Defense Satellite Communications System

The Defense Satellite Communications System (DSCS)[1] provides the United States with military communications to support globally distributed military users. Beginning in 2007, DSCS is being replaced by the Wideband Global SATCOM system. A total of 14 DSCS-III satellites were launched between the early 1980s and 2003. Two satellites were launched aboard the Space Shuttle Atlantis in 1985 during the STS-51-J flight. As of 23 November 2015, seven DSCS-III satellites were still operational.[2] DSCS operations are currently run by the 4th Space Operations Squadron out of Schriever Air Force Base.

Illustration of the DSCS III satellite

Background

DSCS went through three major phases — IDCSP (Interim Defense Communication Satellite Program), DSCS-II, and DSCS-III. Since the first launch, DSCS has been the "workhorse" of military satellite communications. All DSCS III satellites have exceeded their 10-year design life. The National Science Foundation use the DSCS satellites to provide additional bandwidth to Amundsen–Scott South Pole Station and McMurdo Station on Ross Island on the continent of Antarctica.[3]

IDCSP

In April 1960, the Advanced Research Projects Agency (ARPA) began work on the Advent program, which was intended to deliver a military communication satellite. The design concept proved too advanced for the technology of the time, and the program was cancelled in May 1962. IDCSP was one of two recommended follow up approaches to deliver a working satellite.

Philco (now Ford Aerospace) was contracted for the work. The IDCSP delivered a simple, spin-stabilized satellite placed into a sub-synchronous orbit that did not require station-keeping or active altitude control. The capacity was approximately 1 Mbit/s digital data.

The first launch of 7 satellites was conducted in June 1966. The system was declared operational with the 1968 launch, and renamed to Initial Defense Satellite Communication System (IDSCS).

A total of 34 IDSCS satellites were built, with 8 lost in a launch failure in August 1966.[4]

DSCS II
Illustration of a DSCS II satellite
Overview of DSCS II, circa 1977

DSCS II, developed under Program 777[5] provided secure voice and data transmission for the United States Armed Forces. The program was managed by the Defense Communications Agency (DCA), now the Defense Information Systems Agency.

The space vehicles were spin stabilized with a de-spun antenna platform. The body was mounted with solar cells, which produced 535 watts. Three NiCd batteries provided electrical power and it was supported by a hydrazine propulsion subsystem.

The communications payload included two 20-watt X band channels. The transponders were supported by steerable narrow beam antennas and drive mechanism for communications privacy.

The first DSCS II launch was in 1971.[6]

DSCS III

On 12 December 1975 research and development contracts were awarded to General Electric and Hughes Aircraft Company.[7] to begin DSCS III design studies, with the first Block 1 launch on 30 October 1982.[4]

DSCS III satellites support globally distributed Department of Defense (DoD) and national security users. The final 4 of 14 satellites received Service Life Enhancement Program (SLEP) modifications. These changes provided substantial capacity improvements through higher power amplifiers, more sensitive receivers, and additional antenna connectivity options. The DSCS communications payload includes six independent Super High Frequency (SHF) transponder channels that cover a 500 MHz bandwidth. Three receive and five transmit antennas provide selectable options for Earth coverage, area coverage and/or spot beam coverage. A special purpose single-channel transponder is also on board.[8]

DSCS III Spacecraft
Spacecraft Name Other Designation Launch date/time (UTC) NSSDCA/COSPAR ID Rocket Status/Remarks
DSCS III-01 DSCS III-A1 1982-10-30, 04:05:00 1982-106B Titan 34D Decommissioned/Launched with DSCS II-16
USA-11 DSCS III-B4 1985-10-03, 15:15:30 1985-092B Space Shuttle Atlantis
USA-12 DSCS III-B5 1985-10-03, 15:15:30 1985-092C Space Shuttle Atlantis
USA-43 DSCS III-06 or DSCS III-A2 1989-09-04, 05:54:00 1989-069A Titan 34D
USA-44 DSCS III-07 1989-09-04, 05:54:00 1989-069B Titan 34D
USA-78 DSCS III-08 1993-07-19, 22:04:00 1993-046A Atlas II
USA-82 DSCS III-09 1993-07-19, 22:04:00 1993-046A Atlas II
USA-93 DSCS III-10 1993-07-19, 22:04:00 1993-046A Atlas II
USA-97 DSCS III-11 1993-11-28, 23:40:00 1993-074A Atlas II
USA-113 DSCS III-B7 1995-07-31, 23:30:00 1995-038A Atlas IIA
USA-134 DSCS III-B13 1997-10-25, 00:46:00 1997-065A Atlas IIA
USA-148 DSCS III-B11 2000-01-25, 01:03:00 UTC 2000-001A Atlas IIA
USA-167 DSCS III-A3 2003-03-11, 00:59:00 UTC 2003-008A Delta IV
USA-170 DSCS III-B6 2003-08-29, 23:13:00 UTC 2003-040A Delta IV
  • DSCS-2 diagram
  • DSCS-3 diagram
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See also

References
  1. Burroughs, William E. (1986). Deep Black. New York: Berkley Publishing Group. pp. 187. ISBN 0-425-10879-1.
  2. "DSCS III Constellation". Air Force Fact Sheet. Archived from the original on 27 April 2017. Retrieved 26 April 2017.
  3. "DSCS III use for Antarctica". Amundsen-Scott South Pole Station. Archived from the original on 27 April 2017. Retrieved 26 April 2017.
  4. Martin, Donald H. (1986). Communication Satellites 1958-1988. El Segundo: Aerospace Corp. p. 285.
  5. Martin, Donald H. (2000). Communication Satellites. AIAA. ISBN 9781884989094.
  6. "DSCS II". Encyclopedia Astronautica. Archived from the original on 26 June 2017. Retrieved 27 April 2017.
  7. Fiscal year 1977 authorization for military procurement, pt. 6, p. 3769.
  8. "DSCS III". Air Force Fact Sheet. Archived from the original on 27 April 2017. Retrieved 26 April 2017.

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