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.Jonathan's Space Report: NRO Satellite Names The first generation was named simply 'SDS', the second generation was named 'Quasar' and the third generation each had their own designations.Jonathan's Space Report: Satellite Catalogue

Orbital characteristics 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.

Mission 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.

SDS-1

Each SDS-1 satellite had 12 channels available for Ultra high frequency (UHF) communication. They were cylindrical in shape, roughly long. 980 watts of electrical power were available from solar panels and batteries. The SDS-1 had a mass of and was launched on Titan-3B rockets. The SDS-1 satellites had similar orbits to the Air Force's Jumpseat ELINT satellites.National Reconnaissance Office: "NRO Brochure circa 1997"

The partial declassification of JUMPSEAT in late 2025 revealed that USA-21, which had been previously attributed to SDS block 1, was the final JUMPSEAT launch.

It has been speculated that the early satellites served as data relays for the first KH-11 Kennen reconnaissance satellites.

SDS-2 The SDS-2 is significantly more massive at , with three separate communication dishes, including one for a K-band downlink. Two dishes are in diameter, while the third is 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.

Satellites Name COSPAR IDJonathan's Space Report: List of satellite launchesSATCAT № Launch date Launch vehicle Launch site Launch designation Perigee Apogee Inclination Remarks First generation OPS 7837 1976-050A08871 2 June 1976 Titan III(34)B VAFB, SLC-4W SDS F-1 380 km 39315 km 63.3 deg OPS 7940 1976-080A09270 6 August 1976 Titan III(34)B VAFB, SLC-4W SDS F-2 380 km 39315 km 63.3 deg OPS 7310 1978-075A10993 5 August 1978 Titan III(34)B VAFB, SLC-4W SDS F-3 380 km 39315 km 63.3 deg OPS 5805 1980-100A12093 13 December 1980 Titan III(34)B VAFB, SLC-4W USA-4 1984-091A15226 28 August 1984 Titan III(34)B VAFB, SLC-4W SDS F-5A USA-9 195-014A15546 8 February 1985 Titan III(34)B VAFB, SLC-4W USA-9 Second generation USA-40 1989-061B20167 2 June 1989 STS-28/Orbus-21S KSC, LC-39B N/A USA-67 1990-097B20963 15 November 1990 STS-38/Orbus-21S KSC, LC-39A Geosynchronous satellite, deployed along with Prowler and initially misidentified as a Magnum SIGINT spacecraft USA-89 1992-086B22518 2 December 1992 STS-53/Orbus-21S KSC, LC-39A USA-125 1996-038A23945 3 July 1996 Titan IV(405)A CCAFS, LC-40 Third generation USA-137 1998-005A25148 29 January 1998 Atlas IIA CCAFS, SLC-36A NROL-5 Capricorn, Molniya orbit USA-155 2000-080A26635 6 December 2000 Atlas IIAS CCAFS, SLC-36A NROL-10 Great Bear, geosynchronous satellite at 10° West USA-162 2001-046A26948 11 October 2001 Atlas IIAS CCAFS, SLC-36B NROL-12 Aquila, geosynchronous satellite at 144° West USA-179 2004-034A28384 31 August 2004 Atlas IIAS CCAFS, SLC-36A NROL-1 Nemesis, Molniya orbit, final Atlas II launch USA-198 2007-060A32378 10 December 2007 Atlas V 401 CCAFS, SLC-41 NROL-24 Scorpius, Molniya orbit USA-227 2011-011A37377 11 March 2011 Delta IV-M+(4,2) CCAFS, SLC-37B NROL-27 Gryphon, geosynchronous satellite at 10° West, replaced USA-155 USA-236 2012-033A38466 20 June 2012 Atlas V 401 CCAFS, SLC-41 NROL-38 Drake, geosynchronous satellite at 144° West, replacement for USA-162 USA-252 2014-027A39751 22 May 2014 Atlas V 401 CCAFS, SLC-41 NROL-33 Geosynchronous satellite USA-269 41724 28 July 2016 Atlas V 421 CCAFS SLC-41 NROL-61 Spike, Geosynchronous orbit, might be a new generation USA-279 42973 15 October 2017 Atlas V 421 CCAFS, SLC-41 NROL-52 Likely Geosynchronous orbit

References

Vick, Berman, Lindborg, Fellow (March 19, 1997) SDS-1 Military Communications Satellite Federation of American Scientists Accessed April 24, 2004 Vick, Berman, Lindborg, Fellow, Pike, Aftergood (March 19, 1997) SDS-2 Military Communications Satellite Federation of American Scientists Accessed April 24, 2004