Copyright 1986 The New York Times Company
The New York Times
February 25, 1986, Tuesday, Late City Final Edition
SECTION: Section C; Page 1, Column 1; Science Desk
LENGTH: 3318 words




JUST four weeks after history's worst space disaster, much is already known about the events and circumstances preceding the space shuttle Challenger's explosive end. Suspect components, cold weather and some apparent lapses in human judgment all seem to be implicated.

The pieces of the puzzle, when fitted together, begin to tell of the roles of key engineers and managers in critical shuttle decisions, the knowledge available to them and withheld from them and the pressures under which they worked and made the decision to launch the Challenger on its last mission - a mission that would bring the American space enterprise to an indefinite halt.

With public hearings into the disaster set to resume today, a cascade of new disclosures is likely to expose other flaws in shuttle systems and in the decision-making process leading up to the launching on Jan. 28 that killed all seven aboard the Challenger. More questions will undoubtedly be raised about malfunctions in the right booster rocket. New evidence will be presented about serious safety concerns that, for reasons that are still mysterious, were not called to the attention of top space agency managers.

But even now a gripping story has emerged in interviews with participants and expert observers; in testimony before the Senate and the Presidential Commission investigating the disaster, and in videotapes and documents released by the National Aeronautics and Space Administration. At Cape Canaveral, Ominous Weather It was in Florida, and as usual the weather was on everyone's mind, but this time it was the cold and the rain. At the Kennedy Space Center at Cape Canaveral, bad weather had caused two postponements of the Challenger launching in three days.

The launching had been scheduled for Sunday morning, Jan. 26. The night before, however, NASA officials heeded forecasts of rain and decided against trying to go on Sunday. As it turned out, Sunday's weather was perfect for launching, but it was too late to do anything about it.

On Monday, Jan. 27, the skies were cloudy but predicted to clear, and so the crew boarded the Challenger, ready to go. They probably would have, too, if it had not been for a balky handle on the shuttle hatch. Workers struggled two hours to remove the stuck handle. By that time, stiff winds whipped through the launching site and forced a one-day postponement, to 9:38 Tuesday morning.

The winds were bringing in a cold front. The forecast, issued in mid-afternoon, was for freezing temperatures through the night. Concerned about the weather, officials of NASA and the major shuttle contractors, particularly Morton Thiokol Inc., manufacturer of the booster rockets, conferred through the evening.

''When we saw those predicted temperatures, I just knew we had to talk about it,'' said Allan J. McDonald, a Morton Thiokol engineer at the Cape, who argued strongly against proceeding with the countdown.

A decision had to be made by about midnight, after which liquid hydrogen and liquid oxygen would be pumped into the shuttle's huge external fuel tank.

So much was riding on the mission. NASA was pressing to conduct 15 flights of its four shuttles in 1986, six more than in any previous year. This launching was to be the first from pad 39-B, and proving the capability of an extra pad was essential to the success of the accelerated flight schedule.

This was to be the 25th shuttle flight, a symbolic moment that was to affirm the safety and reliability of the new re-usable vehicles and help quell criticism of the program. To accentuate this, the crew included the first ordinary citizen passenger, the schoolteacher Christa McAuliffe.

Space agency officials insist that in the countdown no compromises were made with crew safety. But the delays had been most frustrating. One engineer said, ''Nobody wants to be the one that says 'No' '' to liftoff.

Mr. McDonald cast himself in the naysaying role. By late afternoon on the day before launching, he initiated a telephone conference between engineers at the Cape and at Morton Thiokol's plant near Brigham City, Utah, and with several NASA officials. The Marshall Space Flight Center in Huntsville, Ala., was in charge of the design and performance of shuttle propulsion systems.

According to all accounts, Mr. McDonald and other Thiokol engineers recommended against proceeding with the countdown. They were concerned over the effect of the cold weather on the solid-fuel booster rockets. The lowest temperature at a previous launching, in January 1985, was 53 degrees Fahrenheit. The seals had never been tested below 47 degrees. The forecast was for temperatures in the 20's overnight and in the 30's at launching time.

The seals had a history of problems. These are a double set of synthetic rubber O rings, shaped like giant washers, that fit around the circumference of the rocket casing and are intended to fill the tiny gap that remains after two steel rocket segments are bolted together.

In 1982, a year after the shuttles started flying, engineers discovered that the enormous pressures in the rocket could cause the steel casing to bulge, exerting rotational forces at the joints that could dislodge the backup seal and make it inoperative. In March 1983, L. Michael Weeks, deputy associate administrator for space flight in charge of technical issues, signed the waiver to keep the shuttle flying even though only a single O ring could be counted on in some circumstances to contain the propulsion gases.

A further problem of seal erosion came to light last summer as a result of post-flight inspections. At a high-level management meeting at NASA headquarters in Washington in August, Mr. Weeks said, the recommendation was that ''analysis of the existing data indicates it is safe to continue flying the existing design'' but that ''efforts need to continue at an accelerated pace to eliminate solid motor seal erosion.''

But Richard C. Cook, a budget analyst at NASA headquarters, said that each time a shuttle took off engineers who knew of the seal erosion ''held their breath.''

Thiokol engineers had come to suspect that cold weather could only heighten the chances of a failure of the O ring seals. It made the rubber harden and shrink, increasing the likelihood that the seals would be breached. The consequences, they concluded, could be catastrophic. Heated Talks on Cold End With a Go-Ahead With all this in mind, Mr. McDonald continued arguing against launching, making his case in a meeting with NASA officials, including Lawrence B. Mulloy, the head of NASA's solid-fuel booster rocket project at Marshall, and Stanley Reinartz, the shuttle project manager at Marshall. Both Mr. Mulloy and Mr. Reinartz were at the Cape. Mr. Molloy said the telephone conference with engineers in Utah had ended with a tentative recommendation not to try a liftoff if the temperature was lower than it had been at the January 1985 launching.

Sometime afterward, though, the meeting of NASA and Thiokol officials at the Cape was recessed for a planned five-minute break. The recess lasted more than half an hour, and when the meeting resumed, top Thiokol managers in Utah had reversed themselves, for reasons not yet clear, and approved the launching.

Joe C. Kilminster, a company vice president in Utah, signed a one-page memorandum at 11:45 P.M. and it was transmitted immediately to the Cape. The company warned that the O rings would harden in the cold and thus take longer to ''seat'' properly.

Jesse W. Moore, NASA's associate administrator who had to make the ultimate decision to ''go'' for launching, said that nothing of the heated debate reached him. If he had known, Mr. Moore said, ''I would certainly have asked a lot of questions.''

As predicted, temperatures fell below freezing. At 6 A.M. the temperature was 27 degrees, and the shuttle's orange external tank was white with ice and frost.

Technicians who inspected the Challenger and launching pad three times that morning reported finding icicles one foot to two feet long hanging from water pipes. Arnold D. Aldrich, manager of shuttle integration at the Johnson Space Center in Houston, said the only weather concern discussed at morning meetings was whether the ice might shake loose during liftoff and damage the soft thermal tiles that protect the shuttle from burning up when it descends through the atmosphere.

Mr. Aldrich testified to the Presidential commission that the icing conditions were ''quite within bounds'' for shuttle operations.

At 9:07 A.M., after the astronauts were seated in the Challenger, wearing gloves because the interior was so cold, ground controllers broke into a round of applause. Still, the countdown was halted, primarily to wait for the morning to warm up and melt some of the ice. It turned out to be a two-hour postponement.

The ice team returned to the pad to take optical infrared measurements looking for hazardous conditions. (The team's visits had come at 1:30 A.M., 7 A.M. and 11 A.M.) The team noted readings of 7 and 9 degrees in the right-hand booster rocket, much lower temperatures than in the left booster. Temperatures may have dropped as low as 8 degrees Fahrenheit below zero on a strut connecting the rocket to the external fuel tank. It was later thought this might have been the effect of winds whipping over the Challenger's tank of supercold fuel and refrigerating the rocket. Some experts have theorized that the low temperatures could have also been a result of a leak of very cold hydrogen from the external fuel tank.

Since the team's primary assignment was to check for unwanted ice, the infrared measurements apparently went unheeded. The readings might have been spurious or evidence of a real problem, but they were not brought to the attention of Mr. Moore and other high-level managers.

All this time, the crew was waiting patiently in the Challenger's cabin. Francis R. (Dick) Scobee, the mission commander, and Comdr. Michael J. Smith of the Navy sat at the controls. Behind them in the center flight engineer position sat Dr. Judith A. Resnik, with Lieut. Col. Ellison S. Onizuka of the Air Force seated to her right behind Commander Smith. Below, in the mid-deck, were the other crew members, Dr. Ronald E. McNair, Gregory B. Jarvis and Mrs. McAuliffe.

When at last the countdown was resumed, at T-minus-9 minutes, there were no further delays. The temperature at the pad was 38 degrees. At 6.6 seconds before liftoff the Challenger's three main engines ignited in rapid sequence. When the countdown reached zero, the two 149-foot-tall booster rockets, attached to either side of the external fuel tank, ignited in unison.

''Liftoff,'' announced Hugh W. Harris, the countdown commentator. ''Liftoff of the 25th space shuttle mission, and it has cleared the tower.''

But less than a second later a puff of black smoke erupted from the lower part of the right booster, at or near one of the seals. One of the seals, failing, might have caught fire. Burning rocket fuel gives off a bright, luminous flame. Whatever it was, NASA engineers detected it only later in an analysis of launching photography.

The smoke spread and darkened and then disappeared 12 to 13 seconds after liftoff. Strangely, all visual signs of trouble vanished. All computer data reaching Mission Control were normal. The boosters had been deemed so reliable that they were outfitted with few sensors to monitor possible malfunctions.

At 40 seconds into the flight, just after the main engines had been throttled down to 65 percent thrust, the shuttle flew through stiff, shifting winds and responded, according to data, by automatically pivoting the booster and main engine nozzles to maintain the proper trajectory. At 52 seconds, the three engines began to throttle up to full power.

''Challenger, go with throttle up,'' radioed Mission Control in Houston.

''Roger, go with throttle up,'' responded Mr. Scobee in a calm voice. These were the last words heard from the Challenger.

At 59 seconds, the Challenger went through its time of maximum dynamic pressure, when the vibrations of thrusting rockets, the momentum of ascent and the force of wind resistance combined to exert tremendous stresses on the shuttle structure. At about this time, a relentless sequence of events, none immediately detectable to ground controllers or the crew, was dooming the Challenger.

A new plume of smoke issued from the lower side of the right booster. Pressures inside the two boosters, which should be equal, began to diverge, with those in the right booster dropping sharply to suggest a leak of some sort. At 60.6 seconds, flame erupted from the right booster. At 66.17 seconds, a bright glow appeared on that booster and merged with the fast-burning plume. At 73 seconds, pressure in the right booster plunged further, reaching 24 pounds per square inch less than the pressure in the other booster.

Immediately afterward, at 73.175 seconds, a mysterious cloud spread along the external fuel tank, followed by flashes of light and explosions. The last radioed data from the shuttle, at 73.621 seconds, told of a sudden surge of pressure in the main engines. Intense heat in the fuel pump caused one of the engines to shut down.

Eighteen miles off Cape Canaveral and 10 miles up in the blue sky, a fireball engulfed the Challenger. If the crew had any warning, it came too late for them to do anything, even radio Mission Control. The first sign most flight controllers had that anything was amiss came when their computer screens flashed on and off.

''Obviously a major malfunction,'' reported Stephen Nesbitt, the public affairs officer describing events from Mission Control. ''We have no downlink. We have a report from the flight dynamics officer that the vehicle has exploded.''

Stunned, its image of success and engineering perfection shattered, the space agency began its own investigation within hours of the explosion. Some people immediately suspected failure of the O rings. An interim review board, headed by Jesse Moore, impounded all mission records and flight data, and everyone appeared bent on keeping all proceedings behind closed doors. In two days, however, news reports identified the prime suspect in the case: the right booster rocket.

The New York Times reported pressure readings indicating that the rocket began to fail at least 10 seconds before the explosion and quoted experts as saying that computers and sensors were not programmed to detect flames burning through the side of the rocket. Finally, late Saturday, Feb. 1, NASA released a new set of photographs showing the ''unusual'' plume of smoke and flame erupting from the rocket's side, at or near a seam, at least 14 seconds before the explosion.

Two days later, as questions arose over the advisability of NASA being in the position of investigating itself, President Reagan appointed a 13-member commission to conduct an independent inquiry. The commission, drawn mainly from scientific, educational and business circles, was headed by William P. Rogers, a former Secretary of State, with Neil A. Armstrong, the former astronaut, as vice chairman. Top Inquiry Opened, Documents Demanded It was at the commission's first public hearing, Feb. 6, that the pre-launching weather concerns emerged as an important factor in the case. On the following weekend, The Times reported on NASA documents that years ago warned about problems with the O rings. A memorandum written by Richard Cook, the agency's budget analyst, noted evidence of previous damage to the rings and concluded last summer that flight safety was ''being compromised by potential failure of the seals.''

The Presidential commission reacted by ordering NASA to produce all records relating to problems with the O rings. These documents, released Feb. 12, showed among other things that NASA had waived its requirement for proven redundancy in the booster seals.

A working hypothesis by then was that propulsive gases leaked from the right booster, probably in the area where the lower part of the rocket was attached to the external tank. The hot gases set off a chain of events leading to the explosion of propellants in the huge tank. According to Aviation Week and Space Technology, investigators believed that flames from the leak, or stresses from the plume of fire, severed the struts that held the rocket's base to the fuel tank. As the booster pivoted outward, its nose swung in and ruptured the tank, causing the explosion. At a subsequent commission hearing, Feb. 11, the space agency acknowledged that cold temperatures diminish the effectiveness of the seals.

But it was on a visit to Cape Canaveral later that week that the commission learned of the debate between Thiokol engineers and NASA officials that had raged the night before the launching. Mr. Rogers reportedly was ''appalled'' to discover that information about weather problems did not reach top space agency officials. On Feb. 15, he issued a statement saying the decision-making process at NASA may have been ''flawed'' and ordering officials who participated in the launching decision not to take part in the NASA investigation.

Pressure on NASA

Last week, the inquiry seemed to expand, gain momentum and take its toll on the NASA hierarchy. In an interview, Mr. McDonald, the Thiokol engineer, disclosed that the rocket experts had been almost unanimous in their opposition to launching because of their concern over the cold weather. NASA officials and eventually Thiokol managers favored continuing with the countdown.

Meanwhile, Mr. Moore announced he was stepping down as head of the shuttle program sooner than expected while remaining director of the Johnson Space Center. Mr. Moore was replaced by Richard H. Truly, a Navy rear admiral and former astronaut, who arrived at the Cape yesterday to take the helm of the space agency's own inquiry into the Challenger's destruction. James M. Beggs, the NASA administrator who is on a leave of absence to fight fraud charges unrelated to NASA, was expected to resign soon so that the White House could find someone to take full command of the troubled agency. Dr. William R. Graham Jr. is the Acting Administrator.

The Presidential commission, which must report its findings in April, continued its investigation in Washington, Cape Canaveral, Huntsville and Brigham City. When the panel resumes its hearings today, Mr. Kilminser and Mr. McDonald are among the Thiokol officials due to testify. For NASA, Mr. Mulloy and Mr. Reinartz are set to appear.

As much as is known so far, many important questions remain unanswered. Here are some of the most pressing issues.

The accumulating evidence suggest that NASA was especially eager to get the Challenger's mission under way without more delay. Aside from the normal pressures to maintain schedules, were shuttle managers striving too hard to prove their own ambitious projections of 15 flights in 1986? Were there political pressures to demonstrate shuttle reliability?

It is still not clear why Thiokol managers overruled their engineers the night before the launching and gave their go-ahead. Did NASA apply pressure, real or implied? Did Thiokol officials fear that a reputation for being too cautious and balky might jeopardize the company's future contractual relations with NASA?

If NASA and company engineers had determined that the rocket seals required extensive modifications, why did they believe it was safe to continue flying the shuttles?

Once the Presidential commission establishes the exact cause, or causes, of the explosion, there will still be decisions to make affecting the nation's future in space. Will the shuttles have to undergo such a major redesign that they will not fly again for a year, two years or more? While the shuttles are grounded, what can be done to maintain an American presence in space?

GRAPHIC: diagram (page C8)