The development of Unmanned Combat Air Systems represents one of the most important developments within modern military aviation. About 15 years after the first conceptual discussions on unmanned fighter aircraft named Unmanned Tactical Aircraft was renamed as Unmanned Combat Air Vehicle to point out it belongs to the category of complete air vehicle systems. Later, this terminology was extended to Unmanned Combat Air Systems, reflecting that these systems are integrated ones.
One representative example is the Boeing X-45, being the leader for the J-UCAS program. J-UCAS, initially led by DARPA, was moved to a joint US Navy/US Air Force office in October 2005. The first Phase, called Spiral 0, of this program focused on Boeing X-45 and Northrop Grumman X-47. Demonstrator UAV X-45A achieved several important milestones: these include a successful release of a 250lb inert Small Smart Bomb (SSB) from the internal weapon bay at 35,000 feet and at Mach 0.67.
In 1999, Boeing received a contract from DARPA and the USAF for the demonstration phase involving the manufacture of two X-45A demonstrator air vehicles. The first vehicle was rolled out in September 2001, and its maiden flight took place in May 2002. The X-45A design features a swept-wing stealthy profile with composite construction and a Honeywell F124-GA-100 non-afterburning turbofan engine installed. This 28kN-rated engine is installed with a notched air intake and two-dimensionally yaw-vectoring nozzle exhaust.
Further capability was demonstrated for the X-45A in a series of block tests. Block 1 tests involved timing and positional navigation trials, including autonomous taxiing, and integration of ground mission control elements. Block 2 testing, which began in March 2003, incorporated unmanned vehicles operating in cooperation with manned aircraft. By March 2004, the block 2 software build was finished, and first flight tests were underway with apparent success. Testing of Block 3 included mission replanning during flight and station-keeping maneuvers, whereas Block 4 testing, completed in August 2005, moved decision-making capabilities to the air from the ground-based control station.
Compared to the original X-45 configuration, the X-45C is a more advanced variant with higher payload capacity and enhanced range envelope. Its arrowhead profile is the result of a new wing design. Boeing began assembling the first three X-45C demonstrators in June 2004. The first flight was planned for 2007. The aircraft would subsequently undergo a two-year operational assessment.
Equipped with the most advanced precision-guided munitions, the X-45 series can transport up to 2,000lb bombs or other munitions. The sensor suite includes an Active Electronically Scanned Array Synthetic Aperture Radar and an electronic support measures system developed by Raytheon. This suite allows for near real-time detection, identification, and location of fixed and mobile targets, having data downloaded via secure datalinks to ground control stations, aircraft, or satellites.
The autonomous capabilities in the X-45 also provide for taxi, lift-off, and landing, but these operations may be overridden by the pilot operator when operations require manual operation. The UCAV ground control station, designed and developed by NASA, incorporates artificial intelligence decision aids to support operators in assessing the battlefield and giving clearance to release weapons. BAE Systems Controls is providing the computerized air vehicle management system, and there is also a Milstar satellite communications link on the air vehicle.
Advances in UCAS, such as in the X-45 series, underpin the quantum leaps made in unmanned military aviation. These systems do not just enhance capability but also redefine the strategic contours of modern warfare.