Satellite Data System
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The Satellite Data System (SDS) is a system of United States military communications satellites. At least two generations have been used: SDS-1 from July 1976 to November 1995, and SDS-2 from 1989 to the present. 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. The SDS satellites have been constructed by Hughes.
Each SDS-1 satellite had 12 channels available for ultra-high frequency communication. They were cylindrical in shape, roughly 25 feet 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.
SDS-1 satellites may have also facilitated communication with KH-11 reconnaissance satellites. Additionally, some believe that early SDS-1 birds may have been used to intercept transmissions to the Russian Molniya satellite, as the two had similar orbital paths.
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 meters) in diameter. The solar arrays generate 1238 watts of power. It is believed that the Space Shuttle has been used to launch one or two satellites, possibly one on STS-28, and another on STS-53. Other launches have used the Titan-4 rocket.
References
- Vick, Berman, Lindborg, Fellow (March 19, 1997). SDS-1 Military Communications Satellite (http://www.fas.org/spp/military/program/com/sds_1.htm). Federation of American Scientists. Accessed April 24, 2004.
- Vick, Berman, Lindborg, Fellow, Pike, Aftergood (March 19, 1997). SDS-2 Military Communications Satellite (http://www.fas.org/spp/military/program/com/sds_2.htm). Federation of American Scientists. Accessed April 24, 2004.