The Best Part #2 of CAIB Report

Crater actually written by Apollo engineers! Once again, the guys with
the horn-rimmed glasses and pocket protectors of the '60s shine while
our generation fizzles. Originally written to predict outcomes of
micrometeoroid strikes, then rewritten for small (1") ice, foam or
orbital debris hits. (see Chap. 6, pg. 24 of the CAIB final Report,
shaded box) When our foam strike numbers were fed in and Crater
PREDICTED A BURN THRU our 21st Century engineers made a "qualitative
extrapolation" that the lighter foam wouldn't cause a burn thru. IMO
they just sat around the office and made this up, rather than deal
with the scary ramifications of the software predicting a burn thru.
In the '60s, the engineers would have immediately notified Flight and
reached for their duct tape and slide rules to fashion a patch for the
hole (at least this is how I imagine it).

(see Chap. 6, pg. 145 of the CAIB final Report): "To determine
potential RCC damage, analysts used a Crater-like algorithm that was
calibrated in 1984 by impact data from ice projectiles. At the time
the algorithm was empirically tested, ice was considered the only
realistic threat to RCC integrity. (See Appendix E.4, RCC Impact
Analysis.) The Debris Assessment Team analysis indicated that impact
angles greater than 15 degrees would result in RCC penetration. A
separate "transport" analysis, which attempts to determine the path
the debris took, identified 15 strike regions and angles of impact.
Twelve transport scenarios predicted an impact in regions of Shuttle
tile. Only one scenario predicted an impact on the RCC leading edge,
at a 21-degree angle. Because the foam that struck Columbia was less
dense than ice, Debris Assessment Team analysts used a qualitative
extrapolation of the test data and engineering judgment to conclude
that a foam impact angle up to 21 degrees would not penetrate the RCC.
Although some engineers were uncomfortable with this extrapolation, no
other analyses were performed to assess RCC damage."

Ellen

(ElleninLosAngeles) wrote in message . com...

(see Chap. 6, pg. 145 of the CAIB final Report): "To determine
potential RCC damage, analysts used a Crater-like algorithm that was
calibrated in 1984 by impact data from ice projectiles. At the time
the algorithm was empirically tested, ice was considered the only
realistic threat to RCC integrity.


To me, this seems like the core issue. No one involved seems
to have understood, even back in 1984, just how fragile the
RCC really was. I know I didn't. I always assumed that, since
it was on the leading edge and was "high-tech" material, it
had to be the toughest part of those resilient birds.

- Ed Kyle

(ed kyle) wrote in message news:

To me, this seems like the core issue. No one involved seems
to have understood, even back in 1984, just how fragile the
RCC really was. I know I didn't. I always assumed that, since
it was on the leading edge and was "high-tech" material, it
had to be the toughest part of those resilient birds.

This is interesting. I haven't heard from anyone why reinforced carbon
carbon is supposed to be so amazing in the first place - do you know
what makes it a special material? How is it made? What is it
"reinforced" with? I did find out that it's "specialness" had to do
with its superior ability to withstand HEAT and not necessarily any
superior ability to withstand an impact. Too bad NASA didn't do more
thorough testing

ElleninLosAngeles wrote:

This is interesting. I haven't heard from anyone why reinforced carbon
carbon is supposed to be so amazing in the first place - do you know
what makes it a special material? How is it made? What is it
"reinforced" with? I did find out that it's "specialness" had to do
with its superior ability to withstand HEAT and not necessarily any
superior ability to withstand an impact. Too bad NASA didn't do more
thorough testing

Carbon-carbon is a composite consisting of carbon fibers in a carbon
matrix. It is made by first weaving carbon fibers into the appropriate
shape, then going through a laborious, lengthy process where the
form is filled with some sort of hydrocarbon and then heated to
convert some of that hydrocarbon to carbon + gases. This is repeated
until the porosity is below some specified limit.

The material also has a silicon carbide coating to provide oxidation
resistance, and some TEOS (an organosilicate compound) to renew the
SiC in case of damage.

Paul

(ElleninLosAngeles) writes:

(ed kyle) wrote in message news:

To me, this seems like the core issue. No one involved seems
to have understood, even back in 1984, just how fragile the
RCC really was. I know I didn't. I always assumed that, since
it was on the leading edge and was "high-tech" material, it
had to be the toughest part of those resilient birds.

This is interesting. I haven't heard from anyone why reinforced carbon
carbon is supposed to be so amazing in the first place - do you know
what makes it a special material? How is it made? What is it
"reinforced" with?

See page 55 of the CAIB report.

It *is* pretty tough stuff (especially compared to the very fragile
TPS tiles), but nowhere near as tough as the NASA engineers seemed to assume.

I did find out that it's "specialness" had to do
with its superior ability to withstand HEAT and not necessarily any
superior ability to withstand an impact.

Indeed, it should be noted that impact resistance of the leading edge
material never was a design requirement, and hence it was never really
tested for this kind of thing. A tragedy that this oversight was
never found and addressed earlier.

Note that even even you manage to fix all the foam shedding problems,
impact damage is always still a possibility, just a more remote one.
Bird strikes, other material falling from orbiter, ET, or SRB
components, etc.

--
Richard W Kaszeta

http://www.kaszeta.org/rich

"Paul F. Dietz" wrote
Carbon-carbon is a composite consisting of carbon fibers in a.......

Thanks for the specific info.