Raytheon Sentinel



The Raytheon Sentinel is a Bombardier Global Express modified as an airborne battlefield and ground surveillance platform for the Royal Air Force. Originally known as the ASTOR (Airborne STand-Off Radar) programme the aircraft is operated by a RAF squadron manned by both air force and army personnel. The Sentinel is interoperable with other allied systems such as JSTARS and the NATO Alliance Ground Surveillance (AGS) system.

The UK government's Strategic Defence and Security Review announced its intention to "withdraw the Sentinel airborne ground surveillance aircraft once it is no longer required to support operations in Afghanistan." Sentinel has supported the British Army in Afghanistan. One Sentinel aircraft was deployed to assist French forces in Mali on 25 January 2013.

Design and Development
ASTOR has its roots in the British Army's Corps Airborne Stand-Off Radar (CASTOR) programme which in 1984 modified a BN-2T Islander (G-DLRA/ZG989) with a large nose radome for battlefield surveillance. Gulf War 1 confirmed the requirement for such an aircraft, but the end of the Cold War made funding difficult. The production contract was signed in December 1999 with a projected in-service date of 2005.

The first flight of the modified prototype was in August 2001, which validated the modifications required for the ASTOR system. The first production Sentinel R1 made its 4.4 hour maiden flight on 26 May 2004. The aircraft entered operational service with V (Army Co-operation) Squadron of the Royal Air Force based at RAF Waddington and flew its first operational sortie in Afghanistan in February 2009.

The Sentinel R1 is a modified Bombardier Global Express powered by two Rolls-Royce BR700 turbofan engines, as used in the Nimrod MRA4. The programme involved five aircraft and eight mobile ground stations (six on wheeled all terrain vehicles and two in air transportable containers), and a training facility at RAF Waddington. The programme cost £850m, as budgeted. The support contract is for 3200 flying hours per year.

The Sentinel cockpit has a centrally housed, pull-down screen capable of displaying a moving map, Link 16 datalink information and defensive aids subsystem (DASS) data. The DASS comprises a towed radar decoy, missile approach warning system and chaff and flare dispensers and can be operated in automatic, semi-automatic or manual mode.

The aircraft normally operates at over 40000 ft to ensure a high resolution view of a large battlefield area. It is crewed by a pilot, a co-pilot, an Airborne Mission Commander (AMC) and two image analysts. Mission endurance is approximately nine hours. While the image analysts can analyse the images on board the aircraft it is expected that, unlike the JSTARS, the actual battle management will occur on the ground.

The main radar is a Raytheon Systems/BAE Systems dual-mode Synthetic Aperture / Moving Target Indication (SAR/MTI) radar known as Sentinel Dual Mode Radar Sensor (DMRS). Raytheon claim it could be modified to match the maritime surveillance capability of the cancelled Nimrod MRA4, and the ground stations could be adapted to receive data from Watchkeeper, MQ-9 Reaper and the future Scavenger programme.

Operational History
The UK government's Strategic Defence and Security Review announced its intention to "withdraw the Sentinel airborne ground surveillance aircraft once it is no longer required to support operations in Afghanistan." Sentinel has supported the British Army in Afghanistan. Its role above Libya in 2011 was described as "pivotal" by the head of the RAF. In February 2012 it was announced that Sentinel would be offered as the UK contribution to NATO's Alliance Ground Surveillance (AGS) collaboration, complementing NATO RQ-4 Global Hawks and French Heron TPs. On 25 January 2013, the British Government announced that the RAF would deploy one Sentinel aircraft from RAF Waddington, in support of French operations in Mali.