An experimental spy plane with a wingspan almost the size of a Boeing 747 took to the skies over the Mojave Desert last week in a secret test flight that may introduce robotic planes flying higher, faster and with more firepower, the Los Angeles Times said.
Powered by liquid hydrogen, the massive Global Observer built by AeroVironment Inc. is capable of flying for a week at 65,000 feet, out of range of most anti-aircraft missiles.
Current spy planes can stay airborne for only about 30 hours.
The new plane is built to survey 448,000 sq km - an area larger than Afghanistan - at a single glance.
That would give the Pentagon an "unblinking eye" over the war zone and offer a cheaper and more effective alternative to spy satellites watching from outer space, the newspaper said.
The estimated $30-million robotic aircraft is one of three revolutionary drones being tested in coming weeks at Edwards Air Force Base.
Another is the bat-winged X-47B drone built by Northrop Grumman Corp., which could carry laser-guided bombs and be launched from an aircraft carrier.
The third is Boeing's Phantom Ray drone that could slip behind enemy lines to knock out radar installations, clearing the way for fighters and bombers.
These would represent a major technological advance over the Predator and Reaper drones that the US has deployed in Afghanistan.
Unlike most of the current fleet of more than 7,000 drones, the new remotely piloted planes will have jet engines and the ability to evade enemy radar.
"We are looking at the next generation of unmanned systems," said Phil Finnegan, an aerospace expert with Teal Group, a research firm.
"As the US looks at potential future conflicts, there needs to be more capable systems."
The Global Observer drone is designed to do the work that so far has been done by satellites, including relaying communications between military units and spotting missiles as they are launched, the Times said.
The Pentagon has increasingly focused on drones because they reduce the risk of American casualties and because they can be operated for a fraction of the cost of piloted aircraft.
Currently, combat drones are controlled remotely by a human pilot.
With the X-47B, which resembles a miniature version of the B-2 stealth bomber, a human pilot designs a flight path and sends it on its way, A computer programme would guide it from a ship to the target and back.
"The X-47B represents game-changing technology that will allow American forces to project combat power from longer distances without putting humans in harm's way," said Paul Meyer, general manager of Northrop's Advanced Programs & Technology division.