updated 14 Feb 03

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. I think I see something projecting forward of the leading edge of the left wing in the flipped image. What do other people see?

In order to answer this, I'll first comment (in green) upon the extracts below by highlighting the important areas.

	But first you should look at the diagrams and photos here
	The AW&ST Article suggesting a "Leading Edge" Event
	The Pre-Crash Daugherty Email (2mb pdf file)

All the above is  from this link on Pprune

This appears to be a clarification that the debris struck the leading edge.

The "U-shaped" would be clearer if they'd said "D-shaped" (i.e. with the upright of the D being "the actual front structure of the shuttle wing that is flat". Obviously exposing this flat to the airflow would be catastrophic. However, this further NASA statement below seems to dismiss this as being at all likely:

I am not at all sure that a bolted on carbon-carbon structure would have much structural integrity at all once subjected to an impact of a sharp-edged (ice-heavy) 3lb piece of ET foam moving at speed. All references to the RCC substance refer to it as being very hardened (but I would assume that that "hardening" is against heat - and that it is brittle in respect of any significant sharp-edged (or pointy) impact ). It is possible that the post-impact debris cloud seen was only the iced foam but is it possible that the RCC "D" section at the point of impact could have been shattered? If so, without its structural integrity, how would it stand up to extreme heating? Indeed, once cracked, would that "bolted" RCC D Section have ANY structural integrity for RETENTION - at all????

The cheap and very easy explanation here is that the remote heating was conductively being caused by a solid metallic connection to an intense source of localised heating (such as along a L.E. spar member or other wing major structural (to in-fuselage) element - i.e. NOT along a wire-bundle or via super-heated air-flows). So for this sort of heating to have taken place, there must have been an ongoing major source of intense heat. The question then becomes: "What/where might this have been?"

So we have:

a.  Picky's question (and diagram) about something appearing to be projecting forward of the leading edge

b.  An ET foam debris strike that may well have been on the leading-edge (and not under the wing , i.e. not in vicinity of the wheel-well door)

c.  A photo taken 60 secs before break-up showing (according to A.W.&S.T.) a jagged LHS inboard L.E.

d.  Seemingly inexplicable heating of a quite remote in-fuselage area.

e.  The jagged "projection" is located at the RCC/black-tile transition point on the wing fillet (glove) (RCC carbon-carbon is very hard, best heat resister and is bolted on). Behind the RCC sections, the wing structure is a flat.

f.   A break-up that obviously started (from a Californian Astronomer's observations) from about the re-entry point. Inference here is that the eventual break-up was a function of an ongoing intense heat-soak ablative degradation of a pre-reentry damaged area of the inboard left L.E.

g.  As disclosed by the USAF photo, a LHS inboard trailing plume that has been variously interpreted as an RCS firing, a smoke-trail or a shedding of ablated material.

h.  The information that Columbia (with its ET) had sat on a cold, rain-soaked launch pad for longer than any other Shuttle (before being launched). I think I saw a figure of 39 days.

i.  From this link (The Pate-Cornell/Fishbeck 1994 Paper of "Risk Management for theTiles of the Space Shuttle") the harsh fact that once tile surface integrity is lost (by as little as one tile in a critical area), the ongoing surrounding loss is like a cancer spreading. The wing leading edge is one such critical area. We are also told that Columbia (as the first Orbiter) had a history of early tile problems.

j.  The telemetry-recorded progression of heat-sourced sensor failures (i.e. of wiring bundles) and heat-related damage (shown elsewhere)

k.  The eventual telemetry-end evidence that the "growing" left wing problem had finally run the Orbiter out of lateral controllability.

Looking at point j. first, wire-bundles can be interdicted anywhere along their length so their point of failure is hard to pin down. By comparison. if the remote area of in-fuselage heating was associated with a metallic structure directly connected to the left inboard Leading Edge's front-spar (highly likely) then that was most probably due to heat conducted from a long-term intense heat-source at the leading edge point of failure ( i.e. a bit of a smoking gun here). But why would that area heat up so intensely?

If the ET foam had sat out there in the rain cold-soaking and soaking up moisture for 39 days (TBC), it's not surprising that there should later be foam debris on launch (once the ET was fuel-filled and that water-soaked foam became ice). If that foam was heavier (because iced) and pointedly hit the RCC junction and that RCC section shattered, then its being only "bolted on" would be its downfall -  it would have later separated quite early under the airflow and heat stresses of re-entry. You would then have a flat surface (albeit on an obliquely-swept wing planform) being presented as a flat plate (initially over a short section) to a hypersonic flow. I myself cannot recall any aerodynamic lessons that ever investigated flat-plate hypersonic shock-waves - but the heat energy generated at that point would be extremely intense. It would be a bubble of heat plasma extending hemispherically forward of the wing's Leading Edge. The localized intense heat build-up would weaken the wing's structure locally, and in particular any transiting wiring bundles - but two other areas would also suffer heat effects:

a.  the immediate (and then the more distant) surroundings such as the wheel-well (where the sensors happened to be for pick-up of temperatures for various sub-systems) plus

b.  the sensor for any distant (remote) (in-fuselage) area connected to that tile-failure point via a substantial piece of heat-conducting metal (such as a spar-connect to a fuselage sub-frame).

ANSWER:

How would that radially-radiating flat-plate shockwave and its intense highly-localized thermal source look to the USAF camera? Opaquely like a jagged projection (bubble) forward of the wing leading-edge? I think so.

And what was the plume behind? Ablated RCC carbon-shredding as the heat, shocks and airflow eroded outboard along the L.E., heating it up.

Picky said (10 Feb) "Note added 10th Feb. 2003
Looking at the video shot in Texas it seems obvious that ablated or burning material can and does move ahead of the solid material. So personally I now tend to believe the photo may show ablating material both ahead of and trailing behind the left wing.
 

I don't think so. I do NOT think (either) that it was anything to do with a "not quite overhead shot" or a banked attitude. In fact the damage discussed above may have propagated ALONG the LH leading edge by the time this shot was taken (60 secs prior to break-up).... and explain that loss of definition along that LH leading edge as a combination of heat blur and erosion of tiles.

(of Link ONE and LINK TWO)

 Rather than a tile having been lost, it’s becoming apparent that a section of the “bolted” on RCC (reinforced carbon-carbon) leading edge was hit and shattered (and was then crumbled away by the hypersonic flow). There are a number of mutually confirming reasons for believing that this may have been the case. They’re set out below and in the links.

1. The RCC leading-edge structures are bolted to the wing using Inconel fittings that attach to aluminum flanges on the front of the wing. Hard to believe that “bolted on” reinforced carbon-carbon would retain any structural (or retentive) integrity  under the blow from a large iced piece of tank foam moving with considerable momentum at lift-off plus 81 secs – particularly if it hit pointedly. It is not the "toughened" leading edge that it is being represented as - leastwise not as far as impacts are concerned. The Columbia sat on a cold rain-soaked pad longer than any other shuttle before it (i.e. 39 days) and in the coldest Florida weather spell for about 50 years. The tank foam would have soaked up much moisture. It would appear that its adhesive wasn’t impervious to moisture (or possibly that freeze/melt/freeze cycles are capable of cracking that foam).
2. From the pink-tinged diagram at link two, by reference to the leading-edge photo below and from the foam debris impact videos you can get a good idea of just where that impact probably occurred. If the RCC section in that area was only shattered (and not removed), its pieces would quickly lose their “bolted on” integrity and start to separate. Behind those sections you have an oblique flat-plate presenting to the hypersonic airflow.
3. The “jagged leading edge” (LE.) damage depicted on the USAF photo is actually a camera-opaque superheated plasma bubble projecting ahead of the leading edge – originating around the damaged RCC section. It’s important to note that early on in the space program NACA (NASA’s predecessor) became convinced of the advantages of a blunt leading edge allowing re-entry heat dissipation in the bow-wave ahead (instead of fixed and jettisonable beryllium shields). Think of that flat-plate behind the damaged RCC section as being a very blunt section.
4. You can easily see the proximity to the wheel-well that has now been admitted (by NASA engineers) to have been breached (and heated by super-heated plasma). The initial boundary conditions of intact RCC sections either side of the L.E. breach would have caused that highly localized plasma bubble (which is probably what is shown as a projection ahead of the Left wing in the USAF photo –taken 60 secs before the break-up). Once subjected to the super-heated plasma, the underlying aluminium could have been easily penetrated.
5. From that same pink-tinged diagram you can see the orange lines representing the wiring bundle lines to the sensors that first “dropped out” - and note their immediate proximity to the suggested area of RCC damage.
6. If you scan that (overlaid USAF photo) diagram, you can see that the photographed dense trailing stream of “ablated” material is more outboard than the “more inboard” postulated RCC section damage position. That’s due to a characteristic of the sheet vortex associated with a delta planform at high AoA (called spanwise blowing) – and possibly also indicates that the more outboard sections of RCC were being “peeled” off the swept L.E. by the airflow. Once an RCC section was compromised, the tiles behind (top and bottom surface) would also present a lip to the hypersonic airflow. Shock-waves would form at (and work on) these protuberances. This progressive L.E. and surface degradation would also explain why it took about 15 minutes for the elevons and RCS (Reaction Control System) to run out of lateral controllability.
7. Currently NASA engineers are claiming that the main-wheel tyres would not have burst inside the wheel-well. They are rated at 340psi max at a nominal 75degF. The recovered tyre photo below is showing signs of an overpressure burst (an across-casing split).  The ultimate event (post-telemetry cut-off) may have been due to heat-detonation of the gear's blow-down explosive squibs.

Once the Shuttle’s Thermal Protection System (TPS) loses its integrity at a critical point, it is like a house of cards. As I see it at this point two measures may have avoided this accident:

1. A “re-entry sacrificial” layer of rubberized/vulcanized leading edge tape may have been sufficient to protect the Orbiter’s most impact-vulnerable sections (the bolted on carbon-carbon RCC) from ET iced foam debris hits (shatter-blows) on launch.

2. A policy of NOT leaving a mated launch-ready Shuttle on the pad exposed to the elements for lengthy periods may have avoided the foam-shedding (which was a well-known, but dismissed, phenomena).

As crew escape during re-entry isn’t a viable proposition NASA needs to evolve a protective repair that can be applied in a standard pre-reentry EVA. They also need a remote-controlled camera that can inspect all the critical areas before re-entry, Imagery being sent back to Mission Control for confirmation of the necessity for an interim repair. NASA has previously called in orbit repairs impractical. It's a proposition that deserves another look.