TRW ES-4 DSCS II

The second generation of operational communications satellites for the US military services, was named Defense Satellite Communications System (DSCS) II. Designated ES-4A, the satellites provided communication services from geostationary orbits. The 521 kg satellites were built by TRW, were fitted with two transponders operating in the 7/8 GHz band although later satellites carried six transponders. The satellites were launched in pairs and the operational constellation consisted of four satellites placed at 60°E, 175°E, 12°W and 135°W, as well as two in-orbit back-ups.

Image: Author's collection

ES-4A DSCS II-1 (1971-095A)

Launch dates of the DSCS II series

The next generation of DSCS satellites has been designated as ES-5A.

Background History

IDSCS

The first operational military communications satellite system was the Initial Defense Satellite Communications System (IDSCS) which commenced as a research and development project but was converted into a global operational network for high volume communications in 1968. It was initially known as the Initial Defense Communications Satellite Program (IDCSP).

The system consisted of a string of satellites which were in an orbit which was 90 minutes short of a geostationary orbit, drifting each day from west to east by 27.8° at altitudes of approximately 33,800 km. Built by Philco, each satellite, which had a mass of 45 kg, carried a single transponder operating at 7/8 Mhz.

Photo: Author's collection

IDSCS-1 (1966-053B)

Launch dates of the IDSCS series

Back to Directory of U.S. Military Rockets and Missiles, Appendix 3

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Last Updated: 22 February 2003