The Defense Advanced Research Projects has whittled down the competition for its retrievable drone programme, Gremlins, to Dynetics Inc. and General Atomics Aeronautical Systems, the agency announced last week.

DARPA is working alongside the Air Force Research Laboratory on Gremlins, a programme that envisions swarming UAVs launched from a variety of aircraft before in-flight recovery by a Lockheed C-130. The agency recently completed phase 1 of the programme, which explored design concepts and matured recovery capabilities. Dynetics examined cost requirements during this phase, including a limited airframe design that allows for an expendable UAV, says Tim Keeter, Dynetics deputy programme manager and chief engineer for Gremlins. Phase 2 will include major ground test events, he adds.

Dynetics and General Atomics will work for 12 months on the second phase, which will develop critical technologies for the demonstration in phase 3, Keeter said in a 20 March interview. DARPA will downselect again for the third phase and one contractor will conduct a launch and recovery flight test with multiple UAVs by the end of 2019.

The Defense Department has hyped up Gremlins for the past two years as part of its third offset initiative, but the concept of recoverable air vehicles and unmanned systems is nothing new. The US Air Force attempted aerial recovery as far back as 1945 with the McDonnell XF-85 Goblin, a parasite fighter launched and recovered by a B-36 bomber. Unlike the unmanned Gremlins, a pilot was supposed to sit in the small, bulbous Goblin until it was released from the bomb bay to fight adversaries. During a 1948 flight test with a B-29, turbulent and dangerous air flow under the bomber foiled plans to capture the Goblin with a trapeze system.

In the Vietnam era, the Defense Department tried its hand at recoverable drones with the high-speed Ryan Aeronautical BQM-34F Firebee target UAV. The air force would launch its BQM-34Fs from the ground or from a C-130. After performing its mission, the Firebee was often recovered with the mid-air retrieval system (MARS), in which a helicopter would snatch up the drone by its parachute. Still, the programme did not recover multiple UAVs in a short period of time.

Dynetics took lessons from previous retrienable UAVs, including the Goblin, Keeter says. Like Gremlin’s predecessors, aerial recovery in a turbulent environment remains a challenge. Dynetics must consider safety and potential interactions as the small UAVs come closer to the manned aircraft, he says.

“The key here is not only are we going to dock but you have to then safely retrieve that item into the back of a manned aircraft,” he says.