Solid rocket boosters, like the one now emerging as a prime suspect in last week`s explosion of the space shuttle Challenger, showed serious flaws twice before last Tuesday`s launch and almost caused a catastrophe during the eighth shuttle flight in 1983.
Late last year, NASA sharply criticized the way the two boosters for the Challenger mission were being assembled at Cape Canaveral, citing faulty equipment, ill-trained workers and a failure to follow prescribed procedures. Film released by NASA on Saturday revealed an ”unusal plume” of flame in the lower part of Challenger`s right booster. 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 Challenger 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 hot gasses leaking from the shuttle`s right booster somehow ignited liquid oxygen in the craft`s external fuel tank. On Nov. 8, workers using an overhead crane to assemble Challenger`s left booster cracked a section of the rocket, which had to be replaced, according to an internal NASA report on the incident.
The report cited no specific problems with the assembly of the right rocket booster, but it called for the use of more reliable equipment when putting the 149-foot rockets together from 11 individual weld-free segments of 1/2-inch steel. The report also called for training to make assembly workers more qualified and more responsible.
After being detached, the boosters parachute to the sea where they are recovered for reuse in future shuttlel missions. On the average, ninety-five percent of the hardware in the boosters on any shuttle mission have already been used at least once and often several 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.
Although Graham said Sunday that NASA designers thought the rocket boosters were ”not susceptible to failure,” there had been serious flaws found in other rockets employed before the Challenger mission.
During the eighth shuttle launch, flame from a booster came within seconds of burning through a critical heat shield protecting its nozzle near the bottom. The inside of the bell-shaped nozzle is covered with a 3-inch-thick layer of material that deflects the intense heat of thre intensely burning rocket.
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–is the shield was burning so rapidly that it was in danger of burning through entirely.
Astronaut Daniel Brandenstein, pilot for the eight mission, said afterwards 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 former NASA engineer James 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.” NASA technicians have also sporadically found after missions traces of propellant soot that have gotten through the preliminary seal on booster joints. According to Mizell, the soot is a sign that exhaust gas is edging through the joints.
”These were the very first inklings that something like what happened on Tuesday`s flight was possible,” NASA spokesman Charles Redmond said Sunday.
Despite the cran-related incident in November and the past history of problems with boosters, NASA officials seemed confident that the boosters were fully ready for the Challenger mission. During a high-level, teleconference hookup of officials from three space centers with agency directors in Washington only ”five or ten minutes” out of a three hour meeting were devoted to discussing recent design changes in the boosters, Redmond said.
According to a copy of the readiness review report, the boosters had been changed to improve the parachutes which aid the decline of the reusable rockets into the ocean after they have been detached from the rest of the shuttle.
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 SRB Project; the vice president in charge of the Space Booster Program; and the executive vice president of United Space Boosters Inc.-Booster Production Co.
On Sunday, on the CBS ”Face the Nation” program, Graham called the boosters ”some of the sturdiest parts of the entire shuttle system.
Alluding to the fact that photographs and film did showing the unusual plume were not released until four days after the catastrophe,, Graham said:
”The reason it was after the fact and not in real time was that these very heavy steel casings that constitute the structure of these solid rocket boosters are some of the sturdiest parts of the entire shuttle system–were considered primary structure and not susceptible to failure.
”Of course we designed them that way,” Graham added. ”It wasn`t just a chance that they`re not susceptible–or we thought them not susceptible. They were designed with great care and great thought and everything we could to do keep them from having any failure modes.”
NASA officials declined Sunday to release the report of the inquiry into the Nov. 8 accident. However, a spokesmen for NASA and the manufacturer of the boosters, Chicago-based Morton Thiokol Inc., confirmed its existence.
According to an Associated Press report, the report cited inexperienced and unmotivated workers at the rocket asssembly facility at the Kennedy Space Center
”The investigation was conducted. The segment was not used,” said NASA spokesman James Ball on Sunday. ”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 facilitiate their removal when a sharp, cracking noise was heard.”
The process was stopped and the investigation was conducted which later indicated there was a problem with the crane gauge. It registered less pressure than was being applied, and it tore a pin loose, the AP reported.
As the investigation into the Challenger explosion zeroed in on the booster as the probable first cause of the blast, Charles S. Locke, chief executive officier and chairman of the board of Morton Thiokol cautioned against jumping to premature conclusions.
”It sounds to me like everyone is really digging, looking for a villain,” he said. ”It`s much too soon to come to any conclusons, 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,”
said Locke. ”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 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 assembly site not to work.
Moore confirmed that the board of inquiry made a ”negative” report against 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 Thiokol assembles the booster rocket segments at the Kennedy Space Center, 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.”
Thiokol officials attributed to the near-burn through during the eighth shuttle mission to impurities in the ablative lining, and said the problem was immediately corrected with some redesgning of the engine and by stricter work procedures.
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 blow torch 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 subtstance.
— 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 which 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, accprding 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.
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.
Each booster is made up of four cylindrical segments ranging from 26 to 32 feet long. They are joined together to form the rocket stack, 149 feet high. Two boosters, attached to opposite sides of the external tank, carry solid fuels and provide a total of 5.3 million pounds of thrust and are needed to launch the shuttle and the external fuel tank.
After firing for 2 minutes and seven seconds, the boosters exhaust their fuel and are jettisoned. 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.
The boosters are manufactured in Morton Thiokol`s plant in Promentory Point, Utah. Parts are assembled into four major segments there. Then the segments are shipped by rail to the Kennedy Space Center where they are joined together and assembled in their final form.
Then they are attached to the external liquid fuel tank and the orbiter. They support the shuttle complex on the launch pad.
R. Gilbert Moore, a Thiokol spokesman at the company`s Utah facility, refused to comment Sunday on the ”blow torch” theory.
”You have to remember that although they (NASA) definitely are looking at this strange plume. NASA is also continuing with its examinations of many other components,” he said.
Challenger exploded 74 seconds after launch when it was undergoing the maximum aerodynamic stresses a shuttle experiences during its mission. The craft was nine miles high and travelling 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 smething wasn`t put together right or properly tightened down or there was some electrical system malfunction.”
