Quick question: what’s the biggest limiting factor in today’s aircraft? Answer: the pilot. Fortunately for pilots, they’re also an aircraft’s greatest advantage, which will keep them in the mix, and in the cockpit, for some time to come. Those limitations are bringing unmanned aircraft into the combat picture, however, especially when it comes to the greatest limitation a pilot places on an aircraft: aerial endurance. Remaining awake, active, and effective in a manned fighter aircraft for 72 hours straight is simply not within the realm of possibility. On the other hand, a UAV with that endurance level, flown by pilots on the ground or at sea who can hand the aircraft off to a colleague while they depart for a coffee, bathroom break, or sleep, could easily remain aloft that long. All it needs is an appropriate level of mechanical reliability – and, of course, the ability to take on fuel from an aerial tanker aircraft.
That simple concept has profound implications for the ways in which airpower might be used. Imagine, for instance, a carrier with UCAS-D X-47s on board. The ship receives a crisis call for events 3,000 miles away – and immediately launches its armed complement of X-47 stealth UCAVs toward the area, while the rest of the carrier steams over to catch up. Pilots fly the aircraft via secure satellite links from duty stations within the ship, while USAF aerial tankers keep the X-47s fueled to maintain their surveillance and targeting “orbits” over the crisis area, or even slightly outside of that area. The aircraft are on station much faster, and remain so for a far longer period of time than would normally be possible. The result is effective power projection that attracts as little or as much attention as it chooses, while remaining available for very fast use in the target zone.
UAVs are already being flown over Afghanistan from duty stations near Las Vegas, so part of this scenario has already come true. The missing link? Aerial refueling. Looks like it won’t stay missing for much longer…
Program Goals: Phase II
X-47B Concept
Work began with a 2005 contract to add this capability to its canceled X-45C UCAV, and was followed by successful 2006 and 2007 exercises that used an unmanned Learjet as a surrogate. These Phase I exercises demonstrated that a single UAV could safely maneuver among 7 refueling positions behind a tanker aircraft, and conduct a breakaway maneuver.
Now, the Phase II contract looks set to extend Boeing’s efforts – and take another step toward the kind of UCAV future outlined above. AAR also encompasses manned aircraft, which could also benefit from systems that are able to automate risky maneuvers like air-air refueling.
Phase II Spiral 1 involves designing and testing a multichannel precision-GPS relative navigation system, an automated flight control system, and the required command and control additions to guide the unmanned receiver to the manned tanker. Tests will use the air force’s boom system.
Under a planned Spiral 2, the team will evaluate non-GPS sensors to augment the Spiral 1 system, and support probe-and-drogue refueling.
The goal is to successfully refuel an F-16, acting as an unmanned surrogate, by 2011. The Navy’s UCAS-D program, which uses Northrop Grumman’s developmental X-47B unmanned attack aircraft, is also involved.
A separate DARPA/NASA program called KQ-X will involve the next step beyond, and test air-air refueling where both aircraft involved are UAVs. Northrop Grumman’s RQ-4 Global Hawks will be used as the refueling and receiving platforms.
Contracts and Key Events
Next step beyond
June 30/10: Northrop Grumman announces a $33 million DARPA contract to take the next step forward: UAV-to-UAV aerial refueling. The “KQ-X” program will use a pair of the company’s RQ-4 Global Hawk high altitude UAVs, modified to add a standard Navy hose-and-drogue system. The refueling will be completely automated and autonomous, and will take place at high altitude. Not only would this program mark the first UAV-to-UAV refueling, it would be the first time that Global Hawks or any other HALE UAV have even flown in formation.
Engineering work will be performed at Northrop Grumman’s Unmanned Systems Development Center in Rancho Bernardo, CA, with Sargent Fletcher, Inc. (aerial refueling systems) and Sierra Nevada Corporation as major KQ-X subcontractors. Pilots from NASA, NOAA, and Northrop Grumman will command the Global Hawks from the NASA Dryden Flight Research Center at Edwards Air Force Base, CA. Northrop Grumman Aerospace Systems VP Advanced Concepts, Carl Johnson:
“Demonstrating the refueling of one UAV by another is a historic milestone…. It adds aerial refueling to the list of capabilities that can be accomplished autonomously by Global Hawks; it opens the door to greatly expanded operational utility for UAVs; and, as a side benefit, it promises to increase the safety and reliability of aerial refueling between manned aircraft by reducing pilot workload.”
April 12/10: Northrop Grumman touts the performance of its equipment in recent tests:
“Employing a Learjet as a surrogate for an unmanned aircraft and a modified refueling tanker, Northrop Grumman’s relative navigation software and LN-251 embedded global positioning system (GPS)/fiber-optic inertial navigation system (INS) provided the precise positioning information required in support of the simulated aerial refueling mission. A series of 10 flight tests, which concluded on March 18, demonstrated that Northrop Grumman’s relative navigation software could be successfully hosted in the LN-251. The test also exercised the LN-251’s newly-added Ethernet interface as well as its embedded 24-channel GPS receiver with enhanced tracking capabilities.”
Jan 26/10: Northrop Grumman Integrated Systems Sector in San Diego, CA received an $11 million not-to-exceed modification to a previously awarded cost-plus-incentive-fee contract for autonomous aerial refueling technology maturation and demonstration activities in support of the Navy UCAS-D.
Work will be performed in El Segundo, CA (60%) and Rancho Bernardo, CA (40%), and is expected to be complete in November 2010 (N00019-07-C-0055).
Boeing AAR concept
Jan 12/09: Jane’s confirms that the X-47 UCAS-D program will begin aerial refueling tests performed in 2010, using surrogate aircraft.
Nov 19/08: Boeing in St Louis, MO received a $49 million cost plus fixed fee contract as the automated aerial refueling Phase II integrator. At this point, $1.2 million has been obligated. The Air Force Research Laboratory at Wright-Patterson AFB, OH manages this contract (FA8650-09-C-3902).
Boeing will lead the team, and is partnered is partnered with Northrop Grumman and Lockheed Martin as prime contractors. Other contractors include Northrop Grumman Electronic Systems, GE Aviation, Rockwell Collins, and the Sierra Nevada Corp. Under Phase II of the Automated Aerial Refueling (AAR) program, the industry team will coordinate flight tests that will include autonomous multiship operations, and the actual delivery of fuel to a manned surrogate UAV.
Phase II Spiral 1 involves designing and testing a multichannel precision-GPS relative navigation system, an automated flight control system, and the required command and control additions to guide the unmanned receiver to the manned tanker. Tests will use the air force’s boom system.
Under a planned Spiral 2, the team will evaluate non-GPS sensors to augment the Spiral 1 system, and support probe-and-drogue refueling. Boeing release | Aviation Week
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