D-21B anniversary


Message posted by Peter Merlin on September 28, 2007 at 9:06:38 PST:

Today is the 40th anniversary of the inadvertent "flight" of the first D-21B (Article 501).

On 28 September 1967, Article 501 (attached to its DZ-1 rocket booster) was carried aloft on the wing of a JB-52H from Area 51. The purpose was a captive-carry flight to allow engineers and flight crews to determine the handling characteristics of the mated aircraft and study the drone’s low-speed aerodynamics.

Experiencing some difficulty mating Article 501 to the pylon, a technician used a thread-tap on one of the forward attachment bolts. Although this facilitated the connection, it also weakened the threads on the bolt, leaving it vulnerable to stress.

As the launch control officer performed an in-flight checkout of the drone’s control surfaces, the forward attachment bolt failed. The D-21B/DZ-1 stack pivoted, shearing the aft attachment and causing the vehicle to drop away from the B-52. Five seconds later, the rocket engine ignited as automatic sequencing took over.

Because the drone’s inertial navigation system had not yet been programmed, the vehicle was unguided. The rocket pushed the vehicle to supersonic speeds, but instead of climbing, it lost altitude and crashed.

Article 501 was the only TAGBOARD drone to be carried on both the M-21 and the JB-52H. In its original configuration, it was used for captive tests with the M-21 variant of the Blackbird.


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