WASHINGTON — A detailed study of erosion and charring detected in solid rocket booster seals after space shuttle launchings last year concluded that the problem was not a threat to "flight safety" and could be corrected without suspending scheduled missions, a ranking National Aeronautics and Space Administration official said Sunday.
Michael B. Mann, director of the shuttle program's research analysis branch, said that a series of measures to strengthen seals between sections of space shuttle solid rocket boosters was "implemented immediately" after postflight inspections showed evidence of leakage.
"There was a review of the charring, and at that time the recommendation was that . . . it was not a flight safety issue," Mann said in an interview. "There were some actions taken at the time to alleviate the problem. There were some decisions made to improve the integrity of the seals. They were implemented immediately."
A plume of flame spurting from the side of the space shuttle Challenger's right-hand booster rocket has emerged as a leading suspect in the search for what caused the catastrophic Jan. 28 explosion that destroyed the $1.2-billion spacecraft and its seven-member crew. Four days after the tragedy, the space agency released pictures showing a plume erupting from the side of the rocket casing 13 seconds before Challenger blew apart in a fireball.
NASA sources said it was believed that 6,000-degree emissions spewed from a seam between segments of the multi-sectional rocket, heating the adjoining fuel tank--loaded with liquid hydrogen and liquid oxygen--to the point of rupture and explosion.
However, in a related development Sunday, other space agency sources said investigators were studying photographs that possibly indicate problems in the spacecraft's 154-foot fuel tank even before flames erupted from the right solid booster.
The sources said voluminous photographic coverage of the accident included frames in which smoke or vapor appeared to cling to the wall of the tank before there was visible evidence of a booster rupture.
A failure in the tank before or simultaneous with the failure of the booster would force investigators to look for a common cause. There already has been speculation that unusually cold weather in central Florida on the eve of the launching played a role in the accident, perhaps causing a non-flammable sealant inside the casing at the seams to come loose.
No 'Catastrophic Concern'
Mann said he could not recall how many times after previous flights evidence of leakage and charring had been detected within the system of seals designed to prevent escape of hot propellant from seams between the rockets' 11 sections.
But Mann said that engineers he interviewed did not view the pattern as a "catastrophic concern."
He said: "It wasn't the kind of thing where every launch we watched with bated breath, praying that it wouldn't be a problem."
Mann's characterization of the level of concern conflicted dramatically with the impression created by a July 23 memorandum written to him by a subordinate. The memorandum was among NASA documents obtained by the New York Times from what the newspaper identified as a "solid-fuel rocket analyst." Portions of the documents were quoted in a report published Sunday.
The most damaging of the documents appeared to be a memorandum to Mann by Richard C. Cook, who worked for Mann in the shuttle program's research analysis branch. Its function is to determine budget requirements for the program.
The memorandum, as quoted, said that "there is little question . . . 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."
Cook was also quoted as having written that the charring of seals constituted "a potentially major problem affecting both flight safety and program costs."
Mann said that Cook did not have the scientific wherewithal to draw such drastic conclusions and might not have understood what he had been told by engineers about the problem.
He said that Cook had come to NASA as a speech writer on July 4--three weeks before the memorandum was written--and "at the time didn't even know what an SRB (solid rocket booster) looked like."
"He had no technical understanding of the SRB, and no technical training," Mann said.
According to Mann, Cook was being trained to be a budget analyst for the solid rocket program and as an introductory assignment had been asked to determine what budget impact could be expected because of the seal problem.
He said that Cook subsequently had been criticized for writing reports "based on emotion rather than hard evidence" and only recently left the space agency to work elsewhere.