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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.³

SDS-1

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

SDS-2

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.

Satellites

• Spaceflight portal

• Vick, Berman, Lindborg, Fellow (March 19, 1997) SDS-1 Military Communications Satellite Archived 28 August 2016 at the Wayback Machine Federation of American Scientists Accessed April 24, 2004
• Vick, Berman, Lindborg, Fellow, Pike, Aftergood (March 19, 1997) SDS-2 Military Communications Satellite Archived 20 September 2016 at the Wayback Machine Federation of American Scientists Accessed April 24, 2004

References

1. Jonathan's Space Report: NRO Satellite Names http://planet4589.org/nro/nro.html ↩

2. Jonathan's Space Report: Satellite Catalogue http://planet4589.org/space/log/satcat.txt ↩

3. Richelson, J.T. (2001). The Wizards of Langley. Inside the CIA's Directorate of Science and Technology. Boulder, Colorado: Westview Press. ISBN 9780813340593. 9780813340593 ↩

4. National Reconnaissance Office: "NRO Brochure circa 1997"[permanent dead link] http://www.zianet.com/jpage/black/NRO%20Brochure.pdf ↩

5. Day, Dwayne A. (26 February 2018). "Shadow dancing: the Satellite Data System". The Space Review. http://www.thespacereview.com/article/3440/1 ↩

6. Jonathan's Space Report: List of satellite launches http://planet4589.org/space/log/ ↩

7. "NROL-61 satellite launched Thursday spotted in space by sky-watchers". Spaceflight Now. 30 July 2016. https://spaceflightnow.com/2016/07/30/nrol-61-satellite-launched-thursday-spotted-in-space-by-sky-watchers/ ↩

8. Graham, William (15 October 2017). "Atlas V finally launches with NROL-52". NASASpaceFlight.com. Retrieved 15 October 2017. https://www.nasaspaceflight.com/2017/10/ula-atlas-v-nrol-52-launch-cape-canaveral/ ↩