The US Navy’s Boeing MQ-25A Stingray unmanned tanker program advances

The US Navy’s Boeing MQ-25A Stingray unmanned carrier-borne tanker development program has achieved some significant milestones in recent months with the successful pairing with manned aircraft to provide in-flight command and control of the air vehicle, and with the transfer of fuel to three US Navy carrier-borne types.

The US Navy’s MQ-25 Stingray unmanned air-to-air refuelling system successfully passed fuel to a manned F/A-18F Super Hornet for the first time on June 4.

The refuelling was conducted by Boeing’s T1 test air vehicle using a hose and drogue pod system. Before the successful hook-up and offload, the T1 air vehicle had flown 25 test flights since its first flight in September 2019 to validate its aerodynamics and flight envelope.

“This team of professionals was integral in the successful flight,” the US Navy’s Program Executive Officer for Unmanned Aviation and Strike Weapons, Rear Adm Brian Corey said in a June 7 statement. “Over the next few years, we will work side-by-side with Boeing to deliver this capability that will greatly enhance the future carrier air wing.”

Leanne Caret, president and CEO of Boeing Defense, Space & Security, added, “This history-making event is a credit to our joint Boeing and Navy team that is all-in on delivering MQ-25’s critical aerial refuelling capability to the fleet as soon as possible. Their work is the driving force behind the safe and secure integration of unmanned systems in the immediate future of defense operations.”

The Super Hornet refuelling was followed in July with a successful inflight hook-up with a Northrop Grumman E-2D Hawkeye AEW&C aircraft. The E-2D was originally built without the ability to be refuelled in flight, but this was retrofitted to the fleet and adopted for later build aircraft after Japan specified it for its E-2Ds. The test saw the E-2D approach the MQ-25 at various speeds, conduct multiple ‘plug-ins’, test the wake turbulence effect on the receiver aircraft, and conduct emergency breakaways.

“Once operational, the MQ-25 will refuel every receiver-capable platform including E-2,” the US Navy’s Unmanned Carrier Aviation (PMA-268) program manager, Capt Chad Reed said in a release. “This flight keeps us on a fast track to getting the Stingray out to the fleet where its refuelling capability will greatly increase the range and operational flexibility of the carrier air wing and strike group.”

Capt. Michael France, the US Navy’s Airborne Command & Control and Logistics Wing (ACCLW) commodore added, “MQ-25 is leading the way as naval aviation transforms to include cutting-edge unmanned platforms. Our fleet integration team (FIT) is actively preparing for the Stingray’s arrival and we’re excited for the innovative capabilities of the MQ-25 that will transform our mobility and power projection.”

On September 13 the MQ-25 successfully refuelled a Lockheed Martin F-35C Lightning II in flight, thus completing demonstration hook-ups with each of the US Navy’s three main carrier aircraft types. 

“Every test flight with another Type/Model/Series aircraft gets us one step closer to rapidly delivering a fully mission-capable MQ-25 to the fleet,” Capt Reed said in a September 14 release. “Stingray’s unmatched refuelling capability is going to increase the Navy’s power projection and provide operational flexibility to the Carrier Strike Group commanders.”

DEVELOPMENT
The MQ-25 concept demonstrator airframe – dubbed T1 – is the only example flying so far and is owned by Boeing. T1 first flew in September 2019, and has so far completed more than 120 flight test hours.

The initial US$805m (A$1.1bn) contract was awarded to Boeing in August 2018 and covers the design, development, fabrication, test, and delivery of four MQ-25A Stingray engineering and manufacturing development (EMD) air vehicles and three system demonstration articles, and includes the system’s integration into the carrier air wing. 

The US Navy has a requirement for 69 operational MQ-25As in total, with the requirement of an initial operational capability (IOC) by 2024.

Boeing won the contract ahead of bids by Lockheed Martin and General Atomics (GA-ASI). Some observers had predicted a win by General Atomics considering that company’s pedigree in building the Predator series of unmanned systems, while Lockheed Martin has also recently delivered several covert unmanned systems including the RQ-170 Sentinel. 

Interestingly, Northrop Grumman elected not to bid a variant of its X-47B despite completing a highly successful flight test campaign from 2011 to 2016 that included carrier trials as part of the US Navy’s Unmanned Combat Air System Demonstration (UCAS-D).

The first MQ-25A test articles will be delivered to the US Navy in 2022, but it is unclear how much these and the follow-on production air vehicles will differ from the T1 concept demonstrator.

The US Navy will stand up the fleet replacement squadron, Unmanned Carrier-Launched Multi Role Squadron (VUQ) 10, later this year followed by two MQ-25A squadrons – VUQ-11 and 12 – which will deploy detachments of operational air vehicles and operators to aircraft carriers as required.

The MQ-25A is planned to have a reported offload capability of 15,000lbs of fuel – about double that of a Super Hornet fitted with a buddy refuelling pack – at a range of 250km from a carrier. This will provide outbound or returning combat aircraft with greater range and mission flexibility while also freeing-up the four or five Super Hornets each carrier air wing currently assigns to the refuelling mission.

The air vehicle is designed to be ‘flown’ on a pre-determined mission plan with oversight from an air vehicle operator (AVO) located on the aircraft carrier. While the air vehicle is linked to the AVO at most times and the AVO can intervene to modify the mission plan, it will fly the entire mission autonomously without intervention or if comms links are lost or disrupted.

Alternatively, an airborne AVO such as a F/A-18F or EA-18G back-seater or E-2D air warfare officer can re-task the MQ-25A in a manned-unmanned teaming (MUM-T) arrangement via Link-16 if required.

“We’re building an airplane that goes to war, so we want that airplane to be robust and capable when it goes to war,” Boeing’s MQ-25 program director, Dave Bujold told a media brief at August’s Navy League Sea Air Space conference in Washington DC. “We already know there will be errors and times that the carrier will decide it wants to shut its radios down and move, and our airplane can’t just say: ‘I have to go home’. That’s not OK. We know that; the Navy’s told us that; we’re working that.” 

It is planned that MQ-25As will typically maintain an orbit in the general vicinity of a carrier, topping up outgoing or returning aircraft as required. But it will be capable of flying with a strike package, perhaps not into contested airspace, but a lot further forward than larger manned tankers can safely operate.

Boeing says the E-2D has already been configured to be able to conduct the MUM-T mission, while the F/A-18E/F and EA-18G will require a minor software update to its Link-16 message library and displays to be able to communicate with the MQ-25A. 

The company has already successfully demonstrated the MUM-T concept with an E-2D acting as the ‘tanker king’ during the Super Hornet refuelling trials. Funding for the Super Hornet software update is expected to be included in future MQ-25A development funding.

“Two of our key findings from this early demonstration with existing data links are that initial MUM-T capability between MQ-25, E-2D and F/A-18 is achievable with minimal change to the crew vehicle interface and could be integrated into earlier MQ-25 operational deployments,” said Don ‘BD’ Gaddis, Boeing’s head of MQ-25 Advanced Design.

Part of the MUM-T solution will involve the development of scenarios, or ‘plays’, through a behavioural software framework in the MQ-25A. “As a result, pilots can call a ‘play’ for the unmanned system, much like a coach,” Gaddis explained. “This ‘play call’ ability greatly simplifies the supervising pilot’s workload and minimises the datalink exchanges required. It’s all part of building platform-agnostic, portable, and reusable MUM-T software.” 

This article appeared in the July/August 2021 issue of ADBR.