In yesterday's article about the space shuttle Challenger it was reported, on the basis of information supplied by a spokesman for the National Aeronautics and Space Administration, that the putty used to help seal the joints in the shuttle's booster rockets was manufactured by U.S. Polymeric. Owens-Corning Fiberglas, which owns U.S. Polymeric, denies that its subsidiary makes the putty. U.S. Polymeric also is not the only company providing materials for the shuttle's booster nozzles.
Some of the primary rubber seals that protect a space shuttle's booster rockets from burning through the wall -- the kind of problem that apparently doomed Challenger -- have failed at least 12 times on previous missions, current and former NASA officials said yesterday.
In all previous cases, according to the officials, backup seals prevented the boosters' white-hot gases from burning through. Had both rings failed, the earlier shuttle flights could have sustained the kind of booster burn-through that is thought to have led to the explosion that destroyed Challenger Jan. 28.
The seals are 12-foot-diameter rings of synthetic rubber, called O-rings, that encircle each segment of the booster at levels where its segments are joined. Each booster is made up of four fuel-containing cylindrical segments that are stacked so that the lip of one segment slides into a deep groove on the other. Steel retaining pins hold the tongue-and-groove joint together.
Inside each groove are two O-rings that are supposed to seal the gap and prevent the booster's high-pressure exhaust gases from leaking. The first, or primary, O-ring is supposed to be sufficient, but a secondary O-ring, running parallel to the first, is installed as a backup if the first burns through.
Acting NASA administrator William R. Graham said last Sunday that the plume of flame that burst through the wall of Challenger's right-hand booster was at or near the joint between the two lower segments. This is the same joint at which primary O-rings failed on some previous flights.
Concern about the effectiveness of the seals has been growing since last Thursday when a National Aeronautics and Space Administration official told the presidential commission investigating the disaster that on previous shuttle flights, the first O-ring has burned through. After launch, the boosters normally parachute into the ocean to be recovered, inspected and reloaded with fuel for another flight.
"We have seen evidence of what we call blow-by of those seals, some erosion of those seals, the primary seal," said Judson A. Lovingood, deputy manager of shuttle projects at the Marshall Spaceflight Center in Huntsville, Ala., which is responsible for the boosters. "We've never seen any erosion of the secondary seal. We have seen evidence of soot in between the two seals."
Lovingood told the panel, which is chaired by former secretary of state William P. Rogers, that the "anomaly" was "thoroughly worked and that's completely documented on all the investigative work we did on that."
Although Lovingood said, under oath, that no secondary seals were found damaged after a flight, The New York Times reported yesterday that it had obtained a NASA internal memorandum, dated July 23, 1985, saying, "Not only has the first O-ring been destroyed, but the second has been partially eaten away." According to the memo, the joint at which the seals failed was the same one near which space agency officials say the plume emerged during the Challenger launch.
The memo, to Michael B. Mann, head of the shuttle program's resources analysis branch, from Richard C. Cook, his subordinate, warned that "the charring of seals" posed "a potentially major problem affecting both flight safety and program costs."
"There is little question," the Times quoted the memo as saying, "that flight safety has been and is still being compromised by potential failure of the seals and it is acknowledged that failure during launch would certainly be catastrophic."
Mark Weinberg, a spokesman for the Rogers commission, said yesterday that NASA had been asked to produce all internal documents dealing with the seals. Graham, while refusing to comment on the Times report, said the agency would comply and promised the commission "full cooperation from all NASA employes."
Although NASA maintained the tight lid of secrecy that has been in place since shortly after the explosion, a former official of the space agency confirmed that there had been concern after earlier flights about the reliability of the O-rings.
"It came up on several occasions," said Sam T. Beddingfield, who retired in November as deputy director of shuttle management at the Kennedy Space Center in Florida. "There was some concern but NASA felt it was resolved or they would not have gone ahead."
Beddingfield confirmed that memos were written on the problem but said memos are "written about everything under the sun."
According to Irving Davids, an engineer in the booster program at NASA headquarters in Washington, the O-rings are supposed to be protected from the heat of burning rocket fuel by a layer of fire-resistant putty. The putty, made of zinc chromate, is installed when the booster segments are being fitted together at the Kennedy Space Center. It goes inside the booster wall, partially filling the gap between two segments of solid rocket fuel.
According to a memo Davids wrote about previous flights, the O-rings were probably able to burn because the putty had failed, perhaps developing holes that allowed hot gases to reach the rings.
The putty is manufactured by U.S. Polymeric, which is owned by Owens-Corning Fiberglas of Toledo. U.S. Polymeric also made the carbon cloth material that is used to line the boosters' nozzles. NASA officials have previously said that defects in this lining allowed exhaust gases to burn through the lining and erode pits in the nozzle's metal wall.
The defect was found to result from improper treatment of the cloth that left certain volatile chemicals still in it. As a result, hot exhaust broke through the lining.
It is not known what happened to the putty, but it is conceivable that a similar defect allowed it to break down and crumble away, letting heat reach the O-rings.
A member of the Aerospace Safety Advisory Panel recalled that the O-ring problem was serious enough that NASA engineers briefed his group on it about a year ago.
"There was evidence of erosion of one of these seals, but the secondary seal held," said Seymour C. Himmel, who has served for nine years on the board of outside safety advisers to NASA.