Defense Satellite Communications System

The Defense Satellite Communications System ( DSCS ) is a satellite communication system of the U.S. armed forces, which is used for global communication of military units. The DSCS program was coordinated by the Defense Communications Agency ( DCA) and later the Defense Information Systems Agency ( DISA ).

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

As a follow-up system was originally planned only as a transitional solution Wideband Global SATCOM ( WGS ) system is started from 2007. Each of the WGS satellites, the transmission capacity as the entire DSCS III system.

IDSCP

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

The built by Philco Ford satellites each wore an X -band transponder with an omni-directional antenna. Only IDSCP 19 was an experimental antenna has been aligned to the earth. These were to small satellites of only 45kg off mass that something were in an orbit with a period of 22.2 hours, below geosynchronous orbit. In this orbit, they drifted about 30 ° per day. This ensured that no place in the world was the failure of one of the satellites for a long time without satellite connection.

The power supply was effected by solar cells, which were on the 26 faces of the polyhedral satellite body.

Up to eight satellites could be worn with a titanium -3C in the nearly geostationary orbit, but the payload was at the most take-offs from less IDCSP satellites and one or two experimental satellites. A total of 34 satellites were launched in five flights, of which 27 successfully. The launches were made from the Cape Canaveral Air Force Station.

Once the satellite constellation was taken in an operational setting, it first was named Interim Defense Satellite Communications System ( IDSCS ), later it was called DSCS I. During the Vietnam War reconnaissance photos were transmitted via such satellites.

The concept of sub - synchronous orbit had not been so successful that it was adopted for the later generations of satellites, since the number of satellites required in the planned complex systems, the cost would be massively increase.

DSCS II

The second generation of DSCS system consisted of real geostationary satellite. These satellites were built by TRW with a launch mass of 521 kg each significantly greater than that of the previous system. They had a spin-stabilized body and an antenna platform that were continuously oriented towards the earth. Two 20 W X - band transponders were used for data transmission. For the power supply of the satellite were used solar cells with a power of 535 watts, which were mounted on the cylindrical satellite body. To hedge eclipses the DSCS II satellites had three NiCd batteries. A hydrazine propulsion system allowed corrections to the orbital position.

The satellites were launched in pairs with each Titan -3 ( 23 ) C missiles. The last two copies each started with a satellite of the following DSCS III- generation powerful Titan - 34D missiles.

The operational constellation consists of four satellites that were stationed on the orbit positions 60 ° E, 175 ° E, 12 ° W and 135 ° W and two spare satellites, which were maneuvered necessary, at the respective positions.

DSCS III

The satellites of the third generation were built by General Electric ( later Martin Marietta and Lockheed Martin) established. These were 1235 kg, three-axis stabilized satellites. The power supply was ensured by two solar boom of 1240 watts of power, which had been covered over NiCd batteries. The planned life of the satellites of the third generation was ten years but this was exceeded by most satellites.

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

As part of the Service Life Enhancement Program ( SLEP ) for the last four satellites have been modified so that its data transfer rate was increased by 200%.

First, the DSCS III satellites were like their predecessors in pairs started with both Titan rockets and the space shuttle were used. In each case, upper stages were used, which could carry the satellite directly into their geostationary orbit. When the space shuttle was no longer available for satellite transport after the Challenger disaster, the remaining satellites were rebooked on Atlas II and later Delta IV rocket. Since these carrier systems were not able to perform a direct injection into the geostationary orbit, the DSCS III satellites was given with the IABS stage an additional upper stage, which completed this task.