WASHINGTON -- The explosion in April of a Titan 34D rocket shortly after takeoff most probably was caused by insulation failure near a joint of the solid rocket motor that inspectors did not detect before the flight, the Air Force said Wednesday.
The 'O' ring seals in a joint of the solid-rocket booster that were traced as the cause of theChallenger shuttle explosion in January were not blamed for the Titan failure at Vandenberg Air Force Base, Calif., April 18, an Air Force investigation concluded.
'This was a real surprise to us,' said Brig. Gen. Nathan Lindsay, who headed the investigation. He commanded the Eastern Space Missile Center at Patrick Air Force Base, Fla.
The explosion, the second loss of a $70 million Titan in eight months, meant the destruction of a secret payload said to be a Big Bird spy satellite and contributed to a setback in the nation's space program, already severely retarded by the Challenger failure in January.
The Titan, a backbone of the nation's rocket inventory, exploded about nine seconds after ignition of the two solid-rocket motors and when the rocket was 800 feet above the launch pad, Lindsay said. The explosion caused $70 million worth of damage to the pad and an adjacent facility, he said.
'We believe the cause of the mishap was a failure in the thermal insulation in a segment of one of the two solid rocket motors,' Lindsay said. 'The rubber insulation most likely separated from the steel rocket motor case, allowing damage by the propellent combustion products.
'The failure occurred 5 inches below the joint between motor segments. The 'O' ring seals of the solid rocket motors did not contribute to the mishap.'
There are seven joints that make up the cylindrical tube of the rocket. The failure occurred '5 to 7 inches' below the second joint from the bottom, Lindsay said.
'It was a failure we would have assigned a very, very low probability of happening,' he said.
Lindsay was asked whether there was a failure by pre-flight inspectors to detect the separation of the insulation from the steel inner core of the second rocket motor.
'I believe so,' he replied.
The general predicted the Titans will resume flying early next year after the adoption of new inspection and manufacturing techniques to preclude future failures of a similar nature.
'What we're going to do now is re-establish the confidence,' Lindsay said. 'I feel confident that these vehicles will be back flying in a timely manner.'
Lindsay said separation of the insulation was the 'most probable cause' of the explosion and that further analyses will be made for a definite conclusion about what happened. He said the investigation will take several more months.
There was 'no idea why' the bonding that held the insulation to the steel had separated, the one-star general said.
Separation of the insulation was the 'only way' that the fuel burning at high temperatures could get at the steel, which is three-eighths of an inch thick, he said. The pressures on the steel casing at that point in the rocket motor is 700 pounds per square inch. The pressures and high temperatures eroded the steel, he said.
Lindsay described the insulation material as 'very excellent when working.' He said there had been 940 firings of the rocket motors and about 70 Titan flights with the two boosters without problems with the insulation.
The rocket motor that exploded was 5 years old, but Lindsay said the system has an indefinite shelf life. It was built by the Chemical Systems Division of the United Technologies Corp. of East Hartford, Conn. The motors first were developed between 1962 and 1964, Lindsay said.
The solid rocket boosters aboard the Challenger were built by the Morton Thiokol Co.
'We found no evidence of solid rocket motor design deficiencies,' Lindsay said. 'There is no relationship between this mishap and either the Challenger tragedy last January or the August 1985 loss of another Titan 34D.'
A massive fuel leak and a turbopump failure caused the Titan explosion in August, the Air Force has said.
Before another Titan launch, Lindsay said, there will have to be 'extensive inspection and testing programs. Also, we have recommended an exhaustive audit of manufacturing controls and inspection programs for new solid rocket motor segments.'