Nestled in the bucolic rolling beauty of the English Midlands, just off the M40 motorway on the border between the ancient counties of Northam ptonshire and Oxfordshire, sits the village of Croughton. The village itself has for the past eight centuries or so remained unremarkable, save for the comparatively recent presence of the Royal Air Force airfield built there in 1938.
Since 1950 this airfield has been home to the United States Air Force on long-term lease from the British government. Following the US Air Force acquisition flying activities at RAF Croughton (all airbases, even those in use by the US Air Force in Britain retain their 'RAF' prefix) ceased, the base instead being used by the US Air Force as a pivotal node in its global communications network, in particular hosting a receiver for the Department of Defense's Giant Talk/Scope Signal-III global High Frequency (HF) communications network. Today, the base retains its important role, processing around one-third of all American military communications in Europe with these services being provided by the 422nd Communications Squadron. The provision of strategic satcoms provides a key part of the squadron's mission today, with the large satellite antennae that the base accommodates visible from the nearby road.
Satcoms handled by the facility at RAF Croughton includes traffic utilizing the US Air Force's Milstar (Military Strategic and Tactical Relay) constellation of five spacecraft which was launched between 1994 and 2003. Although Six Milstar satellites were originally launched, one was rendered unserviceable after the upper stage failed to place the Milstar-3 satellite into the proper orbit. Secure voice and data communications are carried over the satellites at a rate of 75-2,400 bits-per-second (bps) for the two Block-I (Low Data Rate) satellites launched first, with this increasing to 4.8-kilobits-per-second (kbps) and as fast as 1.5 megabits-per-second for the following three Block-II (Medium Data Rate) spacecraft.
Despite the last of the Milstar satellites being launched at the beginning of this century, plans are already well underway to replace these spacecraft. At the heart of these efforts is the Advanced Extremely High Frequency (AEHF) constellation developed for the United States Air Force. AEHF will provide Satcom to the US armed forces, in addition to the armed forces of Canada, the Netherlands and the United Kingdom. Compared to the Milstar satellites that they replace, the AEHF spacecraft provide a significant increase in the amount of traffic that they can handle.
Northrop Grumman is building the Satcom payload for these satellites which the company says will typically be able to handle over 8.1mbps of traffic, while Lockheed Martin is building the bus and providing the ground control infrastructure as the AEHF prime contractor. Two AEHF satellites have already been launched, and a third has been delivered to the US Air Force ready for launch this year, possibly by September. Beyond this, work is ongoing on the fourth, fifth and sixth spacecraft which could reach the heavens in the 2016-2019 timeframe. One of the interesting design features of the AEHF spacecraft is that their Satcom payload uses Active Electronically Scanned Antenna technology. This enables the uplink and downlink of traffic, without a need to physically steer an antenna in the direction of a ground-based receiver or transmitter. Moreover, that technology allows the utilization of very narrow beams for Satcoms, which are less susceptible to interference, and therefore harder to jam. Northrop Grumman and Lockheed Martin are not the only two American defence contractors involved in the AEHF initiative.
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