Defense

New Air Force satellites protect, improve space-based communications

The Air Force launched two programs last week that it hopes will protect and greatly improve satellite communications for civilian and military use.

Comment on this article in The Forum.On April 16, the Air Force launched a satellite carrying instruments that, among other things, can measure disturbances, called scintillations, in the Earth's ionosphere. The scintillations can degrade radio signals or knock out communications from military satellites such as the Ultra-High Frequency Satellite Communications System, which Navy ships and ground forces use, as well as degrade positioning signals from Global Positioning System satellites, according to Laila Jeong, program manager at the integrated experiments and evaluation division of the space vehicles directorate of Air Force Research Laboratory at Kirtland Air Force Base, N.M.

Depending on the extent of the turbulence -- which is experienced as signal noise that can degrade data throughput -- communications at a given frequency range could experience a minor degradation or a total outage, Jeong said. The impact of the turbulence could have a "significant" impact on positioning signals from GPS satellites, but she declined to provide specifics.

The instruments aboard the Communication/Navigation Outage Forecasting System satellite, which was built by General Dynamics, will enable space weather forecasters to predict up to six hours ahead of time the effect scintillations will have on signals from satellites operating at or below the 2.5-gigahertz frequency band, Jeong said.

Forecasters will use the satellite to predict which frequency bands will be mostand least affected by the ionospheric turbulence. The new satellite's ability to predict space weather will provide flexibility for Defense, which has become increasingly dependent on space-based communications, Jeong said.

In a separate move, the Air Force 3rd Space Operations Squadron at Schriever Air Force Base in Colorado Springs, Colo., took over operational control of the Boeing-built Wideband Global Satcom satellite on April 15. Col. Tracy Patton, the squadron's director of operations, said the wideband satellite has more capacity than the nine older in-orbit satellites that make up the Defense Satellite Communications System.

Mark Spiwak, Boeing's Wideband Global Satcom program manager, said the new satellite can support data transmissions at a rate of between 2.4 and 3.6 gigabits per second -- that's six to nine times the data rate of the average home high-speed Internet connection in the Washington area. A single satellite in the Defense Satellite Communications System has a rate of 250 megabits per second.

Patton said if a fighter pilot wanted to download images of a potential target using the new satellite, it would provide that image in about 20 seconds. Using the older satellites, the pilot had to wait 20 minutes.

The Wideband Global Satcom system operates in the X-band (8-to-12 GHz), which is used by the Defense Satellite Communications System satellites, as well as the Ka-band (27-to-40 GHz). That higher frequency allows Defense to install smaller terminals, roughly the size of the commercial DirecTV satellite dish, which is slightly larger than a dinner plate, Spiwak said.

Boeing has $1.8 billion to launch a total of six of the wideband satellites between up to early 2011.

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// August 27
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