The Satellite Data System (SDS) is a system of United States military communications satellites. At least three generations have been used: SDS-1 from 1976 to 1987; SDS-2 from 1989 to 1996; SDS-3 from 1998 to the present. It is believed that these satellites were known by the code name Quasar. The first generation were named simply 'SDS', the second generation were named 'Quasar' and the third generation each carried their own designation names.
SDS satellites have a highly elliptical orbit, going from about 300 kilometers at perigee to roughly 39,000 km at apogee in order to allow communications with polar stations that cannot contact geosynchronous satellites. The high apogee meant that the polar regions were visible for long amounts of time, and only two satellites were required in order to achieve constant communications ability. In addition, two geostationary satellites appear to be part of the system. The SDS satellites were constructed by Hughes Aircraft Company.
The primary purpose of the SDS satellites is to relay imagery from low-flying reconnaissance satellites, notably the Keyhole optical reconnaissance and Lacrosse/Onyx radar reconnaissance satellites to ground stations in the United States.
Each SDS-1 satellite had 12 channels available for Ultra high frequency (UHF) communication. They were cylindrical in shape, roughly 25 ft (7.6 m) long. 980 watts of electrical power were available from solar panels and batteries. The SDS-1 had a mass of 630 kg (1,390 lb) and was launched on Titan-3B rockets. The SDS-1 satellites had similar orbits to the Air Force's Jumpseat ELINT satellites.
The SDS-2 is significantly more massive at 2,335 kg (5,148 lb), with three separate communication dishes, including one for a K-band downlink. Two dishes are 4.5 m (15 ft) in diameter, while the third is 2 m (6 ft 7 in) in diameter. The solar arrays generate 1238 watts of power. It is believed that the Space Shuttle has been used to launch several satellites, possibly on missions STS-28, STS-38, and STS-53. Other launches have used the Titan IV launch vehicle.
|Launch date||Launch vehicle||Launch site||Launch designation||Perigee||Apogee||Inclination||Remarks|
|2 June 1976||Titan III(34)B||VAFB, SLC-4W||N/A|
|6 August 1976||Titan III(34)B||VAFB, SLC-4W|
|5 August 1978||Titan III(34)B||VAFB, SLC-4W|
|13 December 1980||Titan III(34)B||VAFB]], SLC-4W|
|28 August 1984||Titan III(34)B||VAFB, SLC-4W|
|8 February 1985||Titan III(34)B||VAFB, SLC-4W|
|15 February 1987||Titan III(34)B||VAFB, SLC-4W|
|2 June 1989||Space Shuttle Columbia
|15 November 1990||Space Shuttle Atlantis
|KSC, LC-39A||Geosynchronous satellite, deployed along with Prowler and initially misidentified as a Magnum SIGINT spacecraft|
|2 December 1992||Space Shuttle Discovery
|3 July 1996||Titan IV(405)A||CCAFS, LC-40|
|29 January 1998||Atlas IIA||CCAFS, SLC-36A||NROL-5||Capricorn, Molniya orbit|
|6 December 2000||Atlas IIAS||CCAFS, SLC-36A||NROL-10||Great Bear, geosynchronous satellite at 10° West|
|11 October 2001||Atlas IIAS||CCAFS, SLC-36B||NROL-12||Aquilla, geosynchronous satellite at 144° West|
|31 August 2004||Atlas IIAS||CCAFS, SLC-36A||NROL-1||Nemesis, Molniya orbit, final Atlas II launch|
|10 December 2007||Atlas V 401||CCAFS, SLC-41||NROL-24||Scorpius, Molniya orbit|
|11 March 2011||Delta IV-M+(4,2)||CCAFS, SLC-37B||NROL-27||Gryphon, geosynchronous satellite at 10° West, replaced USA-155|
|20 June 2012||Atlas V 401||CCAFS, SLC-41||NROL-38||Drake, geosynchronous satellite at 144° West, replacement for USA-162|
|22 May 2014||Atlas V 401||CCAFS, SLC-41||NROL-33||Geosynchronous satellite|
|28 July 2016||Atlas V 421||CCAFS SLC-41||NROL-61||Spike, Geosynchronous orbit, might be a new generation |
|15 October 2017||Atlas V 421||CCAFS, SLC-41||NROL-52||Likely Geosynchronous orbit |