Rocket Motor Explodes During Test : Aerospace: No one is reported injured. Mishap occurs at same Edwards Air Force Base site as a fatal accident last year.

A Titan 4 rocket motor exploded during its first test-firing Monday at the same Edwards Air Force Base site where a crane accident involving the same type of motor killed a worker in September.

No one was injured when the motor, designed as a booster to be strapped onto the side of a Titan 4 rocket, erupted in flames on a test stand at the base’s astronautics laboratory, Air Force officials said. The cause of the accident was unknown and damage was confined to the test area on a desert plateau, officials said.

The explosion at 1:17 p.m. was filmed by television crews invited to the rocket motor’s first test-firing. A gray mushroom cloud of smoke was visible for miles. The smoke posed no danger to residents in surrounding areas, officials said.

Twenty technicians in a nearby fortified bunker were unharmed despite the magnitude of the explosion, which engulfed the test stand “in a couple of seconds,” said Col. Frank Sterling, director of the Titan 4 program.

The test was to last 140 seconds, but just after the rocket motor fired it exploded into a fireball.

“It looked like we had a good ignition sequence, the motor ignited and started to burn,” Sterling said.

Air Force investigators will try to determine whether there was a malfunction in the test stand or in the motor, using information supplied by video cameras and other monitoring equipment, Sterling said.

“Hopefully, when we get in and analyze the video camera data we can figure out what happened,” he said.

The test was conducted under Air Force supervision by Hercules Aerospace Corp. of Utah, a subcontractor building the rocket motor for the manufacturer of the Titan 4 rocket, Martin Marietta Corp., officials said.

Hercules and two other subcontractors were fined a total of $32,000 in February by Cal-OSHA, the state job safety agency, in connection with the September accident. A giant crane collapsed and dropped a motor segment being transported from the test stand, and a flash fire erupted. A technician was killed by falling counterweights. Nine other workers were injured, none seriously.

Monday’s accident occurred at the same test area, said base spokesman Dennis Shoffner.

The 110-foot motor, weighing about 770,000 pounds when filled with solid fuel, had been assembled and put in place during the preceding month for the first in a series of “static” tests in which the motor is fired while secured to the test stand.

The motor consists of three segments coupled with a nose-cone section containing electronic instruments, according to the Air Force.

Asked about the impact on the Titan program, which has been plagued with delays, Sterling said it is too early to tell until the extent of damage at the test site is known. The next test-firing at Edwards, scheduled for June, will probably be pushed back, but the Air Force can still meet its goal of using the new booster on Titan 4 flights by 1993 if no major flaws are discovered, he said.

Booster rockets are used to increase the size of the payload that the main vehicle can carry. They are considered particularly tricky because once they are started they cannot be shut down--even if something goes wrong.

A minor failure, such as a hairline crack in the side of the booster’s casing, can trigger a catastrophic failure, as was demonstrated when a leak in a solid rocket caused the space shuttle Challenger to explode in the worst space accident in U.S. history.

The type of booster being tested Monday has never been used before, and it is designed to increase the motor’s reliability and efficiency, officials said.

When complete, it is also supposed to be able to carry payloads into space 25% greater than the capacity of the booster now being used, Air Force officials said.

Times science writer Lee Dye contributed to this story.

TITAN 4 ROCKET

A development booster rocket for the Titan 4 was destroyed during its inaugural test-firing at Edwards Air Force Base on Monday. No injuries were reported.

Dimensions: The Titan 4 rocket consists of a two-stage, liquid-fueled rocket that is about 200 feet tall, plus 110-foot, strap-on, solid-fueled booster rockets. The boosters are 10 feet in diameter and weigh about 770,000 pounds each.

Launch cost: Approximately $200 million.

Payload: It can lift a 39,000-pound cargo into low Earth orbit or a 10,000-pound payload to a fixed orbit 22,300 miles high. By comparison, the space shuttle can put a 52,000-pound payload into orbit.

Engines: Two solid-propellant boosters. Liquid-fueled main engines.

Fuel: Hydrazine and nitrogen tetroxide propellants for the solid rocket boosters and liquid oxygen / hydrogen for the liquid rockets.

Compiled by Times editorial researcher Michael Meyers