Satellite Data System


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

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

Orbital characteristicsEdit

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.[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 (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.[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 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

First generationEdit

OPS 7837 1976-050A
2 June 1976 Titan III(34)B VAFB, SLC-4W N/A
OPS 7940 1976-080A
6 August 1976 Titan III(34)B VAFB, SLC-4W
OPS 7310 1978-075A
5 August 1978 Titan III(34)B VAFB, SLC-4W
OPS 5805 1980-100A
13 December 1980 Titan III(34)B VAFB, SLC-4W
USA-4 1984-091A
28 August 1984 Titan III(34)B VAFB, SLC-4W
USA-9 195-014A
8 February 1985 Titan III(34)B VAFB, SLC-4W
USA-21 1987-015A
15 February 1987 Titan III(34)B VAFB, SLC-4W

Second generationEdit

USA-40 1989-061B
2 June 1989 Space Shuttle Columbia
USA-67 1990-097B
15 November 1990 Space Shuttle Atlantis
KSC, LC-39A Geosynchronous satellite, deployed along with Prowler and initially misidentified as a Magnum SIGINT spacecraft
USA-89 1992-086B
2 December 1992 Space Shuttle Discovery
USA-125 1996-038A
3 July 1996 Titan IV(405)A CCAFS, LC-40

Third generationEdit

USA-137 1998-005A
29 January 1998 Atlas IIA CCAFS, SLC-36A NROL-5 Capricorn, Molniya orbit
USA-155 2000-080A
6 December 2000 Atlas IIAS CCAFS, SLC-36A NROL-10 Great Bear, geosynchronous satellite at 10° West
USA-162 2001-046A
11 October 2001 Atlas IIAS CCAFS, SLC-36B NROL-12 Aquilla, geosynchronous satellite at 144° West
USA-179 2004-034A
31 August 2004 Atlas IIAS CCAFS, SLC-36A NROL-1 Nemesis, Molniya orbit, final Atlas II launch
USA-198 2007-060A
10 December 2007 Atlas V 401 CCAFS, SLC-41 NROL-24 Scorpius, Molniya orbit
USA-227 2011-011A
11 March 2011 Delta IV-M+(4,2) CCAFS, SLC-37B NROL-27 Gryphon, geosynchronous satellite at 10° West, replaced USA-155
USA-236 2012-033A
20 June 2012 Atlas V 401 CCAFS, SLC-41 NROL-38 Drake, geosynchronous satellite at 144° West, replacement for USA-162
USA-252 2014-027A
22 May 2014 Atlas V 401 CCAFS, SLC-41 NROL-33 Geosynchronous satellite
USA-269 2016-047A
28 July 2016 Atlas V 421 CCAFS SLC-41 NROL-61 Spike, Geosynchronous orbit, might be a new generation [7]
USA-279 2017-066A
15 October 2017 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. Boulder, Colorado: Westview Press. ISBN 9780813340593.
  4. ^ National Reconnaissance Office: "NRO Brochure circa 1997"[permanent dead link]
  5. ^ Day, Dwayne A. (26 February 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. 30 July 2016.
  8. ^ Graham, William (15 October 2017). "Atlas V finally launches with NROL-52". Retrieved 15 October 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