Defense Satellite Communications System

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The Defense Satellite Communications System ( DSCS ) is a satellite communications system used by the US armed forces for global communications between troop units. The DSCS program was coordinated by the Defense Communications Agency (DCA) and later the Defense Information Systems Agency (DISA).

From 1966 to 2003, 34 satellites of the first, 16 satellites of the second and 14 satellites of the third generation were launched.

The system Wideband Global SATCOM (WGS), originally planned as a temporary solution, will be launched as the successor system from 2007. Each of the WGS satellites has the same transmission capacity as the entire DSCS-III system.


Eight IDCSP satellites
Launch of the IDCSP 8-15 satellites on a Titan 3C rocket

The first generation of the system was put into orbit from 1966 under the name Initial Defense Communications Satellite Program ( IDCSP ).

Of Philco Ford satellite built each carrying an X-band - transponder with an omnidirectional antenna. Only IDSCP 19 carried an experimental antenna that was aimed at the earth. These were small satellites with a launch mass of only 45 kg, which were in an orbit with a period of 22.2 hours slightly below the geosynchronous orbit . In this orbit they drifted about 30 ° per day. This ensured that no place in the world would be without a satellite connection for a long time if one of the satellites failed.

The energy was supplied by solar cells that were located on the 26 surfaces of the polyhedral satellite body.

Up to eight satellites could be carried into near geostationary orbit with a Titan-3C , but the payload for most launches consisted of fewer IDCSP satellites and one or two experimental satellites. A total of 34 satellites were launched on five flights, 27 of which were successful. The takeoffs were from Cape Canaveral Air Force Station .

After the satellite constellation was taken into operational use, it was initially called the Interim Defense Satellite Communications System ( IDSCS ), later it was called DSCS I. During the Vietnam War , reconnaissance photos were transmitted using these satellites.

The concept of sub-synchronous orbit had not proven itself so well that it was adopted for the later generations of satellites, since the number of satellites required in the planned more complex systems would have massively increased costs.

satellite Start date rocket comment
IDCSP 1 - 7 June 16, 1966 Titanium-3C Success (7 satellites); together with GHz-1 started
IDCSP (8) - (14) August 26, 1966 Titanium-3C Bust (7 satellites); together with GHz-2 started
IDCSP 8 - 15 January 18, 1967 Titanium-3C Success (8 satellites)
IDCSP 16-19 July 1, 1967 Titanium-3C Success (4 satellites); together with DODGE and LES 5 launched
IDCSP 20-27 June 13, 1968 Titanium-3C Success (8 satellites)


DSCS-II satellite
Launch of DSCS-II satellites on a Titan-3 (23) C rocket

The second generation of the DSCS system consisted of real geostationary satellites. These satellites, built by TRW , had a launch mass of 521 kg each and were significantly larger than those of the previous system. They had a spin-stabilized body and an antenna platform that were steadily aligned with the earth. Two 20-watt X-band transponders were used for data transmission. Solar cells with an output of 535 watts, which were mounted on the cylindrical satellite body, were used to supply the satellites with energy . To hedge eclipses the DSCS II satellites had three NiCd - accumulators . A hydrazine drive system allowed corrections to the orbital position.

The satellites were launched in pairs with Titan-3 (23) C rockets. The last two units each started with a satellite of the subsequent DSCS III generation on more powerful Titan 34D rockets.

The operational constellation consisted of four satellites, which were stationed at the orbit positions 60 ° E, 175 ° E, 12 ° W and 135 ° W, as well as two replacement satellites, which were maneuvered to the respective positions if necessary.

satellite Start date rocket comment
DSCS II 1 (DSCS II A1) 3rd November 1971 Titan-3 (23) C success
DSCS II 3 (DSCS II B3) December 13, 1973 Titan-3 (23) C success
DSCS II 5 (DSCS II B5) May 20, 1975 Titan-3 (23) C Failure to reach low orbit
DSCS II 7 (DSCS II C7) May 12, 1977 Titan-3 (23) C success
DSCS II 9 (DSCS II C9) March 25, 1978 Titan-3 (23) C Failure
DSCS II 11 (DSCS II C11) December 14, 1978 Titan-3 (23) C success
DSCS II 13 (DSCS II D13) November 21, 1979 Titan-3 (23) C success
DSCS II 15 (DSCS II F16) October 30, 1982 Titan-34D IUS Success; started with DSCS III 1
DSCS II 16 (DSCS II E15) 4th September 1989 Titan-34D Transtage Success; started with DSCS III 4


DSCS III satellite
DSCS-III satellites in the payload bay of the space shuttle Atlantis ( STS-51-J )
Atlas 2 rocket with the DSCS III 7 satellite on the launch pad

The third generation satellites were manufactured by General Electric (later Martin Marietta and Lockheed Martin ). These were 1,235 kg heavy, triaxial stabilized satellites. The energy supply was ensured by two solar cell booms with an output of 1240 watts, which were protected by NiCd batteries. The planned lifespan of the third generation satellites was ten years, but most satellites exceeded this.

The communication systems of the DSCS III satellites consisted of six SHF transponders. Two global horn antennas and a 61-beam nulling antenna were used as receiving antennas. The transmitting antennas consisted of two horn antennas, two configurable 19-beam antennas and a swiveling parabolic antenna .

As part of the Service Life Enhancement Program (SLEP), the last four satellites were modified so that their data transmission rate was increased by 200%.

First, like their predecessors, the DSCS III satellites were launched in pairs, using both titanium rockets and the space shuttle . Upper stages were used in each case, which could transport the satellites directly into their geostationary orbit. When the space shuttle was no longer available for satellite transport after the Challenger catastrophe , the remaining satellites were transferred to Atlas II and later Delta IV rockets. Since these carrier systems were not able to carry out a direct injection into the geostationary orbit, the DSCS III satellites were given an additional upper stage with the IABS stage, which carried out this task.

satellite Start date rocket comment
DSCS III 1 (DSCS III A1) October 30, 1982 Titan-34D with IUS Success; started with DSCS II 15
DSCS III 2 (DSCS III B4) 3rd October 1985 Space Shuttle with IUS
( STS-51-J )
DSCS III 4 (DSCS III A2) 4th September 1989 Titan-34D Transtage Success; started with DSCS II 16
DSCS III 5 (DSCS III B14) February 11, 1992 Atlas-2 with IABS success
DSCS III 6 (DSCS III B12) 2nd July 1992 Atlas-2 with IABS success
DSCS III 7 (DSCS III B9) July 19, 1993 Atlas-2 with IABS success
DSCS III 8 (DSCS III B10) November 28, 1993 Atlas-2 with IABS success
DSCS III 9 (DSCS III B7) July 31, 1995 Atlas-2A with IABS success
DSCS III 10 (DSCS III B13) October 25, 1997 Atlas-2A with IABS success
DSCS III 11 (DSCS III B8) January 21, 2000 Atlas-2A with IABS success
DSCS III 12 (DSCS III B11) October 20, 2000 Atlas-2A with IABS success
DSCS III 13 (DSCS III A3) March 11, 2003 Delta IVM with IABS success
DSCS III 14 (DSCS III B6) August 29, 2003 Delta IVM with IABS success

Web links

Commons : Defense Satellite Communications System  - Collection of Pictures, Videos and Audio Files

Individual evidence

  1. ^ Pre-launch ops keep crews busy at the Cape . Spaceflight Now. Retrieved December 19, 2010.
  2. a b Directory of US Military Rockets and Missiles: TRW ES-4 DSCS II
  3. Federation of American Scientists - DSCS 3 ( Memento from August 1, 2012 in the web archive )
  4. Directory of US Military Rockets and Missiles: General Electric ES-5 DSCS III