The Accident Investigation Board, convened by the commander of AFSPC, determined that electrical shorts in the Vehicle Power Supply, VPS, wiring harness most likely caused the vehicle to catastrophically fail 41 seconds into powered flight. The shorts originated in the second stage of the core vehicle.

The Board found clear and convincing evidence that wire insulation damage existed in the VPS wiring harness, resulting in at least one powered conductor with exposed wire that went undetected during pre-launch inspections and tests. After liftoff, the exposed wire intermittently shorted as vehicle vibration increased.

The VPS battery, located in Compartment 2A, supplies power to the VPS and Accessory Power Supply systems. The power is distributed to other compartments, components, and sensors by a series of terminal boards and wire harnesses that are routed inside the vehicle compartments and down cable conduits that run the length of the stages on the outside of the booster.

The shorts within the VPS wiring harness momentarily caused a power outage of the Missile Guidance Computer, resulting in the loss of the synchronization signal to the Inertial Measurement Unit. This electrical interruption caused the rocket to lose its attitude frame of reference. When the intermittent shorting subsided and power was restored, the MGC came back online, responded to an incorrect attitude reference from the IMU, and issued a pitch down and yaw right command. The resulting pitch caused an aerodynamic angle of attack in excess of the structural design limits.

At this point, the vehicle's northernmost Solid Rocket Motor (SRM #1) separated from the core vehicle, leading to vehicle breakup. Once this occurred, the vehicle's self-destruct system activated in order to prevent uncontrolled flight.

The Titan IVA-20/NRO mission launched from Space Launch Complex-41 at Cape Canaveral AS. The booster was the last Titan "A" model scheduled for launch in the Air Force's inventory. The "B" model will continue to provide America's unmanned heavy lift capability until 2002, when the Evolved Expendable Launch Vehicle, EELV, is scheduled to become operational.

The cost of the Titan IVA-20 mishap is more than $1 billion. Costs include the launch vehicle, satellite, and range support. The Air Force, in concert with the Space and Missile Systems Center and Lockheed Martin Astronautics, has taken actions to address the findings of the investigation.

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SPACEDAILY HEADLINES

Nov 02, 2006