The US Air Force's second generation classified Satellite Data System (SDS-2) replaced the SDS-1 system starting with its first launch in 1989. Like their predecessors, the SDS-2 spacecraft have high apogees and low perigees, enabling them to cover the polar regions for Air Force communications in those areas.
The Shuttle payload envelop has defined the satellite's design. The SDS-2 features two 15 foot diameter dish antennas adapted by Hughes from its TDRSS-3 satellite design. It also has a third dish (6.6 feet in diameter) that serves as a k-band antenna downlink. The SDS-2 has two more antennas, one that is used for uplink communications, and another that is a telemetry and command antenna, which is used as a back-up. The body itself, based on LEASAT, is cylindrical and is 14 feet in diameter and 9.5 feet long.
The development of the SDS began in 1973 by the Hughes Aircraft Company. The last of the SDS-1 satellites was launched in 1987. Hughes, however, has continued as the main contractor of the SDS-2 program. The SDS-2 program is operated by the Consolidated Space Test Center. (1)
The SDS-2 has a mass of 5,150 pounds when fueled. The satellite, which is flown on the same body of LEASAT, most likely has a similar lifespan of seven years. The SDS-2 solar arrays generate 1,238 watts of power with support from three 25-amp-hour nickel-cadium batteries.
The Space Shuttle and Titan IV have been the launch vehicles for the SDS-2, with a total of three successful launches out of three attempts. (Quite a bit of mystery surrounds these launches and satellites.) The first launch was on the 8th of August 1989 via STS 28. The second SDS-2 launch, via STS-53, occurred on the 2nd of December 1992. As of early 1997, the most recent launch took place on the 2nd of July 1996, using the "no upper stage" version of the Titan IV.
1. "Assured Missions Support Space Architecture (AMSSA) Study," Requirements, Vol. 3, December 1990, page 40.