Shuttle Launch Was Warned About Cold : Engineers Suggested No Liftoff Below 51

Engineers concerned about the performance of solid rocket seals in cold weather suggested at one point prior to the launching of the space shuttle Challenger that liftoff not be attempted in temperatures below the previous low mark for shuttle departure, a National Aeronautics and Space Administration propulsion expert testified Tuesday.

Nevertheless, the Challenger and its crew of seven lifted off with the launch pad temperature at 38 degrees--13 degrees colder than the previous record low during a launching.

Under persistent questioning from the presidential commission convened to investigate Challenger’s disastrous Jan. 28 explosion, the solid rocket project manager at NASA’s Marshall Space Flight Center in Huntsville, Ala., provided significant elaboration about the level of preflight concern among engineers for Morton Thiokol, manufacturer of the rocket boosters.

“There were data presented,” Lawrence B. Mulloy said, “ . . . by Thiokol engineering that there was a suggestion that possibly the seal shouldn’t be operated below any temperature that it had been operated under in previous flights.”

Previously, NASA officials had admitted there had been discussions among NASA engineers and major shuttle contractors about the possible effect of cold weather on the launching, but said that there was no disagreement with the final decision to proceed. Mulloy’s testimony provided the first details about the nature of the cold weather concerns and revealed that Morton Thiokol’s engineers suggested no launch be attempted below 51 degrees.

Mulloy said any disagreements had been resolved prior to launching but he provided no elaboration.

A January launching in 1985 was conducted in 51-degree weather, the coldest ever in 24 shuttle flights before the Challenger mission. The next coldest liftoff temperature was 57 degrees, NASA officials said.

Photographs of the Challenger before the explosion have shown an unusual plume of hot propellant spewing from the right-hand solid rocket booster at or near one of four major seams in the multi-sectional missile. It has been widely speculated by experts inside and outside the space agency that the ever-widening plume triggered a catastrophic explosion in the shuttle’s adjoining fuel tank.

The rockets are assembled into four sections at a Morton Thiokol plant in Utah and then hauled by rail to the Kennedy Space Center in Florida for final assembly. The joints that hold the sections together are secured with an elaborate system of pins, protected by belts.

Inside the rockets, two rings of synthetic rubber--the O-rings--help prevent the jellylike propellant from blasting through the seams after the rocket is lit. A carefully laid buffer of flame-proof putty prevents the propellant from eroding the O-rings, providing a third line of defense.

Experiment Performed

Commission member Richard P. Feynman, a Nobel Prize-winning physicist from Caltech in Pasadena, began questioning Mulloy about cold weather effects on the O-rings after conducting an impromptu experiment on a small piece of the synthetic rubber material.

While Mulloy testified, the physicist removed an O-ring from a cross-sectional sample of a joint that the NASA official had brought as a visual aid for his testimony. He asked a NASA aide to bring him a small vise and a glass of ice water.

He screwed the rubber into the vise and submerged it in the cold water. Then he pulled it out and removed the vise, watching to see how quickly the synthetic rubber sprang back to its original shape.

It bounced back less quickly than it did without being dunked--evidence, Feynman said, that the rings would be less resilient in cold weather.

The point was important because Mulloy had testified earlier that some previous cases of contamination in the seal system had occurred in the fractional seconds before the pressures of rocket ignition fully set the rings to form a perfect seal.

Thus, if the synthetic rubber responded more slowly in the cold, it might allow the hot propellant more time to seep under the seals and carve a path out of the joint.

Noting his “little experiment,” the physicist asked Mulloy: “Does your data agree with this feature that the immediate resiliences in the first few seconds is very, very much reduced when the temperature is reduced?”

“Yes,” Mulloy said. “In a qualitative sense. I just can’t quantify at this time.”

The NASA official testified that research data indicated the O-rings should operate properly in temperatures as low as minus-30 degrees. But Mulloy said the data “is refuted by some other test data, and that is why we’re carefully running controlled tests under the specific conditions of 51-L (the mission designation) to understand the response of the O-ring seal . . . . “

Test Data Available

He said that “there also is a great deal of test data in (solid rocket boosters) down at temperatures where you can see a difference in the resilience of seals. For instance, down from 75 degrees down to 50 degrees. We have data that was presented on the 27th”--the day before launch--”by Morton Thiokol that indicated a further reduction in the resilience . . . if the temperature was down to 20 and 25 degrees.”

Because there is no insulation protecting the O-rings from outside weather, the temperatures of the rings generally correspond with the temperature outside the rocket, Mulloy said.

The overnight low before launch at the Kennedy Space Center was 28 degrees, according to weather reports from outside agencies. The NASA forecast for the overnight low at the time launch decisions were made the day before was for temperatures to drop to 25 degrees.

Mulloy said, however, that “it was the judgment that under the conditions we would see on launch day . . . that the seal would function at that temperature.

“That was the final judgment.”

An attempt to obtain a response from Morton Thiokol about the testimony was unsuccessful.

William P. Rogers, the former secretary of state heading the commission, cut off questioning about cold weather as several other commissioners began to join Feynman’s line of inquiry.

He said he preferred that the questions be asked at a session scheduled for Thursday at Kennedy Space Center. The press and public will not be allowed to attend that session, NASA officials said.

Earlier in the session, Mulloy had testified that post-flight examinations of solid rocket boosters in 23 other shuttle missions showed that six out of 171 joints between the rocket’s four main sections suffered “some erosion” of the primary O-ring. But he said a secondary O-ring had never failed.

Mulloy and other witnesses testified that the erosion, though viewed as a serious engineering problem, was never considered a threat to flight safety--testimony intended to counter the impression of a memorandum written by a NASA budget officer last July.

The author of the memorandum, which foretold catastrophic results if the seam erosion problem was not eliminated, also testified Tuesday. Richard C. Cook said that he was not an engineering expert but based his conclusions on interviews with engineers.

The commission released Cook’s July 23 memorandum--parts of which appeared in the New York Times on Sunday--and another report he wrote after the Challenger disaster.

In the later memorandum, he raised concerns about the interest of NASA in flight safety, points he conceded were made “in the heat of the moment.”

Cook said he had given notice to NASA that he was taking another job and worked his last day at the space agency last Sunday.

The possibility that the initial rupture of the solid rocket booster occurred through a small plugged hole also was discussed at the commission hearing. Mulloy said he could not rule out failure of a booster “leak test port,” a tiny hole in the booster wall that is plugged with a bolt, but hastened to add it was only one of many scenarios being studied.

The porthole allows technicians to check whether the O-rings were properly seated during assembly of the rocket sections. Each seam has one leak test port, and on the shuttle’s right-hand booster it was located near where the plume of hot gas from the rocket first appears in photographs.

No Checks in Last 38 Days

Meanwhile, at Kennedy Space Center, a NASA official told reporters that the Challenger’s solid rocket boosters were never physically examined by any NASA engineer in the 38 days the spacecraft sat on the launch pad before launching.

Thomas Utsman, deputy director of the Kennedy Space Center, said that no other shuttle ever sat through colder weather for a longer period of time. “Once it is moved to the pad, it is considered a structurally safe vehicle,” Utsman said. “There are no more physical tests to my knowledge.”