Posted on 02/19/2003 8:25:52 AM PST by snopercod
HOUSTON -- There are no firm answers yet as to exactly why shuttle Columbia broke apart Feb. 1, but with public hearings set to start next week, a new wave of theories is beginning to make the rounds.
This week's best guess as to what happened involves a stripped heat protection panel from the leading edge of the left wing, taking into account two facts recently confirmed by the Columbia Accident Investigation Board, chaired by former Navy Admiral Hal Gehman.
First, a major contributor to the loss of the vehicle and crew appears to be the presence of superheated air inside Columbia's left wing, the result of some kind of breach in the structure.
Second, pieces of the shuttle were seen falling from Columbia as the spaceplane approached and flew over the California coast, suggesting the breakup began earlier than initially thought.
The precise link between those two events still remains elusive and the Gehman Board admitted Tuesday that no theory was quickly rising above any other and reaffirmed that nothing has been ruled out.
"What's starting to jump out is that we are not finding an easy fix," Gehman said. "This is going to be hard work."
The board has divided itself into three working groups, with James Hallock of the Department of Transportation leading the engineering and technical analysis group that is trying to piece together what happened.
The leading edge
Among the theories his group will be considering is one in which a reinforced carbon-carbon (RCC) panel on the forward edge of Columbia's left wing was the first major piece to break loose during re-entry as the shuttle approached the California coast.
"We're interested in the leading edge," Hallock confirmed Tuesday.
The U-shaped RCC panels are gray in color and each one is bolted in four places to a flat area on the front of the wing structure. Reinforced carbon-carbon is a manmade composite material that binds carbon-based material with other carbon-based material in a molecular structure designed to take the brunt of the hottest temperatures seen during re-entry -- nearly 3,000 degrees Fahrenheit.
With one missing, hot gas, which is generated all around a shuttle during re-entry, could get inside the wing cavity. Wire bundles would burn and sensors could fail, and the breach could cause other sensors to read increased temperatures. This series of events would account for the facts discussed by NASA and confirmed by the Gehman Board.
With an RCC panel missing, the flow of air moving over the wing was disrupted, the thinking goes, allowing other panels and heat protection tiles to break free, which allowed the breach in the wing to grow and feed on itself.
As the structural integrity of the wing began failing from the hot air inside, the flow of air on the outside of the wing was being met with increased drag, forcing the shuttle's computers to compensate and stay on course by firing Columbia's steering jets.
Other possibilities
Hallock said they would also look at the possibility of a failure in thermal seals surrounding the main landing gear door on the left wing, but according to earlier reports from NASA, sensors inside the wheel well did not detect that kind of temperature rise.
"These are all things we need to at least put a check mark, and yes or no, it's still a possibility or not," Hallock said.
Proving that a dislodged RCC panel instigated the ship's failure might require finding the scorched part somewhere in the Sierra Nevada mountain range in California.
To that end, investigators are seeking help from experts who track meteors entering Earth's atmosphere in order to predict the impact point and later find the meteorite. Officials hope these scientists can point to Columbia debris.
It's possible an RCC panel might survive the heat of re-entry, and reports from the West of sonic booms and rumbling noises like thunder -- similar to what is heard when meteors fall from the sky -- offers hope some kind of debris will be found.
"Obviously, it would be very important to understand what those pieces are, particularly the ones that started falling off at the very beginning,'' Hallock said.
Realistically, according to Hallock, the chances of finding something are slim.
"For us to find something that far back along the path, I think it's going to have to be a pretty substantial piece of the shuttle itself," Hallock said.
Initial cause?
If an RCC panel turns out to be the primary culprit, the key question will be why it fell off in the first place.
Possibilities include corrosion undetected before launch, insulating foam from the external tank striking the wing during launch, or orbital debris flying into the wing after launch, officials said.
But there is an intriguing -- and in terms of history, potentially ironic -- possibility that some kind of electrostatic discharge took place 40 miles high that blew a hole in the RCC panel and could have damaged some nearby heat protection tiles.
Although not a front runner, Hallock said it was something the board has looked at and will be considering again in the future.
"There's not much ionization at that altitude," Hallock told SPACE.com. "It's low enough so that in my mind, while I haven't crossed it off, it's not high on my list."
Little is known about this region of Earth's atmosphere and, in fact, the Israeli science experiment aboard Columbia was designed to study electrical phenomena at high altitudes and scored a space first by capturing an image of one of the so-called "elves."
When lightning strikes
Better known is the effect electricity -- or more specifically, lightning -- has on composite materials, such as the carbon-carbon the RCC panels are made from.
As is well known in the aviation industry and many golfers who use graphite clubs, composites are extremely sensitive to electricity and react to lightning strikes or static electricity discharges in a violent manner.
The files of the National Transportation Safety Board are filled with examples of aircraft that were struck by lightning and the only damage was with parts made of composites.
While it's not likely Columbia was struck by lightning flying through clear skies some 40 miles high, it is possible that some kind of electrical event took place.
At least one image is reported to exist in which it appears something like lightning is striking, or discharging from, the shuttle as it approached the California coast.
NASA confirmed the image exists but shuttle program manager Ron Dittemore said in the days following the tragedy they were still trying to confirm if it was a fake.
Dittemore also wasn't ready to confirm that static electricity played a role in Columbia's loss, but said he'd wait for the experts to tell him.
"I really have no idea whether we had any static electricity, whether or not we had any electrical discharge. I don't know. We are asking experts in the field of atmospheric science if those types of events are even possible," Dittemore said.
But a former shuttle program engineer, who was also a materials scientist for the same Lockheed group that developed the shuttle's tiles, believes it was an electrical event at high altitude during re-entry that was the reason for the RCC panel failure.
Doug Kohl worked for more than 10 years at the Kennedy Space Center as a test conductor, pad leader and part of the handpicked team that prepared Columbia for its first post-Challenger-era flight in 1989.
"I still think that the RCC saw something such as a large static discharge that damaged it and the surrounding thermal protection system tiles, and that the problem progressed from there," Kohl said.
Kohl is particularly interested in this theory because he now lives in California within an hour's drive of where it's possible an RCC panel fell to the ground after breaking loose from Columbia.
He's done some debris searching himself and encouraged his neighbors to report their eyewitness accounts of what they saw and heard Feb. 1 as Columbia flew directly overhead.
"If an electrical event caused the damage it will be readily evident to any materials person familiar with electrical damage in composites, as the fibers will look like a blown out steel belted radial tire where the charge exited the structure," Kohl said.
Foam theory still viable
It's also possible that the external tank foam insulation that was seen striking the left wing during Columbia's Jan. 16 launch played a roll in this scenario, Kohl said.
The foam could have struck and damaged some tiles around the RCC panel enough to set up heating and turbulence that led to the panel popping off. He doubted the insulation would damage an RCC panel itself.
"They're tough," he said. "They take a licking and keep on ticking."
Whatever happened, Kohl remains loyal to his former space colleagues.
"This is a solvable puzzle for the NASA team, and an experience the U.S. space program will learn from, which will lead to corrective action in systems which failed during Columbia's last mission. Then the men and women who work on the space shuttle, and do it so well, will return to the business of launching," Kohl said.
Frankly, my money is on a piece of orbital debris, but your testing proposal is interesting. Destructive testing of this type will probably not yield an "easy fix", so there will be powerful disincentives to that line of investigation. Absent a "fix", the only logical outcome would be grounding the remainder of the fleet, and given the existance of the ISS, that ain't gonna happen.
The Columbia was engulfed in a big pink-orange fireball at the point of the alleged discharge, so I could see how they might not have noticed any kind of electric display back behind them on the wing.
But it seems like "the lights should have flickered" or something. But maybe not. The shuttle electrical systems are mostly 28VDC, with a few 120VAC/400HZ circuits for rotary equipment. All black boxes and other metal pieces are scrupulously bonded to the airframe and checked with a milliohm meter. I can't really remember the spec. but "2 milliohms" sticks in my mind...
If there were any kind of a "lightning strike", it would have passed through the tiles, blankets, fiberglass (or whatever) and passed through the aluminum structure underneath before exiting somewhere else.
I am assuming that the RCC leading edges are conductive, but really don't know for sure. Neither do I know if and how they are bonded. The gaps between the sections would be a bonding concern, I think, but not sure.
If you have ever read anything on lightning strikes on fiberglass aircraft, it's pretty scary.
Tribal knowledge is cute and impressive and all, but for the rest of us...
What is OPF? In plain English?
OPF = Orbiter Processing Facility, the three "hangars" where the shuttles are processed at Kennedy Space Center.
They are an engineering marvel in themselves. Climate controlled, with emergency ventilation in case of a hypergol spill. Everything was explosion proof. Access platforms to reach the required areas. Supplied with all kinds of gasses and fluids necessary for processing.
Whol will "spell" for you?
... seems like "the lights should have flickered" or something.
I have been in a 707 when the wing got hit by a bolt; other than a sharp crack of sound and the cabin lights flickering, nothing else seemed to happen -- no dips, no jerks, no change in engine sounds. WRT the Columbia, we already know that it was inspected for corrosion on the last refit at Palmdale, but how intense is that when done at KSC from the prior flight? Corrosion can play real havoc with electrical/electronic grounding and often cannot be seen without disassembly and microscopic examination.
Static can also punch holes in things, and usually has a high voltage and low current. If the grounding were compromised by either corrosion or misalignment due to the foam strike, that anomaly described on the pics from California could be an important straw on the pile of coincidences.
Bump.
Wasn't me, but I wish we had...that is, if they weren't monitoring FR in the first place. :)
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