A coworker of mine was an SR-71 Reconnaissance Systems Officer (backseater) from 1985 through 1990. We've talked at length about the Blackbird and reconnaissance in general. It's interesting to note that, while the Blackbird has been out of the Air Force inventory for about 14 years, the good old U-2 just keeps on going. In fact, next year will see the 50th anniversary of the U-2A's first flight. All of the operational versions were recently upgraded to the U-2S version.

Why would a seemingly obsolete, vulnerable, and slow plane be kept in the inventory so long? There are several reasons. One, the U-2 is much less expensive to operate to do the same mission. I've read that it cost over $100,000 an hour to operate a Blackbird and I don't know if that included the cost of stationing all those tanker planes (loaded with a special fuel unique to the Blackbird) along the flight route. The Blackbird had to refuel immediately after takeoff and then every hour or so afterwards.

Perhaps more importantly, the U-2 has the ability to loiter over an area for hours. That seems to be the key. If you look at virtually all of the UAV programs out there, almost without exception, they're designed to loiter over an area for hours at a time. For example, the Global Hawk (the likely U-2 replacement) can fly some 1000 miles from its base, loiter over an area for 24 hours or more, and then return home, all the while relaying its data in near real time via satellites.

By contrast, the Blackbird or something presumably faster like the rumored Aurora program, could blast over its target in a matter of seconds. At Mach 3.15 (typical SR-71 cruise speed), the turning radius was several hundred miles. In the end, you got some really sharp photos or other sensor data (such as side looking radar images), but for only an instant in time. The ability to loiter over an area has proven extremely useful.