a. A sacrificial silicone-based elastomeric wedge-shaped leading edge for the inboard areas of the Orbiter's wings that would protect the easily shatterable RCC sections from launch debris strikes. This covering would burn off in the early stages of re-entry and being a simple wedge-shape, would not unduly affect shuttle performance during an in atmosphere launch abort.
b. The solution to in situ in orbit repairs. The two long-handled over-centre locking clamps for mounting a (say) 15ft cable along the leading edge and enabling an EVA astronaut to apply a two part exothermic one-time repair patch.
c. The projection ahead of the inboard left wing leading edge shown in the Starfire Photo is obviously due to the super-heated plasma and the flat-plate effect (and here). This is something that NASA is yet to come to terms with. (quote: "The theory is also supported by a photograph taken by astronomers in Albuquerque, N.M., showing what appears to be a damaged, jagged area of the left wing.")
d. It is only a short step from here (this quote) to relating the super-heated plasma to the flat-plate effect.
"The leading edge theory is supported by several other pieces of evidence. Recovered leading edge panels now at Kennedy Space Center in Florida show that the attachment points were melted, rather than broken." and
"The wing was being eaten from the inside out," board member Roger Tetrault said. Similarly, investigators cannot explain why a piece of the left wing that adjoined the wheel well shows signs that a stream of hot gas had spewed out of the wing. Obviously the superheated plasma was entering forcefully at the leading edge RCC breach. Entry elsewhere would not explain the jagged projection ahead of the inboard L.E. or the "eating out" of the wheel-well interior....or the molten aluminium that was latterly being sprayed over the Shuttle's exterior by the plasma cloud (and embedded in the leading edges of non RCC tiles)
e. From the Washington Post Sunday 23 Feb 03 [page A20] "A worst-case analysis by Boeing Co engineers of the potential damage caused by the tank insulation estimated that the material could have hit the wing at more than 400mph and could have included pieces of ice which would have done more damage than the foam alone. A NASA engineer calculated that if the material was iced, it could have hit the shuttle with a force equivalent to that of a 500lb safe hitting the wing at 365mph."
Columbia moved to launch-pad 39a on 9 Dec 02. Columbia launched 17 Jan 03. By my reckoning it spent 39 days in the coldest temperatures Florida has had on offer in the last 100 years. The fact that, over many temperature cycles, the ET foam "worked" (and then cracked to its substrate due to ingress of moisture) should surprise no-one. Once the tank was filled with liquid hydrogen any trapped water would become adhesive ice and hold the ET foam in place (although cracked) until two things happened - aerodynamic heating and the drop [below the level of the foam's cracks] of the hydrogen fuel (as it was being used up during the launch). At that point (approaching about 400 kts) any weakened area of foam substrate (still stiffened by its water content in the form of ice) would lose its icy adhesion, detach and head for the Orbiter. The aerodynamics of the combo unfortunately had it hitting at what would prove to be the Orbiter's weakest point (the easily shatterable leading edge RCC tiles just forward of the wheel well's outer forward corner).
The Debate on Pprune
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By Michael Cabbage | Sentinel
Space Editor Posted March 7, 2003 |
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An internal letter from shuttle-program manager Ron Dittemore obtained by th
e Orlando Sentinel directs NASA engineers to focus on the following
areas:
The Feb. 27 letter says the changes should be "reviewed and assessed for near-term implementation." All the potential improvements are issues that have surfaced in the wake of shuttle Columbia's Feb. 1 breakup during re-entry that killed seven astronauts.
The move is significant because it could shorten the time needed to return the shuttle fleet's three remaining orbiters to flight. Managers at the National Aeronautics and Space Administration insist any major changes in design or operations must wait until the cause of Columbia's accident is pinpointed and an investigative board has released its findings and recommendations.
By anticipating some of those possible changes, however, the shuttle program could be ready to move ahead more quickly once the panel's work is done. Dittemore testified during the board's first hearing Thursday in Houston that engineers already are at work on improvements.
"It's broader than just what may be determined as the root cause," Dittemore said. "They're going to look and see if there is something else in the system that may have existed for many years. They will come back and make a recommendation to me."
Making changes
The 15-story external fuel tank, in particular, has attracted lots of attention since Columbia's accident.
Foam insulation estimated to weigh more than 2 pounds broke free from the tank's so-called bipod area 82 seconds after launch Jan. 16 and smashed into Columbia's left wing. Experts have theorized the strike caused damage that ultimately led to a fatal breach in the wing during re-entry.
Program managers already were in the process of redesigning a small foam ramp on the tank's bipod area after insulation came loose from the same spot during shuttle Atlantis' launch in October. The changes included lengthening the time taken to spray on the foam and possible removal of a silicon-based ablative material underneath.
The letter tasks the tank project at NASA's Marshall Space Flight Center in Huntsville, Ala., to "review the ET [external tank] bipod area and recommend changes to the ET insulation design and implementation to preclude any loss of insulation."
The directive also suggests that foam-loss problems could become a constraint to launch and no longer accepted as a manageable risk. If so, it would mark a major philosophical change in the almost 22-year-old shuttle program.
Meanwhile, NASA managers in Johnson Space Center's Mission Operations Directorate have been asked to find ways to identify and repair damage to the wings' leading edges and heat tiles while the shuttle is in orbit. Analyses indicate those areas on Columbia were the ones most likely struck by debris as well as where the ship's protective heat armor probably was breached.
With most future shuttle missions headed to the international space station, the plan almost certainly will include maneuvers around the outpost to allow the station's crew to inspect the ship's belly for damage.
Other possible inspection tools include telescopes, spacewalks, use of a camera on the shuttle's robot arm and top-secret military assets on the ground and in orbit.
Fixing damage likely will be harder than finding it.
NASA gave up a previous effort to develop a tile-repair option for astronauts in the early 1980s. A new task force was convened by the space agency Feb. 27 to take another look at the problem.
The panel's considerable challenge is to find a way for spacewalkers to safely repair broken and missing tiles in the weightless vacuum of low Earth orbit, where temperatures can fluctuate by hundreds of degrees in a matter of minutes.
More cameras
Two other changes being looked at would improve photo coverage of the shuttle during launch.
The Shuttle Integration Office at Johnson Space Center will study the system of cameras and radar that follow the ships during their climb to orbit from Kennedy Space Center. Pictures taken during Columbia's liftoff showed debris from the tank striking the orbiter but didn't reveal exactly where.
Several cameras that might have helped identify the area weren't working properly. Shuttle managers are looking at ordering replacements and adding cameras in new locations.
NASA also is considering placing new cameras on parts of the shuttle,
including the external fuel tank and solid-rocket boosters. Cameras
occasionally have flown in those areas in the past to look for possible
foam shedding and to gather data for engineers. They could become
permanent features.
Booster cameras have been largely successful. However, the first and only
camera mounted on the external tank was launched with Atlantis in October.
The camera became blurred two minutes into flight when the shuttle's
boosters were jettisoned and the lens was caked with rocket exhaust.
Another change in operations would affect landing.
The Mission Operations Directorate at Johnson is looking at possible ways
of modifying the shuttle's trajectory during re-entry to minimize heat on
the ship's thermal tiles and the wings' leading edges. Experts think hot
gases found a breach in one of those areas aboard Columbia and burned
through the inside of the ship's left wing like a blowtorch.
The shuttle encounters temperatures up to 3,000 degrees during its fiery
plunge to Earth. NASA managers consistently have maintained that the ship
already flies in an attitude designed to minimize possible heat damage.
However, engineers are studying whether slightly tweaking the orbiter's
trajectory could further reduce heat on critical surfaces.
Sentinel Space Editor Michael Cabbage can be reached at 321-639-0522 or
mcabbage@orlandosentinel.com.
from this link
Roger Tetrault, a board member, said he suspects the melting occurred because of the penetrating gases and also because of the intense heat of falling
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| "We believe that
it's possible that the tires on the left side blew out," said Roger
Tetrault, a member of the Columbia Accident Investigation Board.
"The blowout of the tires would have been a very catastrophic event." The threads from the two left tires were "basically pulled apart," he told reporters in Houston. In contrast, the tires from the right wing look more like those from a more normal airplane accident, Tetrault said. |
through the atmosphere.
"My best guess would be that eventually we'll probably find both," he
said. The melted aluminum, or slag, looks like black soot, and is present
on both the right and left sides of the spacecraft, he said.
"Many of the tiles on the left side have a thin, black deposit on them,
and that deposit has never been seen on any previous flight," Tetrault
said.
He said both tires from the left main landing gear also show evidence of
unusual and extreme heat: They are flat with torn fabric, possibly from a
rupture in the final seconds of the spaceship's flight, Tetrault said.
However, he said the damage to the tires could have been caused by heat
penetrating the wing. That heat, in turn, may have set off the small
explosives that are used to free the landing gear if it gets stuck right
before touchdown.
"I would not speculate that it blew out the door or blew down the landing
gear and that caused the accident. It is the result, not the initiating
event," said Tetrault, a retired corporate executive with experience in
nuclear submarines.
Investigators have theorized that foam or other debris that broke off the
shuttle's big external fuel tank during liftoff Jan. 16 damaged the wing
-- perhaps the leading edge, perhaps the area around the wheel well -- and
allowed hot gases to penetrate the wing and destroy the shuttle.
Meanwhile, the board's chairman, Harold Gehman Jr., said the board will
delve into what role NASA management and the agency's institutional
culture played in the tragedy. But he said it is more important, for now,
to find out what caused the accident.
He was referring to the flurry of e-mails among flight controllers and
other engineers in the last few days of Columbia's flight, in which they
discussed the possibility that the launch debris severely damaged the left
wing. They said they were merely "what-iffing" and did not suspect any
serious problems, even though some of them accurately predicted what might
happen if a breach occurred.
For the first time, the board's weekly news conference was not held at
Johnson Space Center, but rather a few miles away, off NASA property. The
panel wants to distance itself from the space agency and, in fact, has
asked NASA's chief, Sean O'Keefe, to remove some top shuttle program
officials from the investigation.
Gehman said he is satisfied that O'Keefe will comply with his request. He
refused to name which NASA officials he wanted off the investigation.
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This is an excerpt from the most recent set of modifications made to
the Shuttle Fleet. I obtained these documents just prior to NASA
pulling all information about the shuttle from the net on that
fateful Saturday. read carefully. " The area aft of the reinforced carbon-carbon nose cap to the nose landing gear doors has sustained damage (tile slumping) during flight operations from impact during ascent and overheating during re-entry. This area, which previously was covered with high-temperature reusable surface insulation tiles, will now be covered with reinforced carbon-carbon. The low-temperature thermal protection system tiles on Columbia's midbody, payload bay doors and vertical tail were replaced with advanced flexible reusable surface insulation blankets. Because of evidence of plasma flow on the lower wing trailing edge and elevon leading edge tiles (wing/elevon cove) at the outboard elevon tip and inboard elevon, the low-temperature tiles are being replaced with fibrous refractory composite insulation (FRCI-12) and high-temperature (HRSI-22) tiles along with gap fillers on Discovery and Atlantis. On Columbia, only gap fillers are installed in this area." |
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NASA agrees on a Leading Edge Event |
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Shuttle Investigators Closing in |
