questions about Challenger commission report

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2 total messages Started by Phil R. Karn Fri, 17 Oct 1986 06:35

#7675

Author: Phil R. Karn
Date: Fri, 17 Oct 1986 06:35

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I finally got a copy of the Challenger Commission report and have read most
of it. I was most impressed with the overall thoroughness of the
Commission's work and the care with which they avoided jumping to
conclusions.  I do have one question, though.

On page 55, the possibility that a "case membrane failure" was to blame is
discussed: "Fracture mechanics analysis indicates that a hole in the case
larger than one inch would cause the entire case to rupture in a few
milliseconds. This would give rise to the appearance of a large longitudinal
flame, an event that is contrary to the flight films."  Elsewhere, pictures
of the recovered right-hand SRB show that the burn-through in the aft field
joint had grown quite large (several feet in diameter, judging from the
photos on pages 78-81) before the booster was blown up by the range safety
officer. My question is, once the joint burned through, why didn't the
entire case quickly rupture, given the comment on page 55? Is there something
different about the behavior of a hole in the joint versus one between the
joints?  I remember that there was considerable skepticism in the first few
days after the accident about whether the SRBs could be at fault,
considering that they flew away from the explosion more or less intact. Was
this just a fluke?

By the way, note what appears to be a grounding strap attached to the
recovered SRB pieces shown in page 80. Was this a safety precaution to avoid
the possibility of igniting any remaining propellant? Having never actually
seen SRB propellant, I don't know if the brown stuff on the inside of the
piece is propellant or case liner. I thought the propellant was supposed to
be "battleship gray" in color, though.

Phil

Re: questions about Challenger commission report

#7686

Author: Adams Douglas
Date: Sun, 19 Oct 1986 22:32

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In article <358@petrus.UUCP> karn@petrus.UUCP (Phil R. Karn) writes:
>..."Fracture mechanics analysis indicates that a hole in the case
>larger than one inch would cause the entire case to rupture in a few
>milliseconds...My question is, once the joint burned through, why didn't the
>entire case quickly rupture, given the comment on page 55? Is there something
>different about the behavior of a hole in the joint versus one between the
>joints?

Yes, considering that by "case membrane failure" they were referring to a
fatigue or flaw induced crack in the casing. A crack with sharp edges
would propagate rapidly across the casing under the stresses from the
gas pressure. The hole burned in the case at the joint was burning
where there already was a 'crack' (the joint) to absorb the strain.

>By the way, note what appears to be a grounding strap attached to the
>recovered SRB pieces shown in page 80. Was this a safety precaution to avoid
>the possibility of igniting any remaining propellant? Having never actually
>seen SRB propellant, I don't know if the brown stuff on the inside of the
>piece is propellant or case liner. I thought the propellant was supposed to
>be "battleship gray" in color, though.
>
>Phil

The strap was indeed there to guard against igniting the propellant
remaining on the case wall. I don't know what color it is supposed to
be, but remember it had been immersed in seawater for awhile AND you
are looking at the burned surface, not virgin propellant.

-- 
=======================================================
Adams Douglas	ARPA:crash!adamsd@nosc.arpa  AT&T:818-354-3076
JPL/NASA	UUCP:{akgua | hplabs!hp-sdd | sdcsvax | noscvax}!crash!adamsd

My opinions! Do you hear? MINE! Not JPL's.

"Do not be angry with me if I tell you the truth." -- Socrates

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