The Bombardier Raytheon Sentinel currently (2013) serves the Royal Air Force (RAF) as its primary Airborne Battlefield and Ground Surveillance Aircraft. The intra-theater platform is utilized for real-time data collection, intelligence gathering, unarmed maritime patrol and battlefield surveillance. For the moment, the RAF Sentinel fleet maintains an active status though only five examples have been procured in all. The Sentinel is the British equivalent to the USAF E-8 Joint Surveillance Target Attack Radar System.
The Sentinel was born from the Airborne Stand-Off Radar (ASTOR) program of the British Army to which the quick coalition success in the 1991 Persian Gulf War furthered defined the need for a dedicated requirement. The war proved the value of Synthetic Aperture Radar (SAR) as well as Ground Moving Target Indicator (GMTI) when tracking and engaging ground-based foes. Such services were largely supplied by the United States which led the UK to pursue its own stand-alone solution. Prior to the war in 1984, a Britten-Norman BN-2T Islander was outfitted with mission equipment though a dedicated, purpose-built platform was still sought, funding then finally allotted to similarly modify a Bombardier (Canada) Global Express business jet by way of Raytheon equipment. The MoD secured the program - to take on the same of "Sentinel" - in 1993. The end-product would encompass a land and air combination of assets to appropriately fulfill the battlefield role.
The original civilian-minded Global Express business jet program was launched on December 20th, 1993 and went airborne for the first time on October 13th, 1996. The first foreign customer became Malaysia in July of 1999.
The official UK defense procurement contract was awarded in December of 1999. After several years in development which included testing of Rolls-Royce engines and new fuselage additions, an initial prototype recorded its first flight in August of 2001. A production-quality airframe then took to the skies on May 26th, 2004 and completed a flight lasting over four hours - proving the design and its mission suites sound (as well as its new aerodynamic layout). The modified Bombardier aircraft was adopted into RAF service as the "Sentinel R1" and delivered to 5(AC) Squadron ("Army Cooperation") at RAF Waddington - five total airframes were procured in addition to eight mobile ground stations (MGS). While initially expected to have been formally introduced in 2005 delays to the Sentinel program ensured an introduction in 2008.
As can be expected, the Sentinel retains the same basic shape and configuration of the original Bombardier Global Express jet. The design includes a well-streamlined, cylindrical fuselage with the cockpit held well-forward. The fuselage sports a noticeably pointed nose cone at front and tapers to the rear. Wings are low-mounted along the fuselage sides and are capped by winglets for additional stability. The engines are mounted in individual nacelles on short wingstubs just ahead of the tail unit. The empennage itself consists of a single vertical tail fin while horizontal planes are added to the fin to create a "Tee" style configuration. All wing surfaces (main assemblies and tail) are swept for maximum aerodynamic efficiency. The undercarriage is wholly retractable and fits a pair of double-tired main legs at center mass along with a double-tired nose leg under the flight deck. The Sentinel is, however, clearly identified from its civilian-minded breed by the inclusion of a dorsal SATCOM fuselage fairing just aft of the cockpit and an oblong, 15-foot long ventral radome structure housing the applicable mission equipment. Additionally, ventral strakes are noted under the empennage.
The Sentinel is crewed by five personnel including two pilots, the Airborne Mission Commander (AMC) and two image interpretation specialists/analysts (pulled from either RAF or Army Intelligence Corps). The aircraft sports a running length of nearly 100 feet with a wingspan of 93 feet, 6 inches and an overall height of 27 feet. When empty, the airframe weighs in at 54,000lbs and can lift off at 93,500lbs with full mission equipment and fuel. Power is served through 2 x Rolls-Royce BR710 series turbofan engines of 14,750lbs thrust each. This provides the aircraft with a top speed of 570 miles per hour with a range out to 5,800 miles at a maximum service ceiling of 49,000 feet. Mission endurance time is listed at 9 hours and the primary mission altitude is over 40,000 feet to maximize the reach of the onboard radar (range of approximately 300km).
Internally, the Sentinel is outfitted with a bevy of modern mission-tracking and surveillance systems. The primary facility is the modular Raytheon dual-mode Synthetic Aperture / Moving Target Indication (SAR(MTI) system - based on the Lockheed U-2's ASARS-2 system. A real-time moving map assists operators in changing mission parameters and locating enemy forces as well as tracking allies. The integrated datalink system can transmit mission information to operators and mission commanders in the ground control stations for further review/analysis. There are three operator stations aboard the Sentinel. While unarmed, the aircraft is allotted some basic defense measures including a towed radar decoy as well as an automatic chaff/flare dispenser to counter enemy radar/missile tracking. A missile warning receiver identifies potentially lethal incoming aerial threats.
The Sentinel R1 was initially fielded in an active warzone during February of 2009 over Afghanistan airspace in support of coalition forces in the theater (operations were, however, limited). The Sentinel was then brought to bear in support of coalition actions concerning the Libyan Civil War of 2011 with excellent results. Originally designed for a conventional, large-scale war involving columns of enemy armored vehicles, the Sentinel has proven effective in singling out smaller threats to allied ground forces. It has more recently been involved in providing surveillance capabilities during the fluid Mali campaign (January 2013) in support of the French lead in the theater - the campaign centered on neutralizing the growing militant presence in the former French colony and African nation. The Sentinel remains one of the few airborne surveillance options for NATO today.
As it stands, the UK Strategic Defence and Security Review of 2010 suggested the overall retirement of the expensive and highly specialized Sentinel fleet by 2015, particularly citing the upcoming end of British involvement in the Afghanistan Theater. However, the recent showing of the single Sentinel aircraft committed to the Mali campaign could very well stave off the type's disbandment if only for the short-term as the platform has proven to be hugely important to ongoing fighting against militant forces. The aircraft has been able to pin-point origination of indirect fire from enemy elements as well as identify potential threats on the ground from above while coordinating coalition aircraft strikes in turn. It is further suggested that the Sentinel will be relieved of its battlefield role by the winner of the still-to-be-decided "Scavenger" Medium Altitude, Long-Endurance (MALE) Unmanned Aerial Vehicle program which, it is believed, will be a more cost-effective, long-term solution. There has been some noted concern of the Raytheon radar's ability to operate effectively over heavy sea states when in the maritime patrol role, which would severely limit the tactical value of the Sentinel fleet. As such, there are notable divisions amongst RAF authorities as to which direction to ultimately pursue.
December 2015 - Initially slated for retirement in 2018, British Sentinels will remain in service until 2021.
January 2021 - The British Ministry of Defense (MoD) is selling off all five of its aged surplus Sentinel aircraft for scrapping.
March 2021 - The Royal Air Force has officially ended operational flights involving the Sentinel R.1 aircraft.
March 2021 - The RAF Sentinel squadron has been disbanded.
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