Dale.Amon@FAS.RI.CMU.EDU (02/02/86)
I am almost totally in agrteement with dsmith's analysis of the course of events. It is in fact the sequence I described to local media when interviewed for the evening news a few days ago. The only other item I would add is that if the undershuttle explosion (the bright flare of about 10-20 ft length) pierced through to the shuttle bay, there are small O2 and H2 tanks at that point (2 pair on each side I believe) that would have ruptured as well. This might be the reason for the relative brightness. It could also be the O2 line suggested by dmsith, as this line is indeed at the same point and this would explain the almost instantaneous explosion of the O2 tank despite the fact that no fire track could be seen from the midshuttle explosion to the fairly distant main explosion. The burning color could also be due to incomplete combustion: the air is getting thin at that altitude, so the flame would be relatively weak until fed with O2. Aluminum will burn like magnesium in a pure O2 environment. I expect goodly portions of the structure to have burned to ash. I think it is a testament to the violence of the explosion that a 'quarter panel' of the Challenger's nose survived intact. I should point out that even if the tank had only ripped open at the rear, the system would have been ripped apart by aerodynamic stresses. I will in fact hypothesize that up to the point of rupture of the O2 line, we were in fact seeing the the breakup of the ET with some H2 burning off and assisting in the destruction. As dmsith said, the tank unravelled around the side away from us. If you look closely you can see an orange glow on the left side that seems to verify this. Note that the H2 line runs from the intertank to and up the left rear strut, and the O2 line does the same on the right, as viewed from above the shuttle. The interior of the shuttle was a bomb from end to end. Nose: large RCS tanks, MMH & NT Bay: 4 pairs O2 and H2 tanks for fuel cells large IUS tanks, MMH & NT TDRS station keeping fuel, prob MMH & NT Rear Bulkhead: 2 pair (?) APU tanks, MMH & NT OMS pods: 1 pair large OMS tanks in each, MMH & NT 1 pair small RCS tanks in each, MMH & NT Not to mention other assorted hydraulic and coolant fluids, life support O2, and so forth. These fuels are VERY caustic, which is why people have been warned not to handle fragments they might find on the beach. I have problems with the SRB burnthrough concept because the SRB's burn from the core outwards, and a burnthrough should cause asymetric thrust. Also, I would think that the hole size should expand as the new burnfront expands around the pinhole. Both SRB's appeared to be quite stable up to the time the RSO pulled the pin on them. True, they did not go straight, but then they did not tumble or change direction wildly. They simply drifted slowly in direction as one would expect them to do with no guidance. My personal theory is that a material failure occured at or around the left rear support strut, possibly caused by vibration induced fatigue during max Q. The rapid change in acceleration caused by the throttle up caused the weak point to rupture. The H2 fuel ignited in the exhaust and burned weakly in the thin atmosphere. This is the first flare we see, down near the left SRB. Aerodynamic pressures ripped the tank open like a toilet paper tube (a spiral). The increasing amounts of dumped H2 cause the orangish glow to the left. The rip comes into view on the right again just as it strikes the O2 line on the ET. This is the bright flash under the middle of the shuttle. It then propagated nearly instantly up the O2 line to the O2 tank. Velocity drove the H2 into the O2 cloud causing nearly complete combustion. The byproduct, water, was the main constituent of the round cloud. I suspect that the crew felt a violent thump underneath. The flight deck crew saw a blinding flash. The lower deck may have already ruptured from the first explosion. In any case, they had nothing more than an instant of realization. I would be very surprised if any one of them was aware long enough for even a rush of adrenalin. It was mercifully quick.
ATTENBERGER%ORN.MFENET@LLL-MFE.ARPA (02/03/86)
I am new to this list, so forgive me if this is old stuff. Has anyone looked into the possibility of the shuttle explosion being due an electrical discharge between the liquid fuel tank and the shuttle? If the shuttle and solid fuel tanks are connected by grounding straps to the liquid fuel tank, then read no further and send me an enlightening message. However the shuttle is covered with non-conductive tiles, and it seems possible that the entire shuttle and booster system acts like a capacitor, especially in low-humidity conditions. The charging mechanism would be due to the shuttle having an exhaust, while the liquid fuel section does not. If the exhaust stream is highly ionized (I dont know if it is), then the electrons might stream down the pressure gradient faster than the more massive ions, leaving the shuttle with a positive charge relative to the liquid fuel tank. A large enough spark might weaken a very cold seam or even directly heat enough liquid hydrogen to rupture the containment system.
bilbo.niket@LOCUS.UCLA.EDU ("Niket K. Patwardhan") (02/11/86)
According to Aviation Week, the SRB leak caused a failure of the lower supports, causing the SRB to become detached at that point. From rate gyro information, they now believe that the SRB then rammmed the top of the external fuel tank, The top of the SRB was damaged, and a photo showing the drogue parachutte spilling out is provided. An interesting thing was that just prior to the explosion, the shuttle flew through a wind shear, and all five engines immediately swivelled to cocompensate. The thrust levels then reduced (normal part of the program), and then built back up. During this build up the SRB didn't get up to normal power, and the shuttle engines swivelled, but AWST says this was not dramatic, and the shuttle itself stayed on course. If anybody is interested in the actual numbers, I would suggest you get hold of a copy of this weeks issue: it has some pretty good photos too.