Raytheon Sentinel

Raytheon Sentinel R.1 - ZJ690

In December 1999, Raytheon Systems Ltd was awarded a contract for the development of the UK Ministry of Defence airborne stand-off radar (ASTOR). The system, which includes five Bombadier Global Express business jet aircraft fitted with a derivative of the Raytheon ASARS-2 radar, is an airborne battlefield or ground surveillance radar system for operation with the Royal Air Force and the British Army.

The ASTOR is to be known as Sentinel R.1 in RAF service. The first production aircraft was delivered to Raytheon in February 2002 for integration of the ASTOR system. The first ground station vehicle was delivered in October 2002. The first ASTOR Sentinel aircraft made its maiden flight in May 2004, the second in July 2005. ASTOR entered service with the RAF in December 2008. Initial operating capability (IOC) is achieved in October 2009. The main ASTOR operating centre is based at RAF Waddington.

Raytheon Systems Limited, UK, is the prime contractor. The team includes: Bombardier Aerospace, responsible for the Global Express Jet, L-3 Communications, the Ground Station, Lucas Aerospace, the electrical systems, Messier Dowty. The landing gear, AgustaWestland. The doors, and Rolls-Royce, the engines.

The radar is an upgrade of the Raytheon ASARS-2 side looking airborne radar used on the U-2. The radar operates at high altitude and in all weathers to provide high-resolution images. The antenna systems are supplied by BAE Systems, Edinburgh. ASARS-2 has been reported to provide images of the battlefield at ranges of 160km, at altitudes up to 47,000ft. The ASARS-2 derivative has an active scanned array and includes a synthetic aperture radar (SAR) which provides photographic quality images of the area being surveyed and a moving target indicator (MTI radar) which tracks moving vehicles over wide ranges. The SAR operates in spot mode to identify and track specific targets or can be switched to swath mode which provides a large number of strips of pictures which join to form a detailed image of the battlefield.

The SAR/MTI radar identifies the location of hostile forces and their quantity, direction and speed. Additional imagery can be provided by optional optical equipment. The image data is transmitted in real time via secure data links to ground-based processing stations. The radar signal processors develop the data into visual images which can be displayed and exploited by the airborne mission crew, transmitted to image exploitation equipment on the ground, or transmitted to other areas via secure data links, satellite communications and ground networks.

The aircraft is equipped with the Defensive Aids Group (DAG) integrated electronic warfare suite from BAE Systems Information & Electronic Warfare Systems (IEWS) of Nashua, New Hampshire. DAG is based on the defensive aids subsystem (DASS) developed by BAE for the UK's Replacement Maritime Patrol Aircraft, Nimrod MRA.4. DAG includes missile warning system, radar warning receiver, towed radar decoy and chaff and flare dispensers.

The aircraft is flown by two flight deck crew and three mission crew. The Bombardier Aerospace-Short Brothers Global Express aircraft is an ultra-long range business jet and will be modified to accommodate the radars and communications systems required by ASTOR. The modifications include a canoe-shaped radome under the forward fuselage to house the radar antenna, a radome on the upper fuselage to house the SATCOM antenna, a 'bullet-fairing' extension on the vertical stabiliser and delta fins under the aft fuselage. Aircraft modification, systems integration and flight testing is carried out by Raytheon Systems at Broughton, North Wales. The aircraft flies at an altitude of 15,000 m in order to achieve the maximum ground radar surveillance coverage. It has a range of 6500 nm and a mission endurance of over 14 hours.

The engines for the ASTOR aircraft are the same as those deployed on the UK RAF Nimrod MRA.4 aircraft. Each Rolls-Royce BR710 two-shaft turbofan engine produces 14,000lbf to 17,000lbf (63kN to 76kN) flat rated take-off thrust. The engine configuration consists of a 48in wide-chord-fan with 24 solid titanium blades, ten-stage high compressor, annular axial flow combustion chamber, two-stage high-pressure turbine and two-stage low-pressure turbine with dual lane full authority digital engine control (FADEC). The ASTOR is an upgrade of the Raytheon ASARS-2 side-looking airborne radar used on the U-2.

High-speed data links transfer the data from aircraft to ground stations in near real time. The system has directional and broadcast data links which are interoperable with existing U-2Rs, JSTARS and command and control networks. The tactical and operational level ground stations are being developed by L-3 Communications Integrated Systems, Raytheon Systems and Marshall Specialist Vehicles. The tactical ground stations are installed in 10ft shelters mounted on 6x6 improved medium mobility Steyr Pinzgauer 718K trucks. 20ft transportable shelters are provided for operational level ground stations. Ultra Electronics and Cubic Defence Systems are providing the narrowband datalink subsystem (NDLS) which will transmit the radar sensor data between the aircraft and the ground stations. L3 communications is supplying the wide band data link based on a common data link (CDL).

No. 5 (Army Cooperation) Squadron was reformed on 1st April 2004 at RAF Waddington and operate the 5 modified Bombardier Global Express long-range aircraft and 8 ground stations. In RAF service, the aircraft type will be known as the Sentinel R.1, with the R acknowledging its Reconnaissance role.

The first Sentinel R1 arrived at RAF Waddington in 2007 and in February 2009 the aircraft made its operational debut in Afghanistan. The projected procurement cost is just over £1bn.