The DSCS III is the third generation of general purpose military communication satellites. The first DSCS III was launched in 1982. In contrast to its predecessors, DSCS III offers significantly greater capacity and longer life, and improved resistance to hostile activities such as jamming. The DSCS III satellite, which has a design life of ten years, is designed to support all three military services, and its signals can be received by ground antennas that range in diameter from 33 inches to 60 feet. Signals are broadcast on 6 channels between 7250 and 8400 MHz (television broadcasts between 54 MHz and 800 MHz). The satellite also carries a Single Channel Transponder (SCT) that is used to transmit Emergency Action Messages from the President to nuclear forces.
The DSCS III system is built with single- and multiple-beam antennas that provide more flexible coverage than its predecessors. Phase III satellites bring more capacity while providing greater assured communications through improved ability to resist jamming. Antenna design for DSCS III allows users to switch between fixed, Earth coverage, and multiple-beam antennas. The latter provides an Earth coverage beam as well as electrically steerable area and narrow-coverage beams. In addition, a steerable transmit dish antenna provides a spot beam with increased radiated power for users with small receivers. In this way, operators can tailor the communications beams to suit the needs of different size user terminals almost anywhere in the world.(1)
The Air Force began launching the more advanced Phase IIIs in 1982. Previous launch vehicles included Titan 34D/IUS and the Space Shuttle. The 3 October 1985 launch of the Space Shuttle "Atlantis" carried two Defense Satellite Communications System (DSCS-III) satellites, which were propelled to geosynchronous orbit, 22,500 miles above the Earth by an Inertial Upper Stage (IUS). Although NASA and the Defense Department continued their policy of not announcing the payloads of military flights of the Shuttle, the payload of the Atlantis was readily identifiable from public sources. An August 1981 Air Force Space Division fact sheet on the DSCS program stated that the "first launch of a DSCS III on the Shuttle is scheduled for mid-1985." A 1983 press report noted that a "crucial launch appears to be scheduled in 1985, when a pair of DSCS III's are to be launched from the Shuttle using and IUS booster."(2)In fact the STS-51J of October 1985 and STS- 38 of November 1990 and STS-53 of December 1992 launched the DSCA-III payloads. And another trade press report the following year noted that two DSCS III's would "be launched together next year on a single Space Shuttle mission, apparently on the Atlantis mission from the Cape in September."(3) Phase III satellites, with the Integrated Apogee Boost Subsystem (IABS), are currently configured to launch only on the Atlas II launch vehicle. The first Atlas II launch of a DSCS III IABS occurred on 10 February 1992. Additional launches of these satellites are planned at yearly intervals.
DSCS-3 spacecraft weigh 2,580 pounds, and have a design life of ten years, twice as long as the Phase IIs. The spacecraft's rectangular body is 6 feet x 6 feet x 7 feet; with a 38-foot span with solar arrays deployed. Phase III solar arrays generate 1,100 watts, decreasing to 837 watts after five years. Each DSCS III satellite costs about $100,000,000.
The DSCS program is managed by the Air Force Space Division in Los Angeles, CA. The prime contractor is Martin Marietta (formerly GE General Electric) Astro Space Division, of Valley Force, PA. Martin Marietta Astro Space (MMAS) provides DSCS III orbital operations support, including anomaly resolution based on detailed design knowledge, ground system unique software support, and telemetry analysis at Onizuka AS, CA and Falcon AFB, CO. The contractor maintains ground system mission unique software, on orbit spacecraft software, spacecraft simulator hardware and software and technical analyst workstation hardware and software. In addition, Astro Space conducts anomaly analysis and vehicle checkout based on telemetry data, DSCS III design and test histories.(4)
DSCS III satellites (Phase III), which are now used exclusively, were first placed in operation in 1983; nine are currently active (five primary and four reserve), and five are in inventory. The most recent launch was in October 1997 (B-13). Future DSCS III launches are tentatively scheduled for 1999 (B-8), 2000 (B-11), 2002 (B-6), and 2003 (A-3). DSCS III satellites, designed to provide SHF SATCOM capability through the year 2000 and beyond, are being placed in geosynchronous orbital positions 22,300 miles above the equator to provide coverage between 75 o north latitude and 75 o south latitude. The DSCS constellation provides communications services in each of the following five satellite areas: East Pacific (EPAC), West Atlantic (WLANT), East Atlantic (ELANT), Indian Ocean (IO), and West Pacific (WPAC).
DSCS III Footprint
There are two series of DSCS III satellites: A-series and B-series. The A-series are the first-generation DSCS III satellites. The B-series are newer and have received upgrades to various support subsystems and the communications subsystem (Note: Model A-3 awaiting launch will be upgraded and have the same capabilities as a B-series model). The essential difference between the A-series and B-series DCSC III satellites is in the single channel transponder (SCT) package. The A-series DSCS/ SCT has only the UHF downlink capability while the B-series DSCS/ SCT has both UHF and SHF downlink capability. Thus, when the Navy is operating over DSCS III B-series channel one, the regular communications channel will have to share the channel one traveling wave tube (TWT) power amplifier with the SCT community; however there is no power sharing required with the SCT community over the DSCS III A-series satellites. The DSCS III satellites are designed for an operational life span of 10 years.
Current DSCS Satellite Constellation
|East Pacific Primary||B-14||135W|
|East Pacific Reserve||A-1||130W|
|West Atlantic Primary||B-7||52.5W|
|West Atlantic Reserve||B-4||42.5W|
|East Atlantic Primary||B-12||12W|
|Indian Ocean Primary||B-10||60E|
|Indian Ocean Reserve||A-2||57E|
|West Pacific Primary||B-9||175E|
|West Pacific Reserve||B-5||180E|
DSCS III Satellite Capability. The DSCS III satellites provide substantial capability to support high-capacity links between all terminals and to permit AJ communications and control of the satellites during crisis and contingency situations. DSCS III satellites operate in the X-band region, providing uplink services in the 7900-8400 MHz band and downlink services in the 7250-7750 MHz band. The frequency spectrum is divided into six bands by the use of six limited-bandwidth transponders which are switchable between antennas by DSCS ground control. Communications performance is optimized by allowing these independent transponders to be connected to various types of antennas. This permits selection of Earth coverage (EC), area coverage (AC), spot coverage, grouping of channels with similar modulation, and antenna gain-to-noise temperature (G/ T) ratios to meet user needs. Any type of modulation or multiple access may be used since the transponders do not process or modulate the signals. The DSCS III satellites are three-axis stabilized (geostationary) vehicles that have a dry weight of 1,950 pounds and a maximum weight of 2,550 pounds with propellant. The dimensions of the satellite body are approximately 80 inches (6.5 feet) on each side and 460 inches (38 feet) in length, with solar arrays (SA) deployed. Communications antennas include a receive 61-beam multibeam antenna (MBA) and two transmit 19-beam MBAs, two receive and two transmit Earth coverage horns (ECH), and a transmit-only gimballed dish antenna (GDA). In addition, there is one transmit and one receive SCT UHF antenna.
|SATELLITE CHARACTERISTICS||DSCS III||DSCS III SLEP|
|Effective Isotropic Radiated Power (EIRP)||EC Beacon, 27 dBW
NC Beacon, 40 dBW
|EC Beacon, (TBD)
NC Beacon, (TBD)
|Power Output||40-watt RF, Channels 1 and 2
10-watt RF, Channels 3 through 6
|50-watt RF, Channels 1 through 6|
|EC Beacon 1 Frequency||7600 MHz||7600.000000 MHz|
|EC Beacon 2 Frequency||7604 MHz||7604.705882 MHz|
|Beacon EIRP||13 dBW||TBD|
|Satellite Weight||1,950 pounds
(2,550 pounds with propellant)
Length: 9.2 feet with panels
Width: 6.3 feet
Depth: 6.4 feet (no antenna tips)
Fully Extended: 38.1 feet
Length: 9.2 feet with panels
Width: 6.3 feet
Depth: 6.4 feet (no antenna tips)
Fully Extended: 38.1 feet
|Lifetime||10 Years||10 Years|
DSCS III Satellite Block Diagram
The six independent RF channels operate in the SHF band to relay telephone, data, wideband imagery, and secure digital signals. Figure 2-3 shows a typical DSCS III communications subsystem functional block diagram for an individual channel composed of the receive antenna, transponder, frequency standard, frequency generator, and transmit antenna. Figure 2-4 shows the functional relationship of each of the major components that make up the communications subsystem. The communications subsystem operates in the X-band region. The uplink and downlink frequency plan used in the DSCS III satellite Models A-1, A-2, B-4, B-5, and B-7 is illustrated in figure 2-5. Four of the six RF channels have 60-MHz bandwidth. Channel 3 has an 85-MHz bandwidth, and channel 6 has a 50-MHz bandwidth. The total usable bandwidth is 375 MHz. These six RF channels are arranged with uniform 25-MHz guard bands between them. Each uplink channel frequency is translated down by 725 MHz on the downlink with the exception of channel 6, which is translated by 200 MHz. The newer DSCS III satellites including B-9, B-10, B-12, and B-14 (and Models A-3, B-6, B-8, B-11 and B-13 awaiting launch) provide an improved satellite channelization with a total usable bandwidth of 405 MHz, as depicted in figure 2-6. Under this new frequency plan, the bandwidth of channels 2 and 4 is increased through a reduction in the size of the guard bands and a decrease in the bandwidth of channel 1. Channel 1 has a 50-MHz bandwidth; channel 2 has a 75-MHz bandwidth; and channel 4 has an 85-MHz bandwidth. There is a 15-MHz guard band between channels 1, 2, 3, and 4; and a 25-MHz guard band between channels 4, 5, and 6.
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