Solid rocket boosters, like the one now emerging as a prime suspect in the space shuttle explosion, showed signs of potentially lethal flaws after several earlier flights–and in November NASA sharply criticized the way the Challenger boosters were being assembled.
After one Challenger booster was damaged by a crane on Nov. 8, a NASA report decried faulty equipment, ill-trained workers and a failure to follow prescribed procedures at the shuttle assembly facility in the Kennedy Space Center at Cape Canaveral, Fla..
In August, 1983, during the eighth shuttle launch, flame from a booster came within seconds of burning through a critical heat shield protecting the rocket`s nozzle. A burn-through likely would have left the shuttle out of control and caused a catastrophe.
After other missions, according to a NASA spokesman, technicians found that traces of propellant soot had seeped through the preliminary seal on some booster joints, which are supposed to be air- and pressure-tight. To this day, NASA experts do not understand why the seepage occurred, said James Mizell, a former launch operations engineer.
”These were the very first inklings that something like what happened on Tuesday`s flight was possible,” another NASA spokesman, Charles Redmond, said Sunday.
Film released by NASA on Saturday revealed an ”unusal plume” of flame in the lower part of Challenger`s right booster, near a principal seam. On Sunday, William Graham, NASA`s acting administrator, cautioned that the agency still had not determined what, if any, role the plume played in the disaster, but he described it as ”a situation which we have never seen on a launch of a shuttle before.”
The discovery of the plume lent added support to what has become the principal theory about the blast–that fiery gases leaking from the shuttle`s right booster somehow ignited liquid hydrogen in the craft`s huge, external fuel tank.
NASA is reportedly studying whether the gases could have rushed out in a blow-torchlike stream either through a hole in the rocket`s steel casing, or through a separation in one of its seams.
On Sunday, Graham called the boosters ”some of the sturdiest parts of the entire shuttle system,” and said that NASA designers considered them
”not susceptible to failure.”
Partly because of this faith in the reliability of the boosters, they were not equipped with sensors that might have detected and warned of the possible malfunctions NASA is studying, Graham said.
While sensors monitor all the critical elements of the flight, the boosters themselves have only four monitors each at the top, and they may not have been adequate to detect a leak at a bottom seam.
Despite Graham`s comments, there have been several serious problems associated with the 149-foot rocket in recent years.
Most recently, workers using an overhead crane to assemble Challenger`s left booster booster cracked a section, which had to be replaced, according to the internal NASA report on the incident.
The report cited no specific problems with the assembly of the right rocket booster suspected in the Challenger blast. But it called for the use of more reliable equipment when putting the rockets together from 11 individual, weld-free segments of half-inch-thick steel. The report also called for training to make assembly workers more qualified and more responsible.
Two minutes and seven seconds into a mission, the boosters are detached and parachute to the sea, where they are recovered for re-use in future missions. On the average, 95 percent of the hardware in the boosters on any shuttle mission have already been used at least once, and often more times, on earlier missions.
NASA has declined thus far to provide the past flight history of the parts used in the suspect right booster of the Challenger shuttle. But Rocky Raab, a spokesman for Morton Thiokol Inc., which manufactures the boosters, has said that of the 22 segments in both Challenger rockets, seven had been used in two previous flights and 13 in one prior flight. Two were new, Raab said.
As the investigation into the Challenger explosion zeroed in on the booster as a probable first cause of the blast, Charles S. Locke, chief executive officer and chairman of the board of the Chicago-based Morton Thiokol cautioned against jumping to premature conclusions.
”It sounds to me like everyone is really digging, looking for a villain,” Locke said. ”It`s much too soon to come to any conclusions, as many things could have caused that accident not related to the work we did.
”There isn`t enough information available yet to determine anything,”
Locke added. ”This is just smut digging. It`s a bunch of crap. Any comment we make would tend to lend credence to this report, and I don`t want to do that.”
Locke also criticized the report on the November incident, denying that workers used faulty equipment or improper procedures, and maintaining that it is ”very routine” for cranes at the shuttle assembly site not to work.
Despite the incident, NASA officials seemed confident that the rockets were fully ready for the Challenger mission. During a high-level,
teleconference hookup on Jan. 15, a week before the original launch date, officials from three space centers talked with agency directors in Washington. Only ”five or ten minutes” out of a three hour discussion were devoted to design changes in the boosters, Redmond said.
According to a copy of the readiness review report, the boosters had been modified to improve the parachutes that aid in their decline.
When asked if any concern had been voiced about the safety of the boosters, Redmond, said: ”I wouldn`t say no concern, but we felt as if we had licked a lot.”
The readiness report concluded that there were ”no major problems or issues” with the boosters. It was signed by the chief engineer and the manager of the Solid Rocket Booster Project; the vice president in charge of the Space Booster Program; and the executive vice president of United Space Boosters Inc.-Booster Production Co.
The near-tragedy in 1983, during the eighth shuttle launch, was the most serious incident involving a booster prior to last Tuesday`s Challenger explosion. It involved the near-failure of the 3-inch-thick layer of material intended to deflect the intense heat of the burning rocket from its bell-shaped nozzle.
Despite the fact that the shield is constructed to withstand the rocket`s 6,000 degree flame for 240 seconds–almost twice as long as the boosters remain attached to a shuttle during normal launch–the shield was burning so rapidly that it was in danger of burning through entirely.
Astronaut Daniel Brandenstein, pilot for the eighth mission, said afterward that the nozzle would have burned through if the rocket had fired for another 2.7 seconds and that such a burn-through would have destroyed the craft and killed the five astronauts aboard.
NASA officials put the time remaining before a burn-through at 15 to 20 seconds.
”We did not have a burn-through, but it came close,” said NASA spokesman Mizell on Sunday. ”If the solid rocket booster had run for another –I`ve forgotten, how many seconds or so–it may have burned through.”
Morton Thiokol officials attributed to the near-burn-through to impurities in the ablative lining, and said the problem was immediately corrected with some redesigning of the engine and by stricter work procedures. NASA officials declined Sunday to release the report of the inquiry into the Nov. 8 accident. However, spokesmen for NASA and Morton Thiokol confirmed its existence.
”The investigation was conducted. The (damaged) segment was not used,”
said NASA spokesman James Ball. ”We are going to address those issues tomorrow when people are back on base.”
A NASA statement on the incident dated Nov. 11 said workers were removing a a 5.5 ton ring, used for shipping and handling, from the solid rocket motor segment prior to mating the booster`s four propellent-laden segments vertically for the flight.
”The ring is held to the segment structure by numerous pins and several of these had proven difficult to remove,” said the statement. ”An overhead bridge crane was being used to lift the ring and relieve pressure on the pins and facilitate their removal when a sharp, cracking noise was heard.”
The process was stopped and the investigation was conducted that later indicated there was a problem with the crane gauge, according to a report by the Associated Press. The gauge registered less pressure than was being applied, and it tore a pin loose, the AP reported.
Moore confirmed that the board of inquiry made a ”negative” report against Morton Thiokol but said he been ordered not to comment on it by Lockheed Space Operations Co., the prime contractor at the launch site facility. He said that although his company assembles the booster rocket segments at the launch site, they perform the work under a contract with Lockheed, which oversees shuttle assembly.
Lockheed spokesman Stuart Shadbolt also acknowledged the existence of the report but said: ”It would be very inappropriate for a contractor to comment on a NASA report.”
NASA investigators are reportedly looking into three possible ways in which flames from the booster rocket might have touched off an explosion in the aluminum liquid-fuel tank.
— A blowtorch leak from a booster seam would be extremely hot, about 6,000 degrees, and would quickly melt through the skin of the tank, according to experts.
— Flame emanating from the booster could have heated the area outside the tank, causing the liquid hydrogen inside to begin to turn turn to gas. This would have caused added pressure in the tank and caused a slow leak of the highly volatile substance.
— The flame could have shortcircuited wiring on the external tank, causing explosives at the top of the tank to go off. These explosives are designed to destroy the tank in the event of an accident that left the tank careening toward a populated area.
Engineers from Martin Marietta, manufacturers of the external tank, said that they have been told by NASA that pressures monitored inside the tank remained normal until the explosion, indicating that the tank was ruptured from the outside.
An explosion from either an overheated tank or accidental triggering of the detonation devices would have taken longer to develop than one initiated by a direct flame, according to the Marietta officials. In either case, sensors near release vents on the tank probably would have alerted technicians in Houston.
The tragedy is a major puzzle because, according to NASA, none of the monitors at Mission Control showed anything wrong until the instant of explosion.
Marietta officials said that the apricot-colored insulation covering the 154-foot-tall external tank was only designed to withstand temperatures up to 1,800 degrees, and that the aluminum shell of the tank would melt at about 1,000 to 1,200 degrees.
The booster rockets are manufactured in Morton Thiokol`s plant in Promentory Point, Utah. Parts are assembled there into four major segments, which are then shipped by rail to Cape Canaveral. There they are assembled in their final form.
Each booster is made up of four cylindrical segments ranging from 26 to 32 feet long. The segments are not welded. The ends of segments that come together to form the joints are U-shaped with holes for pins to attach one segment to another. A total of 177 high-strength steel pins are used to join each segment together.
The joints are wrapped with reinforced fiber glass tape and sealed with a rubber seal band that is bonded to the case with adhesives.
The boosters carry solid fuels and provide a total of 5.3 million pounds of thrust and are needed to launch the shuttle.
At the launch site, they are attached to the external liquid-fuel tank and the orbiter. They support the shuttle complex on the launch pad.
The external tank, filled with 1.5 million pounds of liquid hydrogen and liquid oxygen, continue fueling the shuttle`s three main engines for a total of 8.5 minutes to push the spaceplane into orbit.
Challenger exploded 74 seconds after launch when it was undergoing the maximum aerodynamic stresses a shuttle experiences during its mission. The craft was 9 miles high and traveling at a speed of 1,900 miles an hour when it blew up, a point at which shock waves and other stresses are the greatest.
Such intense stress could turn a relatively minor flaw into a calamitous disaster, said Hans Mark, former NASA deputy director and a member of the shuttle design committee. Mark is now chancellor of the University of Texas system.
”The design is sound,” said Mark. ”I think something wasn`t put together right or properly tightened down or there was some electrical system malfunction.”
Harold Ritchie, Morton Thiokol`s retired founder, said he doubts a leak caused the Challenger explosion. ”Those boosters would have been cart-wheeling like mad if there was even the smallest hole,” he said.
Had that happened, NASA regulations would have required ground personnel to destroy the shuttle if it appeared to be heading toward a populated area.
