Posted on 02/14/2003 6:58:57 AM PST by thepainster
HOUSTON - The panel investigating the loss of the space shuttle Columbia said Thursday that a hole developed in its aluminum skin, allowing superheated gas to flow into the left wing, causing the ship's destruction.
"Preliminary analysis by a NASA working group this week indicates that the temperature indications seen in Columbia's left wheel well during entry would require the presence of plasma," the superheated gas that surrounds the shuttle as it enters the atmosphere, the board said in a statement released late Thursday.
The statement from the board, led by retired Adm. Harold W. Gehman Jr., means that engineers have all but eliminated an earlier theory of the disaster -- that the aluminum skin was not breached, but that a lost or damaged tile allowed heat to be conducted into the wheel well, where sensor failures gave the first indications of trouble.
"The heat transfer through the structure, as from a missing tile, would not be sufficient to cause the temperature indications seen in the last minutes of flight," the statement said. Instead, the panel said, only a jet of plasma, which can reach 3,000 degrees under the brutal conditions of re-entry, could have caused the heating and failures that were detected before the shuttle disintegrated on Feb. 1.
The board did not address the central mystery: how the hole was created. Early suspicions focused on damage from a piece of falling foam insulation that struck the wing 80 seconds into the launch, and this finding does not rule that out as a possible cause. But other possible sources of damage have since been considered, including a possible collision with space debris or meteoroids.
"We've determined that there was some kind of plasma coming in from the outside to the inside," said Catherine Watson, a NASA spokeswoman. "We don't know how it got in at this point. We know it's in there, but how did it get in?"
The hole could have been in the fuselage, on the surface of the left wing or on its leading edge, or through the seal of the wheel wells or directly through the door of the wheel well, said James Hartsfield, a NASA spokesman. By continuing to trace back the temperature changes and failures in sensors leading up to the loss of the shuttle, engineers hope to determine the precise location of the hole and reconstruct the chain of events, Hartsfield said.
"The engineering teams are optimistic that they can continue the reverse engineering they've been working on, and narrow down the possibilities," he said.
On Thursday, NASA outlined a dramatic, multilayered chronology of the shuttle's final minutes that picks up as the craft hit the upper atmosphere, about 395,000 feet above the Pacific, northwest of Hawaii, about 7:44 a.m. CST About seven minutes later, the vehicle entered the peak heating phase, when temperatures climb above 2,000 degrees. Less than 1 1/2 minutes later, flight controllers in Houston saw the first unusual heat reading, in the left landing gear system in the wheel well.
Scientists and engineers who study the shuttle have previously warned that a plasma breach could be catastrophic.
A 1997 report from the National Research Council on the risk to the shuttle from being struck by meteoroids or orbital debris states: "Impacts that penetrate the leading edge of the wing or the lower surfaces of the wing or the fuselage might not be immediately critical or even detected but the consequent thermal heating on reentry could have a 'blow torch' effect inside the wing that causes loss of flight control or failure of the primary structure resulting in the loss of the vehicle. Major damage to the control surfaces or the hydraulic systems that operate them could result in critical failure during reentry, approach and landing."
A plasma is a gas so hot that it glows and conducts electricity. Plasma torches slice through steel as if it were butter, and high-tech incinerators use plasmas to break down garbage into atoms.
When the space shuttle drops from orbit, friction heats atmospheric gases to 3,000 degrees, about one-third the temperature of the sun's surface, creating a plasma that would ordinarily be devastating to an aircraft's aluminum structure. The shuttle is outfitted with thousands of insulating tiles to protect the aluminum from that heat.
The investigating panel concluded that even if there had been damage to the tiles, allowing the plasma to heat the metal structure, that heat would have been conducted too slowly to have caused the breach. They compared the process to stoking a fire with a metal poker: Even if the poker is red-hot at one end, it takes time before the other end feels warm.
Instead, the panel concluded, a superhot jet of plasma must have pierced the shuttle's structure and quickly spread heat in the same way that a roaring fireplace quickly makes a room uncomfortably hot.
"They can't account for that much energy coming in unless they had a breach and energy was flowing in through a hole in the system," said Dr. John Hansman, professor of aeronautics and astronautics at Massachusetts Institute of Technology. He and other researchers said that they were reserving final judgment until they see the calculations on which the conclusion was based.
The panel left open the question of exactly how the hot plasma could explain the complicated pattern of sensor readings in several parts of the orbiter's left side. If the plasma jet warmed the left wheel well, it was unclear why the sensors in the rear of the left wing suddenly stopped functioning, or how heat was picked up much farther away, on the skin of the fuselage above the wing.
Answering those questions is likely to force the panel to do some highly detailed sleuthing involving the shuttle's mechanical and electrical systems. If the wires leading to the rear sensors were cut by the blowtorch of the plasma jet, for example, the investigators might be able to determine where the breach first occurred.
But that would leave open the question of how the catastrophe started.
Whatever the final conclusions, investigators say that it appears certain that the crew of the Columbia was soaring through the atmosphere with a fatal gash in its wing that did not raise any significant warnings in the cockpit or on the ground.
NASA also released additional information on Thursday on the timeline of the final minutes of the Columbia flight. The new timeline includes a puzzling reading from a sensor that indicated that the left landing gear was down and locked a half minute before contact was lost with the shuttle.
If the sensor reading was correct, the deployed landing gear would have created intense drag and forced Columbia to tumble out of control. But NASA officials discounted the importance of that reading on Wednesday, saying that other sensors suggested that the landing gear had not dropped into place. Also, the amount of drag that would have been caused by the landing gear was far greater than that experienced by the shuttle, they said.
The investigative board agreed, saying: "Other flight data, including gear position indicators and drag information, does not support the scenario of an early deployment of the left gear."
This Report Contains Material From the Washington Post.
Hate to pat myself on the back, but this is exactly the scenario I envisioned after hearing the intial news conference - something damaged a key leading point of the left wing enough to burn a small hole through the skin of the wing, allowing plasma to start working its way through the wing like a blowtorch, which started to eat through wiring and control systems. I would guess that it eventually caused something to fail with the landing gear - either a sudded decompression that made the tire explode or a failure of a control device that partially opened the landing gear bay - either one of which would have caused the catastrophic failure of the left wing.
I believe at that time the pressure was about 100 lbs per square foot and rising.
"The heat transfer through the structure, as from a missing tile, would not be sufficient to cause the temperature indications seen in the last minutes of flight," the statement said. Instead, the panel said, only a jet of plasma, which can reach 3,000 degrees under the brutal conditions of re-entry, could have caused the heating and failures that were detected before the shuttle disintegrated on Feb. 1.
A plasma is a gas so hot that it glows and conducts electricity. Plasma torches slice through steel as if it were butter, and high-tech incinerators use plasmas to break down garbage into atoms.
Conclusion......
The investigating panel concluded that even if there had been damage to the tiles, allowing the plasma to heat the metal structure, that heat would have been conducted too slowly to have caused the breach.
I'm not a PhD in Thermodynamics, but if the tiles were gone and the aluminum frame were exposed to the 3000 degree plasma, what would keep that aluminum from melting?
Name: Aluminum
Symbol: Al
Atomic Number: 13
Atomic Mass: 26.981539 amu
Melting Point: 660.37 °C (933.52 °K, 1220.666 °F)
Boiling Point: 2467.0 °C (2740.15 °K, 4472.6 °F)
Am I missing something really obvious here?
Well, true but they can run up to 21,000 F. Never the less, the whole point of the tiles is to protect the aluminum from melting, yes. As to why a missing tile wouldn't cause a hole, I'm not sure, but it might be due to surrounding airflow spanning and protecting small irregularities.
If I am not mistaken, in the heat critical areas, the tiles are layered and overlapping, so that the loss of one tile does not necessarily expose the metal beneath. Instead, it just reduces the amount of insulation at that point.
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