There has been a lot of speculation about the tiles since the investigation started, and Ron Dittemore, for whom I have the utmost respect, has been reluctant to identify them as the culprit. Having followed this mission, and most others, from start to finish (and this time into the sad beyond), I sympathise with his caution.
It is undoubtedly one of the most critical features of the Orbiter and is only put to the test during re-entry when the craft is exposed to the greatest thermal and aerodynamic stress. The max q occurs at around the altitude and velocity at which Columbia was observed to have failed (
re: previous questions). However, from the earliest flights, Shuttles have returned safely to Earth with some remarkable tile damage without suffering nail-biting damage to the underlying "conventional" structure. Many improvements to tile bonding, and related issues, have been implemented over the years.
The Tile Papers
Just to clear up a couple of points raised by
PickyPerkins &
vaneyck in respect of the (superb) Paté-Cornell/Fischbeck paper
Risk Management For The Tiles Of The Space Shuttle (
et al):
Caution: Please note that the following links may require long download times on slow modems.
1. The original was first published in
1990. The (shorter) "RIsk Management" paper appeared in
1994 and also won an award. I think it gained further awards in later years (not relevant to this thread, however). These documents are not "proper" PDFs in that they are effectively photocopies on Acrobat. Not exactly leading-edge technology
2. The apparent asymmetry in the diagram on
Picky's post is explained by, "
We found that 15 percent of the tiles account for about 85 percent of the risk and that some of the most critical tiles are not in the hottest areas of the orbiter's surface" in the above papers. . . . . IE: It depends on what's underneath the tile (hope that helps).
Whilst this excellent audit did result in significant changes to tile processing and inspection, it did not (and may not have been intended to) discuss loss of the Reinforced Carbon-Carbon (RCC) sections of the heat shield in depth.
KE=½MV² . . . or not ?
And here lies the rub (
sic). What
really happened when that "2.2 lbs (1kg)"
chunk of ET insulation struck the RCC leading edge of the left wing at a relative speed of [±]1090 ft/sec (330 m/sec) ? That's a KE of 40,200 ft lb (54,500 j). Where did it all go ? Did it simply fragment on impact thus dissipating the KE, or did its MV² weaken or fracture part of that
most critical component ? Quite a punch, though. Imagine the effect on your head at such velocity. Ouch ?
Unlike the tiles, the rigid RCC leading-edge sections are
bolted to the wing with more flexible separators between each section. Behind them is further thermal protection, eventually leading to the
flat front of the leading-edge aluminium wing box. Forget the razor-like profile of the old F-104 Starfighter wing, this STS baby is 5 ft thick at max chord. That's one heck of a speed brake if even one RCC fairing is removed at Mach 20 . . . . near the time that Max q was achieved and the anomolies began to appear.
Focus! . . . Focus!
In many aviation-related accidents there have always been "Godarnit" impairments to otherwise vital evidence. What a shame that the critical hi-res cameras, that could have produced photo qualities that we have marvelled at on most post 51-L launches, were out of focus on this particular launch. Is this simply complacent lack of attention to QC, at the relevant sites ?
Equally unfortunate is the much-circulated picture of Columbia from the Starfire Optical Range (SOR, Kirtland AFB, NM) which, according to the
publicity, is allegedly capable of resolving a 1 ft object at 600 miles (OK, I know there are two optical devices). The picture of Columbia at a mere 40 miles-up is unimpressive. It was released to the press as a negative and, either way, is inconclusive but significant. It
just appears to show an anomaly on the left wing leading edge where RCC sections should be. It also shows a more pronounced trail from the left wing immediately aft of that anomaly. It is of course presently a coincidence that drag was observed to be building up on that side at the time.
Dittemore is now (with great relief, no doubt) handing over to an "independent" BOI. I am sure it will do its job well. Be patient. I doubt it was the tiles. The truth will out.