The use of UAVs has been one of the great success stories of recent years. However, although UAVs were initially developed for reconnaissance duties, as the vehicles themselves grew larger the obvious next step was to arm them and the Predator has already successfully destroyed a number of targets with Hellfire missiles.
The development of a stealthy Uninhabited Combat Air Vehicle (UCAV), large enough to carry about two tons of ordnance - the same as a front-line fighter aircraft, is the next goal. Such a UCAV would then be capable of conducting high-risk missions, such as Suppression of Enemy Air Defences (SEAD), without risking the life of a pilot. A UCAV would also be one of the first systems to benefit from the development of the Small Diameter Bomb (SDB) which will have the explosive effect of a 2,000lb bomb and yet weigh only about 250lb. As the concept for a UCAV was developed another part of it called for the vehicles to be capable of being stored, minus their wings, in a purpose-built climate-controlled container which would be wired into the vehicle and monitor the various systems to ensure they remained healthy. The containers would then be stored in a hanger and then used as necessary six such containers would be carried to a forward airfield in a C-17 or twelve in a C-5.
Two UCAVs are currently under development in demonstration programmes. In 1999 Boeing were awarded a contract to build two small development UCAVs named the X-45A which first flew in May 2002. The X-45A has one working weapons bay, with the other bay filled with avionics. Instead of a traditional hydraulic system, with the exception of the nose wheel steering and hiking system, the X-45A was all electric. The single Honeywell F124-GA-100 eingine was fed through an unusual serpentine inlet and used a yaw thrust vectoring system. The X-45A could carry a payload of 1,500lbs, operate at 35,000ft and cruise at Mach 0.75.
Meanwhile Northrop Grumman was also building a small development UCAV for the US Navy the X-47A. Although a similar size to the X-45A, the X-47A was a completely different shape, but had similar performance. The X-47A was designed from the outset to investigate whether UCAV's were suitable for carrier operations and simulated typical carrier operations by landing near a predesignated touchdown point and utilized the Shipboard-Relative Global Positioning Satellite (SRGPS) system, the same as fitted to a F/A-18 Hornet, as its guidance system for a precision landing. The X-47A was powered by a single Pratt & Whitney JT15D-5C engine.
To avoid duplication of effort the two programmes were combined as the Joint Unmanned Combat Air System (J-UCAS) managed by DARPA. The J-UCAS programme is a joint DARPA/Air Force/Navy effort to demonstrate the technical feasibility, military utility and operational value for a networked system of high performance, weaponized unmanned air vehicles to effectively and affordably prosecute 21st century combat missions, including SEAD, surveillance and precision strike within the emerging global command and control architecture. On 12 Oct 04 Boeing was awarded a $767 million to build three X-45Cs UCAV for the USAF, together with two ground based mission control stations. The X-45C will be 39ft long, have a 49ft wingspan, be powered by a single General Electric F404-GE-102D engine, cruise at Mach 0.80 at 40, 000ft, carry a 4,500lb weapon load in two internal weapons bays and have a combat radius of 12,000nm.
In Aug 04 Northrop won a five year $1.04 billion contract to build three X-47Bs and three mission control stations for the US Navy. The X-47B will be just over 38ft long, have a 62ft wingspan, weight 41,997lbs, be powered by a single Pratt & Whitney F100 engine, be capable of wing folding, carrier launch, recovery and in flight refuelling - the aim is for the X-47B to be one-third the purchase cost and one-half the operating cost of an F/A-18C. Both the X-45C and X-47B taxi, take-off, conduct their missions and land fully autonomously, or can be controlled by a pilot operator the UCAVs are both scheduled to fly in 2007. Operational assessment is scheduled for 2008-9, to test the flying qualities of the UCAVs, as well as complete weapon and system integration. Current UCAV development is focused on their role as interdictors, but in time UCAVs will also be equipped with self-defence systems and with their ability to pull 20G, considerably more G than a manned aircraft can sustain, a stealthy UCAV armed with advanced air-to-air missiles would make a formidable opponent.
Although initially conceived as a stealthy means of delivering ordnance onto a target, the excellent reconnaissance capabilities of the UCAVs will also be put to good use, indeed now reconnaissance over heavily defended areas is the primary mission of the US Navy's UCAV. It is planned that UCAVs will be equipped with advanced Electronic Support Measures (ESM) suite, Electro-Optical (EO) and Infra-Red (IR) sensors. Also in development is an advanced X-Band Thin Radar Aperture (XTRA) array which could provide both a Synthetic Aperture Radar (SAR) and Ground Moving Target Indicator (GMTI) capability these sensors combined would enable a UCAV to locate, identify, track and target enemy static or mobile facilities. Also under development are foliage penetrating radar and sub-surface sensors. The data collected by the UCAV will be transmitted via data-link or SATCOM giving the vehicle a near real-time reconnaissance role. Most commentators now recognise that, with many of todays front line fighter aircraft scheduled for retirement in massive numbers beginning in 2015, their replacements will be a mix of manned and unmanned systems and as time goes on the proportion of unmanned systems is likely to increase, rather than decrease.
However, as the J-UCAS programme progressed significant differences between the USAF and USN requirements could not be settled and in 2005 it was cancelled. In particular, the USAF decided that their requirement for a long-rane bomber to enter service around 2018 could not be met by the J-UCAS, the vehicle was simply too small to achieve their target of a 4,500kg (10,00lb) payload delivered over a 3,700km (2,000nm) radius and they are now developing a Long Range Strike (LRS) programme to meet this goal. The USN requirement was always for a much smaller UCAV, dictated by their requirement to operate from an aircraft carrier. The USN are still looking to acquire a UCAV, under a programme re-named the Naval Unmanned Combat Air Strike (N-UCAS), with the focus shifted from persistent intelligence, reconnaissance and surveillance to strike. Both the Northrop X-47B and the Boeing X-45C are being reconfigured to try and meet the N-UCAS requirement for a 1,800kg payload delivered over a 2,000 to 3,000kn radius. Despite the USAF public position, the US Navy Fiscal Year 2007 budget document has disclosed that the old J-UCAS programme was actually split into two new strands: the new N-UCAS programme and a classified USAF programme, primarily for intelligence, surviellance and reconnaissance, but exactly what vehicle results from this programme remains to be seen.
But that is not quite the end of the story, because in 1998 a NASA paper reported that twenty four General Electric J97-GE-100 turbojet engines, built orginally to allow the top secret AQM-91A Compass Arrow UAV to cruise at 80,000ft over communist China, were not scrapped as originally thought when this programme was cancelled. In fact these engines were actually placed in storage at their AMES research centre. It then appears that two of these General Electric J97-GE-3-100 engines may well be used to power a classified USAF UAV programme, funded with money taken from the terminated J-UCAS programme and known as the Penetrating High Altitude Endurance (PHAE). The PHAE is believed to be a stealthy, twin-engined, UAV capable of cruising between 70,000 to 80,000ft and capable of carrying various weapons enabling it to conduct SEAD, as well as traditional ISR missions as necessary so hopefully the money spent on developing the technology for the Compass Arrow has finally been put to the use that was origionally intended. In a nutshell, the USAF version of the UCAS is still alive, despite the best efforts of the pilot mafia at the top end of the USAF, and is now a 'black programme' called the PHAE.