Satellite Data System (SDS) spacecraft are communication relay satellites for transmiting real-time data from US reconnaissance satellites (KH-11 Kennen / Crystal) in polar area. 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 KH-11 data to a ground station at Fort Belvoir, Virginia.
The first generation SDS satellites were launched from 1976 to 1987. Technical details have not been officially published, so the following information might be based on speculation. The SDS-1 has a mass of about 628 kg, and possibly were based on a version of the Hughes spin stabilized Intelsat IV bus called HS-350. The main transmitting antenna of the SDS-1 was over 10 feet in diameter. The primary electrical power for the SDS-1 spacecraft was provided by solar charged batteries with a total of 980 watts of power. SDS-1 uses an elliptical 500 × 39200 km orbit at an inclination of 57° (Molniya-type) which have their apogee in the northern hemisphere for long relay durations in northern areas, which are not visible to geostationary satellites. A constellation of three SDS-1 satellites is needed for constant polar communications coverage. Each SDS-1 spacecraft had reportedly 12 communications channels in the ultra-high frequency bands.
The third and fourth satellite (and possibly later ones) were retrofitted with nuclear detection (NUDET) devices known as bhangmeters.
The code-name QUASAR has been confirmed by leaked budgets in 2013 to be associated with these satellites.
Note: The identification of these satellites beyond the third flight is not definitely confirmed. Some may be in fact Jumpseat SIGINT satellites.
|Type / Application:||Communication|
|Configuration:||HS-350 bus ?|
|Power:||Solar cells (body mounted), batteries|
|Mass:||628 kg ?|
|Orbit:||500 km × 39200 km, 57°|
|Quasar 1 (SDS 1, OPS 7837)||1976-050A||02.06.1976||Va SLC-4W||Titan-3(34)B Agena-D|
|Quasar 2 (SDS 2, OPS 7940)||1976-080A||06.08.1976||Va SLC-4W||Titan-3(34)B Agena-D|
|Quasar 3 (SDS 3, OPS 7310)||1978-075A||05.08.1978||Va SLC-4W||Titan-3(34)B Agena-D|
|Quasar 4 (SDS 4, OPS 5805)||1980-100A||13.12.1980||Va SLC-4W||Titan-3(34)B Agena-D|
|Quasar 5 (SDS 5, USA 4)||1984-091A||28.08.1984||Va SLC-4W||Titan-3(34)B Agena-D|
|Quasar 6 (SDS 6, USA 9)||1985-014A||08.02.1985||Va SLC-4W||Titan-3(34)B Agena-D|
|Quasar 7 (SDS 7, USA 21)||1987-015A||12.02.1987||Va SLC-4W||Titan-3(34)B Agena-D|