A giant solid-rocket motor built by Hercules in Magna blew up Monday afternoon in California during the Titan IV rocket's first static firing, the latest setback for an accident-plagued project that is intended to give the Air Force a new, powerful rocket.

The 110-foot developmental rocket segment blew up at 2:17 p.m. MST, as Hercules workers listened to a live-audio feed from the test facility in California. The firing took place at Edwards Air Force Base, Calif., at the Phillips Laboratory Test Stand."The cause of the incident is not known at this time. Damage was confined to the immediate test stand area. There were no injuries," said Dave Nicponski, manager of government affairs for Hercules' Utah operations.

Hercules has been tightening its corporate belt, with a series of layoffs that are expected to continue for another two months. Much depends on the success of the Titan IV program.

Jack Modzelewski of the New York stock firm Paine Webber said Tuesday morning that the explosion seemed to affect Hercules' stock. "Right now the stock is down 61/2 points on the news, so it's lost literally 15 percent of its value just as it opens up here. That's the first impact that you have.

"Obviously this is an important program to Hercules, and you see it reflected in the stock prices here. The question is, is this fatal to the program, to the Titan IV motor that they're developing? The answer is no."

Hercules, based in Wilmington, Del., has projected revenues of $3 billion this year. Of that, "Titan represents a significant program, but not major," Modzelewski said. "Titan represents between $200 million and $250 million a year to them."

Overall, the program is only 8 percent of the corporation's business. That business is "pretty much spread all over" the country, he said.

Still, the Titan IV program is of major concern to the Hercules operations in Utah.

At a shareholders meeting last week, Tom Gossage, chief executive officer and chairman of the board of Hercules Inc., mentioned that Hercules' initial Titan IV contract was for $585 million. The prime contractor is Martin Marietta of Denver.

On Sept. 7, 1990, a Titan IV motordropped from a 400-foot crane at Edwards AFB and burst into flame. A technician, Alan Quimby, 27, was killed by counterweights that fell from the crane. Nine others were injured - two seriously - when the 270,000 pounds of solid rocket fuel dropped 70 feet to the ground, slid down a hillside and erupted in flames.

Just before that time, the Air Force Space Division at Los Angeles said Hercules Aerospace was already a year or more behind schedule in developing the new Titan IV motor.

In February Hercules was cited for safety violations by California's job safety agency, Cal-OSHA, because of the incident. Hercules and another company involved in the incident, Neil F. Lampson Inc. of the state of Washington, agreed to pay Quimby's family a $2.4 million settlement, according to the Associated Press.

The automated Hercules plant in Magna that cast the propellant for the Titan IV boosters, at the Bacchus West works, was shut down for several months in 1989 after a fire destroyed an 1,800-gallon propellant mixing device. The March 29, 1989, explosion shook the plant when fuel was being prepared for a Delta II rocket booster motor and nobody was injured.

Earlier, a Titan IV unit, a 28-foot center segment, was scrapped when the propellant failed to bond correctly to the case.

Nicpokski said the audio feed from California was lost soon after the explosion. "An Air Force investigation board will be appointed," he added.

When contacted by the Deseret News shortly after the accident Monday, an Edwards Air Force Base spokeswoman would say only that the test was unsuccessful. Later, the base issued a terse statement.

Ranney Adams, public affairs director for the Phillips Laboratory test facilities at Edwards AFB, said Air Force emergency crews responded to the explosion. "Base officials have determined that the test motor incident posed no danger to communities near the Phillips Laboratory," he said.

Edwards AFB doesn't launch missiles; the testing is conducted in a static, or fastened-down, mode to measure thrust levels or performance, he said.

Asked how much damage occurred to the test facilities, Adams said he didn't know yet. But he was trying to set up a press conference concerning the explosion.