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Raytheon Sentinel R1
for the Royal Air Force
By Karl Schwarz
While NATO is still struggling to finally get its Euro 3.3 billion Allied Ground Surveillance (AGS) programme off the ground, Raytheon's Airborne Stand-Off Radar (ASTOR) is on the home stretch. After seven years' development time (including 14 months' slippage) the Royal Air Force should receive its first Sentinel R1 and associated ground stations over the next few weeks.
To operate the five battlefield surveillance aircraft on order, No. 5 (Army Co-operation) Squadron was re-formed in Waddington back in April 2004. Since then it has been making thorough preparations for the entry into service of capabilities that are completely new to the British forces. The simplest task was to organise conversion training for the cockpit crews on the Bombardier Global Express long-range business jet, which serves as the platform for Sentinel. As well as pure flying, in the military version the pilot and co-pilot will have additional tasks such as managing the radio equipment and the Link 16 datalink. They will also be responsible for the extensive electronic self-defence system to be supplied by BAE Systems, with radar and guided missile warning sensors, chaff dispensers and a towed decoy.
The actual surveillance task will be performed by a three-person team in the cabin, comprising one mission commander and two image interpreters who sit at the Compaq consoles with huge Barco colour displays installed down the left-hand side. These are operated with keyboard and mouse, the user interface behaving as per normal Windows principles. Depending on the requirement, they can display data pertaining to control of the radar, processed imagery and information regarding what requests have been submitted.
The Sentinel R1 will of course not be operating in a vacuum, but will be deployed on behalf of the ground forces, which can request information via the ground stations. Hence, Army personnel sit next to the RAF specialists in the cabin. It is already clear today that the Sentinel will be much in demand, for example, in Afghanistan and Iraq. But it is necessary first to work out precisely how these new assets will be deployed. At any rate, there is sufficient flexibility available. Thanks to extensive radio equipment including SATCOM antenna on the forward fuselage, the Sentinel can send its data halfway round the world to Waddington virtually in real-time or relay it to a ground station close to the front. It should also soon be possible to establish contact with the Americans' JointSTARS stations.
Sentinel will produce both high-resolution radar images of the terrain (apparently to a resolution of approx. 30cm) and also moving vehicle “blips”, under any weather conditions and by day or night. Anything bigger than a jeep which moves faster than 5km/h will apparently be detected. The radar developed by Raytheon on the basis of the ASARS-2 system of the U-2 is equipped with an Active Electronically Scanned Array (AESA) antenna which rotates from left to right. It can employ the Moving Target Indication (MTI) and Synthetic Aperture Radar (SAR) operating modes virtually at the same time. The radar apparently has a range of over 300km. This means that a huge amount of terrain can be covered in missions lasting over 11 hours.
The performance of the Sentinel R1, which fulfils all the required performance parameters, is thus pretty impressive. The all-inclusive price is extremely favourable, at least as far as Raytheon is concerned: according to the National Accounting Office, it will cost £954 million (Euro1.42 billion), over £40 million more than the originally estimated cost.
ASTOR development
September 1993: Start of project definition phase.
February 1995: Two study contracts awarded to Raytheon and Lockheed Martin (Gulfstream V).
Autumn 1997: Raytheon, Lockheed Martin and Northrop Grumman submit their tenders, Northrop Grumman offering a system based on Joint STARS.
February 1999: After several changes and reworks, “best and final offers” are submitted.
June 1999: Raytheon is selected as prime contractor, with Lockheed Martin and Northrop Grumman acting as subcontractors.
17 December 1999: The fixed-price contract is signed.
December 2000: BAE Systems is awarded the subcontract to supply the electronic self-protection system.
2001: The requirement changes from a conventional antenna to an AESA system.
3 August 2001: A Global Express equipped with radome and fins begins its flight test programme in Wichita with a view to verifying the aerodynamic modifications.
31 January 2002: The first Global Express (ZJ690) is flown to Greenville, Texas for re-equipping.
February 2003: Design review completed.
7 March 2003: Raytheon Systems commissions the conversion hangar in Broughton, in which four aircraft are fitted with their electronics.
May 2003: The RAF chooses the name Sentinel for the aircraft.
April 2004: 5 (AC) Squadron is re-formed in Waddington.
26 May 2004: Maiden flight of the first Sentinel R1, which was undergoing conversion at Raytheon's plant in Greenville, Texas.
August 2004: The first radar is severely damaged during a laboratory test due to short-circuits in corroded transmit/receive modules and is no longer usable. Design changes are required to protect the electronics more effectively against moisture. The damage costs around $55 million.
25 July 2005: first flight of the first Sentinel R1 in Broughton, still without radar. The “green” airframe had arrived in January 2003.
October 2005: The first AESA radar, installed in June, supplies radar maps for the first time. According to Raytheon, the results are good right from the start. All that remains to be done is fine tuning.
16 March 2006: The first British Sentinel, which had received its radar at the start of the year, flies to the USA to speed up the tests.
Summer 2006: The third aircraft (ZJ692) flies and is presented at the Farnborough Air Show. Raytheon delivers the training system in Waddington (flight simulator, simulator for the operators, simulator for the ground station operators).
November 2006: Planned entry into service with two aircraft and two ground stations. However, it is unclear whether this deadline can be met.
Mid-2007: All the aircraft and ground stations should have been supplied.
2008: The ASTOR system, which is to remain in service for around three decades, should be fully operational.
From FLUG REVUE 11/2006
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