With a rumble and a flash of fire, America's space program headed back to the heavens with the successful test firing of a fully redesigned shuttle rocket.

Thursday's test at Morton Thiokol Inc.'s Wasatch Operations plant west of Brigham City was the last hurdle Utah engineers had to clear before the shuttle Discovery could take off as scheduled in October."The hardware and the data would tell us that this booster is ready to fly," Royce Mitchell, manager of the solid rocket motor program at NASA's Marshall Space Flight Center, told a jubilant crowd. "Everything looks great. We're very anxious to take it apart, which will occur next week. It's a super day for the space program and it's a great feeling overall."

The 126-foot-long white motor was anchored on its side and loaded with 1.2 million pounds of rubbery propellant. The motor was extensively flawed to allow hot gases to leak through to the primary O-ring seals.

The seals held up to the thermal assault, and both Thiokol and NASA officials were smiles all around at the last of five tests required before Discovery's flight.

The design changes incorporated in the booster were ordered in the wake of the January 1986 shuttle Challenger accident, to prevent a repeat of the explosion that grounded America's space program for nearly three years.

"Today's test is significant because it contains some 14 deliberate, man-made flaws" running "tip to toe" on the booster, said Mitchell.

Allan McDonald, vice president of space programs for Morton Thiokol, said it has been a long 2 1/2 years since he first warned against launching Challenger from a frigid Cape Canaveral, Fla.

"I left my daughter when she was 3. Now she's 51/2," McDonald said as he talked of the sacrifices Thiokol and NASA engineers made during the $400 million redesign project.

"I guess this is the final exam. We thought that it would take several days to hear what kind of grade we got," McDonald said, adding, "I think I have enough data now to say we got an A-plus."

With completion of the test in which McDonald said engineers saw "absolutely no indication of leakage" through the myriad of leak paths engineers built into the booster, Morton Thiokol boosters are now certified to fly on Discovery.

"We finally crossed the finish line, but we won't get the prize until Discovery's in orbit," McDonald said.

Mitchell said indications are that a series of glitches at Kennedy Space Center with leak problems on Discovery show the launch date of late September or early October may now be slightly ahead of schedule.

Thrill seekers began lining the two-lane highway straddling the testing area about 10 a.m. The campers and coolers were in place, and cheers ready when the two-minute test went off as expected at 1 p.m.

"That's the longest two minutes I've spent in a long time," said Rear Adm. Richard Truly, deputy space flight director for NASA.

Separations were built in between insulation and the case where the igniter is bolted into the motor.

A hole was deliberately placed in the insulation, and another leak path was drilled into the joint where the motor nozzle is sealed to the booster.

The holes were designed to allow hot gases to leak through and reach the primary O-ring joints. A tiny blowhole in the insulation between two field joints allowed hot gases to pass from the booster and ingnite Challenger's huge external fuel tank.

Engineers also fiddled with the size of the holes and components in the stringent test to verify the booster rocket can withstand anything nature and fate can throw at it.

"Not only is today's test very important because it's the last, it is also a very, very severe test of the redesigned solid rocket motor," said David Ewing, deputy director of program management for Morton Thiokol.

The cheers and whistles were immediate as the 500-foot flame scorched the mountainside and sent smoke and soot thousands of feet into the blue Utah sky. A helicopter and weather balloons soared overhead to measure sulfur and smoke levels from the test.

"It's been a long 2 1/2 years for a lot of people," said Ed Garrison, president of Morton Thiokol's Aerospace Group. "Morale is very high. Everybody is very excited. We got a big job behind us."

Gerald Smith, manager of NASA's solid rocket booster program, was "elated. Ecstatic."

"This was just a major milestone in return to flight. It demonstrates in my opinion we have just an outstanding design," Smith said, as NASA employees slapped each other's backs and shook hands.

John Thomas, who oversaw Thiokol's redesign program for the National Aeronautics and Space Administration, said, "I think this proves we knew what we were doing."

NASA and Thiokol took much criticism from politicians, scientists, the public and the press following the Challenger explosion as questions surfaced about the National Space Agency and Thiokol's rush to launch space shuttles. "I think the joint is the safest thing on the shuttle," said McDonald, who said each $20 million test added more data from which engineers could prove that the design would work.

Disassembly will begin next week, and the booster design will go through final flight-ready evaluation before the end of August at Marshall Space Flight Center in Alabama and in NASA's Washington, D.C, headquarters.

A cold-weather test in which the propellent will be cooled to 40 degrees Fahrenheit is scheduled for December, but is not required before shuttle flights resume.