The US Defense Advanced Research Projects Agency (DARPA) and NASA have demonstrated what is claimed to be the world's first "hands-off" autonomous air refuelling engagement using a satellite-guided approach system invented by Sierra Nevada (SNC).
The flight tests, using a NASA Boeing F/A-18 configured as a surrogate unmanned air vehicle and an Omega Air Refueling Services Boeing 707-300 tanker, are being conducted at Edwards AFB, California. The first autonomous engagement took place on 30 August, during the seventh of eight flights planned for the 15-month autonomous airborne refuelling demonstration (AARD) programme. The AARD aims to prove the feasibility of overcoming the two key challenges to in-flight refuelling UAVs, namely aligning the refuelling and receiving aircraft on an identical heading, and precisely closing the final space between the receiver's probe or receptacle and the tanker's basket or boom.
The F/A-18 pilot gave approval at some stages of the manoeuvre, but the procedure was otherwise autonomous
SNC, which pioneered precision landing systems for UAVs, proposed a derivative technology test for UAVs to DARPA around two years ago based on differential GPS, which corrects for positioning errors between moving aircraft and a fixed location. The resulting AARD programme couples SNC's concept - which uses relative GPS to transmit navigation corrections between two or more moving aircraft - with an optical tracker system.
DARPA says that during the test "the pilot [in the F/A-18] provided approval to proceed at several stages of the manoeuvre, but was otherwise hands-off".
NASA test pilot Dick Ewers, who acted as safety pilot, adds that during the final seconds of the manoeuvre there were "none of the last-second, high-gain stabs at the basket that we often see with human pilots. The computer approach was unbelievably stable and smooth, with deliberate movements throughout". The AARD system did make several misses, engaging just twice out of six attempts. However DARPA says "as important as the successful engagements, the system safely recovered from each missed attempt".