Satellite Data System


The current SDS-3 constellation, consisting of three Molniya orbit type and two geostationary satellites

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.[1] The first generation were named simply 'SDS', the second generation were named 'Quasar' and the third generation each carried their own designation names.[2]

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.


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.[3]


Releasable Picture of NRO satellite, possible SDS-1
The SDS 3-4 satellite (USA 179, 2004-034A) created a tiny trail perpendicular to the star trails in this 10 second exposure with a Zeiss Sonnar MC 2.8/180mm lens made by amateur satellite observer Marco Langbroek

Each SDS-1 satellite had 12 channels available for ultra-high frequency communication. They were cylindrical in shape, roughly 25 feet (7.6 m) long. 980 watts of electrical power were available from solar panels and batteries.

The SDS-1 had a mass of 1385 pounds (630 kilograms) and was launched on Titan-3B rockets. The SDS-1 satellites had similar orbits to the Air Force's Jumpseat ELINT satellites.[4]

It has been speculated that the early satellites served as data relays for the first KH-11 Kennen reconnaissance satellites.[5]


The SDS-2 is significantly more massive at 5150 pounds (2335 kg), with three separate communication dishes, including one for a K band downlink. Two dishes are 15 feet (4.5 meters) in diameter, while the third is 6.6 feet (2 m) 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-4 rocket.



Launch date Launch vehicle Launch site Launch designation Perigee Apogee Inclination Remarks

First generation

OPS 7837 1976-050A
1976-06-02 Titan III(34)B VAFB SLC-4W N/A
OPS 7940 1976-080A
1976-08-06 Titan III(34)B VAFB SLC-4W
OPS 7310 1978-075A
1978-08-05 Titan III(34)B VAFB SLC-4W
OPS 5805 1980-100A
1980-12-13 Titan III(34)B VAFB SLC-4W
USA-4 1984-091A
1984-08-28 Titan III(34)B VAFB SLC-4W
USA-9 195-014A
1985-02-08 Titan III(34)B VAFB SLC-4W
USA-21 1987-015A
1987-02-15 Titan III(34)B VAFB SLC-4W

Second generation

USA-40 1989-061B
1989-06-02 Space Shuttle Columbia
USA-67 1990-097B
1990-11-15 Space Shuttle Atlantis
KSC LC-39A Geosynchronous satellite, deployed along with Prowler and initially misidentified as a Magnum SIGINT spacecraft
USA-89 1992-086B
1992-12-02 Space Shuttle Discovery
USA-125 1996-038A
1996-07-03 Titan IV(405)A CCAFS LC-40

Third generation

USA-137 1998-005A
1998-01-29 Atlas IIA CCAFS SLC-36A NROL-5 Capricorn, Molniya orbit
USA-155 2000-080A
2000-12-06 Atlas IIAS CCAFS SLC-36A NROL-10 Great Bear, geosynchronous satellite at 10° West
USA-162 2001-046A
2001-10-11 Atlas IIAS CCAFS SLC-36B NROL-12 Aquilla, geosynchronous satellite at 144° West
USA-179 2004-034A
2004-08-31 Atlas IIAS CCAFS SLC-36A NROL-1 Nemesis, Molniya orbit, final Atlas II launch
USA-198 2007-060A
2007-12-10 Atlas V 401 CCAFS SLC-41 NROL-24 Scorpius, Molniya orbit
USA-227 2011-011A
2011-03-11 Delta IV-M+(4,2) CCAFS SLC-37B NROL-27 Gryphon, geosynchronous satellite at 10° West, replaced USA-155
USA-236 2012-033A
2012-06-20 Atlas V 401 CCAFS SLC-41 NROL-38 Drake, geosynchronous satellite at 144° West, replacement for USA-162
USA-252 2014-027A
2014-05-22 Atlas V 401 CCAFS SLC-41 NROL-33 Geosynchronous satellite
USA-269 2016-047A
2016-07-28 Atlas V 421 CCAFS SLC-41 NROL-61 Spike, Geosynchronous orbit, might be a new generation[7]
USA-279 2017-066A
2017-10-15 Atlas V 421 CCAFS SLC-41 NROL-52 Likely Geosynchronous orbit[8]


  1. ^ Jonathan's Space Report: NRO Satellite Names
  2. ^ Jonathan's Space Report: Satellite Catalogue
  3. ^ Richelson J.T., 2001: The Wizards of Langley. Inside the CIA's Directorate of Science and Technology. Westview press, Boulder
  4. ^ National Reconnaissance Office: "NRO Brochure circa 1997"[permanent dead link]
  5. ^ Day, Dwayne A. (February 26, 2018). "Shadow dancing: the Satellite Data System". The Space Review.
  6. ^ Jonathan's Space Report: List of satellite launches
  7. ^ "NROL-61 satellite launched Thursday spotted in space by sky-watchers". Spaceflight Now. July 30, 2016.
  8. ^ Graham, William (October 15, 2017). "Atlas V finally launches with NROL-52". Retrieved October 15, 2017.
  • 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.