Flight tests beginning in the mid-2000s have pioneered methods for automation in refuelling routines – summer 2012 may see tests of one unmanned aircraft refuelling another.
“In-flight refuelling has proven invaluable to manned military aviation, and there’s no reason to expect that the same wouldn’t be true for unmanned systems, especially as the demand for unmanned aircraft has grown in recent years,” said Jim McCormick, the Defense Advanced Research Projects Agency programme manager for KQ-X, a programme testing Global Hawk remotely piloted aircraft as unmanned tankers and receivers.
Achieving autonomy crosses many functional domains and “involves a very broad range of technologies, including robotics and expert systems, telemetry and communications, electro-optics, cybersecurity, process measurement and control, sensors, wireless applications, systems integration, test measurement, and many, many more,” according to the Automation Federation.
The Air Force also wanted to develop something different, namely, an automated system suitable for its boom-equipped tankers. The main advantage of a boom is greatly increased fuel flow rates of up to 1,200 gallons per minute.
In 2010, Northrop Grumman demonstrated its capability for positioning aircraft. “The success of this flight test is especially notable because it demonstrates the ability of an embedded GPS/INS to host relative navigation processing,” said Alex Fax, director of positioning, navigation, and timing solutions at Northrop Grumman’s Navigation Systems Division. Success with manned aircraft tankers refuelling autonomously operated receivers was not the end. The next hurdle was the unmanned tanker.
Global Hawks were the natural candidate for the KQ-X programme. The high-altitude surveillance airplanes had been flying in combat all during the 2000s with proven reliability. Their internal fuel capacity, of about 17,300 pounds, made the Global Hawk a suitable “tanker” that could carry aloft enough fuel for both its own missions and potential offload.
According to DARPA, the programme is addressing the challenges of unmanned systems, sensing, and aerodynamics to a much greater degree than AARD. “Tackling these complexities in a fully unmanned refueling scenario, with the real-world Global Hawk system, should increase our confidence that unmanned systems can be autonomously refueled in a safe, flexible, and affordable manner,” said McCormick, the programme manager.
DARPA took up the challenge with its new KQ-X programme in 2010—and followed a pragmatic approach. “We’re using proven Global Hawk aircraft and ground stations, algorithms developed under AARD, and off-the-shelf refuelling hardware,” McCormick explained. The DARPA program takes full advantage of the work carried out over the previous decade and will use it to reduce risk. “We’re mostly avoiding new technology, so we can focus on the challenges of integration and unmanned operation,” he noted.
The Autonomous High-Altitude Long-Endurance Refuelling programme set out to demonstrate “repeatable probability of success with limited flight performance aircraft under high-altitude conditions, redundant safe separation, and unmanned flight operations,” stated DARPA officials.
“We think this is important because a next generation HALE platform designed to refuel may be much more affordable, capable, and effective,” McCormick said.
Two older Global Hawks operated by NASA were designated for the programme. Step 1 was risk reduction. Northrop Grumman’s Proteus test aircraft flew within 40 feet of the NASA Global Hawk while at 45,000 feet.
“When you add autonomous flight of both aircraft into the mix, … you gain a capability that has mission applications far beyond just aerial refueling,” said Geoffrey Sommer, KQ-X program manager for Northrop Grumman.
The concept for double unmanned refuelling was a bit different from the routine scenario of receiver trailing tanker. In this case, plans called for the tanker Global Hawk to fly behind the receiver Global Hawk. “We want the aircraft with the smarts and the maneuvering capabilities in the rear,” Northrop Grumman official Mark Gamache explained to news site Xconomy San Diego at the outset of the programme.
According to McCormick, 2012 is a make-or-break year. “We plan to complete, this summer, a convincing demonstration that includes repeated transfer of fuel,” he said. “In the process, we will learn better how this type of aircraft operates in close formation and gain valuable experience with complex unmanned operations.”
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Source: Air Force Magazine