May 28, 2013
Credit: Northrop Grumman
Carrier-based flight trials of the U.S. Navy’s X-47B Unmanned Combat Air System-Demonstrator (UCAS-D) aboard the USS George H.W. Bush were briefly brought to a halt last week due to an unlikely frequency-sharing issue between the air vehicle and officials of the National Oceanic and Atmospheric Administration, which is trying to fix a problem with a faulty weather satellite.
The U.S. Navy was able to restart flights of the Northrop Grumman X-47B demonstrator quickly after a brief stand down, which was necessitated because priority use of the Wallops Island facility in Virginia, the UCAS-D backup landing site, was given to NOAA as it worked to recover control of its Geostationary Operational Environmental Satellite (GOES)-13.
Trials are now complete and the X-47B performed nine touch-and-go landings on the carrier deck, according to Capt. Jamie Engdahl, Navy program manager.
NOAA began losing data from GOES-13 on May 21 when the satellite lost attitude control. NOAA officials operate the GOES satellites from a Command and Acquisition Data Station at Wallops. Without a backup landing site, UCAS-D was stuck on the carrier.
At issue was the fact that both NOAA’s GOES data and the Navy’s UCAS telemetry are transmitted in the same S-band frequency, according to program officials.
GOES-13, the first of a three-satellite series made by Boeing, is parked 22,000 mi. over the Eastern U.S. It is instrumental in predicting hurricane activity. Because it is so far from the receivers at Wallops, those receivers are designed to be very sensitive. UCAS blasts its communications, by contrast. Thus, NOAA was worried about harming its antennas if UCAS diverted to land while operators were communicating with the satellite. Because NOAA officials have been working on a software fix for the GOES-13 attitude control problem, they require constant use of the antennas. NOAA officials are still working on a fix for GOES-13 and are temporarily using data from GOES-14, its in-orbit backup, to maintain some continuity, though the latter is orbiting farther west than the primary GOES-13.
The temperamental satellite and unavailability of the backup landing site at Wallops prompted Navy officials to cancel the UCAS flight from the carrier deck on May 22. “There have been no other impacts to our [carrier] operations due to the GOES-13 failure,” Engdahl says. The primary landing site for the carrier operations was NAS Patuxent River, Md.
The X-47B began the first-ever flight trials of a stealthy, tailless unmanned air vehicle with a historic catapult launch from the deck of the aircraft carrier on May 14. The two Northrop Grumman X-47B aircraft are designed for intelligence collection and limited strike. They are being used by the Navy to demonstrate whether such aircraft can function on and around the carrier deck without interrupting the tempo of the air wing’s operations.
The frequency conflict only affected one planned flight, and the ship-based portion of the UCAS-D trials wrapped up last week.