Satellite Data System (SDS) spacecraft are communication relay satellites for transmitting real-time data from US reconnaissance satellites (e.g. KH-11) in polar areas. They are also used for communications to USAF air craft on polar routes 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 third generation of the system, the SDS-3. Some of them (#1, #4, #5) are in highly elliptical Molniya orbits, but the other (#2, 3, 6, 7) have a geostationary position. Unlike the Trumpet Follow On Elint satellites, the SDS-3 satellites are not placed directly into the Molniya orbit, but use a lower apogee transfer orbit.
The code-name QUASAR has been suspected to be associated with these satellites.
There are reports, that the satellites launched from 2011 onwards might represent a fourth generation.
|Type / Application:||Comsat / Relay, early warning|
|Orbit:||Molniya Orbit (#1, #4, #5), GEO (#2, #3, #6, #7)|
|SDS-3 1 ? (USA 137, NROL 5)||29.01.1998||CC SLC-36A||Atlas-2A|
|SDS-3 2 (USA 155, NROL 10)||06.12.2000||CC SLC-36A||Atlas-2AS|
|SDS-3 3 (USA 162, NROL 12)||11.10.2001||CC SLC-36B||Atlas-2AS|
|SDS-3 4 (USA 179, NROL 1)||31.08.2004||CC SLC-36A||Atlas-2AS|
|SDS-3 5 (USA 198, NROL 24)||10.12.2007||CC SLC-41||Atlas-5(401)|
|SDS-3 6 (USA 227, NROL 27)||11.03.2011||CC SLC-37B||Delta-4M+(4,2)|
|SDS-3 7 (USA 236, NROL 38)||20.06.2012||CC SLC-41||Atlas-5(401)|