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Pastimes : Shuttle Columbia STS-107 -- Ignore unavailable to you. Want to Upgrade?

To: H-Man who wrote (295)	2/4/2003 4:49:22 PM
From: Bill Jackson	Respond to of 627

H-man. Well, I have a theory about foam and what might have happened. When I analyze this, the shed foam may well be slightly longer than the gap between the two craft. This was a fairly large piece, larger than most ever seen. This foam will be low in density, but might be 5-10 pounds per cubic foot, possibly more to stand the 1000 MPH slipstream, with a tough outer skin and be of closed cell construction.(they would make it closed cell to stop water vapour from penetrating and condensing into ice next to the cold tank.) An object like this is fairly strong in compression, but weak in other respects. While falling it is possible that this foam will wedge between the two craft, bridging the gap transiently In the wedged position it will be subject to the ~1000 MPH slipstream, it will of course break promptly, but before it breaks it will generate large end forces. One end may well indent the foam on the lower portion of the tank, in addition they other end might well rest on the door covering the wheel well and subject it to the same end force. This may make it bulge inwards, allowing hot gas leakage into the wheel well, and possible shearing off of some tiles. This hot gas leakage into the wheel well would cause that heat surge read by the instruments and may have caused this wheel well cover to fail and fall away into the slipstream. Being a large cross section, light object it should be findable upstream of the main debris field. The thinness should make it slow down rapidly and it will thus not burn up. The speeding shuttle will outpace it and thus it may well be a hundred miles or more away from the dense object debris field. A second interpretation is the bang may have flexed the cover, causing a large number of tiles to fall off due to the deformation, leaving the cover intact, but untiled. A large untiled area would heat and fail, while the loss of a tile here and there is not felt to be a problem. I tend towards the bent cover theory, since as many as 300 tiles have been shed on a single landing and nothing untowards happened, thus an untiled cover is tolerable. A bent cover with lifted seams is not. At those speeds the plasma entering the wheel well is able to transfer a large emount of heat, even though it is not especially dense. Thus it would be wise to inspect the foam remaining on the external tank(if any) and the external tank itself. The tank will also show some indentation due to this wedged piece of foam. This just a theory, but I seems to explain why the wheel well became hot shortly after they entered the atmosphere. If the wheel well cover was intact, but had a few tiles missing, the gasses would not have entered, would not have burned away the sensor wires. Remember, wires will get hot a lot faster than the tire temperature will rise, due to the differences in thermal masses. There is also the possibility that the cover was shed a long time ago, early in the flight. It could also have been shed at the first gusts of plasma. however I would expect them to have some door open sensors to tell that tale. I had not know of the foam problem before this time. Reports of earlier damage are terrifying in their implications, esp in 20:20 hind sight. I certainly would have wound that foam cover with a layer of fiberglass or carbon fiber to make it stay together. That foam may well have a higher density, as it was expected to stand 1000 MPH slipstream impact. It is not acceptable to have bits of that breaking off and hitting the shuttle. Bill