DARPA Will Reel-In Its Gremlins Drones and Pluck Them Out Of The Sky Like Flying Fish

The unmanned aircraft will link up with their C-130 mothership using a system similar to the probe-and-drogue refueling method.

byJoseph Trevithick|
Swarms photo


The Defense Advanced Research Projects Agency, or DARPA, has chosen defense contractor Dynetics, along with the rest of its team, to proceed to the third phase of its Germlins drone swarm program. In its own announcement, the company revealed that a video we at The War Zone previously reported on actually showed a special docking system that a C-130 Hercules aircraft will tow behind it so that the unmanned aircraft can latch on for a mid-air recovery, not one of the vehicles themselves.

The Pentagon quietly slipped news of the contract award, with a total value of more than $32 million, into a daily contracting notice on April 17, 2018. The release says the work, which will include flight tests of the complete system, including the Gremlins drones and the aircraft-mounted launch and recovery systems, should be completed by January 2020. Ground and limited flight tests will begin in 2018, according to a press release Dynetics issued on April 18, 2018. DARPA launched the first phase of the project, which involved four different industry teams, in August 2015 and started the second phase in 2017.

While Dynetics is responsible for the overall design of the unmanned vehicles, Williams International is supplying the small turbofan for each one, Moog is building the control actuation systems, and the Sierra Nevada Corporation is designing the drone’s precision navigation system, as well as what the company’s own press release calls “multi-vehicle control services.” It’s worth noting that Williams has a long history of building small, high-efficiency jet engines for cruise missiles, such as the Tomahawk Land Attack Missile and the AGM-86 Air Launched Cruise Missile, as well as various X-planes, including Lockheed Martin’s secretive X-44A.

Airborne Systems is also producing a parachute recovery system for the drones. Kratos, one of the previous Gremlins competitors, has now joined Dynetics and will be responsible for putting together complete drones. Applied Systems Engineering, Inc. is building the flight computer that will tie everything together.

An earlier artist's conception of Dynetics' Gremlins proposal, showing a B-1B bomber and C-130 aircraft at left deploying the drones and additional C-130s at right recovering them in mid-air., Dynetics

“The unmanned air vehicles utilized in these future operations will carry a variety of different sensors and other payloads, working together to manage and conduct complex, highly-adaptive operations in contested environments,” Tim Keeter, Dynetics’ Gremlins deputy program manager and chief engineer, said in the company's press release. “When they complete their mission, they return to airborne manned platforms to be recovered to a forward operating base where they can be quickly refurbished and put back into the fight.  The potential to overwhelm an adversary continuously with multiple volleys is tremendous.”

Keeter’s description gets the core of DARPA’s plans for the project. From the very beginning, the goal has been to develop a complete drone swarm system wherein C-130-type aircraft, and maybe even eventually fighter jets and bombers, launch the vehicles at stand-off distance away from enemy defenses.

Systima is fabricating the underwing launch pylons to go on the experimental C-130 mothership, along with the launch controller hardware. International Air Response is supplying the aircraft itself.

The drones then conduct their missions autonomously or semi-autonomously as a cohesive group before returning to a designated spot where another C-130-type scoops them right out of the sky. Dynetics proposal for getting the unmanned aircraft back on board is to reel them in like fish using a docking apparatus that extends via a tether from the Hercules’ cargo bay. The company says the concept is similar at its most basic level to probe-and-drogue aerial refueling systems.

A portion of Dynetics' new concept art showing its planned method of retrieving the Gremlins drones in mid-air., Dynetics

Based on the artwork Dynetics has now released, after linking up with the mothership, the crew retracts the line and a mechanical arm physically grabs the drone and pulls it fully into the aircraft. This is very close to what we at The War Zone posited could have been the case when we discovered a video clip of the prototype system in action. DARPA included that footage in a video montage it put online in 2017, but edited it out of the larger feature sometime afterward.

The method is definitely workable, at least in theory. In 2015, Northrop Grumman demonstrated an unmanned combat air vehicle could autonomously link up with a manned tanker using the probe-and-drogue method with its X-47B aircraft. Before that, NASA, in cooperation with DARPA, had thoroughly tested autonomous refueling between drones using a similar system. 

In 2009, the U.S. Navy also began looking into ways to stabilize the refueling system's "basket" just to make things simpler for manned aircraft, but it was a development that had obvious applications for unmanned systems, as well. In 2011, the Unmanned Aerial Vehicle Lab at Western Michigan University demonstrated a subscale prototype system that used four computer-controlled fins – akin to the four grid fins seen on Dynetics' dock – to help keep the drogue from making overly erratic movements. 

The video below shows Western Michigan University's UAV Lab's concept from 2011.

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But it's an arrangement that still might present significant challenges when it comes to retrieving a large number of small drones and doing so rapidly. It seems very likely that the parachute recovery setup that Airborne Systems is providing for each of the Gremlins drones is, at least in part, a failsafe in case they run out of fuel while attempting to dock with the C-130.

According to Aviation Week’s Graham Warwick, DARPA wants Dynetics to show it can recover at least four Gremlins within the space of 30 minutes during a demonstration scheduled for late 2019. Otherwise, the program remains focused on the larger overall goal of demonstrating that the small swarm of unmanned aircraft can perform intelligence, surveillance, and reconnaissance and other “non-kinetic” tasks, such as electronic warfare, all of which makes good sense.

Swarms of drones acting together could readily serve as distributed sensor nodes, gathering imagery or other intelligence across a wide area in a relatively short amount of time. Carrying jamming systems or mimicking the signals of larger aircraft, they could also confuse or otherwise disrupt enemy integrated air defenses ahead of a larger operation or just divert their attention away from the path of the real attacking force.

But, as Dynetics noted in its own press release, that’s just a small portion of what the Gremlins might eventually

be able to do over the battlefield. Depending on how low-observable the final unmanned aircraft design is – and from the available artwork it looks like it could include stealthy design features – it might be able to perform discreet and persistent surveillance in heavily defended denied areas.

They might be able to act as loitering munitions, waiting to strike at the most opportune time. In that mode, they could potentially zero in on certain types of emissions to attack radar emitters, air defense nodes, or communications equipment or strike targets after visually matching targets to images stored in an onboard memory database.

Different variants might only have to carry one type of equipment, such as navigation systems, sensors, or weapons only, with the entire group sharing route and targeting information and acting as single coorporative strike package. This would allow the underlying drone design to remain relatively small and simple, and therefore reduce costs.

DARPA's own initial Gremlins concept art., DARPA

Keeping the price point low is essential for this concept since the drones have to be practical to use in large numbers and potentially with high attrition. DARPA already says each prototype vehicle only needs to keep working for at least 20 individual sorties.

“The Phase 1 program showed the feasibility of airborne UAS [unmanned aircraft systems] launch and recovery systems that would require minimal modification to the host aircraft,” Scott Wierzbanowski, DARPA program manager for Gremlins, said in March 2017. “We’re aiming in Phase 2 to mature two system concepts to enable ‘aircraft carriers in the sky’ using air-recoverable UASs that could carry various payloads – advances that would greatly extend the range, flexibility, and affordability of UAS operations for the U.S. military.”

Dynetics seems to have impressed Wierzbanowski and his colleagues enough with its concepts and prototypes to now move on to the next phase. It will be exciting to eventually see a demonstration of the complete system the company and its team are developing.

Contact the author: jtrevithickpr@gmail.com