?||2017-066A||15.10.2017||CC SLC-41||Atlas-5(421)¹|