Titan 4 Motor Explosion Blamed on Design Flaw

In its first detailed explanation of the April explosion of a prototype Titan 4 rocket motor at Edwards Air Force Base, the Air Force on Tuesday said the spectacular blast appears to have been caused by wayward combustion gases that partially blocked the solid fuel’s hollow core, through which the fiery thrust jet passes.

But Air Force officials said the problem should be relatively easy to fix.

“We consider this a defect in the design,” not in the manufacturing process, said Capt. Mark Borkowski, deputy program manager for the Air Force’s Titan 4 solid rocket motor upgrade program.

The blast caused about $40 million damage to a test stand and delayed the development program by at least a year.

Coming nearly two months after the April 1 explosion, Borkowski’s comments and a related Air Force written statement were the first substantial information released not only on what caused the explosion, but also on the extent of the damage at the test site and its effect on the program.

The blast caused the latest in a series of delays to the Air Force’s efforts to develop a more powerful solid-fuel rocket motor enabling its Titan 4 rockets to carry larger payloads--generally satellites.

The Titan 4 is the nation’s largest-capacity space vehicle after the space shuttle. In flight, a pair of the planned rocket motors would serve as boosters for the main Titan 4 rocket.

Air Force officials at the same time released their formal investigation report on an earlier Titan 4-related accident at Edwards, a Sept. 7 incident that killed one civilian worker and injured nine others when a crane collapsed and dropped one part of the three-segment rocket motor.

The April blast demolished a large portion of the test stand, which Air Force officials predicted will require the rest of this year to repair. That and time for Hercules Inc., the manufacturer, to replace the motor--with necessary modifications--will contribute to the yearlong delay, Air Force officials said.

The delay does not affect Titan 4 launches that use existing rocket motors, which are planned through next year by the Air Force and Martin Marietta Corp., the main contractor on the $7.3-billion program. But it will push back the Air Force’s 1993 date for receiving the more powerful next-stage motor, which had already been delayed by weather problems and a fire at a Hercules plant in March, 1989.

Borkowski said his office believes that the April blast occurred because hot gases generated by ignition of the rocket’s solid fuel were unable to escape freely through a 40-inch-diameter channel in the fuel, which funnels the thrust jet to the base of the rocket. The obstruction, Borkowski said, was created by burning gases shooting horizontally across the hollow core, which also pushed a portion of the solid fuel into the channel, creating more blockage.