SDS (Satellite Data System)
United States Air Force satellites, in Molniya-type
orbits, used to relay images from optical and digital reconnaissance
satellites. They also provide communications for Air Force units out of
range of geostationary communications satellites, via an AFSATCOM (Air Force
Satellite Communications System) transponder, and nuclear blast detection.
Six first-generation SDS satellites were launched from 1976 to 1987. SDS-1
had a mass of about 630kg, a cylindrical body about 4m long and 3m in diameter,
and a main transmitting antenna over 3m in diameter. SDS-2 satellites are
much larger, with a mass of about 3,000kg, and are equipped with several
big antennas and the HERITAGE infrared missile launch detection sensors.
Based on the TDRS-3 (Tracking and Data Relay
Satellite 3) design, they are built to fit inside the Space
Shuttle's payload bay. The first three were launched by the Shuttle
in 1989-92, and a fourth by a Titan IV in 1996. See also communications
AND SPACE PROBES