Thank you for accepting my findings as your official answer. I've
reposted the material below, with an additional NASA link that I hope
will be of interest.
Foam shedding had been observed on previous shuttle flights. Since the
earlier incidents had no serious consequences, the dangerous
significance of such incidents was discounted, much as the known
problems with O-rings had been shrugged off before the Challenger
"Foam ejection during launch has been a problem with quite a long
history. Four previous shuttle launches had foam falling from the
bipod area: Challenger in 1983, Columbia in 1990 and 1992, and
Atlantis last October. Engineers had made many changes in the foam
design in the past few years, but the problem had not been solved."
CSA: Columbia Shuttle Tragedy
"From the day of Columbia's breakup forward, shuttle program manager
Ron Dittemore has defended the NASA analysis finding that the foam
impact could not possibly have caused enough damage to trigger
Columbia's destruction 16 days after launch.
Dittemore cited as evidence previous incidents involving foam from the
external tank. During a number of flights in recent years, the
external tank insulation beneath the orbiter 'popcorned' during ascent
because of escaping gas beneath the sprayed-on foam, creating dings in
hundreds of tiles. The damage was never severe enough to notice during
descent. Just in October, a larger chunk of foam came free from the
external tank and caused only minor damage to one of Atlantis'
solid-fuel booster rockets.
The logic, though, appears to mirror that used by NASA 17 years
earlier, when it discounted the significance of partial burn-through
of rubbery booster-rocket O-rings it had seen in previous flights."
Palm Beach Post: NASA mind-set yields comparison, clues
"Before the shuttle mission preceding Columbia's fateful flight, NASA
flagged as a major concern a loss of foam in the same area on fuel
tanks where investigators now believe debris broke away and smashed
against Columbia's left wing.
The space agency concluded that damage from such breakaway foam did
not threaten shuttle safety and determined the fuel tank attached to
Endeavour was 'safe to fly with no new concerns and no added risk,'
according to newly released documents from the National Aeronautics
and Space Administration.
The documents revealed for the first time some of NASA's reasons for
deciding months ago that such risks were insufficient to delay shuttle
launches, even as agency officials already were looking into what they
perceived as a frustrating, recurring problem."
CBS News: Shuttle Foam Had History Of Problems
"What Are the 'Echoes' of Challenger? Former shuttle astronaut Sally
Ride served on the Rogers Commission that investigated the January
1986 Challenger accident, which claimed the lives of seven astronauts,
and on CAIB. During the Columbia investigation, she said she heard
'echoes' of Challenger as it became clear that the accident resulted
from NASA failing to recognize that a technical failure (bipod ramp
foam shedding) that had occurred on previous shuttle flights could
have safety-of-flight implications even if the earlier missions were
completed successfully. In the case of CRS-4 Challenger, it was
erosion of seals (O-rings) between segments of the Solid Rocket
Booster, which had been noted on previous missions. Some engineers
warned NASA not to launch Challenger that day because unusually cold
weather could have weakened the resiliency of the O-rings. They were
overruled. CAIB concluded that 'both accidents were failures of
foresight' - and the parallels between them demonstrate that: 'the
causes of the institutional failure responsible for Challenger have
not been fixed; if these persistent, systemic flaws are not resolved,
the scene is set for another accident'; and that while individuals
must be accountable for their actions, 'NASA?s problems cannot be
solved simply by retirements, resignations, or transferring
NASA History Division: NASA?s Space Shuttle Columbia: Synopsis of the
Report of the Columbia Accident Investigation Board
My Google search strategy:
Google Web Search: shuttle columbia foam previous
Very best regards,