🚀 go-pugleaf

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