karn@petrus.UUCP (Phil R. Karn) (10/17/86)
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
adamsd@crash.UUCP (Adams Douglas) (10/20/86)
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