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.
All the above is from this link on Pprune
|STS-107 SECOND DAILY REPORT …….. At approximately 81 seconds mission elapsed time (MET), a large light-colored piece of debris was seen to originate from an area near the ET/Orbiter forward attach bipod. The debris appeared to move outboard and then fall aft along the left side of the Orbiter fuselage, striking the leading edge of the left wing. The
strike appears to have occurred on or relatively close to the wing glove near the Orbiter fuselage. After striking the left wing the debris broke into a spray of white-colored particles that fell aft along the underside of the Orbiter left wing. ………..
-------- End quote ---------
However, in all the news conferences, the debris was said to have struck the underside of the wing.
This appears to be a clarification that the debris struck the leading edge.
|KENNEDY SPACE CENTER, Florida (CNN) -- Photographs taken by an Air Force tracking camera shortly before the space shuttle Columbia disintegrated show serious structural damage to the shuttle's
.left wing, an aviation magazine reported Friday.
The images, captured about a minute before the shuttle broke apart, show
a jagged edge on the left wing structure near where the wing begins to intersect with the fuselage, according to a report in Aviation Week & Space Technology. Columbia's right wing and fuselage appear normal in the photos, the magazine said.
The damage to the left wing indicates either a small structural breach, such as a crack,
or that a small piece of the wing's leading edge fell off, according to the magazine. It said NASA investigators at Johnson Space Center in Houston, Texas, are analyzing the pictures
Another key factor is that the leading edge of the shuttle wing, where the jagged shape was photographed, transitions from black thermal protection tiles to a much different mechanical system made of reinforced carbon-carbon material that is bolted on, rather than glued on as the tiles are.
This means that in addition to the possible failure of black tile at the point where the wing joins the fuselage, a failure involving the attachment mechanisms for the leading edge sections could also be a factor, either related or not to the debris impact.
The actual front structure of a shuttle wing is flat. To provide aerodynamic shape and heat protection, each wing is fitted with 22
U-shaped reinforced carbon-carbon (RCC) leading-edge structures. The carbon material in the leading edge, as well as the orbiter nose-cap, is designed to protect the shuttle from temperatures above 2,300F during re-entry. Any breach of this leading-edge material would have
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:
|The third and final summary issued on Jan. 27 discusses the black tiles again, but also specifically says "Damage to the RCC [wing leading edge] should be limited to [its] coating only and have no mission impact."
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 sequence of sensor measurements and failures is puzzling,
particularly one reading — in a part of the mid-fuselage not connected to any of the wire bundles linked to the other sensors that were going haywire.
“Whether that’s important or not, we don’t know,” Dittemore said.
Though the sensor data are being closely examined, it’s possible
the source of heat might not have been near them.
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:
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
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.
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.
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:
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.