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After two historic carrier landings, Navy's X-47B drone scrubs a third

A X47-B Navy drone approaches the deck as it lands aboard the nuclear aircraft carrier USS George H. W. Bush off the Coast of Virginia Wednesday, July...
A X-47B Navy drone approaches the deck as it lands aboard the nuclear aircraft carrier USS George H. W. Bush off the Coast of Virginia Wednesday, July 10, 2013. It is the first landing by a drone on a Navy carrier. Steve Helber

The third time was a miss. After two successful landings on an aircraft carrier — including the first ever by an autonomous drone — the X-47B drone "Salty Dog 502" aborted a third landing attempt after one of its three on-board navigation systems failed.

An X-47B pilot-less drone combat aircraft comes to a stop after landing on the deck of the USS George H.W. Bush aircraft carrier in the Atlantic Ocean...
An X-47B pilot-less drone combat aircraft comes to a stop after landing on the deck of the USS George H.W. Bush aircraft carrier in the Atlantic Ocean off the coast of Norfolk, Virginia July 10, 2013. Rich-Joseph Facun

The anomaly was picked up by the functioning two computers, which alerted the crew monitoring the flight. An operator greenlit the backup plan to divert the drone to NASA's Wallops Flight Facility in Virginia, U.S. Navy officials reported Thursday.

At a teleconference, Navy and Northrop Grumman representatives shared details about the first series of landings performed Wednesday by the X-47B "Salty Dog 502" on the USS George H. W. Bush aircraft carrier, off the coast of Virginia.

While operators weren't planning for the glitch that cancelled the third landing, such an abnormality was not atypical for such a test flight, said Rear Admiral Mat Winter, program executive officer for unmanned aviation and strike weapons. "It's to be expected," he said.

A X47-B Navy drone touches down as it lands aboard the nuclear aircraft carrier USS George H. W. Bush off the Coast of Virginia Wednesday, July 10, 20...
The landing of the X-47B experimental aircraft means the Navy can move forward with its plans to develop another unmanned aircraft that will join the existing fleet. Steve Helber

Except for that one hiccup, the long-anticipated demonstration went off as the 100 or so witnesses on board the aircraft carrier had hoped.

"The ability to bring together the technical and operational capabilities into the carrier environment was nothing short of amazing," Winter said today.

"What struck me was the ease at which everything happened," Capt. Jaime Engdahl, navy unmanned combat air system program manager, added.

One of only two X-47B drones in the program, Salty Dog 502 touched down for the first time at 1:39 p.m. Wednesday, and snagged the third wire that stretched across the deck (one of many possible wires to grab) before coming to a rapid "arrested" stop. Carrier engineers then launched the aircraft once again from the deck, and after circling, the craft performed a second successful landing, this time hooking the second wire.

After a "hot refueling" — in which an aircraft's tank is topped up when it's still operating, another first for the X-47B — the drone was back in the air.

Drones that fly today have an element of independence, or "autonomy," a period in which the machine uses a pre-programmed set of instructions to take off, navigate and land. The X-47B was built to test the viability of maneuvering, operating and landing an autonomous craft while miles out at sea.

The fact the craft doesn't have a tail makes it harder to stabilize and control. Winter said it was a "deliberate decision" to lose the tail early in the design process, to better stress and test the control algorithms that were being developed to launch, fly and land the bird.

One of the two X-47B drones (there's also a "Salty Dog 501") will be launched for more tests on the carrier on Monday, to repeat similar launch and landing maneuvers, but no new objectives are lined up. The Navy is "assessing other uses" for the two X-47B aircrafts before they are packed away for display in museums.

Nidhi Subbaraman writes about technology and science. Follow her on Facebook, Twitter and Google+.