On Fri, 23 Jan 2009 15:51:19 -0800, "Reunite Gondwanaland (Mary
Shafer)" wrote:


The idea didn't appear out of the blue after Columbia, especially
since Columbia's age played no role in the accident, but the CAIB put
all its weight behind the idea.

The age of the leading edge material, and the number of reentries it
had made, was a factor in the accident, I thought. It had become
brittle in extended use and was, therefore, not resistant to the
impact of the foam.

Mary "Or was this just a hypothesis?"

From the CAIB...

"Findings:
F3.3-1 The original design specifications required the RCC components
to have essentially no impact resistance.
F3.3-2 Current inspection techniques are not adequate to assess
structural integrity of the RCC components.
F3.3-3 After manufacturer's acceptance non-destructive evaluation,
only periodic visual and touch tests are conducted.
F3.3-4 RCC components are weakened by mass loss caused by oxidation
within the substrate, which accumulates with age. The extent of
oxidation is not directly measurable, and the resulting mission life
reduction is developed analytically.
F3.3-5 To date, only two flown RCC panels, having achieved 15 and 19
missions, have been destructively tested to determine actual loss of
strength due to oxidation.
F3.3-6 Contamination from zinc leaching from a primer under the paint
topcoat on the launch pad structure increases the opportunities for
localized oxidation."

Sounds to me like they're saying the RCC panels weaken over time, but
they don't know how much and the panels weren't supposed to take any
impacts anyway. :-/

In any case, age wasn't a contributing factor in the accident. The
SWRI impact test would have smashed a brand-new RCC panel too.

Brian