Our colleague Zach Rosenberg filed on the US Defense Advanced Research Projects Agency's completion of a flight test programme intended to prove the viability of autonomous high-altitude refuelling involving unmanned air vehicles.
Performed using a pair of NASA-owned Northrop Grumman RQ-4 Global Hawks, the activity showed that refuelling could have been successfully conducted during 60% of the attempts made, DARPA says. The work didn't stretch as far as making contact between the hose-and-drogue-equipped aircraft - which in this case is actually the one that would be receiving the fuel - and the probe-fitted "tanker" though.
A series of photos from the test programme included this weird-looking angle of the two high-altitude, long-endurance aircraft. A Global Hawk biplane? Looks like a cool idea to me.