Shuttle Rocket Looks Flawless in Firing Test

The guttural roar of the world’s biggest solid rocket motor reverberated through the valleys of the Wasatch Mountains on Sunday, heralding the revival of the United States’ moribund space program.

Marking a critical milestone in the comeback of the grounded space shuttle, engineers carried out an apparently flawless captive firing of the shuttle’s 126-foot-long booster rocket.

It was the first full-scale test of the rocket since extensive modifications to a leaky seal that caused the destruction of the shuttle Challenger in January, 1986.

Inspections to Be Done

Officials of Morton Thiokol Inc., the rocket builder, and the National Aeronautics and Space Administration were jubilant at reaching the milestone with preliminary indications of success, but they cautioned that they will not fully know the outcome until the spent rocket is taken apart and inspected over the next month.

As many as 10,000 spectators lined a highway next to the Morton Thiokol test area as the booster, cradled in a horizontal test stand, ignited with a thrust of 1.2 million pounds.

A 500-foot-long orange plume shot against the base of a mountain and spewed upward, sending a boiling cloud of gray ash into the atmosphere.

Early indications were that the rocket, closely resembling the two boosters that will power the shuttle Discovery on a launch now scheduled for next June, performed flawlessly.

Minutes after the expended casing was flooded with carbon dioxide, turning it into a huge tube of dry ice, test officials inspected it at a distance through field glasses and found that the redesigned joints showed no sign of damage.

“From all indications, the redesign is three for three,” said John Thomas, chief of NASA’s redesign team, referring to two earlier scale-model tests of the new seal.

Later Sunday, engineers began analyzing data from nearly 500 sensors attached to the booster at critical points during the firing. To speed the answer to the vital question of whether the newly designed seal between the rocket’s segments survived the firing undamaged, a few engineers will crawl through the nozzle into the blackened interior of the casing for a preliminary inspection before the sections are taken apart later this week.

Cooling Problems

Sunday’s test came three days after problems with a water hose--designed to cool the casing after the firing--triggered a series of events leading to a postponement. During the Sunday firing, the cooling system failed again. Engineers inspecting the spent rocket said the paint on its lower segment was blistered. That indicated that the molten residue left after the engine shut down had burned the insulation inside the segment, making it doubtful that the segment could be reused.

The first close-up look at whether the redesigned seals survived the firing undamaged will come when inspectors enter the spent casing before it is taken apart.

“With the data we have now, it sure looks good to me,” said Richard H. Truly, NASA’s associate administrator for spaceflight. “I can assure you it is a major step along the way to returning the shuttle to flight.”

In recent weeks, Discovery has had its electronic systems reactivated at Kennedy Space Center in Florida, and in Mississippi the shuttle main engine has been fired for a duration of 16 minutes.

Major Factor

Acknowledging that NASA faces a foreboding task in meeting the scheduled Discovery launch in June, Truly said Sunday that the testing of the huge solid boosters in the Utah desert will continue to be the major event that determines the outcome.

If the new seal design, undertaken at a cost of $460 million, stands up under the scrutiny it will get in the next month, NASA and Morton Thiokol plan a test-firing in November of a booster identical to those to be used in flight.

But not until September, 1988, does the test plan call for a firing of a booster under cold conditions. Abnormally cold temperatures in Florida were found to be a contributing factor to the solid booster failure that destroyed the Challenger 72 seconds after liftoff 19 months ago.

Besides adding a third O-ring seal and a mechanical “capture feature” in the new design, engineers have equipped the joints of the modified booster with heaters to assure that the seals are at no less than 75 degrees at launch.

Cold Firing

Nevertheless, the test program calls for firing of a motor in which more than a million pounds of solid propellant has been chilled.

Because the heaters will assure that the joints are warm and because the first flights of the shuttle are planned for warm months in Florida, officials deemed it acceptable to restore the vehicle to flight status before conducting the cold test.

In tests with scale models, flaws have been introduced to see whether the new design is prone to leak, but so far there has been no damage to the rubber O-rings serving as the barrier to the escape of searing gases through the seal between the rocket’s joints.

Although they could not yet declare the critical test a success, officials emerged from the firing bunker Sunday afternoon with wide grins, and Thomas declared: “I think it is going to look as good from the inside as out.”

With a special committee of the National Research Council looking over their shoulders, NASA and Morton Thiokol officials settled last October on the new designs for the seals between the booster segments and between its lower segments and the rocket nozzle.

100 Bolts

Although some engineers outside NASA and Morton Thiokol have criticized the design for adding potential hazards with a ring of 100 bolts added to strengthen the joints, officials renewed their confidence in the design even before seeing final results of the critical test.

Royce Mitchell, chief of the solid rocket motor program office at Marshall Space Flight Center, called the redesigned motor “the most analyzed and inspected in history.”

Truly said Sunday that knowledge of the redesigned booster already exceeds that accumulated on the old rocket before the Challenger accident.

NASA and Morton Thiokol officials were aware of damage to seals in the booster rocket on several occasions before the Challenger accident but had pressed ahead with the launch schedule anyway.

When the accident occurred, photographs clearly showed that a seal in Challenger’s right booster had leaked an instant after ignition, with hot gases finally cutting through the steel casing to turn the shuttle into a fireball 10 miles above the coast of Florida.

Although expressing confidence in the hardware now being prepared for the resumption of flights, Truly said again Sunday that spaceflight can never be risk-free.

“The only way to have a risk-free space program,” he said, “is to get out of this business.”

The boosters for the first post-Challenger shuttle flight are to be shipped in December from Morton Thiokol to Kennedy Space Center.