This article first appeared in Aerospace Daily & Defense Report.

The U.S. Air Force is considering -- once again -- delaying the retirement date for its workhorse intelligence collector, the U-2 Dragon Lady, as developers work out issues with integrating a signals intelligence payload onto the Global Hawk unmanned aerial vehicle (UAV), according to service officials.

The current plan calls for the completion of U-2 retirement in the third quarter of fiscal 2012. But the Pentagon is considering delaying the retirement to fiscal 2014 or possibly later, depending on the maturity of the Global Hawk. And retiring a mainstay intelligence collector like the U-2 during wars that require massive amounts of sensor data is also unlikely, according to one USAF official.

The USAF has wrangled for years with various dates for U-2 retirement. Earlier plans called for the retirement to start as soon as FY '07. But the date has continually slipped. Regional commanders such as in the Pacific realm rely heavily on the U-2. Key advantages of the aircraft over the Global Hawk include higher altitude (above 70,000 feet) and more available onboard power to run a larger selection of intelligence-gathering sensors.

The U-2 can collect data from all seven of its available bands (versus the Global Hawk's five) simultaneously. They include green, red, near infrared (visible), two shortwave infrared bands and a midwave infrared (which can be tuned to day or night collection). The seventh band is a redundant, midwave thermal infrared channel. The shortwave bands collect images in the invisible reflected solar wavelengths and are most useful in detecting objects in adverse conditions such as haze, fog or smoke.

The latest variants of the decade-old U-2S (part of the U.S. fleet of 33 remaining Dragon Ladies) also carry the Advanced Synthetic Aperture Radar System (ASARS) 2A designed by Raytheon (originally for mapping) that's so sensitive it can detect disturbed earth in areas where explosive devices and mines have been planted.

Its signals intelligence package gathers information about electronic emissions and communications and associates them with moving targets. The Air Force also procured a dual-data link that allows the aircraft to simultaneously feed information to the Distributed Common Ground Station network and also to a ground station within line-of-sight.

The Pentagon has said it will not retire the U-2 at least until the Global Hawk Block 30, which will carry the Advanced Signals Intelligence Payload, is flying. A USAF official said that flight could take place imminently. Another major milestone will be integration of the Multi-Platform Radar Technology Insertion Program sensor onto the Global Hawk Block 40 next summer.

Read the rest of this story, take a look at Poland's fighter buy, see the Zephyr UAV and the Russians' rocket-delivered UAV.

-- Christian