DARPA Wants Swarms of Cheap “Gremlin” Drones

DARPA is looking for swarms of nearly disposable UAVs that can launch and be retrieved in mid-air

3 min read
DARPA Wants Swarms of Cheap “Gremlin” Drones
Image: DARPA

A gremlin is a sort of mythical fairy that RAF pilots blamed for causing mechanical problems with their aircraft as far back as World War I. This sounds like a bad thing, but apparently, gremlins were actually good luck charms for pilots. As long as you listen to your Irish girlfriend and feed them cream. Or something.

Anyway, Gremlins is also the name of a new DARPA program that’s seeking proposals to develop the technology to launch swarms of low-cost, reusable unmanned aerial vehicles (UAVs) over great distances and then retrieve them in mid-air.

In November of last year, DARPA asked for ideas for how to turn military planes into flying drone aircraft carriers. Gremlins seems to be an extension of that, with a particular focus on safe, reliable aerial launch and recovery of multiple UAVs. From a recent DARPA release:

The program envisions launching groups of gremlins from large aircraft such as bombers or transport aircraft, as well as from fighters and other small, fixed-wing platforms while those planes are out of range of adversary defenses. When the gremlins complete their mission, a C-130 transport aircraft would retrieve them in the air and carry them home, where ground crews would prepare them for their next use within 24 hours.

The gremlins themselves are somewhere in between disposable drones and conventional drones that are intended to last for years or decades. DARPA wants each gremlin to be able to fly a few dozen missions at most, making them more cost effective than disposable systems but also way cheaper than bigger, more complex drones that need continuous maintenance. Plus, the gremlins can always be used like disposable drones if necessary, undertaking missions that might be too risky for a more expensive drone.

The real tricky bit about this whole business is going to be the mid-air retrieval: how could a massive C-130 possibly go and snatch an in-flight drone? DARPA suggests UAV capture systems for ships might provide some inspiration. Specifically, DARPA references SideArm, a project that Aurora Flight Sciences has been working on that might look something like this:


In this concept image, which may or may not represent what the final SideArm system will look like, you’ve got a drone with a hook thingy on it, and a ship with a dangly thingy on it. The drone approaches the ship at speed and does its best to engage its hook thingy with the dangly thingy on the ship as it flies past. If everything goes well, the drone will be brought to a very abrupt and dangling stop. Fundamentally it’s a lot like the ground capture system (called SkyHook) that Boeing has for its ScanEagle UAV:

In this case, the ScanEagle UAV runs into a vertical wire with its wing, and the wire catches a hook on the UAV’s wingtip. It doesn’t look like a heck of a lot of fun for the UAV, but it was designed for this, so it doesn’t mind. So far, this is just about the best general idea we’ve got for stopping a UAV at a fixed point, and (for whatever it’s worth), it’s the best general ideal we’ve got for stopping a manned aircraft at a fixed point, too.

If we let our imagination go wild for a second, or maybe not even that wild, we could imagine a SkyHook-type system that could be attached to the back of a C-130, where UAVs hook onto it and slide right on into the cargo bay, one after another. And that’s even a little bit what the concept picture at the top of this article looks like, doesn’t it?

Before we end, if this whole thing sounds vaguely familiar in a retro sort of way, that’s because you’re thinking of goblins, not gremlins. The McDonnell XF-85 Goblin was a prototype for a chubby little jet fighter that could be deployed, retrieved, refueled, rearmed, and deployed again from the bay of a B-36 bomber in flight. There’s a lot of parallels between the Goblin and DARPA’s vision for Gremlins, if you throw a half century in between them. And from half a century ago (give or take), here’s an overview video of the Goblin test flight program:


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Robot with threads near a fallen branch

RoMan, the Army Research Laboratory's robotic manipulator, considers the best way to grasp and move a tree branch at the Adelphi Laboratory Center, in Maryland.

Evan Ackerman

This article is part of our special report on AI, “The Great AI Reckoning.

"I should probably not be standing this close," I think to myself, as the robot slowly approaches a large tree branch on the floor in front of me. It's not the size of the branch that makes me nervous—it's that the robot is operating autonomously, and that while I know what it's supposed to do, I'm not entirely sure what it will do. If everything works the way the roboticists at the U.S. Army Research Laboratory (ARL) in Adelphi, Md., expect, the robot will identify the branch, grasp it, and drag it out of the way. These folks know what they're doing, but I've spent enough time around robots that I take a small step backwards anyway.

The robot, named RoMan, for Robotic Manipulator, is about the size of a large lawn mower, with a tracked base that helps it handle most kinds of terrain. At the front, it has a squat torso equipped with cameras and depth sensors, as well as a pair of arms that were harvested from a prototype disaster-response robot originally developed at NASA's Jet Propulsion Laboratory for a DARPA robotics competition. RoMan's job today is roadway clearing, a multistep task that ARL wants the robot to complete as autonomously as possible. Instead of instructing the robot to grasp specific objects in specific ways and move them to specific places, the operators tell RoMan to "go clear a path." It's then up to the robot to make all the decisions necessary to achieve that objective.

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